forked from OSchip/llvm-project
605 lines
21 KiB
C++
605 lines
21 KiB
C++
//===- OutputSections.cpp -------------------------------------------------===//
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//
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// The LLVM Linker
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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#include "OutputSections.h"
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#include "Config.h"
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#include "LinkerScript.h"
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#include "Memory.h"
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#include "Strings.h"
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#include "SymbolTable.h"
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#include "SyntheticSections.h"
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#include "Target.h"
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#include "Threads.h"
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#include "llvm/BinaryFormat/Dwarf.h"
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#include "llvm/Support/Compression.h"
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#include "llvm/Support/MD5.h"
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#include "llvm/Support/MathExtras.h"
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#include "llvm/Support/SHA1.h"
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using namespace llvm;
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using namespace llvm::dwarf;
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using namespace llvm::object;
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using namespace llvm::support::endian;
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using namespace llvm::ELF;
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using namespace lld;
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using namespace lld::elf;
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uint8_t Out::First;
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OutputSection *Out::Opd;
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uint8_t *Out::OpdBuf;
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PhdrEntry *Out::TlsPhdr;
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OutputSection *Out::DebugInfo;
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OutputSection *Out::ElfHeader;
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OutputSection *Out::ProgramHeaders;
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OutputSection *Out::PreinitArray;
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OutputSection *Out::InitArray;
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OutputSection *Out::FiniArray;
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std::vector<OutputSection *> elf::OutputSections;
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uint32_t OutputSection::getPhdrFlags() const {
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uint32_t Ret = PF_R;
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if (Flags & SHF_WRITE)
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Ret |= PF_W;
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if (Flags & SHF_EXECINSTR)
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Ret |= PF_X;
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return Ret;
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}
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template <class ELFT>
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void OutputSection::writeHeaderTo(typename ELFT::Shdr *Shdr) {
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Shdr->sh_entsize = Entsize;
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Shdr->sh_addralign = Alignment;
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Shdr->sh_type = Type;
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Shdr->sh_offset = Offset;
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Shdr->sh_flags = Flags;
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Shdr->sh_info = Info;
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Shdr->sh_link = Link;
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Shdr->sh_addr = Addr;
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Shdr->sh_size = Size;
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Shdr->sh_name = ShName;
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}
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OutputSection::OutputSection(StringRef Name, uint32_t Type, uint64_t Flags)
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: BaseCommand(OutputSectionKind),
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SectionBase(Output, Name, Flags, /*Entsize*/ 0, /*Alignment*/ 1, Type,
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/*Info*/ 0,
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/*Link*/ 0),
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SectionIndex(INT_MAX) {
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Live = false;
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}
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static uint64_t updateOffset(uint64_t Off, InputSection *S) {
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Off = alignTo(Off, S->Alignment);
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S->OutSecOff = Off;
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return Off + S->getSize();
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}
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void OutputSection::addSection(InputSection *S) {
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assert(S->Live);
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Live = true;
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S->Parent = this;
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this->updateAlignment(S->Alignment);
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// The actual offsets will be computed by assignAddresses. For now, use
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// crude approximation so that it is at least easy for other code to know the
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// section order. It is also used to calculate the output section size early
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// for compressed debug sections.
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this->Size = updateOffset(Size, S);
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// If this section contains a table of fixed-size entries, sh_entsize
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// holds the element size. Consequently, if this contains two or more
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// input sections, all of them must have the same sh_entsize. However,
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// you can put different types of input sections into one output
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// sectin by using linker scripts. I don't know what to do here.
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// Probably we sholuld handle that as an error. But for now we just
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// pick the largest sh_entsize.
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this->Entsize = std::max(this->Entsize, S->Entsize);
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if (!S->Assigned) {
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S->Assigned = true;
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if (Commands.empty() || !isa<InputSectionDescription>(Commands.back()))
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Commands.push_back(make<InputSectionDescription>(""));
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auto *ISD = cast<InputSectionDescription>(Commands.back());
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ISD->Sections.push_back(S);
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}
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}
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static SectionKey createKey(InputSectionBase *C, StringRef OutsecName) {
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// The ELF spec just says
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// ----------------------------------------------------------------
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// In the first phase, input sections that match in name, type and
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// attribute flags should be concatenated into single sections.
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// ----------------------------------------------------------------
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//
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// However, it is clear that at least some flags have to be ignored for
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// section merging. At the very least SHF_GROUP and SHF_COMPRESSED have to be
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// ignored. We should not have two output .text sections just because one was
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// in a group and another was not for example.
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//
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// It also seems that that wording was a late addition and didn't get the
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// necessary scrutiny.
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//
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// Merging sections with different flags is expected by some users. One
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// reason is that if one file has
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//
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// int *const bar __attribute__((section(".foo"))) = (int *)0;
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//
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// gcc with -fPIC will produce a read only .foo section. But if another
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// file has
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//
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// int zed;
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// int *const bar __attribute__((section(".foo"))) = (int *)&zed;
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//
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// gcc with -fPIC will produce a read write section.
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//
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// Last but not least, when using linker script the merge rules are forced by
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// the script. Unfortunately, linker scripts are name based. This means that
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// expressions like *(.foo*) can refer to multiple input sections with
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// different flags. We cannot put them in different output sections or we
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// would produce wrong results for
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//
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// start = .; *(.foo.*) end = .; *(.bar)
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//
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// and a mapping of .foo1 and .bar1 to one section and .foo2 and .bar2 to
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// another. The problem is that there is no way to layout those output
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// sections such that the .foo sections are the only thing between the start
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// and end symbols.
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//
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// Given the above issues, we instead merge sections by name and error on
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// incompatible types and flags.
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uint32_t Alignment = 0;
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uint64_t Flags = 0;
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if (Config->Relocatable && (C->Flags & SHF_MERGE)) {
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Alignment = std::max<uint64_t>(C->Alignment, C->Entsize);
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Flags = C->Flags & (SHF_MERGE | SHF_STRINGS);
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}
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return SectionKey{OutsecName, Flags, Alignment};
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}
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OutputSectionFactory::OutputSectionFactory() {}
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static uint64_t getIncompatibleFlags(uint64_t Flags) {
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return Flags & (SHF_ALLOC | SHF_TLS);
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}
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// We allow sections of types listed below to merged into a
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// single progbits section. This is typically done by linker
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// scripts. Merging nobits and progbits will force disk space
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// to be allocated for nobits sections. Other ones don't require
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// any special treatment on top of progbits, so there doesn't
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// seem to be a harm in merging them.
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static bool canMergeToProgbits(unsigned Type) {
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return Type == SHT_NOBITS || Type == SHT_PROGBITS || Type == SHT_INIT_ARRAY ||
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Type == SHT_PREINIT_ARRAY || Type == SHT_FINI_ARRAY ||
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Type == SHT_NOTE;
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}
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void elf::sortByOrder(MutableArrayRef<InputSection *> In,
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std::function<int(InputSectionBase *S)> Order) {
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typedef std::pair<int, InputSection *> Pair;
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auto Comp = [](const Pair &A, const Pair &B) { return A.first < B.first; };
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std::vector<Pair> V;
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for (InputSection *S : In)
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V.push_back({Order(S), S});
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std::stable_sort(V.begin(), V.end(), Comp);
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for (size_t I = 0; I < V.size(); ++I)
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In[I] = V[I].second;
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}
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void elf::reportDiscarded(InputSectionBase *IS) {
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if (!Config->PrintGcSections)
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return;
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message("removing unused section from '" + IS->Name + "' in file '" +
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IS->File->getName() + "'");
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}
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static OutputSection *addSection(InputSectionBase *IS, StringRef OutsecName,
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OutputSection *Sec) {
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if (Sec && Sec->Live) {
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if (getIncompatibleFlags(Sec->Flags) != getIncompatibleFlags(IS->Flags))
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error("incompatible section flags for " + Sec->Name + "\n>>> " +
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toString(IS) + ": 0x" + utohexstr(IS->Flags) +
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"\n>>> output section " + Sec->Name + ": 0x" +
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utohexstr(Sec->Flags));
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if (Sec->Type != IS->Type) {
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if (canMergeToProgbits(Sec->Type) && canMergeToProgbits(IS->Type))
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Sec->Type = SHT_PROGBITS;
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else
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error("section type mismatch for " + IS->Name + "\n>>> " +
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toString(IS) + ": " +
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getELFSectionTypeName(Config->EMachine, IS->Type) +
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"\n>>> output section " + Sec->Name + ": " +
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getELFSectionTypeName(Config->EMachine, Sec->Type));
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}
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Sec->Flags |= IS->Flags;
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} else {
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if (!Sec) {
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Sec = Script->createOutputSection(OutsecName, "<internal>");
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Script->Opt.Commands.push_back(Sec);
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}
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Sec->Type = IS->Type;
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Sec->Flags = IS->Flags;
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}
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Sec->addSection(cast<InputSection>(IS));
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return Sec;
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}
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void OutputSectionFactory::addInputSec(InputSectionBase *IS,
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StringRef OutsecName,
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OutputSection *OS) {
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if (!IS->Live) {
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reportDiscarded(IS);
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return;
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}
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// If we have destination output section - use it directly.
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if (OS) {
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addSection(IS, OutsecName, OS);
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return;
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}
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// Sections with SHT_GROUP or SHF_GROUP attributes reach here only when the -r
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// option is given. A section with SHT_GROUP defines a "section group", and
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// its members have SHF_GROUP attribute. Usually these flags have already been
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// stripped by InputFiles.cpp as section groups are processed and uniquified.
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// However, for the -r option, we want to pass through all section groups
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// as-is because adding/removing members or merging them with other groups
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// change their semantics.
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if (IS->Type == SHT_GROUP || (IS->Flags & SHF_GROUP)) {
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addSection(IS, OutsecName, nullptr);
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return;
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}
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// Imagine .zed : { *(.foo) *(.bar) } script. Both foo and bar may have
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// relocation sections .rela.foo and .rela.bar for example. Most tools do
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// not allow multiple REL[A] sections for output section. Hence we
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// should combine these relocation sections into single output.
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// We skip synthetic sections because it can be .rela.dyn/.rela.plt or any
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// other REL[A] sections created by linker itself.
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if (!isa<SyntheticSection>(IS) &&
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(IS->Type == SHT_REL || IS->Type == SHT_RELA)) {
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auto *Sec = cast<InputSection>(IS);
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OutputSection *Out = Sec->getRelocatedSection()->getOutputSection();
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Out->RelocationSection = addSection(IS, OutsecName, Out->RelocationSection);
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return;
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}
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SectionKey Key = createKey(IS, OutsecName);
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OutputSection *&Sec = Map[Key];
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Sec = addSection(IS, OutsecName, Sec);
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}
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OutputSectionFactory::~OutputSectionFactory() {}
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SectionKey DenseMapInfo<SectionKey>::getEmptyKey() {
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return SectionKey{DenseMapInfo<StringRef>::getEmptyKey(), 0, 0};
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}
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SectionKey DenseMapInfo<SectionKey>::getTombstoneKey() {
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return SectionKey{DenseMapInfo<StringRef>::getTombstoneKey(), 0, 0};
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}
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unsigned DenseMapInfo<SectionKey>::getHashValue(const SectionKey &Val) {
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return hash_combine(Val.Name, Val.Flags, Val.Alignment);
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}
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bool DenseMapInfo<SectionKey>::isEqual(const SectionKey &LHS,
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const SectionKey &RHS) {
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return DenseMapInfo<StringRef>::isEqual(LHS.Name, RHS.Name) &&
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LHS.Flags == RHS.Flags && LHS.Alignment == RHS.Alignment;
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}
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uint64_t elf::getHeaderSize() {
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if (Config->OFormatBinary)
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return 0;
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return Out::ElfHeader->Size + Out::ProgramHeaders->Size;
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}
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bool OutputSection::classof(const BaseCommand *C) {
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return C->Kind == OutputSectionKind;
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}
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void OutputSection::sort(std::function<int(InputSectionBase *S)> Order) {
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assert(Commands.size() == 1);
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sortByOrder(cast<InputSectionDescription>(Commands[0])->Sections, Order);
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}
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// Fill [Buf, Buf + Size) with Filler.
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// This is used for linker script "=fillexp" command.
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static void fill(uint8_t *Buf, size_t Size, uint32_t Filler) {
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size_t I = 0;
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for (; I + 4 < Size; I += 4)
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memcpy(Buf + I, &Filler, 4);
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memcpy(Buf + I, &Filler, Size - I);
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}
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// Compress section contents if this section contains debug info.
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template <class ELFT> void OutputSection::maybeCompress() {
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typedef typename ELFT::Chdr Elf_Chdr;
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// Compress only DWARF debug sections.
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if (!Config->CompressDebugSections || (Flags & SHF_ALLOC) ||
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!Name.startswith(".debug_"))
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return;
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// Create a section header.
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ZDebugHeader.resize(sizeof(Elf_Chdr));
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auto *Hdr = reinterpret_cast<Elf_Chdr *>(ZDebugHeader.data());
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Hdr->ch_type = ELFCOMPRESS_ZLIB;
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Hdr->ch_size = Size;
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Hdr->ch_addralign = Alignment;
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// Write section contents to a temporary buffer and compress it.
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std::vector<uint8_t> Buf(Size);
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writeTo<ELFT>(Buf.data());
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if (Error E = zlib::compress(toStringRef(Buf), CompressedData))
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fatal("compress failed: " + llvm::toString(std::move(E)));
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// Update section headers.
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Size = sizeof(Elf_Chdr) + CompressedData.size();
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Flags |= SHF_COMPRESSED;
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}
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static void writeInt(uint8_t *Buf, uint64_t Data, uint64_t Size) {
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if (Size == 1)
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*Buf = Data;
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else if (Size == 2)
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write16(Buf, Data, Config->Endianness);
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else if (Size == 4)
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write32(Buf, Data, Config->Endianness);
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else if (Size == 8)
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write64(Buf, Data, Config->Endianness);
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else
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llvm_unreachable("unsupported Size argument");
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}
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template <class ELFT> void OutputSection::writeTo(uint8_t *Buf) {
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if (Type == SHT_NOBITS)
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return;
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Loc = Buf;
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// If -compress-debug-section is specified and if this is a debug seciton,
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// we've already compressed section contents. If that's the case,
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// just write it down.
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if (!CompressedData.empty()) {
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memcpy(Buf, ZDebugHeader.data(), ZDebugHeader.size());
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memcpy(Buf + ZDebugHeader.size(), CompressedData.data(),
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CompressedData.size());
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return;
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}
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// Write leading padding.
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std::vector<InputSection *> Sections;
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for (BaseCommand *Cmd : Commands)
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if (auto *ISD = dyn_cast<InputSectionDescription>(Cmd))
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for (InputSection *IS : ISD->Sections)
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if (IS->Live)
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Sections.push_back(IS);
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uint32_t Filler = getFiller();
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if (Filler)
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fill(Buf, Sections.empty() ? Size : Sections[0]->OutSecOff, Filler);
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parallelForEachN(0, Sections.size(), [=](size_t I) {
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InputSection *IS = Sections[I];
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IS->writeTo<ELFT>(Buf);
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// Fill gaps between sections.
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if (Filler) {
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uint8_t *Start = Buf + IS->OutSecOff + IS->getSize();
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uint8_t *End;
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if (I + 1 == Sections.size())
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End = Buf + Size;
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else
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End = Buf + Sections[I + 1]->OutSecOff;
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fill(Start, End - Start, Filler);
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}
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});
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// Linker scripts may have BYTE()-family commands with which you
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// can write arbitrary bytes to the output. Process them if any.
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for (BaseCommand *Base : Commands)
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if (auto *Data = dyn_cast<BytesDataCommand>(Base))
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writeInt(Buf + Data->Offset, Data->Expression().getValue(), Data->Size);
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}
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static bool compareByFilePosition(InputSection *A, InputSection *B) {
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// Synthetic doesn't have link order dependecy, stable_sort will keep it last
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if (A->kind() == InputSectionBase::Synthetic ||
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B->kind() == InputSectionBase::Synthetic)
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return false;
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InputSection *LA = A->getLinkOrderDep();
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InputSection *LB = B->getLinkOrderDep();
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OutputSection *AOut = LA->getParent();
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OutputSection *BOut = LB->getParent();
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if (AOut != BOut)
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return AOut->SectionIndex < BOut->SectionIndex;
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return LA->OutSecOff < LB->OutSecOff;
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}
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template <class ELFT>
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static void finalizeShtGroup(OutputSection *OS,
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ArrayRef<InputSection *> Sections) {
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assert(Config->Relocatable && Sections.size() == 1);
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// sh_link field for SHT_GROUP sections should contain the section index of
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// the symbol table.
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OS->Link = InX::SymTab->getParent()->SectionIndex;
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// sh_info then contain index of an entry in symbol table section which
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// provides signature of the section group.
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ObjFile<ELFT> *Obj = Sections[0]->getFile<ELFT>();
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ArrayRef<SymbolBody *> Symbols = Obj->getSymbols();
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OS->Info = InX::SymTab->getSymbolIndex(Symbols[Sections[0]->Info]);
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}
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template <class ELFT> void OutputSection::finalize() {
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// Link order may be distributed across several InputSectionDescriptions
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// but sort must consider them all at once.
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std::vector<InputSection **> ScriptSections;
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std::vector<InputSection *> Sections;
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for (BaseCommand *Base : Commands)
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if (auto *ISD = dyn_cast<InputSectionDescription>(Base))
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for (InputSection *&IS : ISD->Sections) {
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ScriptSections.push_back(&IS);
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Sections.push_back(IS);
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}
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if (Flags & SHF_LINK_ORDER) {
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std::stable_sort(Sections.begin(), Sections.end(), compareByFilePosition);
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for (int I = 0, N = Sections.size(); I < N; ++I)
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*ScriptSections[I] = Sections[I];
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// We must preserve the link order dependency of sections with the
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// SHF_LINK_ORDER flag. The dependency is indicated by the sh_link field. We
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// need to translate the InputSection sh_link to the OutputSection sh_link,
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// all InputSections in the OutputSection have the same dependency.
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if (auto *D = Sections.front()->getLinkOrderDep())
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Link = D->getParent()->SectionIndex;
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}
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if (Type == SHT_GROUP) {
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finalizeShtGroup<ELFT>(this, Sections);
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return;
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}
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if (!Config->CopyRelocs || (Type != SHT_RELA && Type != SHT_REL))
|
|
return;
|
|
|
|
InputSection *First = Sections[0];
|
|
if (isa<SyntheticSection>(First))
|
|
return;
|
|
|
|
Link = InX::SymTab->getParent()->SectionIndex;
|
|
// sh_info for SHT_REL[A] sections should contain the section header index of
|
|
// the section to which the relocation applies.
|
|
InputSectionBase *S = First->getRelocatedSection();
|
|
Info = S->getOutputSection()->SectionIndex;
|
|
Flags |= SHF_INFO_LINK;
|
|
}
|
|
|
|
// Returns true if S matches /Filename.?\.o$/.
|
|
static bool isCrtBeginEnd(StringRef S, StringRef Filename) {
|
|
if (!S.endswith(".o"))
|
|
return false;
|
|
S = S.drop_back(2);
|
|
if (S.endswith(Filename))
|
|
return true;
|
|
return !S.empty() && S.drop_back().endswith(Filename);
|
|
}
|
|
|
|
static bool isCrtbegin(StringRef S) { return isCrtBeginEnd(S, "crtbegin"); }
|
|
static bool isCrtend(StringRef S) { return isCrtBeginEnd(S, "crtend"); }
|
|
|
|
// .ctors and .dtors are sorted by this priority from highest to lowest.
|
|
//
|
|
// 1. The section was contained in crtbegin (crtbegin contains
|
|
// some sentinel value in its .ctors and .dtors so that the runtime
|
|
// can find the beginning of the sections.)
|
|
//
|
|
// 2. The section has an optional priority value in the form of ".ctors.N"
|
|
// or ".dtors.N" where N is a number. Unlike .{init,fini}_array,
|
|
// they are compared as string rather than number.
|
|
//
|
|
// 3. The section is just ".ctors" or ".dtors".
|
|
//
|
|
// 4. The section was contained in crtend, which contains an end marker.
|
|
//
|
|
// In an ideal world, we don't need this function because .init_array and
|
|
// .ctors are duplicate features (and .init_array is newer.) However, there
|
|
// are too many real-world use cases of .ctors, so we had no choice to
|
|
// support that with this rather ad-hoc semantics.
|
|
static bool compCtors(const InputSection *A, const InputSection *B) {
|
|
bool BeginA = isCrtbegin(A->File->getName());
|
|
bool BeginB = isCrtbegin(B->File->getName());
|
|
if (BeginA != BeginB)
|
|
return BeginA;
|
|
bool EndA = isCrtend(A->File->getName());
|
|
bool EndB = isCrtend(B->File->getName());
|
|
if (EndA != EndB)
|
|
return EndB;
|
|
StringRef X = A->Name;
|
|
StringRef Y = B->Name;
|
|
assert(X.startswith(".ctors") || X.startswith(".dtors"));
|
|
assert(Y.startswith(".ctors") || Y.startswith(".dtors"));
|
|
X = X.substr(6);
|
|
Y = Y.substr(6);
|
|
if (X.empty() && Y.empty())
|
|
return false;
|
|
return X < Y;
|
|
}
|
|
|
|
// Sorts input sections by the special rules for .ctors and .dtors.
|
|
// Unfortunately, the rules are different from the one for .{init,fini}_array.
|
|
// Read the comment above.
|
|
void OutputSection::sortCtorsDtors() {
|
|
assert(Commands.size() == 1);
|
|
auto *ISD = cast<InputSectionDescription>(Commands[0]);
|
|
std::stable_sort(ISD->Sections.begin(), ISD->Sections.end(), compCtors);
|
|
}
|
|
|
|
// If an input string is in the form of "foo.N" where N is a number,
|
|
// return N. Otherwise, returns 65536, which is one greater than the
|
|
// lowest priority.
|
|
int elf::getPriority(StringRef S) {
|
|
size_t Pos = S.rfind('.');
|
|
if (Pos == StringRef::npos)
|
|
return 65536;
|
|
int V;
|
|
if (!to_integer(S.substr(Pos + 1), V, 10))
|
|
return 65536;
|
|
return V;
|
|
}
|
|
|
|
// Sorts input sections by section name suffixes, so that .foo.N comes
|
|
// before .foo.M if N < M. Used to sort .{init,fini}_array.N sections.
|
|
// We want to keep the original order if the priorities are the same
|
|
// because the compiler keeps the original initialization order in a
|
|
// translation unit and we need to respect that.
|
|
// For more detail, read the section of the GCC's manual about init_priority.
|
|
void OutputSection::sortInitFini() {
|
|
// Sort sections by priority.
|
|
sort([](InputSectionBase *S) { return getPriority(S->Name); });
|
|
}
|
|
|
|
uint32_t OutputSection::getFiller() {
|
|
if (Filler)
|
|
return *Filler;
|
|
if (Flags & SHF_EXECINSTR)
|
|
return Target->TrapInstr;
|
|
return 0;
|
|
}
|
|
|
|
template void OutputSection::writeHeaderTo<ELF32LE>(ELF32LE::Shdr *Shdr);
|
|
template void OutputSection::writeHeaderTo<ELF32BE>(ELF32BE::Shdr *Shdr);
|
|
template void OutputSection::writeHeaderTo<ELF64LE>(ELF64LE::Shdr *Shdr);
|
|
template void OutputSection::writeHeaderTo<ELF64BE>(ELF64BE::Shdr *Shdr);
|
|
|
|
template void OutputSection::writeTo<ELF32LE>(uint8_t *Buf);
|
|
template void OutputSection::writeTo<ELF32BE>(uint8_t *Buf);
|
|
template void OutputSection::writeTo<ELF64LE>(uint8_t *Buf);
|
|
template void OutputSection::writeTo<ELF64BE>(uint8_t *Buf);
|
|
|
|
template void OutputSection::maybeCompress<ELF32LE>();
|
|
template void OutputSection::maybeCompress<ELF32BE>();
|
|
template void OutputSection::maybeCompress<ELF64LE>();
|
|
template void OutputSection::maybeCompress<ELF64BE>();
|
|
|
|
template void OutputSection::finalize<ELF32LE>();
|
|
template void OutputSection::finalize<ELF32BE>();
|
|
template void OutputSection::finalize<ELF64LE>();
|
|
template void OutputSection::finalize<ELF64BE>();
|