forked from OSchip/llvm-project
2984 lines
111 KiB
C++
2984 lines
111 KiB
C++
//===- Writer.cpp ---------------------------------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#include "Writer.h"
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#include "AArch64ErrataFix.h"
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#include "ARMErrataFix.h"
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#include "CallGraphSort.h"
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#include "Config.h"
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#include "InputFiles.h"
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#include "LinkerScript.h"
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#include "MapFile.h"
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#include "OutputSections.h"
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#include "Relocations.h"
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#include "SymbolTable.h"
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#include "Symbols.h"
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#include "SyntheticSections.h"
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#include "Target.h"
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#include "lld/Common/Arrays.h"
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#include "lld/Common/CommonLinkerContext.h"
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#include "lld/Common/Filesystem.h"
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#include "lld/Common/Strings.h"
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#include "llvm/ADT/StringMap.h"
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#include "llvm/Support/BLAKE3.h"
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#include "llvm/Support/Parallel.h"
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#include "llvm/Support/RandomNumberGenerator.h"
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#include "llvm/Support/TimeProfiler.h"
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#include "llvm/Support/xxhash.h"
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#include <climits>
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#define DEBUG_TYPE "lld"
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using namespace llvm;
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using namespace llvm::ELF;
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using namespace llvm::object;
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using namespace llvm::support;
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using namespace llvm::support::endian;
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using namespace lld;
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using namespace lld::elf;
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namespace {
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// The writer writes a SymbolTable result to a file.
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template <class ELFT> class Writer {
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public:
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LLVM_ELF_IMPORT_TYPES_ELFT(ELFT)
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Writer() : buffer(errorHandler().outputBuffer) {}
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void run();
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private:
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void copyLocalSymbols();
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void addSectionSymbols();
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void sortSections();
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void resolveShfLinkOrder();
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void finalizeAddressDependentContent();
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void optimizeBasicBlockJumps();
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void sortInputSections();
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void finalizeSections();
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void checkExecuteOnly();
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void setReservedSymbolSections();
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SmallVector<PhdrEntry *, 0> createPhdrs(Partition &part);
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void addPhdrForSection(Partition &part, unsigned shType, unsigned pType,
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unsigned pFlags);
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void assignFileOffsets();
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void assignFileOffsetsBinary();
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void setPhdrs(Partition &part);
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void checkSections();
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void fixSectionAlignments();
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void openFile();
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void writeTrapInstr();
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void writeHeader();
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void writeSections();
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void writeSectionsBinary();
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void writeBuildId();
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std::unique_ptr<FileOutputBuffer> &buffer;
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void addRelIpltSymbols();
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void addStartEndSymbols();
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void addStartStopSymbols(OutputSection &osec);
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uint64_t fileSize;
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uint64_t sectionHeaderOff;
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};
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} // anonymous namespace
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static bool needsInterpSection() {
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return !config->relocatable && !config->shared &&
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!config->dynamicLinker.empty() && script->needsInterpSection();
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}
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template <class ELFT> void elf::writeResult() {
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Writer<ELFT>().run();
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}
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static void removeEmptyPTLoad(SmallVector<PhdrEntry *, 0> &phdrs) {
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auto it = std::stable_partition(
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phdrs.begin(), phdrs.end(), [&](const PhdrEntry *p) {
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if (p->p_type != PT_LOAD)
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return true;
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if (!p->firstSec)
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return false;
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uint64_t size = p->lastSec->addr + p->lastSec->size - p->firstSec->addr;
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return size != 0;
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});
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// Clear OutputSection::ptLoad for sections contained in removed
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// segments.
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DenseSet<PhdrEntry *> removed(it, phdrs.end());
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for (OutputSection *sec : outputSections)
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if (removed.count(sec->ptLoad))
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sec->ptLoad = nullptr;
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phdrs.erase(it, phdrs.end());
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}
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void elf::copySectionsIntoPartitions() {
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SmallVector<InputSectionBase *, 0> newSections;
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for (unsigned part = 2; part != partitions.size() + 1; ++part) {
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for (InputSectionBase *s : inputSections) {
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if (!(s->flags & SHF_ALLOC) || !s->isLive())
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continue;
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InputSectionBase *copy;
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if (s->type == SHT_NOTE)
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copy = make<InputSection>(cast<InputSection>(*s));
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else if (auto *es = dyn_cast<EhInputSection>(s))
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copy = make<EhInputSection>(*es);
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else
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continue;
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copy->partition = part;
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newSections.push_back(copy);
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}
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}
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inputSections.insert(inputSections.end(), newSections.begin(),
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newSections.end());
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}
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void elf::combineEhSections() {
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llvm::TimeTraceScope timeScope("Combine EH sections");
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for (InputSectionBase *&s : inputSections) {
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// Ignore dead sections and the partition end marker (.part.end),
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// whose partition number is out of bounds.
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if (!s->isLive() || s->partition == 255)
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continue;
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Partition &part = s->getPartition();
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if (auto *es = dyn_cast<EhInputSection>(s)) {
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part.ehFrame->addSection(es);
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s = nullptr;
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} else if (s->kind() == SectionBase::Regular && part.armExidx &&
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part.armExidx->addSection(cast<InputSection>(s))) {
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s = nullptr;
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}
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}
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llvm::erase_value(inputSections, nullptr);
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}
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static Defined *addOptionalRegular(StringRef name, SectionBase *sec,
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uint64_t val, uint8_t stOther = STV_HIDDEN) {
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Symbol *s = symtab->find(name);
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if (!s || s->isDefined() || s->isCommon())
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return nullptr;
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s->resolve(Defined{nullptr, StringRef(), STB_GLOBAL, stOther, STT_NOTYPE, val,
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/*size=*/0, sec});
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s->isUsedInRegularObj = true;
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return cast<Defined>(s);
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}
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static Defined *addAbsolute(StringRef name) {
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Symbol *sym = symtab->addSymbol(Defined{nullptr, name, STB_GLOBAL, STV_HIDDEN,
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STT_NOTYPE, 0, 0, nullptr});
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sym->isUsedInRegularObj = true;
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return cast<Defined>(sym);
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}
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// The linker is expected to define some symbols depending on
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// the linking result. This function defines such symbols.
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void elf::addReservedSymbols() {
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if (config->emachine == EM_MIPS) {
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// Define _gp for MIPS. st_value of _gp symbol will be updated by Writer
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// so that it points to an absolute address which by default is relative
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// to GOT. Default offset is 0x7ff0.
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// See "Global Data Symbols" in Chapter 6 in the following document:
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// ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
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ElfSym::mipsGp = addAbsolute("_gp");
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// On MIPS O32 ABI, _gp_disp is a magic symbol designates offset between
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// start of function and 'gp' pointer into GOT.
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if (symtab->find("_gp_disp"))
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ElfSym::mipsGpDisp = addAbsolute("_gp_disp");
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// The __gnu_local_gp is a magic symbol equal to the current value of 'gp'
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// pointer. This symbol is used in the code generated by .cpload pseudo-op
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// in case of using -mno-shared option.
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// https://sourceware.org/ml/binutils/2004-12/msg00094.html
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if (symtab->find("__gnu_local_gp"))
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ElfSym::mipsLocalGp = addAbsolute("__gnu_local_gp");
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} else if (config->emachine == EM_PPC) {
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// glibc *crt1.o has a undefined reference to _SDA_BASE_. Since we don't
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// support Small Data Area, define it arbitrarily as 0.
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addOptionalRegular("_SDA_BASE_", nullptr, 0, STV_HIDDEN);
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} else if (config->emachine == EM_PPC64) {
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addPPC64SaveRestore();
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}
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// The Power Architecture 64-bit v2 ABI defines a TableOfContents (TOC) which
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// combines the typical ELF GOT with the small data sections. It commonly
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// includes .got .toc .sdata .sbss. The .TOC. symbol replaces both
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// _GLOBAL_OFFSET_TABLE_ and _SDA_BASE_ from the 32-bit ABI. It is used to
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// represent the TOC base which is offset by 0x8000 bytes from the start of
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// the .got section.
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// We do not allow _GLOBAL_OFFSET_TABLE_ to be defined by input objects as the
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// correctness of some relocations depends on its value.
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StringRef gotSymName =
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(config->emachine == EM_PPC64) ? ".TOC." : "_GLOBAL_OFFSET_TABLE_";
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if (Symbol *s = symtab->find(gotSymName)) {
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if (s->isDefined()) {
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error(toString(s->file) + " cannot redefine linker defined symbol '" +
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gotSymName + "'");
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return;
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}
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uint64_t gotOff = 0;
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if (config->emachine == EM_PPC64)
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gotOff = 0x8000;
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s->resolve(Defined{/*file=*/nullptr, StringRef(), STB_GLOBAL, STV_HIDDEN,
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STT_NOTYPE, gotOff, /*size=*/0, Out::elfHeader});
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ElfSym::globalOffsetTable = cast<Defined>(s);
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}
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// __ehdr_start is the location of ELF file headers. Note that we define
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// this symbol unconditionally even when using a linker script, which
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// differs from the behavior implemented by GNU linker which only define
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// this symbol if ELF headers are in the memory mapped segment.
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addOptionalRegular("__ehdr_start", Out::elfHeader, 0, STV_HIDDEN);
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// __executable_start is not documented, but the expectation of at
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// least the Android libc is that it points to the ELF header.
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addOptionalRegular("__executable_start", Out::elfHeader, 0, STV_HIDDEN);
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// __dso_handle symbol is passed to cxa_finalize as a marker to identify
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// each DSO. The address of the symbol doesn't matter as long as they are
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// different in different DSOs, so we chose the start address of the DSO.
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addOptionalRegular("__dso_handle", Out::elfHeader, 0, STV_HIDDEN);
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// If linker script do layout we do not need to create any standard symbols.
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if (script->hasSectionsCommand)
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return;
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auto add = [](StringRef s, int64_t pos) {
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return addOptionalRegular(s, Out::elfHeader, pos, STV_DEFAULT);
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};
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ElfSym::bss = add("__bss_start", 0);
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ElfSym::end1 = add("end", -1);
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ElfSym::end2 = add("_end", -1);
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ElfSym::etext1 = add("etext", -1);
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ElfSym::etext2 = add("_etext", -1);
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ElfSym::edata1 = add("edata", -1);
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ElfSym::edata2 = add("_edata", -1);
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}
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static OutputSection *findSection(StringRef name, unsigned partition = 1) {
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for (SectionCommand *cmd : script->sectionCommands)
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if (auto *osd = dyn_cast<OutputDesc>(cmd))
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if (osd->osec.name == name && osd->osec.partition == partition)
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return &osd->osec;
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return nullptr;
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}
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template <class ELFT> void elf::createSyntheticSections() {
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// Initialize all pointers with NULL. This is needed because
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// you can call lld::elf::main more than once as a library.
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Out::tlsPhdr = nullptr;
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Out::preinitArray = nullptr;
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Out::initArray = nullptr;
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Out::finiArray = nullptr;
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// Add the .interp section first because it is not a SyntheticSection.
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// The removeUnusedSyntheticSections() function relies on the
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// SyntheticSections coming last.
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if (needsInterpSection()) {
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for (size_t i = 1; i <= partitions.size(); ++i) {
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InputSection *sec = createInterpSection();
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sec->partition = i;
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inputSections.push_back(sec);
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}
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}
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auto add = [](SyntheticSection &sec) { inputSections.push_back(&sec); };
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in.shStrTab = std::make_unique<StringTableSection>(".shstrtab", false);
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Out::programHeaders = make<OutputSection>("", 0, SHF_ALLOC);
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Out::programHeaders->alignment = config->wordsize;
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if (config->strip != StripPolicy::All) {
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in.strTab = std::make_unique<StringTableSection>(".strtab", false);
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in.symTab = std::make_unique<SymbolTableSection<ELFT>>(*in.strTab);
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in.symTabShndx = std::make_unique<SymtabShndxSection>();
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}
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in.bss = std::make_unique<BssSection>(".bss", 0, 1);
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add(*in.bss);
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// If there is a SECTIONS command and a .data.rel.ro section name use name
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// .data.rel.ro.bss so that we match in the .data.rel.ro output section.
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// This makes sure our relro is contiguous.
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bool hasDataRelRo = script->hasSectionsCommand && findSection(".data.rel.ro");
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in.bssRelRo = std::make_unique<BssSection>(
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hasDataRelRo ? ".data.rel.ro.bss" : ".bss.rel.ro", 0, 1);
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add(*in.bssRelRo);
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// Add MIPS-specific sections.
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if (config->emachine == EM_MIPS) {
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if (!config->shared && config->hasDynSymTab) {
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in.mipsRldMap = std::make_unique<MipsRldMapSection>();
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add(*in.mipsRldMap);
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}
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if ((in.mipsAbiFlags = MipsAbiFlagsSection<ELFT>::create()))
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add(*in.mipsAbiFlags);
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if ((in.mipsOptions = MipsOptionsSection<ELFT>::create()))
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add(*in.mipsOptions);
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if ((in.mipsReginfo = MipsReginfoSection<ELFT>::create()))
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add(*in.mipsReginfo);
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}
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StringRef relaDynName = config->isRela ? ".rela.dyn" : ".rel.dyn";
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for (Partition &part : partitions) {
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auto add = [&](SyntheticSection &sec) {
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sec.partition = part.getNumber();
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inputSections.push_back(&sec);
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};
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if (!part.name.empty()) {
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part.elfHeader = std::make_unique<PartitionElfHeaderSection<ELFT>>();
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part.elfHeader->name = part.name;
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add(*part.elfHeader);
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part.programHeaders =
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std::make_unique<PartitionProgramHeadersSection<ELFT>>();
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add(*part.programHeaders);
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}
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if (config->buildId != BuildIdKind::None) {
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part.buildId = std::make_unique<BuildIdSection>();
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add(*part.buildId);
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}
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part.dynStrTab = std::make_unique<StringTableSection>(".dynstr", true);
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part.dynSymTab =
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std::make_unique<SymbolTableSection<ELFT>>(*part.dynStrTab);
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part.dynamic = std::make_unique<DynamicSection<ELFT>>();
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if (config->emachine == EM_AARCH64 &&
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config->androidMemtagMode != ELF::NT_MEMTAG_LEVEL_NONE) {
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part.memtagAndroidNote = std::make_unique<MemtagAndroidNote>();
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add(*part.memtagAndroidNote);
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}
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if (config->androidPackDynRelocs)
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part.relaDyn =
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std::make_unique<AndroidPackedRelocationSection<ELFT>>(relaDynName);
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else
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part.relaDyn = std::make_unique<RelocationSection<ELFT>>(
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relaDynName, config->zCombreloc);
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if (config->hasDynSymTab) {
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add(*part.dynSymTab);
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part.verSym = std::make_unique<VersionTableSection>();
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add(*part.verSym);
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if (!namedVersionDefs().empty()) {
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part.verDef = std::make_unique<VersionDefinitionSection>();
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add(*part.verDef);
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}
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part.verNeed = std::make_unique<VersionNeedSection<ELFT>>();
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add(*part.verNeed);
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if (config->gnuHash) {
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part.gnuHashTab = std::make_unique<GnuHashTableSection>();
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add(*part.gnuHashTab);
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}
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if (config->sysvHash) {
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part.hashTab = std::make_unique<HashTableSection>();
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add(*part.hashTab);
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}
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add(*part.dynamic);
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add(*part.dynStrTab);
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add(*part.relaDyn);
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}
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if (config->relrPackDynRelocs) {
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part.relrDyn = std::make_unique<RelrSection<ELFT>>();
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add(*part.relrDyn);
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}
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if (!config->relocatable) {
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if (config->ehFrameHdr) {
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part.ehFrameHdr = std::make_unique<EhFrameHeader>();
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add(*part.ehFrameHdr);
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}
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part.ehFrame = std::make_unique<EhFrameSection>();
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add(*part.ehFrame);
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}
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if (config->emachine == EM_ARM && !config->relocatable) {
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// The ARMExidxsyntheticsection replaces all the individual .ARM.exidx
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// InputSections.
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part.armExidx = std::make_unique<ARMExidxSyntheticSection>();
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add(*part.armExidx);
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}
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}
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if (partitions.size() != 1) {
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// Create the partition end marker. This needs to be in partition number 255
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// so that it is sorted after all other partitions. It also has other
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// special handling (see createPhdrs() and combineEhSections()).
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in.partEnd =
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std::make_unique<BssSection>(".part.end", config->maxPageSize, 1);
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in.partEnd->partition = 255;
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add(*in.partEnd);
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in.partIndex = std::make_unique<PartitionIndexSection>();
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addOptionalRegular("__part_index_begin", in.partIndex.get(), 0);
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addOptionalRegular("__part_index_end", in.partIndex.get(),
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in.partIndex->getSize());
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add(*in.partIndex);
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}
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// Add .got. MIPS' .got is so different from the other archs,
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// it has its own class.
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if (config->emachine == EM_MIPS) {
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in.mipsGot = std::make_unique<MipsGotSection>();
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add(*in.mipsGot);
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} else {
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in.got = std::make_unique<GotSection>();
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add(*in.got);
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}
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if (config->emachine == EM_PPC) {
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in.ppc32Got2 = std::make_unique<PPC32Got2Section>();
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add(*in.ppc32Got2);
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}
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if (config->emachine == EM_PPC64) {
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in.ppc64LongBranchTarget = std::make_unique<PPC64LongBranchTargetSection>();
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add(*in.ppc64LongBranchTarget);
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}
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in.gotPlt = std::make_unique<GotPltSection>();
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add(*in.gotPlt);
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in.igotPlt = std::make_unique<IgotPltSection>();
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add(*in.igotPlt);
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|
|
// _GLOBAL_OFFSET_TABLE_ is defined relative to either .got.plt or .got. Treat
|
|
// it as a relocation and ensure the referenced section is created.
|
|
if (ElfSym::globalOffsetTable && config->emachine != EM_MIPS) {
|
|
if (target->gotBaseSymInGotPlt)
|
|
in.gotPlt->hasGotPltOffRel = true;
|
|
else
|
|
in.got->hasGotOffRel = true;
|
|
}
|
|
|
|
if (config->gdbIndex)
|
|
add(*GdbIndexSection::create<ELFT>());
|
|
|
|
// We always need to add rel[a].plt to output if it has entries.
|
|
// Even for static linking it can contain R_[*]_IRELATIVE relocations.
|
|
in.relaPlt = std::make_unique<RelocationSection<ELFT>>(
|
|
config->isRela ? ".rela.plt" : ".rel.plt", /*sort=*/false);
|
|
add(*in.relaPlt);
|
|
|
|
// The relaIplt immediately follows .rel[a].dyn to ensure that the IRelative
|
|
// relocations are processed last by the dynamic loader. We cannot place the
|
|
// iplt section in .rel.dyn when Android relocation packing is enabled because
|
|
// that would cause a section type mismatch. However, because the Android
|
|
// dynamic loader reads .rel.plt after .rel.dyn, we can get the desired
|
|
// behaviour by placing the iplt section in .rel.plt.
|
|
in.relaIplt = std::make_unique<RelocationSection<ELFT>>(
|
|
config->androidPackDynRelocs ? in.relaPlt->name : relaDynName,
|
|
/*sort=*/false);
|
|
add(*in.relaIplt);
|
|
|
|
if ((config->emachine == EM_386 || config->emachine == EM_X86_64) &&
|
|
(config->andFeatures & GNU_PROPERTY_X86_FEATURE_1_IBT)) {
|
|
in.ibtPlt = std::make_unique<IBTPltSection>();
|
|
add(*in.ibtPlt);
|
|
}
|
|
|
|
if (config->emachine == EM_PPC)
|
|
in.plt = std::make_unique<PPC32GlinkSection>();
|
|
else
|
|
in.plt = std::make_unique<PltSection>();
|
|
add(*in.plt);
|
|
in.iplt = std::make_unique<IpltSection>();
|
|
add(*in.iplt);
|
|
|
|
if (config->andFeatures)
|
|
add(*make<GnuPropertySection>());
|
|
|
|
// .note.GNU-stack is always added when we are creating a re-linkable
|
|
// object file. Other linkers are using the presence of this marker
|
|
// section to control the executable-ness of the stack area, but that
|
|
// is irrelevant these days. Stack area should always be non-executable
|
|
// by default. So we emit this section unconditionally.
|
|
if (config->relocatable)
|
|
add(*make<GnuStackSection>());
|
|
|
|
if (in.symTab)
|
|
add(*in.symTab);
|
|
if (in.symTabShndx)
|
|
add(*in.symTabShndx);
|
|
add(*in.shStrTab);
|
|
if (in.strTab)
|
|
add(*in.strTab);
|
|
}
|
|
|
|
// The main function of the writer.
|
|
template <class ELFT> void Writer<ELFT>::run() {
|
|
copyLocalSymbols();
|
|
|
|
if (config->copyRelocs)
|
|
addSectionSymbols();
|
|
|
|
// Now that we have a complete set of output sections. This function
|
|
// completes section contents. For example, we need to add strings
|
|
// to the string table, and add entries to .got and .plt.
|
|
// finalizeSections does that.
|
|
finalizeSections();
|
|
checkExecuteOnly();
|
|
|
|
// If --compressed-debug-sections is specified, compress .debug_* sections.
|
|
// Do it right now because it changes the size of output sections.
|
|
for (OutputSection *sec : outputSections)
|
|
sec->maybeCompress<ELFT>();
|
|
|
|
if (script->hasSectionsCommand)
|
|
script->allocateHeaders(mainPart->phdrs);
|
|
|
|
// Remove empty PT_LOAD to avoid causing the dynamic linker to try to mmap a
|
|
// 0 sized region. This has to be done late since only after assignAddresses
|
|
// we know the size of the sections.
|
|
for (Partition &part : partitions)
|
|
removeEmptyPTLoad(part.phdrs);
|
|
|
|
if (!config->oFormatBinary)
|
|
assignFileOffsets();
|
|
else
|
|
assignFileOffsetsBinary();
|
|
|
|
for (Partition &part : partitions)
|
|
setPhdrs(part);
|
|
|
|
// Handle --print-map(-M)/--Map and --cref. Dump them before checkSections()
|
|
// because the files may be useful in case checkSections() or openFile()
|
|
// fails, for example, due to an erroneous file size.
|
|
writeMapAndCref();
|
|
|
|
if (config->checkSections)
|
|
checkSections();
|
|
|
|
// It does not make sense try to open the file if we have error already.
|
|
if (errorCount())
|
|
return;
|
|
|
|
{
|
|
llvm::TimeTraceScope timeScope("Write output file");
|
|
// Write the result down to a file.
|
|
openFile();
|
|
if (errorCount())
|
|
return;
|
|
|
|
if (!config->oFormatBinary) {
|
|
if (config->zSeparate != SeparateSegmentKind::None)
|
|
writeTrapInstr();
|
|
writeHeader();
|
|
writeSections();
|
|
} else {
|
|
writeSectionsBinary();
|
|
}
|
|
|
|
// Backfill .note.gnu.build-id section content. This is done at last
|
|
// because the content is usually a hash value of the entire output file.
|
|
writeBuildId();
|
|
if (errorCount())
|
|
return;
|
|
|
|
if (auto e = buffer->commit())
|
|
error("failed to write to the output file: " + toString(std::move(e)));
|
|
}
|
|
}
|
|
|
|
template <class ELFT, class RelTy>
|
|
static void markUsedLocalSymbolsImpl(ObjFile<ELFT> *file,
|
|
llvm::ArrayRef<RelTy> rels) {
|
|
for (const RelTy &rel : rels) {
|
|
Symbol &sym = file->getRelocTargetSym(rel);
|
|
if (sym.isLocal())
|
|
sym.used = true;
|
|
}
|
|
}
|
|
|
|
// The function ensures that the "used" field of local symbols reflects the fact
|
|
// that the symbol is used in a relocation from a live section.
|
|
template <class ELFT> static void markUsedLocalSymbols() {
|
|
// With --gc-sections, the field is already filled.
|
|
// See MarkLive<ELFT>::resolveReloc().
|
|
if (config->gcSections)
|
|
return;
|
|
for (ELFFileBase *file : objectFiles) {
|
|
ObjFile<ELFT> *f = cast<ObjFile<ELFT>>(file);
|
|
for (InputSectionBase *s : f->getSections()) {
|
|
InputSection *isec = dyn_cast_or_null<InputSection>(s);
|
|
if (!isec)
|
|
continue;
|
|
if (isec->type == SHT_REL)
|
|
markUsedLocalSymbolsImpl(f, isec->getDataAs<typename ELFT::Rel>());
|
|
else if (isec->type == SHT_RELA)
|
|
markUsedLocalSymbolsImpl(f, isec->getDataAs<typename ELFT::Rela>());
|
|
}
|
|
}
|
|
}
|
|
|
|
static bool shouldKeepInSymtab(const Defined &sym) {
|
|
if (sym.isSection())
|
|
return false;
|
|
|
|
// If --emit-reloc or -r is given, preserve symbols referenced by relocations
|
|
// from live sections.
|
|
if (sym.used && config->copyRelocs)
|
|
return true;
|
|
|
|
// Exclude local symbols pointing to .ARM.exidx sections.
|
|
// They are probably mapping symbols "$d", which are optional for these
|
|
// sections. After merging the .ARM.exidx sections, some of these symbols
|
|
// may become dangling. The easiest way to avoid the issue is not to add
|
|
// them to the symbol table from the beginning.
|
|
if (config->emachine == EM_ARM && sym.section &&
|
|
sym.section->type == SHT_ARM_EXIDX)
|
|
return false;
|
|
|
|
if (config->discard == DiscardPolicy::None)
|
|
return true;
|
|
if (config->discard == DiscardPolicy::All)
|
|
return false;
|
|
|
|
// In ELF assembly .L symbols are normally discarded by the assembler.
|
|
// If the assembler fails to do so, the linker discards them if
|
|
// * --discard-locals is used.
|
|
// * The symbol is in a SHF_MERGE section, which is normally the reason for
|
|
// the assembler keeping the .L symbol.
|
|
if (sym.getName().startswith(".L") &&
|
|
(config->discard == DiscardPolicy::Locals ||
|
|
(sym.section && (sym.section->flags & SHF_MERGE))))
|
|
return false;
|
|
return true;
|
|
}
|
|
|
|
static bool includeInSymtab(const Symbol &b) {
|
|
if (auto *d = dyn_cast<Defined>(&b)) {
|
|
// Always include absolute symbols.
|
|
SectionBase *sec = d->section;
|
|
if (!sec)
|
|
return true;
|
|
|
|
if (auto *s = dyn_cast<MergeInputSection>(sec))
|
|
return s->getSectionPiece(d->value).live;
|
|
return sec->isLive();
|
|
}
|
|
return b.used || !config->gcSections;
|
|
}
|
|
|
|
// Local symbols are not in the linker's symbol table. This function scans
|
|
// each object file's symbol table to copy local symbols to the output.
|
|
template <class ELFT> void Writer<ELFT>::copyLocalSymbols() {
|
|
if (!in.symTab)
|
|
return;
|
|
llvm::TimeTraceScope timeScope("Add local symbols");
|
|
if (config->copyRelocs && config->discard != DiscardPolicy::None)
|
|
markUsedLocalSymbols<ELFT>();
|
|
for (ELFFileBase *file : objectFiles) {
|
|
for (Symbol *b : file->getLocalSymbols()) {
|
|
assert(b->isLocal() && "should have been caught in initializeSymbols()");
|
|
auto *dr = dyn_cast<Defined>(b);
|
|
|
|
// No reason to keep local undefined symbol in symtab.
|
|
if (!dr)
|
|
continue;
|
|
if (includeInSymtab(*b) && shouldKeepInSymtab(*dr))
|
|
in.symTab->addSymbol(b);
|
|
}
|
|
}
|
|
}
|
|
|
|
// Create a section symbol for each output section so that we can represent
|
|
// relocations that point to the section. If we know that no relocation is
|
|
// referring to a section (that happens if the section is a synthetic one), we
|
|
// don't create a section symbol for that section.
|
|
template <class ELFT> void Writer<ELFT>::addSectionSymbols() {
|
|
for (SectionCommand *cmd : script->sectionCommands) {
|
|
auto *osd = dyn_cast<OutputDesc>(cmd);
|
|
if (!osd)
|
|
continue;
|
|
OutputSection &osec = osd->osec;
|
|
InputSectionBase *isec = nullptr;
|
|
// Iterate over all input sections and add a STT_SECTION symbol if any input
|
|
// section may be a relocation target.
|
|
for (SectionCommand *cmd : osec.commands) {
|
|
auto *isd = dyn_cast<InputSectionDescription>(cmd);
|
|
if (!isd)
|
|
continue;
|
|
for (InputSectionBase *s : isd->sections) {
|
|
// Relocations are not using REL[A] section symbols.
|
|
if (s->type == SHT_REL || s->type == SHT_RELA)
|
|
continue;
|
|
|
|
// Unlike other synthetic sections, mergeable output sections contain
|
|
// data copied from input sections, and there may be a relocation
|
|
// pointing to its contents if -r or --emit-reloc is given.
|
|
if (isa<SyntheticSection>(s) && !(s->flags & SHF_MERGE))
|
|
continue;
|
|
|
|
isec = s;
|
|
break;
|
|
}
|
|
}
|
|
if (!isec)
|
|
continue;
|
|
|
|
// Set the symbol to be relative to the output section so that its st_value
|
|
// equals the output section address. Note, there may be a gap between the
|
|
// start of the output section and isec.
|
|
in.symTab->addSymbol(makeDefined(isec->file, "", STB_LOCAL, /*stOther=*/0,
|
|
STT_SECTION,
|
|
/*value=*/0, /*size=*/0, &osec));
|
|
}
|
|
}
|
|
|
|
// Today's loaders have a feature to make segments read-only after
|
|
// processing dynamic relocations to enhance security. PT_GNU_RELRO
|
|
// is defined for that.
|
|
//
|
|
// This function returns true if a section needs to be put into a
|
|
// PT_GNU_RELRO segment.
|
|
static bool isRelroSection(const OutputSection *sec) {
|
|
if (!config->zRelro)
|
|
return false;
|
|
if (sec->relro)
|
|
return true;
|
|
|
|
uint64_t flags = sec->flags;
|
|
|
|
// Non-allocatable or non-writable sections don't need RELRO because
|
|
// they are not writable or not even mapped to memory in the first place.
|
|
// RELRO is for sections that are essentially read-only but need to
|
|
// be writable only at process startup to allow dynamic linker to
|
|
// apply relocations.
|
|
if (!(flags & SHF_ALLOC) || !(flags & SHF_WRITE))
|
|
return false;
|
|
|
|
// Once initialized, TLS data segments are used as data templates
|
|
// for a thread-local storage. For each new thread, runtime
|
|
// allocates memory for a TLS and copy templates there. No thread
|
|
// are supposed to use templates directly. Thus, it can be in RELRO.
|
|
if (flags & SHF_TLS)
|
|
return true;
|
|
|
|
// .init_array, .preinit_array and .fini_array contain pointers to
|
|
// functions that are executed on process startup or exit. These
|
|
// pointers are set by the static linker, and they are not expected
|
|
// to change at runtime. But if you are an attacker, you could do
|
|
// interesting things by manipulating pointers in .fini_array, for
|
|
// example. So they are put into RELRO.
|
|
uint32_t type = sec->type;
|
|
if (type == SHT_INIT_ARRAY || type == SHT_FINI_ARRAY ||
|
|
type == SHT_PREINIT_ARRAY)
|
|
return true;
|
|
|
|
// .got contains pointers to external symbols. They are resolved by
|
|
// the dynamic linker when a module is loaded into memory, and after
|
|
// that they are not expected to change. So, it can be in RELRO.
|
|
if (in.got && sec == in.got->getParent())
|
|
return true;
|
|
|
|
// .toc is a GOT-ish section for PowerPC64. Their contents are accessed
|
|
// through r2 register, which is reserved for that purpose. Since r2 is used
|
|
// for accessing .got as well, .got and .toc need to be close enough in the
|
|
// virtual address space. Usually, .toc comes just after .got. Since we place
|
|
// .got into RELRO, .toc needs to be placed into RELRO too.
|
|
if (sec->name.equals(".toc"))
|
|
return true;
|
|
|
|
// .got.plt contains pointers to external function symbols. They are
|
|
// by default resolved lazily, so we usually cannot put it into RELRO.
|
|
// However, if "-z now" is given, the lazy symbol resolution is
|
|
// disabled, which enables us to put it into RELRO.
|
|
if (sec == in.gotPlt->getParent())
|
|
return config->zNow;
|
|
|
|
// .dynamic section contains data for the dynamic linker, and
|
|
// there's no need to write to it at runtime, so it's better to put
|
|
// it into RELRO.
|
|
if (sec->name == ".dynamic")
|
|
return true;
|
|
|
|
// Sections with some special names are put into RELRO. This is a
|
|
// bit unfortunate because section names shouldn't be significant in
|
|
// ELF in spirit. But in reality many linker features depend on
|
|
// magic section names.
|
|
StringRef s = sec->name;
|
|
return s == ".data.rel.ro" || s == ".bss.rel.ro" || s == ".ctors" ||
|
|
s == ".dtors" || s == ".jcr" || s == ".eh_frame" ||
|
|
s == ".fini_array" || s == ".init_array" ||
|
|
s == ".openbsd.randomdata" || s == ".preinit_array";
|
|
}
|
|
|
|
// We compute a rank for each section. The rank indicates where the
|
|
// section should be placed in the file. Instead of using simple
|
|
// numbers (0,1,2...), we use a series of flags. One for each decision
|
|
// point when placing the section.
|
|
// Using flags has two key properties:
|
|
// * It is easy to check if a give branch was taken.
|
|
// * It is easy two see how similar two ranks are (see getRankProximity).
|
|
enum RankFlags {
|
|
RF_NOT_ADDR_SET = 1 << 27,
|
|
RF_NOT_ALLOC = 1 << 26,
|
|
RF_PARTITION = 1 << 18, // Partition number (8 bits)
|
|
RF_NOT_PART_EHDR = 1 << 17,
|
|
RF_NOT_PART_PHDR = 1 << 16,
|
|
RF_NOT_INTERP = 1 << 15,
|
|
RF_NOT_NOTE = 1 << 14,
|
|
RF_WRITE = 1 << 13,
|
|
RF_EXEC_WRITE = 1 << 12,
|
|
RF_EXEC = 1 << 11,
|
|
RF_RODATA = 1 << 10,
|
|
RF_NOT_RELRO = 1 << 9,
|
|
RF_NOT_TLS = 1 << 8,
|
|
RF_BSS = 1 << 7,
|
|
RF_PPC_NOT_TOCBSS = 1 << 6,
|
|
RF_PPC_TOCL = 1 << 5,
|
|
RF_PPC_TOC = 1 << 4,
|
|
RF_PPC_GOT = 1 << 3,
|
|
RF_PPC_BRANCH_LT = 1 << 2,
|
|
RF_MIPS_GPREL = 1 << 1,
|
|
RF_MIPS_NOT_GOT = 1 << 0
|
|
};
|
|
|
|
static unsigned getSectionRank(const OutputSection &osec) {
|
|
unsigned rank = osec.partition * RF_PARTITION;
|
|
|
|
// We want to put section specified by -T option first, so we
|
|
// can start assigning VA starting from them later.
|
|
if (config->sectionStartMap.count(osec.name))
|
|
return rank;
|
|
rank |= RF_NOT_ADDR_SET;
|
|
|
|
// Allocatable sections go first to reduce the total PT_LOAD size and
|
|
// so debug info doesn't change addresses in actual code.
|
|
if (!(osec.flags & SHF_ALLOC))
|
|
return rank | RF_NOT_ALLOC;
|
|
|
|
if (osec.type == SHT_LLVM_PART_EHDR)
|
|
return rank;
|
|
rank |= RF_NOT_PART_EHDR;
|
|
|
|
if (osec.type == SHT_LLVM_PART_PHDR)
|
|
return rank;
|
|
rank |= RF_NOT_PART_PHDR;
|
|
|
|
// Put .interp first because some loaders want to see that section
|
|
// on the first page of the executable file when loaded into memory.
|
|
if (osec.name == ".interp")
|
|
return rank;
|
|
rank |= RF_NOT_INTERP;
|
|
|
|
// Put .note sections (which make up one PT_NOTE) at the beginning so that
|
|
// they are likely to be included in a core file even if core file size is
|
|
// limited. In particular, we want a .note.gnu.build-id and a .note.tag to be
|
|
// included in a core to match core files with executables.
|
|
if (osec.type == SHT_NOTE)
|
|
return rank;
|
|
rank |= RF_NOT_NOTE;
|
|
|
|
// Sort sections based on their access permission in the following
|
|
// order: R, RX, RWX, RW. This order is based on the following
|
|
// considerations:
|
|
// * Read-only sections come first such that they go in the
|
|
// PT_LOAD covering the program headers at the start of the file.
|
|
// * Read-only, executable sections come next.
|
|
// * Writable, executable sections follow such that .plt on
|
|
// architectures where it needs to be writable will be placed
|
|
// between .text and .data.
|
|
// * Writable sections come last, such that .bss lands at the very
|
|
// end of the last PT_LOAD.
|
|
bool isExec = osec.flags & SHF_EXECINSTR;
|
|
bool isWrite = osec.flags & SHF_WRITE;
|
|
|
|
if (isExec) {
|
|
if (isWrite)
|
|
rank |= RF_EXEC_WRITE;
|
|
else
|
|
rank |= RF_EXEC;
|
|
} else if (isWrite) {
|
|
rank |= RF_WRITE;
|
|
} else if (osec.type == SHT_PROGBITS) {
|
|
// Make non-executable and non-writable PROGBITS sections (e.g .rodata
|
|
// .eh_frame) closer to .text. They likely contain PC or GOT relative
|
|
// relocations and there could be relocation overflow if other huge sections
|
|
// (.dynstr .dynsym) were placed in between.
|
|
rank |= RF_RODATA;
|
|
}
|
|
|
|
// Place RelRo sections first. After considering SHT_NOBITS below, the
|
|
// ordering is PT_LOAD(PT_GNU_RELRO(.data.rel.ro .bss.rel.ro) | .data .bss),
|
|
// where | marks where page alignment happens. An alternative ordering is
|
|
// PT_LOAD(.data | PT_GNU_RELRO( .data.rel.ro .bss.rel.ro) | .bss), but it may
|
|
// waste more bytes due to 2 alignment places.
|
|
if (!isRelroSection(&osec))
|
|
rank |= RF_NOT_RELRO;
|
|
|
|
// If we got here we know that both A and B are in the same PT_LOAD.
|
|
|
|
// The TLS initialization block needs to be a single contiguous block in a R/W
|
|
// PT_LOAD, so stick TLS sections directly before the other RelRo R/W
|
|
// sections. Since p_filesz can be less than p_memsz, place NOBITS sections
|
|
// after PROGBITS.
|
|
if (!(osec.flags & SHF_TLS))
|
|
rank |= RF_NOT_TLS;
|
|
|
|
// Within TLS sections, or within other RelRo sections, or within non-RelRo
|
|
// sections, place non-NOBITS sections first.
|
|
if (osec.type == SHT_NOBITS)
|
|
rank |= RF_BSS;
|
|
|
|
// Some architectures have additional ordering restrictions for sections
|
|
// within the same PT_LOAD.
|
|
if (config->emachine == EM_PPC64) {
|
|
// PPC64 has a number of special SHT_PROGBITS+SHF_ALLOC+SHF_WRITE sections
|
|
// that we would like to make sure appear is a specific order to maximize
|
|
// their coverage by a single signed 16-bit offset from the TOC base
|
|
// pointer. Conversely, the special .tocbss section should be first among
|
|
// all SHT_NOBITS sections. This will put it next to the loaded special
|
|
// PPC64 sections (and, thus, within reach of the TOC base pointer).
|
|
StringRef name = osec.name;
|
|
if (name != ".tocbss")
|
|
rank |= RF_PPC_NOT_TOCBSS;
|
|
|
|
if (name == ".toc1")
|
|
rank |= RF_PPC_TOCL;
|
|
|
|
if (name == ".toc")
|
|
rank |= RF_PPC_TOC;
|
|
|
|
if (name == ".got")
|
|
rank |= RF_PPC_GOT;
|
|
|
|
if (name == ".branch_lt")
|
|
rank |= RF_PPC_BRANCH_LT;
|
|
}
|
|
|
|
if (config->emachine == EM_MIPS) {
|
|
// All sections with SHF_MIPS_GPREL flag should be grouped together
|
|
// because data in these sections is addressable with a gp relative address.
|
|
if (osec.flags & SHF_MIPS_GPREL)
|
|
rank |= RF_MIPS_GPREL;
|
|
|
|
if (osec.name != ".got")
|
|
rank |= RF_MIPS_NOT_GOT;
|
|
}
|
|
|
|
return rank;
|
|
}
|
|
|
|
static bool compareSections(const SectionCommand *aCmd,
|
|
const SectionCommand *bCmd) {
|
|
const OutputSection *a = &cast<OutputDesc>(aCmd)->osec;
|
|
const OutputSection *b = &cast<OutputDesc>(bCmd)->osec;
|
|
|
|
if (a->sortRank != b->sortRank)
|
|
return a->sortRank < b->sortRank;
|
|
|
|
if (!(a->sortRank & RF_NOT_ADDR_SET))
|
|
return config->sectionStartMap.lookup(a->name) <
|
|
config->sectionStartMap.lookup(b->name);
|
|
return false;
|
|
}
|
|
|
|
void PhdrEntry::add(OutputSection *sec) {
|
|
lastSec = sec;
|
|
if (!firstSec)
|
|
firstSec = sec;
|
|
p_align = std::max(p_align, sec->alignment);
|
|
if (p_type == PT_LOAD)
|
|
sec->ptLoad = this;
|
|
}
|
|
|
|
// The beginning and the ending of .rel[a].plt section are marked
|
|
// with __rel[a]_iplt_{start,end} symbols if it is a statically linked
|
|
// executable. The runtime needs these symbols in order to resolve
|
|
// all IRELATIVE relocs on startup. For dynamic executables, we don't
|
|
// need these symbols, since IRELATIVE relocs are resolved through GOT
|
|
// and PLT. For details, see http://www.airs.com/blog/archives/403.
|
|
template <class ELFT> void Writer<ELFT>::addRelIpltSymbols() {
|
|
if (config->relocatable || config->isPic)
|
|
return;
|
|
|
|
// By default, __rela_iplt_{start,end} belong to a dummy section 0
|
|
// because .rela.plt might be empty and thus removed from output.
|
|
// We'll override Out::elfHeader with In.relaIplt later when we are
|
|
// sure that .rela.plt exists in output.
|
|
ElfSym::relaIpltStart = addOptionalRegular(
|
|
config->isRela ? "__rela_iplt_start" : "__rel_iplt_start",
|
|
Out::elfHeader, 0, STV_HIDDEN);
|
|
|
|
ElfSym::relaIpltEnd = addOptionalRegular(
|
|
config->isRela ? "__rela_iplt_end" : "__rel_iplt_end",
|
|
Out::elfHeader, 0, STV_HIDDEN);
|
|
}
|
|
|
|
// This function generates assignments for predefined symbols (e.g. _end or
|
|
// _etext) and inserts them into the commands sequence to be processed at the
|
|
// appropriate time. This ensures that the value is going to be correct by the
|
|
// time any references to these symbols are processed and is equivalent to
|
|
// defining these symbols explicitly in the linker script.
|
|
template <class ELFT> void Writer<ELFT>::setReservedSymbolSections() {
|
|
if (ElfSym::globalOffsetTable) {
|
|
// The _GLOBAL_OFFSET_TABLE_ symbol is defined by target convention usually
|
|
// to the start of the .got or .got.plt section.
|
|
InputSection *sec = in.gotPlt.get();
|
|
if (!target->gotBaseSymInGotPlt)
|
|
sec = in.mipsGot.get() ? cast<InputSection>(in.mipsGot.get())
|
|
: cast<InputSection>(in.got.get());
|
|
ElfSym::globalOffsetTable->section = sec;
|
|
}
|
|
|
|
// .rela_iplt_{start,end} mark the start and the end of in.relaIplt.
|
|
if (ElfSym::relaIpltStart && in.relaIplt->isNeeded()) {
|
|
ElfSym::relaIpltStart->section = in.relaIplt.get();
|
|
ElfSym::relaIpltEnd->section = in.relaIplt.get();
|
|
ElfSym::relaIpltEnd->value = in.relaIplt->getSize();
|
|
}
|
|
|
|
PhdrEntry *last = nullptr;
|
|
PhdrEntry *lastRO = nullptr;
|
|
|
|
for (Partition &part : partitions) {
|
|
for (PhdrEntry *p : part.phdrs) {
|
|
if (p->p_type != PT_LOAD)
|
|
continue;
|
|
last = p;
|
|
if (!(p->p_flags & PF_W))
|
|
lastRO = p;
|
|
}
|
|
}
|
|
|
|
if (lastRO) {
|
|
// _etext is the first location after the last read-only loadable segment.
|
|
if (ElfSym::etext1)
|
|
ElfSym::etext1->section = lastRO->lastSec;
|
|
if (ElfSym::etext2)
|
|
ElfSym::etext2->section = lastRO->lastSec;
|
|
}
|
|
|
|
if (last) {
|
|
// _edata points to the end of the last mapped initialized section.
|
|
OutputSection *edata = nullptr;
|
|
for (OutputSection *os : outputSections) {
|
|
if (os->type != SHT_NOBITS)
|
|
edata = os;
|
|
if (os == last->lastSec)
|
|
break;
|
|
}
|
|
|
|
if (ElfSym::edata1)
|
|
ElfSym::edata1->section = edata;
|
|
if (ElfSym::edata2)
|
|
ElfSym::edata2->section = edata;
|
|
|
|
// _end is the first location after the uninitialized data region.
|
|
if (ElfSym::end1)
|
|
ElfSym::end1->section = last->lastSec;
|
|
if (ElfSym::end2)
|
|
ElfSym::end2->section = last->lastSec;
|
|
}
|
|
|
|
if (ElfSym::bss)
|
|
ElfSym::bss->section = findSection(".bss");
|
|
|
|
// Setup MIPS _gp_disp/__gnu_local_gp symbols which should
|
|
// be equal to the _gp symbol's value.
|
|
if (ElfSym::mipsGp) {
|
|
// Find GP-relative section with the lowest address
|
|
// and use this address to calculate default _gp value.
|
|
for (OutputSection *os : outputSections) {
|
|
if (os->flags & SHF_MIPS_GPREL) {
|
|
ElfSym::mipsGp->section = os;
|
|
ElfSym::mipsGp->value = 0x7ff0;
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
// We want to find how similar two ranks are.
|
|
// The more branches in getSectionRank that match, the more similar they are.
|
|
// Since each branch corresponds to a bit flag, we can just use
|
|
// countLeadingZeros.
|
|
static int getRankProximityAux(const OutputSection &a, const OutputSection &b) {
|
|
return countLeadingZeros(a.sortRank ^ b.sortRank);
|
|
}
|
|
|
|
static int getRankProximity(OutputSection *a, SectionCommand *b) {
|
|
auto *osd = dyn_cast<OutputDesc>(b);
|
|
return (osd && osd->osec.hasInputSections)
|
|
? getRankProximityAux(*a, osd->osec)
|
|
: -1;
|
|
}
|
|
|
|
// When placing orphan sections, we want to place them after symbol assignments
|
|
// so that an orphan after
|
|
// begin_foo = .;
|
|
// foo : { *(foo) }
|
|
// end_foo = .;
|
|
// doesn't break the intended meaning of the begin/end symbols.
|
|
// We don't want to go over sections since findOrphanPos is the
|
|
// one in charge of deciding the order of the sections.
|
|
// We don't want to go over changes to '.', since doing so in
|
|
// rx_sec : { *(rx_sec) }
|
|
// . = ALIGN(0x1000);
|
|
// /* The RW PT_LOAD starts here*/
|
|
// rw_sec : { *(rw_sec) }
|
|
// would mean that the RW PT_LOAD would become unaligned.
|
|
static bool shouldSkip(SectionCommand *cmd) {
|
|
if (auto *assign = dyn_cast<SymbolAssignment>(cmd))
|
|
return assign->name != ".";
|
|
return false;
|
|
}
|
|
|
|
// We want to place orphan sections so that they share as much
|
|
// characteristics with their neighbors as possible. For example, if
|
|
// both are rw, or both are tls.
|
|
static SmallVectorImpl<SectionCommand *>::iterator
|
|
findOrphanPos(SmallVectorImpl<SectionCommand *>::iterator b,
|
|
SmallVectorImpl<SectionCommand *>::iterator e) {
|
|
OutputSection *sec = &cast<OutputDesc>(*e)->osec;
|
|
|
|
// Find the first element that has as close a rank as possible.
|
|
auto i = std::max_element(b, e, [=](SectionCommand *a, SectionCommand *b) {
|
|
return getRankProximity(sec, a) < getRankProximity(sec, b);
|
|
});
|
|
if (i == e)
|
|
return e;
|
|
if (!isa<OutputDesc>(*i))
|
|
return e;
|
|
auto foundSec = &cast<OutputDesc>(*i)->osec;
|
|
|
|
// Consider all existing sections with the same proximity.
|
|
int proximity = getRankProximity(sec, *i);
|
|
unsigned sortRank = sec->sortRank;
|
|
if (script->hasPhdrsCommands() || !script->memoryRegions.empty())
|
|
// Prevent the orphan section to be placed before the found section. If
|
|
// custom program headers are defined, that helps to avoid adding it to a
|
|
// previous segment and changing flags of that segment, for example, making
|
|
// a read-only segment writable. If memory regions are defined, an orphan
|
|
// section should continue the same region as the found section to better
|
|
// resemble the behavior of GNU ld.
|
|
sortRank = std::max(sortRank, foundSec->sortRank);
|
|
for (; i != e; ++i) {
|
|
auto *curSecDesc = dyn_cast<OutputDesc>(*i);
|
|
if (!curSecDesc || !curSecDesc->osec.hasInputSections)
|
|
continue;
|
|
if (getRankProximity(sec, curSecDesc) != proximity ||
|
|
sortRank < curSecDesc->osec.sortRank)
|
|
break;
|
|
}
|
|
|
|
auto isOutputSecWithInputSections = [](SectionCommand *cmd) {
|
|
auto *osd = dyn_cast<OutputDesc>(cmd);
|
|
return osd && osd->osec.hasInputSections;
|
|
};
|
|
auto j =
|
|
std::find_if(std::make_reverse_iterator(i), std::make_reverse_iterator(b),
|
|
isOutputSecWithInputSections);
|
|
i = j.base();
|
|
|
|
// As a special case, if the orphan section is the last section, put
|
|
// it at the very end, past any other commands.
|
|
// This matches bfd's behavior and is convenient when the linker script fully
|
|
// specifies the start of the file, but doesn't care about the end (the non
|
|
// alloc sections for example).
|
|
auto nextSec = std::find_if(i, e, isOutputSecWithInputSections);
|
|
if (nextSec == e)
|
|
return e;
|
|
|
|
while (i != e && shouldSkip(*i))
|
|
++i;
|
|
return i;
|
|
}
|
|
|
|
// Adds random priorities to sections not already in the map.
|
|
static void maybeShuffle(DenseMap<const InputSectionBase *, int> &order) {
|
|
if (config->shuffleSections.empty())
|
|
return;
|
|
|
|
SmallVector<InputSectionBase *, 0> matched, sections = inputSections;
|
|
matched.reserve(sections.size());
|
|
for (const auto &patAndSeed : config->shuffleSections) {
|
|
matched.clear();
|
|
for (InputSectionBase *sec : sections)
|
|
if (patAndSeed.first.match(sec->name))
|
|
matched.push_back(sec);
|
|
const uint32_t seed = patAndSeed.second;
|
|
if (seed == UINT32_MAX) {
|
|
// If --shuffle-sections <section-glob>=-1, reverse the section order. The
|
|
// section order is stable even if the number of sections changes. This is
|
|
// useful to catch issues like static initialization order fiasco
|
|
// reliably.
|
|
std::reverse(matched.begin(), matched.end());
|
|
} else {
|
|
std::mt19937 g(seed ? seed : std::random_device()());
|
|
llvm::shuffle(matched.begin(), matched.end(), g);
|
|
}
|
|
size_t i = 0;
|
|
for (InputSectionBase *&sec : sections)
|
|
if (patAndSeed.first.match(sec->name))
|
|
sec = matched[i++];
|
|
}
|
|
|
|
// Existing priorities are < 0, so use priorities >= 0 for the missing
|
|
// sections.
|
|
int prio = 0;
|
|
for (InputSectionBase *sec : sections) {
|
|
if (order.try_emplace(sec, prio).second)
|
|
++prio;
|
|
}
|
|
}
|
|
|
|
// Builds section order for handling --symbol-ordering-file.
|
|
static DenseMap<const InputSectionBase *, int> buildSectionOrder() {
|
|
DenseMap<const InputSectionBase *, int> sectionOrder;
|
|
// Use the rarely used option --call-graph-ordering-file to sort sections.
|
|
if (!config->callGraphProfile.empty())
|
|
return computeCallGraphProfileOrder();
|
|
|
|
if (config->symbolOrderingFile.empty())
|
|
return sectionOrder;
|
|
|
|
struct SymbolOrderEntry {
|
|
int priority;
|
|
bool present;
|
|
};
|
|
|
|
// Build a map from symbols to their priorities. Symbols that didn't
|
|
// appear in the symbol ordering file have the lowest priority 0.
|
|
// All explicitly mentioned symbols have negative (higher) priorities.
|
|
DenseMap<CachedHashStringRef, SymbolOrderEntry> symbolOrder;
|
|
int priority = -config->symbolOrderingFile.size();
|
|
for (StringRef s : config->symbolOrderingFile)
|
|
symbolOrder.insert({CachedHashStringRef(s), {priority++, false}});
|
|
|
|
// Build a map from sections to their priorities.
|
|
auto addSym = [&](Symbol &sym) {
|
|
auto it = symbolOrder.find(CachedHashStringRef(sym.getName()));
|
|
if (it == symbolOrder.end())
|
|
return;
|
|
SymbolOrderEntry &ent = it->second;
|
|
ent.present = true;
|
|
|
|
maybeWarnUnorderableSymbol(&sym);
|
|
|
|
if (auto *d = dyn_cast<Defined>(&sym)) {
|
|
if (auto *sec = dyn_cast_or_null<InputSectionBase>(d->section)) {
|
|
int &priority = sectionOrder[cast<InputSectionBase>(sec)];
|
|
priority = std::min(priority, ent.priority);
|
|
}
|
|
}
|
|
};
|
|
|
|
// We want both global and local symbols. We get the global ones from the
|
|
// symbol table and iterate the object files for the local ones.
|
|
for (Symbol *sym : symtab->symbols())
|
|
addSym(*sym);
|
|
|
|
for (ELFFileBase *file : objectFiles)
|
|
for (Symbol *sym : file->getLocalSymbols())
|
|
addSym(*sym);
|
|
|
|
if (config->warnSymbolOrdering)
|
|
for (auto orderEntry : symbolOrder)
|
|
if (!orderEntry.second.present)
|
|
warn("symbol ordering file: no such symbol: " + orderEntry.first.val());
|
|
|
|
return sectionOrder;
|
|
}
|
|
|
|
// Sorts the sections in ISD according to the provided section order.
|
|
static void
|
|
sortISDBySectionOrder(InputSectionDescription *isd,
|
|
const DenseMap<const InputSectionBase *, int> &order) {
|
|
SmallVector<InputSection *, 0> unorderedSections;
|
|
SmallVector<std::pair<InputSection *, int>, 0> orderedSections;
|
|
uint64_t unorderedSize = 0;
|
|
|
|
for (InputSection *isec : isd->sections) {
|
|
auto i = order.find(isec);
|
|
if (i == order.end()) {
|
|
unorderedSections.push_back(isec);
|
|
unorderedSize += isec->getSize();
|
|
continue;
|
|
}
|
|
orderedSections.push_back({isec, i->second});
|
|
}
|
|
llvm::sort(orderedSections, llvm::less_second());
|
|
|
|
// Find an insertion point for the ordered section list in the unordered
|
|
// section list. On targets with limited-range branches, this is the mid-point
|
|
// of the unordered section list. This decreases the likelihood that a range
|
|
// extension thunk will be needed to enter or exit the ordered region. If the
|
|
// ordered section list is a list of hot functions, we can generally expect
|
|
// the ordered functions to be called more often than the unordered functions,
|
|
// making it more likely that any particular call will be within range, and
|
|
// therefore reducing the number of thunks required.
|
|
//
|
|
// For example, imagine that you have 8MB of hot code and 32MB of cold code.
|
|
// If the layout is:
|
|
//
|
|
// 8MB hot
|
|
// 32MB cold
|
|
//
|
|
// only the first 8-16MB of the cold code (depending on which hot function it
|
|
// is actually calling) can call the hot code without a range extension thunk.
|
|
// However, if we use this layout:
|
|
//
|
|
// 16MB cold
|
|
// 8MB hot
|
|
// 16MB cold
|
|
//
|
|
// both the last 8-16MB of the first block of cold code and the first 8-16MB
|
|
// of the second block of cold code can call the hot code without a thunk. So
|
|
// we effectively double the amount of code that could potentially call into
|
|
// the hot code without a thunk.
|
|
size_t insPt = 0;
|
|
if (target->getThunkSectionSpacing() && !orderedSections.empty()) {
|
|
uint64_t unorderedPos = 0;
|
|
for (; insPt != unorderedSections.size(); ++insPt) {
|
|
unorderedPos += unorderedSections[insPt]->getSize();
|
|
if (unorderedPos > unorderedSize / 2)
|
|
break;
|
|
}
|
|
}
|
|
|
|
isd->sections.clear();
|
|
for (InputSection *isec : makeArrayRef(unorderedSections).slice(0, insPt))
|
|
isd->sections.push_back(isec);
|
|
for (std::pair<InputSection *, int> p : orderedSections)
|
|
isd->sections.push_back(p.first);
|
|
for (InputSection *isec : makeArrayRef(unorderedSections).slice(insPt))
|
|
isd->sections.push_back(isec);
|
|
}
|
|
|
|
static void sortSection(OutputSection &osec,
|
|
const DenseMap<const InputSectionBase *, int> &order) {
|
|
StringRef name = osec.name;
|
|
|
|
// Never sort these.
|
|
if (name == ".init" || name == ".fini")
|
|
return;
|
|
|
|
// IRelative relocations that usually live in the .rel[a].dyn section should
|
|
// be processed last by the dynamic loader. To achieve that we add synthetic
|
|
// sections in the required order from the beginning so that the in.relaIplt
|
|
// section is placed last in an output section. Here we just do not apply
|
|
// sorting for an output section which holds the in.relaIplt section.
|
|
if (in.relaIplt->getParent() == &osec)
|
|
return;
|
|
|
|
// Sort input sections by priority using the list provided by
|
|
// --symbol-ordering-file or --shuffle-sections=. This is a least significant
|
|
// digit radix sort. The sections may be sorted stably again by a more
|
|
// significant key.
|
|
if (!order.empty())
|
|
for (SectionCommand *b : osec.commands)
|
|
if (auto *isd = dyn_cast<InputSectionDescription>(b))
|
|
sortISDBySectionOrder(isd, order);
|
|
|
|
if (script->hasSectionsCommand)
|
|
return;
|
|
|
|
if (name == ".init_array" || name == ".fini_array") {
|
|
osec.sortInitFini();
|
|
} else if (name == ".ctors" || name == ".dtors") {
|
|
osec.sortCtorsDtors();
|
|
} else if (config->emachine == EM_PPC64 && name == ".toc") {
|
|
// .toc is allocated just after .got and is accessed using GOT-relative
|
|
// relocations. Object files compiled with small code model have an
|
|
// addressable range of [.got, .got + 0xFFFC] for GOT-relative relocations.
|
|
// To reduce the risk of relocation overflow, .toc contents are sorted so
|
|
// that sections having smaller relocation offsets are at beginning of .toc
|
|
assert(osec.commands.size() == 1);
|
|
auto *isd = cast<InputSectionDescription>(osec.commands[0]);
|
|
llvm::stable_sort(isd->sections,
|
|
[](const InputSection *a, const InputSection *b) -> bool {
|
|
return a->file->ppc64SmallCodeModelTocRelocs &&
|
|
!b->file->ppc64SmallCodeModelTocRelocs;
|
|
});
|
|
}
|
|
}
|
|
|
|
// If no layout was provided by linker script, we want to apply default
|
|
// sorting for special input sections. This also handles --symbol-ordering-file.
|
|
template <class ELFT> void Writer<ELFT>::sortInputSections() {
|
|
// Build the order once since it is expensive.
|
|
DenseMap<const InputSectionBase *, int> order = buildSectionOrder();
|
|
maybeShuffle(order);
|
|
for (SectionCommand *cmd : script->sectionCommands)
|
|
if (auto *osd = dyn_cast<OutputDesc>(cmd))
|
|
sortSection(osd->osec, order);
|
|
}
|
|
|
|
template <class ELFT> void Writer<ELFT>::sortSections() {
|
|
llvm::TimeTraceScope timeScope("Sort sections");
|
|
|
|
// Don't sort if using -r. It is not necessary and we want to preserve the
|
|
// relative order for SHF_LINK_ORDER sections.
|
|
if (config->relocatable) {
|
|
script->adjustOutputSections();
|
|
return;
|
|
}
|
|
|
|
sortInputSections();
|
|
|
|
for (SectionCommand *cmd : script->sectionCommands)
|
|
if (auto *osd = dyn_cast<OutputDesc>(cmd))
|
|
osd->osec.sortRank = getSectionRank(osd->osec);
|
|
if (!script->hasSectionsCommand) {
|
|
// We know that all the OutputSections are contiguous in this case.
|
|
auto isSection = [](SectionCommand *cmd) { return isa<OutputDesc>(cmd); };
|
|
std::stable_sort(
|
|
llvm::find_if(script->sectionCommands, isSection),
|
|
llvm::find_if(llvm::reverse(script->sectionCommands), isSection).base(),
|
|
compareSections);
|
|
}
|
|
|
|
// Process INSERT commands and update output section attributes. From this
|
|
// point onwards the order of script->sectionCommands is fixed.
|
|
script->processInsertCommands();
|
|
script->adjustOutputSections();
|
|
|
|
if (!script->hasSectionsCommand)
|
|
return;
|
|
|
|
// Orphan sections are sections present in the input files which are
|
|
// not explicitly placed into the output file by the linker script.
|
|
//
|
|
// The sections in the linker script are already in the correct
|
|
// order. We have to figuere out where to insert the orphan
|
|
// sections.
|
|
//
|
|
// The order of the sections in the script is arbitrary and may not agree with
|
|
// compareSections. This means that we cannot easily define a strict weak
|
|
// ordering. To see why, consider a comparison of a section in the script and
|
|
// one not in the script. We have a two simple options:
|
|
// * Make them equivalent (a is not less than b, and b is not less than a).
|
|
// The problem is then that equivalence has to be transitive and we can
|
|
// have sections a, b and c with only b in a script and a less than c
|
|
// which breaks this property.
|
|
// * Use compareSectionsNonScript. Given that the script order doesn't have
|
|
// to match, we can end up with sections a, b, c, d where b and c are in the
|
|
// script and c is compareSectionsNonScript less than b. In which case d
|
|
// can be equivalent to c, a to b and d < a. As a concrete example:
|
|
// .a (rx) # not in script
|
|
// .b (rx) # in script
|
|
// .c (ro) # in script
|
|
// .d (ro) # not in script
|
|
//
|
|
// The way we define an order then is:
|
|
// * Sort only the orphan sections. They are in the end right now.
|
|
// * Move each orphan section to its preferred position. We try
|
|
// to put each section in the last position where it can share
|
|
// a PT_LOAD.
|
|
//
|
|
// There is some ambiguity as to where exactly a new entry should be
|
|
// inserted, because Commands contains not only output section
|
|
// commands but also other types of commands such as symbol assignment
|
|
// expressions. There's no correct answer here due to the lack of the
|
|
// formal specification of the linker script. We use heuristics to
|
|
// determine whether a new output command should be added before or
|
|
// after another commands. For the details, look at shouldSkip
|
|
// function.
|
|
|
|
auto i = script->sectionCommands.begin();
|
|
auto e = script->sectionCommands.end();
|
|
auto nonScriptI = std::find_if(i, e, [](SectionCommand *cmd) {
|
|
if (auto *osd = dyn_cast<OutputDesc>(cmd))
|
|
return osd->osec.sectionIndex == UINT32_MAX;
|
|
return false;
|
|
});
|
|
|
|
// Sort the orphan sections.
|
|
std::stable_sort(nonScriptI, e, compareSections);
|
|
|
|
// As a horrible special case, skip the first . assignment if it is before any
|
|
// section. We do this because it is common to set a load address by starting
|
|
// the script with ". = 0xabcd" and the expectation is that every section is
|
|
// after that.
|
|
auto firstSectionOrDotAssignment =
|
|
std::find_if(i, e, [](SectionCommand *cmd) { return !shouldSkip(cmd); });
|
|
if (firstSectionOrDotAssignment != e &&
|
|
isa<SymbolAssignment>(**firstSectionOrDotAssignment))
|
|
++firstSectionOrDotAssignment;
|
|
i = firstSectionOrDotAssignment;
|
|
|
|
while (nonScriptI != e) {
|
|
auto pos = findOrphanPos(i, nonScriptI);
|
|
OutputSection *orphan = &cast<OutputDesc>(*nonScriptI)->osec;
|
|
|
|
// As an optimization, find all sections with the same sort rank
|
|
// and insert them with one rotate.
|
|
unsigned rank = orphan->sortRank;
|
|
auto end = std::find_if(nonScriptI + 1, e, [=](SectionCommand *cmd) {
|
|
return cast<OutputDesc>(cmd)->osec.sortRank != rank;
|
|
});
|
|
std::rotate(pos, nonScriptI, end);
|
|
nonScriptI = end;
|
|
}
|
|
|
|
script->adjustSectionsAfterSorting();
|
|
}
|
|
|
|
static bool compareByFilePosition(InputSection *a, InputSection *b) {
|
|
InputSection *la = a->flags & SHF_LINK_ORDER ? a->getLinkOrderDep() : nullptr;
|
|
InputSection *lb = b->flags & SHF_LINK_ORDER ? b->getLinkOrderDep() : nullptr;
|
|
// SHF_LINK_ORDER sections with non-zero sh_link are ordered before
|
|
// non-SHF_LINK_ORDER sections and SHF_LINK_ORDER sections with zero sh_link.
|
|
if (!la || !lb)
|
|
return la && !lb;
|
|
OutputSection *aOut = la->getParent();
|
|
OutputSection *bOut = lb->getParent();
|
|
|
|
if (aOut != bOut)
|
|
return aOut->addr < bOut->addr;
|
|
return la->outSecOff < lb->outSecOff;
|
|
}
|
|
|
|
template <class ELFT> void Writer<ELFT>::resolveShfLinkOrder() {
|
|
llvm::TimeTraceScope timeScope("Resolve SHF_LINK_ORDER");
|
|
for (OutputSection *sec : outputSections) {
|
|
if (!(sec->flags & SHF_LINK_ORDER))
|
|
continue;
|
|
|
|
// The ARM.exidx section use SHF_LINK_ORDER, but we have consolidated
|
|
// this processing inside the ARMExidxsyntheticsection::finalizeContents().
|
|
if (!config->relocatable && config->emachine == EM_ARM &&
|
|
sec->type == SHT_ARM_EXIDX)
|
|
continue;
|
|
|
|
// Link order may be distributed across several InputSectionDescriptions.
|
|
// Sorting is performed separately.
|
|
SmallVector<InputSection **, 0> scriptSections;
|
|
SmallVector<InputSection *, 0> sections;
|
|
for (SectionCommand *cmd : sec->commands) {
|
|
auto *isd = dyn_cast<InputSectionDescription>(cmd);
|
|
if (!isd)
|
|
continue;
|
|
bool hasLinkOrder = false;
|
|
scriptSections.clear();
|
|
sections.clear();
|
|
for (InputSection *&isec : isd->sections) {
|
|
if (isec->flags & SHF_LINK_ORDER) {
|
|
InputSection *link = isec->getLinkOrderDep();
|
|
if (link && !link->getParent())
|
|
error(toString(isec) + ": sh_link points to discarded section " +
|
|
toString(link));
|
|
hasLinkOrder = true;
|
|
}
|
|
scriptSections.push_back(&isec);
|
|
sections.push_back(isec);
|
|
}
|
|
if (hasLinkOrder && errorCount() == 0) {
|
|
llvm::stable_sort(sections, compareByFilePosition);
|
|
for (int i = 0, n = sections.size(); i != n; ++i)
|
|
*scriptSections[i] = sections[i];
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
static void finalizeSynthetic(SyntheticSection *sec) {
|
|
if (sec && sec->isNeeded() && sec->getParent()) {
|
|
llvm::TimeTraceScope timeScope("Finalize synthetic sections", sec->name);
|
|
sec->finalizeContents();
|
|
}
|
|
}
|
|
|
|
// We need to generate and finalize the content that depends on the address of
|
|
// InputSections. As the generation of the content may also alter InputSection
|
|
// addresses we must converge to a fixed point. We do that here. See the comment
|
|
// in Writer<ELFT>::finalizeSections().
|
|
template <class ELFT> void Writer<ELFT>::finalizeAddressDependentContent() {
|
|
llvm::TimeTraceScope timeScope("Finalize address dependent content");
|
|
ThunkCreator tc;
|
|
AArch64Err843419Patcher a64p;
|
|
ARMErr657417Patcher a32p;
|
|
script->assignAddresses();
|
|
// .ARM.exidx and SHF_LINK_ORDER do not require precise addresses, but they
|
|
// do require the relative addresses of OutputSections because linker scripts
|
|
// can assign Virtual Addresses to OutputSections that are not monotonically
|
|
// increasing.
|
|
for (Partition &part : partitions)
|
|
finalizeSynthetic(part.armExidx.get());
|
|
resolveShfLinkOrder();
|
|
|
|
// Converts call x@GDPLT to call __tls_get_addr
|
|
if (config->emachine == EM_HEXAGON)
|
|
hexagonTLSSymbolUpdate(outputSections);
|
|
|
|
int assignPasses = 0;
|
|
for (;;) {
|
|
bool changed = target->needsThunks && tc.createThunks(outputSections);
|
|
|
|
// With Thunk Size much smaller than branch range we expect to
|
|
// converge quickly; if we get to 15 something has gone wrong.
|
|
if (changed && tc.pass >= 15) {
|
|
error("thunk creation not converged");
|
|
break;
|
|
}
|
|
|
|
if (config->fixCortexA53Errata843419) {
|
|
if (changed)
|
|
script->assignAddresses();
|
|
changed |= a64p.createFixes();
|
|
}
|
|
if (config->fixCortexA8) {
|
|
if (changed)
|
|
script->assignAddresses();
|
|
changed |= a32p.createFixes();
|
|
}
|
|
|
|
if (in.mipsGot)
|
|
in.mipsGot->updateAllocSize();
|
|
|
|
for (Partition &part : partitions) {
|
|
changed |= part.relaDyn->updateAllocSize();
|
|
if (part.relrDyn)
|
|
changed |= part.relrDyn->updateAllocSize();
|
|
}
|
|
|
|
const Defined *changedSym = script->assignAddresses();
|
|
if (!changed) {
|
|
// Some symbols may be dependent on section addresses. When we break the
|
|
// loop, the symbol values are finalized because a previous
|
|
// assignAddresses() finalized section addresses.
|
|
if (!changedSym)
|
|
break;
|
|
if (++assignPasses == 5) {
|
|
errorOrWarn("assignment to symbol " + toString(*changedSym) +
|
|
" does not converge");
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
|
|
if (config->relocatable)
|
|
for (OutputSection *sec : outputSections)
|
|
sec->addr = 0;
|
|
|
|
// If addrExpr is set, the address may not be a multiple of the alignment.
|
|
// Warn because this is error-prone.
|
|
for (SectionCommand *cmd : script->sectionCommands)
|
|
if (auto *osd = dyn_cast<OutputDesc>(cmd)) {
|
|
OutputSection *osec = &osd->osec;
|
|
if (osec->addr % osec->alignment != 0)
|
|
warn("address (0x" + Twine::utohexstr(osec->addr) + ") of section " +
|
|
osec->name + " is not a multiple of alignment (" +
|
|
Twine(osec->alignment) + ")");
|
|
}
|
|
}
|
|
|
|
// If Input Sections have been shrunk (basic block sections) then
|
|
// update symbol values and sizes associated with these sections. With basic
|
|
// block sections, input sections can shrink when the jump instructions at
|
|
// the end of the section are relaxed.
|
|
static void fixSymbolsAfterShrinking() {
|
|
for (InputFile *File : objectFiles) {
|
|
parallelForEach(File->getSymbols(), [&](Symbol *Sym) {
|
|
auto *def = dyn_cast<Defined>(Sym);
|
|
if (!def)
|
|
return;
|
|
|
|
const SectionBase *sec = def->section;
|
|
if (!sec)
|
|
return;
|
|
|
|
const InputSectionBase *inputSec = dyn_cast<InputSectionBase>(sec);
|
|
if (!inputSec || !inputSec->bytesDropped)
|
|
return;
|
|
|
|
const size_t OldSize = inputSec->rawData.size();
|
|
const size_t NewSize = OldSize - inputSec->bytesDropped;
|
|
|
|
if (def->value > NewSize && def->value <= OldSize) {
|
|
LLVM_DEBUG(llvm::dbgs()
|
|
<< "Moving symbol " << Sym->getName() << " from "
|
|
<< def->value << " to "
|
|
<< def->value - inputSec->bytesDropped << " bytes\n");
|
|
def->value -= inputSec->bytesDropped;
|
|
return;
|
|
}
|
|
|
|
if (def->value + def->size > NewSize && def->value <= OldSize &&
|
|
def->value + def->size <= OldSize) {
|
|
LLVM_DEBUG(llvm::dbgs()
|
|
<< "Shrinking symbol " << Sym->getName() << " from "
|
|
<< def->size << " to " << def->size - inputSec->bytesDropped
|
|
<< " bytes\n");
|
|
def->size -= inputSec->bytesDropped;
|
|
}
|
|
});
|
|
}
|
|
}
|
|
|
|
// If basic block sections exist, there are opportunities to delete fall thru
|
|
// jumps and shrink jump instructions after basic block reordering. This
|
|
// relaxation pass does that. It is only enabled when --optimize-bb-jumps
|
|
// option is used.
|
|
template <class ELFT> void Writer<ELFT>::optimizeBasicBlockJumps() {
|
|
assert(config->optimizeBBJumps);
|
|
|
|
script->assignAddresses();
|
|
// For every output section that has executable input sections, this
|
|
// does the following:
|
|
// 1. Deletes all direct jump instructions in input sections that
|
|
// jump to the following section as it is not required.
|
|
// 2. If there are two consecutive jump instructions, it checks
|
|
// if they can be flipped and one can be deleted.
|
|
for (OutputSection *osec : outputSections) {
|
|
if (!(osec->flags & SHF_EXECINSTR))
|
|
continue;
|
|
SmallVector<InputSection *, 0> sections = getInputSections(*osec);
|
|
size_t numDeleted = 0;
|
|
// Delete all fall through jump instructions. Also, check if two
|
|
// consecutive jump instructions can be flipped so that a fall
|
|
// through jmp instruction can be deleted.
|
|
for (size_t i = 0, e = sections.size(); i != e; ++i) {
|
|
InputSection *next = i + 1 < sections.size() ? sections[i + 1] : nullptr;
|
|
InputSection &sec = *sections[i];
|
|
numDeleted += target->deleteFallThruJmpInsn(sec, sec.file, next);
|
|
}
|
|
if (numDeleted > 0) {
|
|
script->assignAddresses();
|
|
LLVM_DEBUG(llvm::dbgs()
|
|
<< "Removing " << numDeleted << " fall through jumps\n");
|
|
}
|
|
}
|
|
|
|
fixSymbolsAfterShrinking();
|
|
|
|
for (OutputSection *osec : outputSections)
|
|
for (InputSection *is : getInputSections(*osec))
|
|
is->trim();
|
|
}
|
|
|
|
// In order to allow users to manipulate linker-synthesized sections,
|
|
// we had to add synthetic sections to the input section list early,
|
|
// even before we make decisions whether they are needed. This allows
|
|
// users to write scripts like this: ".mygot : { .got }".
|
|
//
|
|
// Doing it has an unintended side effects. If it turns out that we
|
|
// don't need a .got (for example) at all because there's no
|
|
// relocation that needs a .got, we don't want to emit .got.
|
|
//
|
|
// To deal with the above problem, this function is called after
|
|
// scanRelocations is called to remove synthetic sections that turn
|
|
// out to be empty.
|
|
static void removeUnusedSyntheticSections() {
|
|
// All input synthetic sections that can be empty are placed after
|
|
// all regular ones. Reverse iterate to find the first synthetic section
|
|
// after a non-synthetic one which will be our starting point.
|
|
auto start = std::find_if(inputSections.rbegin(), inputSections.rend(),
|
|
[](InputSectionBase *s) {
|
|
return !isa<SyntheticSection>(s);
|
|
})
|
|
.base();
|
|
|
|
// Remove unused synthetic sections from inputSections;
|
|
DenseSet<InputSectionBase *> unused;
|
|
auto end =
|
|
std::remove_if(start, inputSections.end(), [&](InputSectionBase *s) {
|
|
auto *sec = cast<SyntheticSection>(s);
|
|
if (sec->getParent() && sec->isNeeded())
|
|
return false;
|
|
unused.insert(sec);
|
|
return true;
|
|
});
|
|
inputSections.erase(end, inputSections.end());
|
|
|
|
// Remove unused synthetic sections from the corresponding input section
|
|
// description and orphanSections.
|
|
for (auto *sec : unused)
|
|
if (OutputSection *osec = cast<SyntheticSection>(sec)->getParent())
|
|
for (SectionCommand *cmd : osec->commands)
|
|
if (auto *isd = dyn_cast<InputSectionDescription>(cmd))
|
|
llvm::erase_if(isd->sections, [&](InputSection *isec) {
|
|
return unused.count(isec);
|
|
});
|
|
llvm::erase_if(script->orphanSections, [&](const InputSectionBase *sec) {
|
|
return unused.count(sec);
|
|
});
|
|
}
|
|
|
|
// Create output section objects and add them to OutputSections.
|
|
template <class ELFT> void Writer<ELFT>::finalizeSections() {
|
|
Out::preinitArray = findSection(".preinit_array");
|
|
Out::initArray = findSection(".init_array");
|
|
Out::finiArray = findSection(".fini_array");
|
|
|
|
// The linker needs to define SECNAME_start, SECNAME_end and SECNAME_stop
|
|
// symbols for sections, so that the runtime can get the start and end
|
|
// addresses of each section by section name. Add such symbols.
|
|
if (!config->relocatable) {
|
|
addStartEndSymbols();
|
|
for (SectionCommand *cmd : script->sectionCommands)
|
|
if (auto *osd = dyn_cast<OutputDesc>(cmd))
|
|
addStartStopSymbols(osd->osec);
|
|
}
|
|
|
|
// Add _DYNAMIC symbol. Unlike GNU gold, our _DYNAMIC symbol has no type.
|
|
// It should be okay as no one seems to care about the type.
|
|
// Even the author of gold doesn't remember why gold behaves that way.
|
|
// https://sourceware.org/ml/binutils/2002-03/msg00360.html
|
|
if (mainPart->dynamic->parent)
|
|
symtab->addSymbol(Defined{/*file=*/nullptr, "_DYNAMIC", STB_WEAK, STV_HIDDEN, STT_NOTYPE,
|
|
/*value=*/0, /*size=*/0, mainPart->dynamic.get()})->isUsedInRegularObj = true;
|
|
|
|
// Define __rel[a]_iplt_{start,end} symbols if needed.
|
|
addRelIpltSymbols();
|
|
|
|
// RISC-V's gp can address +/- 2 KiB, set it to .sdata + 0x800. This symbol
|
|
// should only be defined in an executable. If .sdata does not exist, its
|
|
// value/section does not matter but it has to be relative, so set its
|
|
// st_shndx arbitrarily to 1 (Out::elfHeader).
|
|
if (config->emachine == EM_RISCV && !config->shared) {
|
|
OutputSection *sec = findSection(".sdata");
|
|
ElfSym::riscvGlobalPointer =
|
|
addOptionalRegular("__global_pointer$", sec ? sec : Out::elfHeader,
|
|
0x800, STV_DEFAULT);
|
|
}
|
|
|
|
if (config->emachine == EM_386 || config->emachine == EM_X86_64) {
|
|
// On targets that support TLSDESC, _TLS_MODULE_BASE_ is defined in such a
|
|
// way that:
|
|
//
|
|
// 1) Without relaxation: it produces a dynamic TLSDESC relocation that
|
|
// computes 0.
|
|
// 2) With LD->LE relaxation: _TLS_MODULE_BASE_@tpoff = 0 (lowest address in
|
|
// the TLS block).
|
|
//
|
|
// 2) is special cased in @tpoff computation. To satisfy 1), we define it as
|
|
// an absolute symbol of zero. This is different from GNU linkers which
|
|
// define _TLS_MODULE_BASE_ relative to the first TLS section.
|
|
Symbol *s = symtab->find("_TLS_MODULE_BASE_");
|
|
if (s && s->isUndefined()) {
|
|
s->resolve(Defined{/*file=*/nullptr, StringRef(), STB_GLOBAL, STV_HIDDEN,
|
|
STT_TLS, /*value=*/0, 0,
|
|
/*section=*/nullptr});
|
|
ElfSym::tlsModuleBase = cast<Defined>(s);
|
|
}
|
|
}
|
|
|
|
{
|
|
llvm::TimeTraceScope timeScope("Finalize .eh_frame");
|
|
// This responsible for splitting up .eh_frame section into
|
|
// pieces. The relocation scan uses those pieces, so this has to be
|
|
// earlier.
|
|
for (Partition &part : partitions)
|
|
finalizeSynthetic(part.ehFrame.get());
|
|
}
|
|
|
|
if (config->hasDynSymTab) {
|
|
parallelForEach(symtab->symbols(), [](Symbol *sym) {
|
|
sym->isPreemptible = computeIsPreemptible(*sym);
|
|
});
|
|
}
|
|
|
|
// Change values of linker-script-defined symbols from placeholders (assigned
|
|
// by declareSymbols) to actual definitions.
|
|
script->processSymbolAssignments();
|
|
|
|
{
|
|
llvm::TimeTraceScope timeScope("Scan relocations");
|
|
// Scan relocations. This must be done after every symbol is declared so
|
|
// that we can correctly decide if a dynamic relocation is needed. This is
|
|
// called after processSymbolAssignments() because it needs to know whether
|
|
// a linker-script-defined symbol is absolute.
|
|
ppc64noTocRelax.clear();
|
|
if (!config->relocatable) {
|
|
// Scan all relocations. Each relocation goes through a series of tests to
|
|
// determine if it needs special treatment, such as creating GOT, PLT,
|
|
// copy relocations, etc. Note that relocations for non-alloc sections are
|
|
// directly processed by InputSection::relocateNonAlloc.
|
|
for (InputSectionBase *sec : inputSections)
|
|
if (sec->isLive() && isa<InputSection>(sec) && (sec->flags & SHF_ALLOC))
|
|
scanRelocations<ELFT>(*sec);
|
|
for (Partition &part : partitions) {
|
|
for (EhInputSection *sec : part.ehFrame->sections)
|
|
scanRelocations<ELFT>(*sec);
|
|
if (part.armExidx && part.armExidx->isLive())
|
|
for (InputSection *sec : part.armExidx->exidxSections)
|
|
scanRelocations<ELFT>(*sec);
|
|
}
|
|
|
|
reportUndefinedSymbols();
|
|
postScanRelocations();
|
|
}
|
|
}
|
|
|
|
if (in.plt && in.plt->isNeeded())
|
|
in.plt->addSymbols();
|
|
if (in.iplt && in.iplt->isNeeded())
|
|
in.iplt->addSymbols();
|
|
|
|
if (config->unresolvedSymbolsInShlib != UnresolvedPolicy::Ignore) {
|
|
auto diagnose =
|
|
config->unresolvedSymbolsInShlib == UnresolvedPolicy::ReportError
|
|
? errorOrWarn
|
|
: warn;
|
|
// Error on undefined symbols in a shared object, if all of its DT_NEEDED
|
|
// entries are seen. These cases would otherwise lead to runtime errors
|
|
// reported by the dynamic linker.
|
|
//
|
|
// ld.bfd traces all DT_NEEDED to emulate the logic of the dynamic linker to
|
|
// catch more cases. That is too much for us. Our approach resembles the one
|
|
// used in ld.gold, achieves a good balance to be useful but not too smart.
|
|
for (SharedFile *file : sharedFiles) {
|
|
bool allNeededIsKnown =
|
|
llvm::all_of(file->dtNeeded, [&](StringRef needed) {
|
|
return symtab->soNames.count(CachedHashStringRef(needed));
|
|
});
|
|
if (!allNeededIsKnown)
|
|
continue;
|
|
for (Symbol *sym : file->requiredSymbols)
|
|
if (sym->isUndefined() && !sym->isWeak())
|
|
diagnose(toString(file) + ": undefined reference to " +
|
|
toString(*sym) + " [--no-allow-shlib-undefined]");
|
|
}
|
|
}
|
|
|
|
{
|
|
llvm::TimeTraceScope timeScope("Add symbols to symtabs");
|
|
// Now that we have defined all possible global symbols including linker-
|
|
// synthesized ones. Visit all symbols to give the finishing touches.
|
|
for (Symbol *sym : symtab->symbols()) {
|
|
if (!sym->isUsedInRegularObj || !includeInSymtab(*sym))
|
|
continue;
|
|
if (!config->relocatable)
|
|
sym->binding = sym->computeBinding();
|
|
if (in.symTab)
|
|
in.symTab->addSymbol(sym);
|
|
|
|
if (sym->includeInDynsym()) {
|
|
partitions[sym->partition - 1].dynSymTab->addSymbol(sym);
|
|
if (auto *file = dyn_cast_or_null<SharedFile>(sym->file))
|
|
if (file->isNeeded && !sym->isUndefined())
|
|
addVerneed(sym);
|
|
}
|
|
}
|
|
|
|
// We also need to scan the dynamic relocation tables of the other
|
|
// partitions and add any referenced symbols to the partition's dynsym.
|
|
for (Partition &part : MutableArrayRef<Partition>(partitions).slice(1)) {
|
|
DenseSet<Symbol *> syms;
|
|
for (const SymbolTableEntry &e : part.dynSymTab->getSymbols())
|
|
syms.insert(e.sym);
|
|
for (DynamicReloc &reloc : part.relaDyn->relocs)
|
|
if (reloc.sym && reloc.needsDynSymIndex() &&
|
|
syms.insert(reloc.sym).second)
|
|
part.dynSymTab->addSymbol(reloc.sym);
|
|
}
|
|
}
|
|
|
|
if (in.mipsGot)
|
|
in.mipsGot->build();
|
|
|
|
removeUnusedSyntheticSections();
|
|
script->diagnoseOrphanHandling();
|
|
|
|
sortSections();
|
|
|
|
// Create a list of OutputSections, assign sectionIndex, and populate
|
|
// in.shStrTab.
|
|
for (SectionCommand *cmd : script->sectionCommands)
|
|
if (auto *osd = dyn_cast<OutputDesc>(cmd)) {
|
|
OutputSection *osec = &osd->osec;
|
|
outputSections.push_back(osec);
|
|
osec->sectionIndex = outputSections.size();
|
|
osec->shName = in.shStrTab->addString(osec->name);
|
|
}
|
|
|
|
// Prefer command line supplied address over other constraints.
|
|
for (OutputSection *sec : outputSections) {
|
|
auto i = config->sectionStartMap.find(sec->name);
|
|
if (i != config->sectionStartMap.end())
|
|
sec->addrExpr = [=] { return i->second; };
|
|
}
|
|
|
|
// With the outputSections available check for GDPLT relocations
|
|
// and add __tls_get_addr symbol if needed.
|
|
if (config->emachine == EM_HEXAGON && hexagonNeedsTLSSymbol(outputSections)) {
|
|
Symbol *sym = symtab->addSymbol(Undefined{
|
|
nullptr, "__tls_get_addr", STB_GLOBAL, STV_DEFAULT, STT_NOTYPE});
|
|
sym->isPreemptible = true;
|
|
partitions[0].dynSymTab->addSymbol(sym);
|
|
}
|
|
|
|
// This is a bit of a hack. A value of 0 means undef, so we set it
|
|
// to 1 to make __ehdr_start defined. The section number is not
|
|
// particularly relevant.
|
|
Out::elfHeader->sectionIndex = 1;
|
|
Out::elfHeader->size = sizeof(typename ELFT::Ehdr);
|
|
|
|
// Binary and relocatable output does not have PHDRS.
|
|
// The headers have to be created before finalize as that can influence the
|
|
// image base and the dynamic section on mips includes the image base.
|
|
if (!config->relocatable && !config->oFormatBinary) {
|
|
for (Partition &part : partitions) {
|
|
part.phdrs = script->hasPhdrsCommands() ? script->createPhdrs()
|
|
: createPhdrs(part);
|
|
if (config->emachine == EM_ARM) {
|
|
// PT_ARM_EXIDX is the ARM EHABI equivalent of PT_GNU_EH_FRAME
|
|
addPhdrForSection(part, SHT_ARM_EXIDX, PT_ARM_EXIDX, PF_R);
|
|
}
|
|
if (config->emachine == EM_MIPS) {
|
|
// Add separate segments for MIPS-specific sections.
|
|
addPhdrForSection(part, SHT_MIPS_REGINFO, PT_MIPS_REGINFO, PF_R);
|
|
addPhdrForSection(part, SHT_MIPS_OPTIONS, PT_MIPS_OPTIONS, PF_R);
|
|
addPhdrForSection(part, SHT_MIPS_ABIFLAGS, PT_MIPS_ABIFLAGS, PF_R);
|
|
}
|
|
}
|
|
Out::programHeaders->size = sizeof(Elf_Phdr) * mainPart->phdrs.size();
|
|
|
|
// Find the TLS segment. This happens before the section layout loop so that
|
|
// Android relocation packing can look up TLS symbol addresses. We only need
|
|
// to care about the main partition here because all TLS symbols were moved
|
|
// to the main partition (see MarkLive.cpp).
|
|
for (PhdrEntry *p : mainPart->phdrs)
|
|
if (p->p_type == PT_TLS)
|
|
Out::tlsPhdr = p;
|
|
}
|
|
|
|
// Some symbols are defined in term of program headers. Now that we
|
|
// have the headers, we can find out which sections they point to.
|
|
setReservedSymbolSections();
|
|
|
|
{
|
|
llvm::TimeTraceScope timeScope("Finalize synthetic sections");
|
|
|
|
finalizeSynthetic(in.bss.get());
|
|
finalizeSynthetic(in.bssRelRo.get());
|
|
finalizeSynthetic(in.symTabShndx.get());
|
|
finalizeSynthetic(in.shStrTab.get());
|
|
finalizeSynthetic(in.strTab.get());
|
|
finalizeSynthetic(in.got.get());
|
|
finalizeSynthetic(in.mipsGot.get());
|
|
finalizeSynthetic(in.igotPlt.get());
|
|
finalizeSynthetic(in.gotPlt.get());
|
|
finalizeSynthetic(in.relaIplt.get());
|
|
finalizeSynthetic(in.relaPlt.get());
|
|
finalizeSynthetic(in.plt.get());
|
|
finalizeSynthetic(in.iplt.get());
|
|
finalizeSynthetic(in.ppc32Got2.get());
|
|
finalizeSynthetic(in.partIndex.get());
|
|
|
|
// Dynamic section must be the last one in this list and dynamic
|
|
// symbol table section (dynSymTab) must be the first one.
|
|
for (Partition &part : partitions) {
|
|
if (part.relaDyn) {
|
|
// Compute DT_RELACOUNT to be used by part.dynamic.
|
|
part.relaDyn->partitionRels();
|
|
finalizeSynthetic(part.relaDyn.get());
|
|
}
|
|
|
|
finalizeSynthetic(part.dynSymTab.get());
|
|
finalizeSynthetic(part.gnuHashTab.get());
|
|
finalizeSynthetic(part.hashTab.get());
|
|
finalizeSynthetic(part.verDef.get());
|
|
finalizeSynthetic(part.relrDyn.get());
|
|
finalizeSynthetic(part.ehFrameHdr.get());
|
|
finalizeSynthetic(part.verSym.get());
|
|
finalizeSynthetic(part.verNeed.get());
|
|
finalizeSynthetic(part.dynamic.get());
|
|
}
|
|
}
|
|
|
|
if (!script->hasSectionsCommand && !config->relocatable)
|
|
fixSectionAlignments();
|
|
|
|
// This is used to:
|
|
// 1) Create "thunks":
|
|
// Jump instructions in many ISAs have small displacements, and therefore
|
|
// they cannot jump to arbitrary addresses in memory. For example, RISC-V
|
|
// JAL instruction can target only +-1 MiB from PC. It is a linker's
|
|
// responsibility to create and insert small pieces of code between
|
|
// sections to extend the ranges if jump targets are out of range. Such
|
|
// code pieces are called "thunks".
|
|
//
|
|
// We add thunks at this stage. We couldn't do this before this point
|
|
// because this is the earliest point where we know sizes of sections and
|
|
// their layouts (that are needed to determine if jump targets are in
|
|
// range).
|
|
//
|
|
// 2) Update the sections. We need to generate content that depends on the
|
|
// address of InputSections. For example, MIPS GOT section content or
|
|
// android packed relocations sections content.
|
|
//
|
|
// 3) Assign the final values for the linker script symbols. Linker scripts
|
|
// sometimes using forward symbol declarations. We want to set the correct
|
|
// values. They also might change after adding the thunks.
|
|
finalizeAddressDependentContent();
|
|
|
|
// All information needed for OutputSection part of Map file is available.
|
|
if (errorCount())
|
|
return;
|
|
|
|
{
|
|
llvm::TimeTraceScope timeScope("Finalize synthetic sections");
|
|
// finalizeAddressDependentContent may have added local symbols to the
|
|
// static symbol table.
|
|
finalizeSynthetic(in.symTab.get());
|
|
finalizeSynthetic(in.ppc64LongBranchTarget.get());
|
|
}
|
|
|
|
// Relaxation to delete inter-basic block jumps created by basic block
|
|
// sections. Run after in.symTab is finalized as optimizeBasicBlockJumps
|
|
// can relax jump instructions based on symbol offset.
|
|
if (config->optimizeBBJumps)
|
|
optimizeBasicBlockJumps();
|
|
|
|
// Fill other section headers. The dynamic table is finalized
|
|
// at the end because some tags like RELSZ depend on result
|
|
// of finalizing other sections.
|
|
for (OutputSection *sec : outputSections)
|
|
sec->finalize();
|
|
}
|
|
|
|
// Ensure data sections are not mixed with executable sections when
|
|
// --execute-only is used. --execute-only make pages executable but not
|
|
// readable.
|
|
template <class ELFT> void Writer<ELFT>::checkExecuteOnly() {
|
|
if (!config->executeOnly)
|
|
return;
|
|
|
|
for (OutputSection *osec : outputSections)
|
|
if (osec->flags & SHF_EXECINSTR)
|
|
for (InputSection *isec : getInputSections(*osec))
|
|
if (!(isec->flags & SHF_EXECINSTR))
|
|
error("cannot place " + toString(isec) + " into " +
|
|
toString(osec->name) +
|
|
": --execute-only does not support intermingling data and code");
|
|
}
|
|
|
|
// The linker is expected to define SECNAME_start and SECNAME_end
|
|
// symbols for a few sections. This function defines them.
|
|
template <class ELFT> void Writer<ELFT>::addStartEndSymbols() {
|
|
// If a section does not exist, there's ambiguity as to how we
|
|
// define _start and _end symbols for an init/fini section. Since
|
|
// the loader assume that the symbols are always defined, we need to
|
|
// always define them. But what value? The loader iterates over all
|
|
// pointers between _start and _end to run global ctors/dtors, so if
|
|
// the section is empty, their symbol values don't actually matter
|
|
// as long as _start and _end point to the same location.
|
|
//
|
|
// That said, we don't want to set the symbols to 0 (which is
|
|
// probably the simplest value) because that could cause some
|
|
// program to fail to link due to relocation overflow, if their
|
|
// program text is above 2 GiB. We use the address of the .text
|
|
// section instead to prevent that failure.
|
|
//
|
|
// In rare situations, the .text section may not exist. If that's the
|
|
// case, use the image base address as a last resort.
|
|
OutputSection *Default = findSection(".text");
|
|
if (!Default)
|
|
Default = Out::elfHeader;
|
|
|
|
auto define = [=](StringRef start, StringRef end, OutputSection *os) {
|
|
if (os && !script->isDiscarded(os)) {
|
|
addOptionalRegular(start, os, 0);
|
|
addOptionalRegular(end, os, -1);
|
|
} else {
|
|
addOptionalRegular(start, Default, 0);
|
|
addOptionalRegular(end, Default, 0);
|
|
}
|
|
};
|
|
|
|
define("__preinit_array_start", "__preinit_array_end", Out::preinitArray);
|
|
define("__init_array_start", "__init_array_end", Out::initArray);
|
|
define("__fini_array_start", "__fini_array_end", Out::finiArray);
|
|
|
|
if (OutputSection *sec = findSection(".ARM.exidx"))
|
|
define("__exidx_start", "__exidx_end", sec);
|
|
}
|
|
|
|
// If a section name is valid as a C identifier (which is rare because of
|
|
// the leading '.'), linkers are expected to define __start_<secname> and
|
|
// __stop_<secname> symbols. They are at beginning and end of the section,
|
|
// respectively. This is not requested by the ELF standard, but GNU ld and
|
|
// gold provide the feature, and used by many programs.
|
|
template <class ELFT>
|
|
void Writer<ELFT>::addStartStopSymbols(OutputSection &osec) {
|
|
StringRef s = osec.name;
|
|
if (!isValidCIdentifier(s))
|
|
return;
|
|
addOptionalRegular(saver().save("__start_" + s), &osec, 0,
|
|
config->zStartStopVisibility);
|
|
addOptionalRegular(saver().save("__stop_" + s), &osec, -1,
|
|
config->zStartStopVisibility);
|
|
}
|
|
|
|
static bool needsPtLoad(OutputSection *sec) {
|
|
if (!(sec->flags & SHF_ALLOC))
|
|
return false;
|
|
|
|
// Don't allocate VA space for TLS NOBITS sections. The PT_TLS PHDR is
|
|
// responsible for allocating space for them, not the PT_LOAD that
|
|
// contains the TLS initialization image.
|
|
if ((sec->flags & SHF_TLS) && sec->type == SHT_NOBITS)
|
|
return false;
|
|
return true;
|
|
}
|
|
|
|
// Linker scripts are responsible for aligning addresses. Unfortunately, most
|
|
// linker scripts are designed for creating two PT_LOADs only, one RX and one
|
|
// RW. This means that there is no alignment in the RO to RX transition and we
|
|
// cannot create a PT_LOAD there.
|
|
static uint64_t computeFlags(uint64_t flags) {
|
|
if (config->omagic)
|
|
return PF_R | PF_W | PF_X;
|
|
if (config->executeOnly && (flags & PF_X))
|
|
return flags & ~PF_R;
|
|
if (config->singleRoRx && !(flags & PF_W))
|
|
return flags | PF_X;
|
|
return flags;
|
|
}
|
|
|
|
// Decide which program headers to create and which sections to include in each
|
|
// one.
|
|
template <class ELFT>
|
|
SmallVector<PhdrEntry *, 0> Writer<ELFT>::createPhdrs(Partition &part) {
|
|
SmallVector<PhdrEntry *, 0> ret;
|
|
auto addHdr = [&](unsigned type, unsigned flags) -> PhdrEntry * {
|
|
ret.push_back(make<PhdrEntry>(type, flags));
|
|
return ret.back();
|
|
};
|
|
|
|
unsigned partNo = part.getNumber();
|
|
bool isMain = partNo == 1;
|
|
|
|
// Add the first PT_LOAD segment for regular output sections.
|
|
uint64_t flags = computeFlags(PF_R);
|
|
PhdrEntry *load = nullptr;
|
|
|
|
// nmagic or omagic output does not have PT_PHDR, PT_INTERP, or the readonly
|
|
// PT_LOAD.
|
|
if (!config->nmagic && !config->omagic) {
|
|
// The first phdr entry is PT_PHDR which describes the program header
|
|
// itself.
|
|
if (isMain)
|
|
addHdr(PT_PHDR, PF_R)->add(Out::programHeaders);
|
|
else
|
|
addHdr(PT_PHDR, PF_R)->add(part.programHeaders->getParent());
|
|
|
|
// PT_INTERP must be the second entry if exists.
|
|
if (OutputSection *cmd = findSection(".interp", partNo))
|
|
addHdr(PT_INTERP, cmd->getPhdrFlags())->add(cmd);
|
|
|
|
// Add the headers. We will remove them if they don't fit.
|
|
// In the other partitions the headers are ordinary sections, so they don't
|
|
// need to be added here.
|
|
if (isMain) {
|
|
load = addHdr(PT_LOAD, flags);
|
|
load->add(Out::elfHeader);
|
|
load->add(Out::programHeaders);
|
|
}
|
|
}
|
|
|
|
// PT_GNU_RELRO includes all sections that should be marked as
|
|
// read-only by dynamic linker after processing relocations.
|
|
// Current dynamic loaders only support one PT_GNU_RELRO PHDR, give
|
|
// an error message if more than one PT_GNU_RELRO PHDR is required.
|
|
PhdrEntry *relRo = make<PhdrEntry>(PT_GNU_RELRO, PF_R);
|
|
bool inRelroPhdr = false;
|
|
OutputSection *relroEnd = nullptr;
|
|
for (OutputSection *sec : outputSections) {
|
|
if (sec->partition != partNo || !needsPtLoad(sec))
|
|
continue;
|
|
if (isRelroSection(sec)) {
|
|
inRelroPhdr = true;
|
|
if (!relroEnd)
|
|
relRo->add(sec);
|
|
else
|
|
error("section: " + sec->name + " is not contiguous with other relro" +
|
|
" sections");
|
|
} else if (inRelroPhdr) {
|
|
inRelroPhdr = false;
|
|
relroEnd = sec;
|
|
}
|
|
}
|
|
|
|
for (OutputSection *sec : outputSections) {
|
|
if (!needsPtLoad(sec))
|
|
continue;
|
|
|
|
// Normally, sections in partitions other than the current partition are
|
|
// ignored. But partition number 255 is a special case: it contains the
|
|
// partition end marker (.part.end). It needs to be added to the main
|
|
// partition so that a segment is created for it in the main partition,
|
|
// which will cause the dynamic loader to reserve space for the other
|
|
// partitions.
|
|
if (sec->partition != partNo) {
|
|
if (isMain && sec->partition == 255)
|
|
addHdr(PT_LOAD, computeFlags(sec->getPhdrFlags()))->add(sec);
|
|
continue;
|
|
}
|
|
|
|
// Segments are contiguous memory regions that has the same attributes
|
|
// (e.g. executable or writable). There is one phdr for each segment.
|
|
// Therefore, we need to create a new phdr when the next section has
|
|
// different flags or is loaded at a discontiguous address or memory
|
|
// region using AT or AT> linker script command, respectively. At the same
|
|
// time, we don't want to create a separate load segment for the headers,
|
|
// even if the first output section has an AT or AT> attribute.
|
|
uint64_t newFlags = computeFlags(sec->getPhdrFlags());
|
|
bool sameLMARegion =
|
|
load && !sec->lmaExpr && sec->lmaRegion == load->firstSec->lmaRegion;
|
|
if (!(load && newFlags == flags && sec != relroEnd &&
|
|
sec->memRegion == load->firstSec->memRegion &&
|
|
(sameLMARegion || load->lastSec == Out::programHeaders))) {
|
|
load = addHdr(PT_LOAD, newFlags);
|
|
flags = newFlags;
|
|
}
|
|
|
|
load->add(sec);
|
|
}
|
|
|
|
// Add a TLS segment if any.
|
|
PhdrEntry *tlsHdr = make<PhdrEntry>(PT_TLS, PF_R);
|
|
for (OutputSection *sec : outputSections)
|
|
if (sec->partition == partNo && sec->flags & SHF_TLS)
|
|
tlsHdr->add(sec);
|
|
if (tlsHdr->firstSec)
|
|
ret.push_back(tlsHdr);
|
|
|
|
// Add an entry for .dynamic.
|
|
if (OutputSection *sec = part.dynamic->getParent())
|
|
addHdr(PT_DYNAMIC, sec->getPhdrFlags())->add(sec);
|
|
|
|
if (relRo->firstSec)
|
|
ret.push_back(relRo);
|
|
|
|
// PT_GNU_EH_FRAME is a special section pointing on .eh_frame_hdr.
|
|
if (part.ehFrame->isNeeded() && part.ehFrameHdr &&
|
|
part.ehFrame->getParent() && part.ehFrameHdr->getParent())
|
|
addHdr(PT_GNU_EH_FRAME, part.ehFrameHdr->getParent()->getPhdrFlags())
|
|
->add(part.ehFrameHdr->getParent());
|
|
|
|
// PT_OPENBSD_RANDOMIZE is an OpenBSD-specific feature. That makes
|
|
// the dynamic linker fill the segment with random data.
|
|
if (OutputSection *cmd = findSection(".openbsd.randomdata", partNo))
|
|
addHdr(PT_OPENBSD_RANDOMIZE, cmd->getPhdrFlags())->add(cmd);
|
|
|
|
if (config->zGnustack != GnuStackKind::None) {
|
|
// PT_GNU_STACK is a special section to tell the loader to make the
|
|
// pages for the stack non-executable. If you really want an executable
|
|
// stack, you can pass -z execstack, but that's not recommended for
|
|
// security reasons.
|
|
unsigned perm = PF_R | PF_W;
|
|
if (config->zGnustack == GnuStackKind::Exec)
|
|
perm |= PF_X;
|
|
addHdr(PT_GNU_STACK, perm)->p_memsz = config->zStackSize;
|
|
}
|
|
|
|
// PT_OPENBSD_WXNEEDED is a OpenBSD-specific header to mark the executable
|
|
// is expected to perform W^X violations, such as calling mprotect(2) or
|
|
// mmap(2) with PROT_WRITE | PROT_EXEC, which is prohibited by default on
|
|
// OpenBSD.
|
|
if (config->zWxneeded)
|
|
addHdr(PT_OPENBSD_WXNEEDED, PF_X);
|
|
|
|
if (OutputSection *cmd = findSection(".note.gnu.property", partNo))
|
|
addHdr(PT_GNU_PROPERTY, PF_R)->add(cmd);
|
|
|
|
// Create one PT_NOTE per a group of contiguous SHT_NOTE sections with the
|
|
// same alignment.
|
|
PhdrEntry *note = nullptr;
|
|
for (OutputSection *sec : outputSections) {
|
|
if (sec->partition != partNo)
|
|
continue;
|
|
if (sec->type == SHT_NOTE && (sec->flags & SHF_ALLOC)) {
|
|
if (!note || sec->lmaExpr || note->lastSec->alignment != sec->alignment)
|
|
note = addHdr(PT_NOTE, PF_R);
|
|
note->add(sec);
|
|
} else {
|
|
note = nullptr;
|
|
}
|
|
}
|
|
return ret;
|
|
}
|
|
|
|
template <class ELFT>
|
|
void Writer<ELFT>::addPhdrForSection(Partition &part, unsigned shType,
|
|
unsigned pType, unsigned pFlags) {
|
|
unsigned partNo = part.getNumber();
|
|
auto i = llvm::find_if(outputSections, [=](OutputSection *cmd) {
|
|
return cmd->partition == partNo && cmd->type == shType;
|
|
});
|
|
if (i == outputSections.end())
|
|
return;
|
|
|
|
PhdrEntry *entry = make<PhdrEntry>(pType, pFlags);
|
|
entry->add(*i);
|
|
part.phdrs.push_back(entry);
|
|
}
|
|
|
|
// Place the first section of each PT_LOAD to a different page (of maxPageSize).
|
|
// This is achieved by assigning an alignment expression to addrExpr of each
|
|
// such section.
|
|
template <class ELFT> void Writer<ELFT>::fixSectionAlignments() {
|
|
const PhdrEntry *prev;
|
|
auto pageAlign = [&](const PhdrEntry *p) {
|
|
OutputSection *cmd = p->firstSec;
|
|
if (!cmd)
|
|
return;
|
|
cmd->alignExpr = [align = cmd->alignment]() { return align; };
|
|
if (!cmd->addrExpr) {
|
|
// Prefer advancing to align(dot, maxPageSize) + dot%maxPageSize to avoid
|
|
// padding in the file contents.
|
|
//
|
|
// When -z separate-code is used we must not have any overlap in pages
|
|
// between an executable segment and a non-executable segment. We align to
|
|
// the next maximum page size boundary on transitions between executable
|
|
// and non-executable segments.
|
|
//
|
|
// SHT_LLVM_PART_EHDR marks the start of a partition. The partition
|
|
// sections will be extracted to a separate file. Align to the next
|
|
// maximum page size boundary so that we can find the ELF header at the
|
|
// start. We cannot benefit from overlapping p_offset ranges with the
|
|
// previous segment anyway.
|
|
if (config->zSeparate == SeparateSegmentKind::Loadable ||
|
|
(config->zSeparate == SeparateSegmentKind::Code && prev &&
|
|
(prev->p_flags & PF_X) != (p->p_flags & PF_X)) ||
|
|
cmd->type == SHT_LLVM_PART_EHDR)
|
|
cmd->addrExpr = [] {
|
|
return alignTo(script->getDot(), config->maxPageSize);
|
|
};
|
|
// PT_TLS is at the start of the first RW PT_LOAD. If `p` includes PT_TLS,
|
|
// it must be the RW. Align to p_align(PT_TLS) to make sure
|
|
// p_vaddr(PT_LOAD)%p_align(PT_LOAD) = 0. Otherwise, if
|
|
// sh_addralign(.tdata) < sh_addralign(.tbss), we will set p_align(PT_TLS)
|
|
// to sh_addralign(.tbss), while p_vaddr(PT_TLS)=p_vaddr(PT_LOAD) may not
|
|
// be congruent to 0 modulo p_align(PT_TLS).
|
|
//
|
|
// Technically this is not required, but as of 2019, some dynamic loaders
|
|
// don't handle p_vaddr%p_align != 0 correctly, e.g. glibc (i386 and
|
|
// x86-64) doesn't make runtime address congruent to p_vaddr modulo
|
|
// p_align for dynamic TLS blocks (PR/24606), FreeBSD rtld has the same
|
|
// bug, musl (TLS Variant 1 architectures) before 1.1.23 handled TLS
|
|
// blocks correctly. We need to keep the workaround for a while.
|
|
else if (Out::tlsPhdr && Out::tlsPhdr->firstSec == p->firstSec)
|
|
cmd->addrExpr = [] {
|
|
return alignTo(script->getDot(), config->maxPageSize) +
|
|
alignTo(script->getDot() % config->maxPageSize,
|
|
Out::tlsPhdr->p_align);
|
|
};
|
|
else
|
|
cmd->addrExpr = [] {
|
|
return alignTo(script->getDot(), config->maxPageSize) +
|
|
script->getDot() % config->maxPageSize;
|
|
};
|
|
}
|
|
};
|
|
|
|
for (Partition &part : partitions) {
|
|
prev = nullptr;
|
|
for (const PhdrEntry *p : part.phdrs)
|
|
if (p->p_type == PT_LOAD && p->firstSec) {
|
|
pageAlign(p);
|
|
prev = p;
|
|
}
|
|
}
|
|
}
|
|
|
|
// Compute an in-file position for a given section. The file offset must be the
|
|
// same with its virtual address modulo the page size, so that the loader can
|
|
// load executables without any address adjustment.
|
|
static uint64_t computeFileOffset(OutputSection *os, uint64_t off) {
|
|
// The first section in a PT_LOAD has to have congruent offset and address
|
|
// modulo the maximum page size.
|
|
if (os->ptLoad && os->ptLoad->firstSec == os)
|
|
return alignTo(off, os->ptLoad->p_align, os->addr);
|
|
|
|
// File offsets are not significant for .bss sections other than the first one
|
|
// in a PT_LOAD/PT_TLS. By convention, we keep section offsets monotonically
|
|
// increasing rather than setting to zero.
|
|
if (os->type == SHT_NOBITS &&
|
|
(!Out::tlsPhdr || Out::tlsPhdr->firstSec != os))
|
|
return off;
|
|
|
|
// If the section is not in a PT_LOAD, we just have to align it.
|
|
if (!os->ptLoad)
|
|
return alignTo(off, os->alignment);
|
|
|
|
// If two sections share the same PT_LOAD the file offset is calculated
|
|
// using this formula: Off2 = Off1 + (VA2 - VA1).
|
|
OutputSection *first = os->ptLoad->firstSec;
|
|
return first->offset + os->addr - first->addr;
|
|
}
|
|
|
|
template <class ELFT> void Writer<ELFT>::assignFileOffsetsBinary() {
|
|
// Compute the minimum LMA of all non-empty non-NOBITS sections as minAddr.
|
|
auto needsOffset = [](OutputSection &sec) {
|
|
return sec.type != SHT_NOBITS && (sec.flags & SHF_ALLOC) && sec.size > 0;
|
|
};
|
|
uint64_t minAddr = UINT64_MAX;
|
|
for (OutputSection *sec : outputSections)
|
|
if (needsOffset(*sec)) {
|
|
sec->offset = sec->getLMA();
|
|
minAddr = std::min(minAddr, sec->offset);
|
|
}
|
|
|
|
// Sections are laid out at LMA minus minAddr.
|
|
fileSize = 0;
|
|
for (OutputSection *sec : outputSections)
|
|
if (needsOffset(*sec)) {
|
|
sec->offset -= minAddr;
|
|
fileSize = std::max(fileSize, sec->offset + sec->size);
|
|
}
|
|
}
|
|
|
|
static std::string rangeToString(uint64_t addr, uint64_t len) {
|
|
return "[0x" + utohexstr(addr) + ", 0x" + utohexstr(addr + len - 1) + "]";
|
|
}
|
|
|
|
// Assign file offsets to output sections.
|
|
template <class ELFT> void Writer<ELFT>::assignFileOffsets() {
|
|
Out::programHeaders->offset = Out::elfHeader->size;
|
|
uint64_t off = Out::elfHeader->size + Out::programHeaders->size;
|
|
|
|
PhdrEntry *lastRX = nullptr;
|
|
for (Partition &part : partitions)
|
|
for (PhdrEntry *p : part.phdrs)
|
|
if (p->p_type == PT_LOAD && (p->p_flags & PF_X))
|
|
lastRX = p;
|
|
|
|
// Layout SHF_ALLOC sections before non-SHF_ALLOC sections. A non-SHF_ALLOC
|
|
// will not occupy file offsets contained by a PT_LOAD.
|
|
for (OutputSection *sec : outputSections) {
|
|
if (!(sec->flags & SHF_ALLOC))
|
|
continue;
|
|
off = computeFileOffset(sec, off);
|
|
sec->offset = off;
|
|
if (sec->type != SHT_NOBITS)
|
|
off += sec->size;
|
|
|
|
// If this is a last section of the last executable segment and that
|
|
// segment is the last loadable segment, align the offset of the
|
|
// following section to avoid loading non-segments parts of the file.
|
|
if (config->zSeparate != SeparateSegmentKind::None && lastRX &&
|
|
lastRX->lastSec == sec)
|
|
off = alignTo(off, config->maxPageSize);
|
|
}
|
|
for (OutputSection *osec : outputSections)
|
|
if (!(osec->flags & SHF_ALLOC)) {
|
|
osec->offset = alignTo(off, osec->alignment);
|
|
off = osec->offset + osec->size;
|
|
}
|
|
|
|
sectionHeaderOff = alignTo(off, config->wordsize);
|
|
fileSize = sectionHeaderOff + (outputSections.size() + 1) * sizeof(Elf_Shdr);
|
|
|
|
// Our logic assumes that sections have rising VA within the same segment.
|
|
// With use of linker scripts it is possible to violate this rule and get file
|
|
// offset overlaps or overflows. That should never happen with a valid script
|
|
// which does not move the location counter backwards and usually scripts do
|
|
// not do that. Unfortunately, there are apps in the wild, for example, Linux
|
|
// kernel, which control segment distribution explicitly and move the counter
|
|
// backwards, so we have to allow doing that to support linking them. We
|
|
// perform non-critical checks for overlaps in checkSectionOverlap(), but here
|
|
// we want to prevent file size overflows because it would crash the linker.
|
|
for (OutputSection *sec : outputSections) {
|
|
if (sec->type == SHT_NOBITS)
|
|
continue;
|
|
if ((sec->offset > fileSize) || (sec->offset + sec->size > fileSize))
|
|
error("unable to place section " + sec->name + " at file offset " +
|
|
rangeToString(sec->offset, sec->size) +
|
|
"; check your linker script for overflows");
|
|
}
|
|
}
|
|
|
|
// Finalize the program headers. We call this function after we assign
|
|
// file offsets and VAs to all sections.
|
|
template <class ELFT> void Writer<ELFT>::setPhdrs(Partition &part) {
|
|
for (PhdrEntry *p : part.phdrs) {
|
|
OutputSection *first = p->firstSec;
|
|
OutputSection *last = p->lastSec;
|
|
|
|
if (first) {
|
|
p->p_filesz = last->offset - first->offset;
|
|
if (last->type != SHT_NOBITS)
|
|
p->p_filesz += last->size;
|
|
|
|
p->p_memsz = last->addr + last->size - first->addr;
|
|
p->p_offset = first->offset;
|
|
p->p_vaddr = first->addr;
|
|
|
|
// File offsets in partitions other than the main partition are relative
|
|
// to the offset of the ELF headers. Perform that adjustment now.
|
|
if (part.elfHeader)
|
|
p->p_offset -= part.elfHeader->getParent()->offset;
|
|
|
|
if (!p->hasLMA)
|
|
p->p_paddr = first->getLMA();
|
|
}
|
|
|
|
if (p->p_type == PT_GNU_RELRO) {
|
|
p->p_align = 1;
|
|
// musl/glibc ld.so rounds the size down, so we need to round up
|
|
// to protect the last page. This is a no-op on FreeBSD which always
|
|
// rounds up.
|
|
p->p_memsz = alignTo(p->p_offset + p->p_memsz, config->commonPageSize) -
|
|
p->p_offset;
|
|
}
|
|
}
|
|
}
|
|
|
|
// A helper struct for checkSectionOverlap.
|
|
namespace {
|
|
struct SectionOffset {
|
|
OutputSection *sec;
|
|
uint64_t offset;
|
|
};
|
|
} // namespace
|
|
|
|
// Check whether sections overlap for a specific address range (file offsets,
|
|
// load and virtual addresses).
|
|
static void checkOverlap(StringRef name, std::vector<SectionOffset> §ions,
|
|
bool isVirtualAddr) {
|
|
llvm::sort(sections, [=](const SectionOffset &a, const SectionOffset &b) {
|
|
return a.offset < b.offset;
|
|
});
|
|
|
|
// Finding overlap is easy given a vector is sorted by start position.
|
|
// If an element starts before the end of the previous element, they overlap.
|
|
for (size_t i = 1, end = sections.size(); i < end; ++i) {
|
|
SectionOffset a = sections[i - 1];
|
|
SectionOffset b = sections[i];
|
|
if (b.offset >= a.offset + a.sec->size)
|
|
continue;
|
|
|
|
// If both sections are in OVERLAY we allow the overlapping of virtual
|
|
// addresses, because it is what OVERLAY was designed for.
|
|
if (isVirtualAddr && a.sec->inOverlay && b.sec->inOverlay)
|
|
continue;
|
|
|
|
errorOrWarn("section " + a.sec->name + " " + name +
|
|
" range overlaps with " + b.sec->name + "\n>>> " + a.sec->name +
|
|
" range is " + rangeToString(a.offset, a.sec->size) + "\n>>> " +
|
|
b.sec->name + " range is " +
|
|
rangeToString(b.offset, b.sec->size));
|
|
}
|
|
}
|
|
|
|
// Check for overlapping sections and address overflows.
|
|
//
|
|
// In this function we check that none of the output sections have overlapping
|
|
// file offsets. For SHF_ALLOC sections we also check that the load address
|
|
// ranges and the virtual address ranges don't overlap
|
|
template <class ELFT> void Writer<ELFT>::checkSections() {
|
|
// First, check that section's VAs fit in available address space for target.
|
|
for (OutputSection *os : outputSections)
|
|
if ((os->addr + os->size < os->addr) ||
|
|
(!ELFT::Is64Bits && os->addr + os->size > UINT32_MAX))
|
|
errorOrWarn("section " + os->name + " at 0x" + utohexstr(os->addr) +
|
|
" of size 0x" + utohexstr(os->size) +
|
|
" exceeds available address space");
|
|
|
|
// Check for overlapping file offsets. In this case we need to skip any
|
|
// section marked as SHT_NOBITS. These sections don't actually occupy space in
|
|
// the file so Sec->Offset + Sec->Size can overlap with others. If --oformat
|
|
// binary is specified only add SHF_ALLOC sections are added to the output
|
|
// file so we skip any non-allocated sections in that case.
|
|
std::vector<SectionOffset> fileOffs;
|
|
for (OutputSection *sec : outputSections)
|
|
if (sec->size > 0 && sec->type != SHT_NOBITS &&
|
|
(!config->oFormatBinary || (sec->flags & SHF_ALLOC)))
|
|
fileOffs.push_back({sec, sec->offset});
|
|
checkOverlap("file", fileOffs, false);
|
|
|
|
// When linking with -r there is no need to check for overlapping virtual/load
|
|
// addresses since those addresses will only be assigned when the final
|
|
// executable/shared object is created.
|
|
if (config->relocatable)
|
|
return;
|
|
|
|
// Checking for overlapping virtual and load addresses only needs to take
|
|
// into account SHF_ALLOC sections since others will not be loaded.
|
|
// Furthermore, we also need to skip SHF_TLS sections since these will be
|
|
// mapped to other addresses at runtime and can therefore have overlapping
|
|
// ranges in the file.
|
|
std::vector<SectionOffset> vmas;
|
|
for (OutputSection *sec : outputSections)
|
|
if (sec->size > 0 && (sec->flags & SHF_ALLOC) && !(sec->flags & SHF_TLS))
|
|
vmas.push_back({sec, sec->addr});
|
|
checkOverlap("virtual address", vmas, true);
|
|
|
|
// Finally, check that the load addresses don't overlap. This will usually be
|
|
// the same as the virtual addresses but can be different when using a linker
|
|
// script with AT().
|
|
std::vector<SectionOffset> lmas;
|
|
for (OutputSection *sec : outputSections)
|
|
if (sec->size > 0 && (sec->flags & SHF_ALLOC) && !(sec->flags & SHF_TLS))
|
|
lmas.push_back({sec, sec->getLMA()});
|
|
checkOverlap("load address", lmas, false);
|
|
}
|
|
|
|
// The entry point address is chosen in the following ways.
|
|
//
|
|
// 1. the '-e' entry command-line option;
|
|
// 2. the ENTRY(symbol) command in a linker control script;
|
|
// 3. the value of the symbol _start, if present;
|
|
// 4. the number represented by the entry symbol, if it is a number;
|
|
// 5. the address 0.
|
|
static uint64_t getEntryAddr() {
|
|
// Case 1, 2 or 3
|
|
if (Symbol *b = symtab->find(config->entry))
|
|
return b->getVA();
|
|
|
|
// Case 4
|
|
uint64_t addr;
|
|
if (to_integer(config->entry, addr))
|
|
return addr;
|
|
|
|
// Case 5
|
|
if (config->warnMissingEntry)
|
|
warn("cannot find entry symbol " + config->entry +
|
|
"; not setting start address");
|
|
return 0;
|
|
}
|
|
|
|
static uint16_t getELFType() {
|
|
if (config->isPic)
|
|
return ET_DYN;
|
|
if (config->relocatable)
|
|
return ET_REL;
|
|
return ET_EXEC;
|
|
}
|
|
|
|
template <class ELFT> void Writer<ELFT>::writeHeader() {
|
|
writeEhdr<ELFT>(Out::bufferStart, *mainPart);
|
|
writePhdrs<ELFT>(Out::bufferStart + sizeof(Elf_Ehdr), *mainPart);
|
|
|
|
auto *eHdr = reinterpret_cast<Elf_Ehdr *>(Out::bufferStart);
|
|
eHdr->e_type = getELFType();
|
|
eHdr->e_entry = getEntryAddr();
|
|
eHdr->e_shoff = sectionHeaderOff;
|
|
|
|
// Write the section header table.
|
|
//
|
|
// The ELF header can only store numbers up to SHN_LORESERVE in the e_shnum
|
|
// and e_shstrndx fields. When the value of one of these fields exceeds
|
|
// SHN_LORESERVE ELF requires us to put sentinel values in the ELF header and
|
|
// use fields in the section header at index 0 to store
|
|
// the value. The sentinel values and fields are:
|
|
// e_shnum = 0, SHdrs[0].sh_size = number of sections.
|
|
// e_shstrndx = SHN_XINDEX, SHdrs[0].sh_link = .shstrtab section index.
|
|
auto *sHdrs = reinterpret_cast<Elf_Shdr *>(Out::bufferStart + eHdr->e_shoff);
|
|
size_t num = outputSections.size() + 1;
|
|
if (num >= SHN_LORESERVE)
|
|
sHdrs->sh_size = num;
|
|
else
|
|
eHdr->e_shnum = num;
|
|
|
|
uint32_t strTabIndex = in.shStrTab->getParent()->sectionIndex;
|
|
if (strTabIndex >= SHN_LORESERVE) {
|
|
sHdrs->sh_link = strTabIndex;
|
|
eHdr->e_shstrndx = SHN_XINDEX;
|
|
} else {
|
|
eHdr->e_shstrndx = strTabIndex;
|
|
}
|
|
|
|
for (OutputSection *sec : outputSections)
|
|
sec->writeHeaderTo<ELFT>(++sHdrs);
|
|
}
|
|
|
|
// Open a result file.
|
|
template <class ELFT> void Writer<ELFT>::openFile() {
|
|
uint64_t maxSize = config->is64 ? INT64_MAX : UINT32_MAX;
|
|
if (fileSize != size_t(fileSize) || maxSize < fileSize) {
|
|
std::string msg;
|
|
raw_string_ostream s(msg);
|
|
s << "output file too large: " << Twine(fileSize) << " bytes\n"
|
|
<< "section sizes:\n";
|
|
for (OutputSection *os : outputSections)
|
|
s << os->name << ' ' << os->size << "\n";
|
|
error(s.str());
|
|
return;
|
|
}
|
|
|
|
unlinkAsync(config->outputFile);
|
|
unsigned flags = 0;
|
|
if (!config->relocatable)
|
|
flags |= FileOutputBuffer::F_executable;
|
|
if (!config->mmapOutputFile)
|
|
flags |= FileOutputBuffer::F_no_mmap;
|
|
Expected<std::unique_ptr<FileOutputBuffer>> bufferOrErr =
|
|
FileOutputBuffer::create(config->outputFile, fileSize, flags);
|
|
|
|
if (!bufferOrErr) {
|
|
error("failed to open " + config->outputFile + ": " +
|
|
llvm::toString(bufferOrErr.takeError()));
|
|
return;
|
|
}
|
|
buffer = std::move(*bufferOrErr);
|
|
Out::bufferStart = buffer->getBufferStart();
|
|
}
|
|
|
|
template <class ELFT> void Writer<ELFT>::writeSectionsBinary() {
|
|
for (OutputSection *sec : outputSections)
|
|
if (sec->flags & SHF_ALLOC)
|
|
sec->writeTo<ELFT>(Out::bufferStart + sec->offset);
|
|
}
|
|
|
|
static void fillTrap(uint8_t *i, uint8_t *end) {
|
|
for (; i + 4 <= end; i += 4)
|
|
memcpy(i, &target->trapInstr, 4);
|
|
}
|
|
|
|
// Fill the last page of executable segments with trap instructions
|
|
// instead of leaving them as zero. Even though it is not required by any
|
|
// standard, it is in general a good thing to do for security reasons.
|
|
//
|
|
// We'll leave other pages in segments as-is because the rest will be
|
|
// overwritten by output sections.
|
|
template <class ELFT> void Writer<ELFT>::writeTrapInstr() {
|
|
for (Partition &part : partitions) {
|
|
// Fill the last page.
|
|
for (PhdrEntry *p : part.phdrs)
|
|
if (p->p_type == PT_LOAD && (p->p_flags & PF_X))
|
|
fillTrap(Out::bufferStart +
|
|
alignDown(p->firstSec->offset + p->p_filesz, 4),
|
|
Out::bufferStart + alignTo(p->firstSec->offset + p->p_filesz,
|
|
config->maxPageSize));
|
|
|
|
// Round up the file size of the last segment to the page boundary iff it is
|
|
// an executable segment to ensure that other tools don't accidentally
|
|
// trim the instruction padding (e.g. when stripping the file).
|
|
PhdrEntry *last = nullptr;
|
|
for (PhdrEntry *p : part.phdrs)
|
|
if (p->p_type == PT_LOAD)
|
|
last = p;
|
|
|
|
if (last && (last->p_flags & PF_X))
|
|
last->p_memsz = last->p_filesz =
|
|
alignTo(last->p_filesz, config->maxPageSize);
|
|
}
|
|
}
|
|
|
|
// Write section contents to a mmap'ed file.
|
|
template <class ELFT> void Writer<ELFT>::writeSections() {
|
|
llvm::TimeTraceScope timeScope("Write sections");
|
|
|
|
// In -r or --emit-relocs mode, write the relocation sections first as in
|
|
// ELf_Rel targets we might find out that we need to modify the relocated
|
|
// section while doing it.
|
|
for (OutputSection *sec : outputSections)
|
|
if (sec->type == SHT_REL || sec->type == SHT_RELA)
|
|
sec->writeTo<ELFT>(Out::bufferStart + sec->offset);
|
|
|
|
for (OutputSection *sec : outputSections)
|
|
if (sec->type != SHT_REL && sec->type != SHT_RELA)
|
|
sec->writeTo<ELFT>(Out::bufferStart + sec->offset);
|
|
|
|
// Finally, check that all dynamic relocation addends were written correctly.
|
|
if (config->checkDynamicRelocs && config->writeAddends) {
|
|
for (OutputSection *sec : outputSections)
|
|
if (sec->type == SHT_REL || sec->type == SHT_RELA)
|
|
sec->checkDynRelAddends(Out::bufferStart);
|
|
}
|
|
}
|
|
|
|
// Computes a hash value of Data using a given hash function.
|
|
// In order to utilize multiple cores, we first split data into 1MB
|
|
// chunks, compute a hash for each chunk, and then compute a hash value
|
|
// of the hash values.
|
|
static void
|
|
computeHash(llvm::MutableArrayRef<uint8_t> hashBuf,
|
|
llvm::ArrayRef<uint8_t> data,
|
|
std::function<void(uint8_t *dest, ArrayRef<uint8_t> arr)> hashFn) {
|
|
std::vector<ArrayRef<uint8_t>> chunks = split(data, 1024 * 1024);
|
|
const size_t hashesSize = chunks.size() * hashBuf.size();
|
|
std::unique_ptr<uint8_t[]> hashes(new uint8_t[hashesSize]);
|
|
|
|
// Compute hash values.
|
|
parallelForEachN(0, chunks.size(), [&](size_t i) {
|
|
hashFn(hashes.get() + i * hashBuf.size(), chunks[i]);
|
|
});
|
|
|
|
// Write to the final output buffer.
|
|
hashFn(hashBuf.data(), makeArrayRef(hashes.get(), hashesSize));
|
|
}
|
|
|
|
template <class ELFT> void Writer<ELFT>::writeBuildId() {
|
|
if (!mainPart->buildId || !mainPart->buildId->getParent())
|
|
return;
|
|
|
|
if (config->buildId == BuildIdKind::Hexstring) {
|
|
for (Partition &part : partitions)
|
|
part.buildId->writeBuildId(config->buildIdVector);
|
|
return;
|
|
}
|
|
|
|
// Compute a hash of all sections of the output file.
|
|
size_t hashSize = mainPart->buildId->hashSize;
|
|
std::unique_ptr<uint8_t[]> buildId(new uint8_t[hashSize]);
|
|
MutableArrayRef<uint8_t> output(buildId.get(), hashSize);
|
|
llvm::ArrayRef<uint8_t> input{Out::bufferStart, size_t(fileSize)};
|
|
|
|
// Fedora introduced build ID as "approximation of true uniqueness across all
|
|
// binaries that might be used by overlapping sets of people". It does not
|
|
// need some security goals that some hash algorithms strive to provide, e.g.
|
|
// (second-)preimage and collision resistance. In practice people use 'md5'
|
|
// and 'sha1' just for different lengths. Implement them with the more
|
|
// efficient BLAKE3.
|
|
switch (config->buildId) {
|
|
case BuildIdKind::Fast:
|
|
computeHash(output, input, [](uint8_t *dest, ArrayRef<uint8_t> arr) {
|
|
write64le(dest, xxHash64(arr));
|
|
});
|
|
break;
|
|
case BuildIdKind::Md5:
|
|
computeHash(output, input, [&](uint8_t *dest, ArrayRef<uint8_t> arr) {
|
|
memcpy(dest, BLAKE3::hash<16>(arr).data(), hashSize);
|
|
});
|
|
break;
|
|
case BuildIdKind::Sha1:
|
|
computeHash(output, input, [&](uint8_t *dest, ArrayRef<uint8_t> arr) {
|
|
memcpy(dest, BLAKE3::hash<20>(arr).data(), hashSize);
|
|
});
|
|
break;
|
|
case BuildIdKind::Uuid:
|
|
if (auto ec = llvm::getRandomBytes(buildId.get(), hashSize))
|
|
error("entropy source failure: " + ec.message());
|
|
break;
|
|
default:
|
|
llvm_unreachable("unknown BuildIdKind");
|
|
}
|
|
for (Partition &part : partitions)
|
|
part.buildId->writeBuildId(output);
|
|
}
|
|
|
|
template void elf::createSyntheticSections<ELF32LE>();
|
|
template void elf::createSyntheticSections<ELF32BE>();
|
|
template void elf::createSyntheticSections<ELF64LE>();
|
|
template void elf::createSyntheticSections<ELF64BE>();
|
|
|
|
template void elf::writeResult<ELF32LE>();
|
|
template void elf::writeResult<ELF32BE>();
|
|
template void elf::writeResult<ELF64LE>();
|
|
template void elf::writeResult<ELF64BE>();
|