forked from OSchip/llvm-project
520 lines
18 KiB
C++
520 lines
18 KiB
C++
//===- OutputSections.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 "OutputSections.h"
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#include "Config.h"
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#include "LinkerScript.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 "lld/Common/Memory.h"
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#include "lld/Common/Strings.h"
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#include "lld/Common/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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#include <regex>
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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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namespace lld {
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namespace elf {
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uint8_t *Out::bufferStart;
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uint8_t Out::first;
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PhdrEntry *Out::tlsPhdr;
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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 *> outputSections;
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uint32_t OutputSection::getPhdrFlags() const {
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uint32_t ret = 0;
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if (config->emachine != EM_ARM || !(flags & SHF_ARM_PURECODE))
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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, /*Link*/ 0) {}
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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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// Record that isec will be placed in the OutputSection. isec does not become
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// permanent until finalizeInputSections() is called. The function should not be
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// used after finalizeInputSections() is called. If you need to add an
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// InputSection post finalizeInputSections(), then you must do the following:
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//
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// 1. Find or create an InputSectionDescription to hold InputSection.
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// 2. Add the InputSection to the InputSectionDescription::sections.
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// 3. Call commitSection(isec).
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void OutputSection::recordSection(InputSectionBase *isec) {
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partition = isec->partition;
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isec->parent = this;
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if (sectionCommands.empty() ||
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!isa<InputSectionDescription>(sectionCommands.back()))
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sectionCommands.push_back(make<InputSectionDescription>(""));
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auto *isd = cast<InputSectionDescription>(sectionCommands.back());
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isd->sectionBases.push_back(isec);
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}
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// Update fields (type, flags, alignment, etc) according to the InputSection
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// isec. Also check whether the InputSection flags and type are consistent with
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// other InputSections.
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void OutputSection::commitSection(InputSection *isec) {
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if (!hasInputSections) {
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// If IS is the first section to be added to this section,
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// initialize type, entsize and flags from isec.
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hasInputSections = true;
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type = isec->type;
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entsize = isec->entsize;
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flags = isec->flags;
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} else {
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// Otherwise, check if new type or flags are compatible with existing ones.
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unsigned mask = SHF_TLS | SHF_LINK_ORDER;
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if ((flags & mask) != (isec->flags & mask))
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error("incompatible section flags for " + name + "\n>>> " + toString(isec) +
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": 0x" + utohexstr(isec->flags) + "\n>>> output section " + name +
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": 0x" + utohexstr(flags));
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if (type != isec->type) {
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if (!canMergeToProgbits(type) || !canMergeToProgbits(isec->type))
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error("section type mismatch for " + isec->name + "\n>>> " +
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toString(isec) + ": " +
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getELFSectionTypeName(config->emachine, isec->type) +
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"\n>>> output section " + name + ": " +
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getELFSectionTypeName(config->emachine, type));
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type = SHT_PROGBITS;
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}
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}
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if (noload)
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type = SHT_NOBITS;
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isec->parent = this;
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uint64_t andMask =
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config->emachine == EM_ARM ? (uint64_t)SHF_ARM_PURECODE : 0;
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uint64_t orMask = ~andMask;
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uint64_t andFlags = (flags & isec->flags) & andMask;
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uint64_t orFlags = (flags | isec->flags) & orMask;
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flags = andFlags | orFlags;
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if (nonAlloc)
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flags &= ~(uint64_t)SHF_ALLOC;
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alignment = std::max(alignment, isec->alignment);
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// If this section contains a table of fixed-size entries, sh_entsize
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// holds the element size. If it contains elements of different size we
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// set sh_entsize to 0.
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if (entsize != isec->entsize)
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entsize = 0;
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}
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// This function scans over the InputSectionBase list sectionBases to create
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// InputSectionDescription::sections.
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//
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// It removes MergeInputSections from the input section array and adds
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// new synthetic sections at the location of the first input section
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// that it replaces. It then finalizes each synthetic section in order
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// to compute an output offset for each piece of each input section.
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void OutputSection::finalizeInputSections() {
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std::vector<MergeSyntheticSection *> mergeSections;
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for (BaseCommand *base : sectionCommands) {
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auto *cmd = dyn_cast<InputSectionDescription>(base);
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if (!cmd)
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continue;
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cmd->sections.reserve(cmd->sectionBases.size());
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for (InputSectionBase *s : cmd->sectionBases) {
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MergeInputSection *ms = dyn_cast<MergeInputSection>(s);
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if (!ms) {
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cmd->sections.push_back(cast<InputSection>(s));
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continue;
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}
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// We do not want to handle sections that are not alive, so just remove
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// them instead of trying to merge.
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if (!ms->isLive())
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continue;
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auto i = llvm::find_if(mergeSections, [=](MergeSyntheticSection *sec) {
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// While we could create a single synthetic section for two different
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// values of Entsize, it is better to take Entsize into consideration.
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//
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// With a single synthetic section no two pieces with different Entsize
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// could be equal, so we may as well have two sections.
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//
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// Using Entsize in here also allows us to propagate it to the synthetic
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// section.
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//
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// SHF_STRINGS section with different alignments should not be merged.
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return sec->flags == ms->flags && sec->entsize == ms->entsize &&
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(sec->alignment == ms->alignment || !(sec->flags & SHF_STRINGS));
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});
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if (i == mergeSections.end()) {
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MergeSyntheticSection *syn =
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createMergeSynthetic(name, ms->type, ms->flags, ms->alignment);
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mergeSections.push_back(syn);
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i = std::prev(mergeSections.end());
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syn->entsize = ms->entsize;
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cmd->sections.push_back(syn);
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}
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(*i)->addSection(ms);
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}
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// sectionBases should not be used from this point onwards. Clear it to
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// catch misuses.
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cmd->sectionBases.clear();
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// Some input sections may be removed from the list after ICF.
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for (InputSection *s : cmd->sections)
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commitSection(s);
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}
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for (auto *ms : mergeSections)
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ms->finalizeContents();
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}
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static void sortByOrder(MutableArrayRef<InputSection *> in,
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llvm::function_ref<int(InputSectionBase *s)> order) {
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std::vector<std::pair<int, InputSection *>> v;
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for (InputSection *s : in)
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v.push_back({order(s), s});
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llvm::stable_sort(v, less_first());
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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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uint64_t 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(llvm::function_ref<int(InputSectionBase *s)> order) {
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assert(isLive());
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for (BaseCommand *b : sectionCommands)
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if (auto *isd = dyn_cast<InputSectionDescription>(b))
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sortByOrder(isd->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,
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const std::array<uint8_t, 4> &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.data(), 4);
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memcpy(buf + i, filler.data(), 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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using Elf_Chdr = typename ELFT::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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// We chose 1 as the default compression level because it is the fastest. If
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// -O2 is given, we use level 6 to compress debug info more by ~15%. We found
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// that level 7 to 9 doesn't make much difference (~1% more compression) while
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// they take significant amount of time (~2x), so level 6 seems enough.
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if (Error e = zlib::compress(toStringRef(buf), compressedData,
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config->optimize >= 2 ? 6 : 1))
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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);
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else if (size == 4)
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write32(buf, data);
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else if (size == 8)
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write64(buf, data);
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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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// If -compress-debug-section is specified and if this is a debug section,
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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 = getInputSections(this);
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std::array<uint8_t, 4> filler = getFiller();
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bool nonZeroFiller = read32(filler.data()) != 0;
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if (nonZeroFiller)
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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 *isec = sections[i];
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isec->writeTo<ELFT>(buf);
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// Fill gaps between sections.
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if (nonZeroFiller) {
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uint8_t *start = buf + isec->outSecOff + isec->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 : sectionCommands)
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if (auto *data = dyn_cast<ByteCommand>(base))
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writeInt(buf + data->offset, data->expression().getValue(), data->size);
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}
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static void finalizeShtGroup(OutputSection *os,
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InputSection *section) {
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assert(config->relocatable);
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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 = in.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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ArrayRef<Symbol *> symbols = section->file->getSymbols();
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os->info = in.symTab->getSymbolIndex(symbols[section->info]);
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}
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void OutputSection::finalize() {
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InputSection *first = getFirstInputSection(this);
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if (flags & SHF_LINK_ORDER) {
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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 *ex = dyn_cast<ARMExidxSyntheticSection>(first))
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link = ex->getLinkOrderDep()->getParent()->sectionIndex;
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else if (auto *d = first->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(this, first);
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return;
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}
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if (!config->copyRelocs || (type != SHT_RELA && type != SHT_REL))
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return;
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if (isa<SyntheticSection>(first))
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return;
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link = in.symTab->getParent()->sectionIndex;
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// sh_info for SHT_REL[A] sections should contain the section header index of
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// the section to which the relocation applies.
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InputSectionBase *s = first->getRelocatedSection();
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info = s->getOutputSection()->sectionIndex;
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flags |= SHF_INFO_LINK;
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}
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// Returns true if S is in one of the many forms the compiler driver may pass
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// crtbegin files.
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//
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// Gcc uses any of crtbegin[<empty>|S|T].o.
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// Clang uses Gcc's plus clang_rt.crtbegin[<empty>|S|T][-<arch>|<empty>].o.
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static bool isCrtbegin(StringRef s) {
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static std::regex re(R"((clang_rt\.)?crtbegin[ST]?(-.*)?\.o)");
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s = sys::path::filename(s);
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return std::regex_match(s.begin(), s.end(), re);
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}
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static bool isCrtend(StringRef s) {
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static std::regex re(R"((clang_rt\.)?crtend[ST]?(-.*)?\.o)");
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s = sys::path::filename(s);
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return std::regex_match(s.begin(), s.end(), re);
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}
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// .ctors and .dtors are sorted by this priority from highest to lowest.
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//
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// 1. The section was contained in crtbegin (crtbegin contains
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// some sentinel value in its .ctors and .dtors so that the runtime
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// can find the beginning of the sections.)
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//
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// 2. The section has an optional priority value in the form of ".ctors.N"
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// or ".dtors.N" where N is a number. Unlike .{init,fini}_array,
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// they are compared as string rather than number.
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//
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// 3. The section is just ".ctors" or ".dtors".
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//
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// 4. The section was contained in crtend, which contains an end marker.
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//
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// In an ideal world, we don't need this function because .init_array and
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// .ctors are duplicate features (and .init_array is newer.) However, there
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// are too many real-world use cases of .ctors, so we had no choice to
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// support that with this rather ad-hoc semantics.
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static bool compCtors(const InputSection *a, const InputSection *b) {
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bool beginA = isCrtbegin(a->file->getName());
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bool beginB = isCrtbegin(b->file->getName());
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if (beginA != beginB)
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return beginA;
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bool endA = isCrtend(a->file->getName());
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bool endB = isCrtend(b->file->getName());
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if (endA != endB)
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return endB;
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StringRef x = a->name;
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StringRef y = b->name;
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assert(x.startswith(".ctors") || x.startswith(".dtors"));
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assert(y.startswith(".ctors") || y.startswith(".dtors"));
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x = x.substr(6);
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y = y.substr(6);
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return x < y;
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}
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// Sorts input sections by the special rules for .ctors and .dtors.
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// Unfortunately, the rules are different from the one for .{init,fini}_array.
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// Read the comment above.
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void OutputSection::sortCtorsDtors() {
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assert(sectionCommands.size() == 1);
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auto *isd = cast<InputSectionDescription>(sectionCommands[0]);
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llvm::stable_sort(isd->sections, compCtors);
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}
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// If an input string is in the form of "foo.N" where N is a number,
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// return N. Otherwise, returns 65536, which is one greater than the
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// lowest priority.
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int getPriority(StringRef s) {
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size_t pos = s.rfind('.');
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if (pos == StringRef::npos)
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return 65536;
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int v;
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if (!to_integer(s.substr(pos + 1), v, 10))
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return 65536;
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return v;
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}
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InputSection *getFirstInputSection(const OutputSection *os) {
|
|
for (BaseCommand *base : os->sectionCommands)
|
|
if (auto *isd = dyn_cast<InputSectionDescription>(base))
|
|
if (!isd->sections.empty())
|
|
return isd->sections[0];
|
|
return nullptr;
|
|
}
|
|
|
|
std::vector<InputSection *> getInputSections(const OutputSection *os) {
|
|
std::vector<InputSection *> ret;
|
|
for (BaseCommand *base : os->sectionCommands)
|
|
if (auto *isd = dyn_cast<InputSectionDescription>(base))
|
|
ret.insert(ret.end(), isd->sections.begin(), isd->sections.end());
|
|
return ret;
|
|
}
|
|
|
|
// 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); });
|
|
}
|
|
|
|
std::array<uint8_t, 4> OutputSection::getFiller() {
|
|
if (filler)
|
|
return *filler;
|
|
if (flags & SHF_EXECINSTR)
|
|
return target->trapInstr;
|
|
return {0, 0, 0, 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>();
|
|
|
|
} // namespace elf
|
|
} // namespace lld
|