forked from OSchip/llvm-project
1846 lines
65 KiB
C++
1846 lines
65 KiB
C++
//===- Writer.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 "Writer.h"
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#include "Config.h"
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#include "LinkerScript.h"
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#include "MapFile.h"
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#include "Memory.h"
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#include "OutputSections.h"
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#include "Relocations.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 "llvm/ADT/StringMap.h"
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#include "llvm/ADT/StringSwitch.h"
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#include "llvm/Support/FileOutputBuffer.h"
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#include "llvm/Support/FileSystem.h"
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#include "llvm/Support/raw_ostream.h"
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#include <climits>
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#include <thread>
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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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typedef typename ELFT::uint uintX_t;
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typedef typename ELFT::Shdr Elf_Shdr;
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typedef typename ELFT::Ehdr Elf_Ehdr;
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typedef typename ELFT::Phdr Elf_Phdr;
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typedef typename ELFT::Sym Elf_Sym;
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typedef typename ELFT::SymRange Elf_Sym_Range;
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typedef typename ELFT::Rela Elf_Rela;
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void run();
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private:
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void createSyntheticSections();
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void copyLocalSymbols();
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void addSectionSymbols();
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void addReservedSymbols();
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void createSections();
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void forEachRelSec(std::function<void(InputSectionBase &)> Fn);
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void sortSections();
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void finalizeSections();
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void addPredefinedSections();
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std::vector<PhdrEntry> createPhdrs();
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void removeEmptyPTLoad();
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void addPtArmExid(std::vector<PhdrEntry> &Phdrs);
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void assignAddresses();
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void assignFileOffsets();
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void assignFileOffsetsBinary();
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void setPhdrs();
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void fixHeaders();
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void fixSectionAlignments();
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void fixPredefinedSymbols();
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void openFile();
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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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std::vector<OutputSection *> OutputSections;
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OutputSectionFactory Factory{OutputSections};
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void addRelIpltSymbols();
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void addStartEndSymbols();
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void addStartStopSymbols(OutputSection *Sec);
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uintX_t getEntryAddr();
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OutputSection *findSection(StringRef Name);
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std::vector<PhdrEntry> Phdrs;
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uintX_t FileSize;
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uintX_t SectionHeaderOff;
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bool AllocateHeader = true;
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};
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} // anonymous namespace
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StringRef elf::getOutputSectionName(StringRef Name) {
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if (Config->Relocatable)
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return Name;
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// If -emit-relocs is given (which is rare), we need to copy
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// relocation sections to the output. If input section .foo is
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// output as .bar, we want to rename .rel.foo .rel.bar as well.
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if (Config->EmitRelocs) {
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for (StringRef V : {".rel.", ".rela."}) {
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if (Name.startswith(V)) {
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StringRef Inner = getOutputSectionName(Name.substr(V.size() - 1));
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return Saver.save(Twine(V.drop_back()) + Inner);
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}
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}
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}
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for (StringRef V :
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{".text.", ".rodata.", ".data.rel.ro.", ".data.", ".bss.rel.ro.",
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".bss.", ".init_array.", ".fini_array.", ".ctors.", ".dtors.", ".tbss.",
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".gcc_except_table.", ".tdata.", ".ARM.exidx."}) {
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StringRef Prefix = V.drop_back();
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if (Name.startswith(V) || Name == Prefix)
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return Prefix;
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}
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// CommonSection is identified as "COMMON" in linker scripts.
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// By default, it should go to .bss section.
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if (Name == "COMMON")
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return ".bss";
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// ".zdebug_" is a prefix for ZLIB-compressed sections.
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// Because we decompressed input sections, we want to remove 'z'.
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if (Name.startswith(".zdebug_"))
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return Saver.save(Twine(".") + Name.substr(2));
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return Name;
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}
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template <class ELFT> static bool needsInterpSection() {
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return !Symtab<ELFT>::X->getSharedFiles().empty() &&
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!Config->DynamicLinker.empty() &&
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!Script<ELFT>::X->ignoreInterpSection();
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}
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template <class ELFT> void elf::writeResult() { Writer<ELFT>().run(); }
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template <class ELFT> void Writer<ELFT>::removeEmptyPTLoad() {
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auto I = std::remove_if(Phdrs.begin(), Phdrs.end(), [&](const PhdrEntry &P) {
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if (P.p_type != PT_LOAD)
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return false;
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if (!P.First)
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return true;
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uintX_t Size = P.Last->Addr + P.Last->Size - P.First->Addr;
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return Size == 0;
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});
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Phdrs.erase(I, Phdrs.end());
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}
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template <class ELFT>
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static typename ELFT::uint getOutFlags(InputSectionBase *S) {
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return S->Flags & ~(typename ELFT::uint)(SHF_GROUP | SHF_COMPRESSED);
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}
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// This function scans over the input sections and creates mergeable
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// synthetic sections. It removes MergeInputSections from array and
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// adds new synthetic ones. Each synthetic section is added to the
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// location of the first input section it replaces.
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template <class ELFT> static void combineMergableSections() {
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typedef typename ELFT::uint uintX_t;
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std::vector<MergeSyntheticSection *> MergeSections;
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for (InputSectionBase *&S : InputSections) {
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MergeInputSection *MS = dyn_cast<MergeInputSection>(S);
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if (!MS)
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continue;
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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->Live)
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continue;
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StringRef OutsecName = getOutputSectionName(MS->Name);
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uintX_t Flags = getOutFlags<ELFT>(MS);
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uintX_t Alignment = std::max<uintX_t>(MS->Alignment, MS->Entsize);
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auto I =
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llvm::find_if(MergeSections, [=](MergeSyntheticSection *Sec) {
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return Sec->Name == OutsecName && Sec->Flags == Flags &&
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Sec->Alignment == Alignment;
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});
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if (I == MergeSections.end()) {
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MergeSyntheticSection *Syn =
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make<MergeSyntheticSection>(OutsecName, MS->Type, Flags, Alignment);
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MergeSections.push_back(Syn);
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I = std::prev(MergeSections.end());
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S = Syn;
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} else {
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S = nullptr;
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}
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(*I)->addSection(MS);
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}
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std::vector<InputSectionBase *> &V = InputSections;
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V.erase(std::remove(V.begin(), V.end(), nullptr), V.end());
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}
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// The main function of the writer.
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template <class ELFT> void Writer<ELFT>::run() {
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// Create linker-synthesized sections such as .got or .plt.
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// Such sections are of type input section.
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createSyntheticSections();
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combineMergableSections<ELFT>();
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// We need to create some reserved symbols such as _end. Create them.
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if (!Config->Relocatable)
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addReservedSymbols();
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// Create output sections.
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Script<ELFT>::X->OutputSections = &OutputSections;
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if (ScriptConfig->HasSections) {
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// If linker script contains SECTIONS commands, let it create sections.
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Script<ELFT>::X->processCommands(Factory);
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// Linker scripts may have left some input sections unassigned.
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// Assign such sections using the default rule.
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Script<ELFT>::X->addOrphanSections(Factory);
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} else {
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// If linker script does not contain SECTIONS commands, create
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// output sections by default rules. We still need to give the
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// linker script a chance to run, because it might contain
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// non-SECTIONS commands such as ASSERT.
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createSections();
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Script<ELFT>::X->processCommands(Factory);
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}
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if (Config->Discard != DiscardPolicy::All)
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copyLocalSymbols();
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if (Config->copyRelocs())
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addSectionSymbols();
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// Now that we have a complete set of output sections. This function
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// completes section contents. For example, we need to add strings
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// to the string table, and add entries to .got and .plt.
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// finalizeSections does that.
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finalizeSections();
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if (ErrorCount)
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return;
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if (Config->Relocatable) {
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assignFileOffsets();
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} else {
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if (ScriptConfig->HasSections) {
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Script<ELFT>::X->assignAddresses(Phdrs);
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} else {
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fixSectionAlignments();
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assignAddresses();
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}
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// Remove empty PT_LOAD to avoid causing the dynamic linker to try to mmap a
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// 0 sized region. This has to be done late since only after assignAddresses
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// we know the size of the sections.
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removeEmptyPTLoad();
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if (!Config->OFormatBinary)
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assignFileOffsets();
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else
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assignFileOffsetsBinary();
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setPhdrs();
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fixPredefinedSymbols();
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}
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// It does not make sense try to open the file if we have error already.
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if (ErrorCount)
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return;
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// Write the result down to a file.
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openFile();
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if (ErrorCount)
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return;
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if (!Config->OFormatBinary) {
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writeHeader();
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writeSections();
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} else {
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writeSectionsBinary();
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}
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// Backfill .note.gnu.build-id section content. This is done at last
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// because the content is usually a hash value of the entire output file.
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writeBuildId();
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if (ErrorCount)
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return;
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// Handle -Map option.
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writeMapFile<ELFT>(OutputSections);
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if (ErrorCount)
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return;
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if (auto EC = Buffer->commit())
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error("failed to write to the output file: " + EC.message());
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// Flush the output streams and exit immediately. A full shutdown
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// is a good test that we are keeping track of all allocated memory,
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// but actually freeing it is a waste of time in a regular linker run.
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if (Config->ExitEarly)
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exitLld(0);
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}
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// Initialize Out members.
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template <class ELFT> void Writer<ELFT>::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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memset(&Out::First, 0, sizeof(Out));
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auto Add = [](InputSectionBase *Sec) { InputSections.push_back(Sec); };
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In<ELFT>::DynStrTab = make<StringTableSection<ELFT>>(".dynstr", true);
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In<ELFT>::Dynamic = make<DynamicSection<ELFT>>();
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In<ELFT>::RelaDyn = make<RelocationSection<ELFT>>(
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Config->Rela ? ".rela.dyn" : ".rel.dyn", Config->ZCombreloc);
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In<ELFT>::ShStrTab = make<StringTableSection<ELFT>>(".shstrtab", false);
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Out::ElfHeader = make<OutputSection>("", 0, SHF_ALLOC);
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Out::ElfHeader->Size = sizeof(Elf_Ehdr);
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Out::ProgramHeaders = make<OutputSection>("", 0, SHF_ALLOC);
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Out::ProgramHeaders->updateAlignment(sizeof(uintX_t));
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if (needsInterpSection<ELFT>()) {
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In<ELFT>::Interp = createInterpSection();
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Add(In<ELFT>::Interp);
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} else {
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In<ELFT>::Interp = nullptr;
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}
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if (!Config->Relocatable)
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Add(createCommentSection<ELFT>());
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if (Config->Strip != StripPolicy::All) {
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In<ELFT>::StrTab = make<StringTableSection<ELFT>>(".strtab", false);
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In<ELFT>::SymTab = make<SymbolTableSection<ELFT>>(*In<ELFT>::StrTab);
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}
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if (Config->BuildId != BuildIdKind::None) {
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In<ELFT>::BuildId = make<BuildIdSection<ELFT>>();
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Add(In<ELFT>::BuildId);
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}
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InputSection *Common = createCommonSection<ELFT>();
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if (!Common->Data.empty()) {
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In<ELFT>::Common = Common;
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Add(Common);
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}
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In<ELFT>::Bss = make<BssRelSection<ELFT>>(false /*RelRo*/);
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Add(In<ELFT>::Bss);
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In<ELFT>::BssRelRo = make<BssRelSection<ELFT>>(true /*RelRo*/);
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Add(In<ELFT>::BssRelRo);
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// Add MIPS-specific sections.
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bool HasDynSymTab =
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!Symtab<ELFT>::X->getSharedFiles().empty() || Config->pic() ||
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Config->ExportDynamic;
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if (Config->EMachine == EM_MIPS) {
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if (!Config->Shared && HasDynSymTab) {
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In<ELFT>::MipsRldMap = make<MipsRldMapSection<ELFT>>();
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Add(In<ELFT>::MipsRldMap);
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}
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if (auto *Sec = MipsAbiFlagsSection<ELFT>::create())
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Add(Sec);
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if (auto *Sec = MipsOptionsSection<ELFT>::create())
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Add(Sec);
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if (auto *Sec = MipsReginfoSection<ELFT>::create())
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Add(Sec);
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}
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if (HasDynSymTab) {
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In<ELFT>::DynSymTab = make<SymbolTableSection<ELFT>>(*In<ELFT>::DynStrTab);
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Add(In<ELFT>::DynSymTab);
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In<ELFT>::VerSym = make<VersionTableSection<ELFT>>();
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Add(In<ELFT>::VerSym);
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if (!Config->VersionDefinitions.empty()) {
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In<ELFT>::VerDef = make<VersionDefinitionSection<ELFT>>();
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Add(In<ELFT>::VerDef);
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}
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In<ELFT>::VerNeed = make<VersionNeedSection<ELFT>>();
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Add(In<ELFT>::VerNeed);
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if (Config->GnuHash) {
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In<ELFT>::GnuHashTab = make<GnuHashTableSection<ELFT>>();
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Add(In<ELFT>::GnuHashTab);
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}
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if (Config->SysvHash) {
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In<ELFT>::HashTab = make<HashTableSection<ELFT>>();
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Add(In<ELFT>::HashTab);
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}
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Add(In<ELFT>::Dynamic);
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Add(In<ELFT>::DynStrTab);
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Add(In<ELFT>::RelaDyn);
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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<ELFT>::MipsGot = make<MipsGotSection<ELFT>>();
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Add(In<ELFT>::MipsGot);
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} else {
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In<ELFT>::Got = make<GotSection<ELFT>>();
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Add(In<ELFT>::Got);
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}
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In<ELFT>::GotPlt = make<GotPltSection<ELFT>>();
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Add(In<ELFT>::GotPlt);
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In<ELFT>::IgotPlt = make<IgotPltSection<ELFT>>();
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Add(In<ELFT>::IgotPlt);
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if (Config->GdbIndex) {
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In<ELFT>::GdbIndex = make<GdbIndexSection<ELFT>>();
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Add(In<ELFT>::GdbIndex);
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}
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// We always need to add rel[a].plt to output if it has entries.
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// Even for static linking it can contain R_[*]_IRELATIVE relocations.
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In<ELFT>::RelaPlt = make<RelocationSection<ELFT>>(
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Config->Rela ? ".rela.plt" : ".rel.plt", false /*Sort*/);
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Add(In<ELFT>::RelaPlt);
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// The RelaIplt immediately follows .rel.plt (.rel.dyn for ARM) to ensure
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// that the IRelative relocations are processed last by the dynamic loader
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In<ELFT>::RelaIplt = make<RelocationSection<ELFT>>(
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(Config->EMachine == EM_ARM) ? ".rel.dyn" : In<ELFT>::RelaPlt->Name,
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false /*Sort*/);
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Add(In<ELFT>::RelaIplt);
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In<ELFT>::Plt = make<PltSection<ELFT>>(Target->PltHeaderSize);
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Add(In<ELFT>::Plt);
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In<ELFT>::Iplt = make<PltSection<ELFT>>(0);
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Add(In<ELFT>::Iplt);
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if (Config->EhFrameHdr) {
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In<ELFT>::EhFrameHdr = make<EhFrameHeader<ELFT>>();
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Add(In<ELFT>::EhFrameHdr);
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}
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if (!Config->Relocatable) {
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In<ELFT>::EhFrame = make<EhFrameSection<ELFT>>();
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Add(In<ELFT>::EhFrame);
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}
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if (In<ELFT>::SymTab)
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Add(In<ELFT>::SymTab);
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Add(In<ELFT>::ShStrTab);
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if (In<ELFT>::StrTab)
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Add(In<ELFT>::StrTab);
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}
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template <class ELFT>
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static bool shouldKeepInSymtab(InputSectionBase *Sec, StringRef SymName,
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const SymbolBody &B) {
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if (B.isFile() || B.isSection())
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return false;
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// If sym references a section in a discarded group, don't keep it.
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if (Sec == &InputSection::Discarded)
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return false;
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if (Config->Discard == DiscardPolicy::None)
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return true;
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// In ELF assembly .L symbols are normally discarded by the assembler.
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// If the assembler fails to do so, the linker discards them if
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// * --discard-locals is used.
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// * The symbol is in a SHF_MERGE section, which is normally the reason for
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// the assembler keeping the .L symbol.
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if (!SymName.startswith(".L") && !SymName.empty())
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return true;
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if (Config->Discard == DiscardPolicy::Locals)
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return false;
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return !Sec || !(Sec->Flags & SHF_MERGE);
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}
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template <class ELFT> static bool includeInSymtab(const SymbolBody &B) {
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if (!B.isLocal() && !B.symbol()->IsUsedInRegularObj)
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return false;
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if (auto *D = dyn_cast<DefinedRegular>(&B)) {
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// Always include absolute symbols.
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if (!D->Section)
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return true;
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// Exclude symbols pointing to garbage-collected sections.
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if (!D->Section->Live)
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return false;
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if (auto *S = dyn_cast<MergeInputSection>(D->Section))
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if (!S->getSectionPiece(D->Value)->Live)
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return false;
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}
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return true;
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}
|
|
|
|
// 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<ELFT>::SymTab)
|
|
return;
|
|
for (elf::ObjectFile<ELFT> *F : Symtab<ELFT>::X->getObjectFiles()) {
|
|
for (SymbolBody *B : F->getLocalSymbols()) {
|
|
if (!B->IsLocal)
|
|
fatal(toString(F) +
|
|
": broken object: getLocalSymbols returns a non-local symbol");
|
|
auto *DR = dyn_cast<DefinedRegular>(B);
|
|
|
|
// No reason to keep local undefined symbol in symtab.
|
|
if (!DR)
|
|
continue;
|
|
if (!includeInSymtab<ELFT>(*B))
|
|
continue;
|
|
|
|
InputSectionBase *Sec = DR->Section;
|
|
if (!shouldKeepInSymtab<ELFT>(Sec, B->getName(), *B))
|
|
continue;
|
|
In<ELFT>::SymTab->addSymbol(B);
|
|
}
|
|
}
|
|
}
|
|
|
|
template <class ELFT> void Writer<ELFT>::addSectionSymbols() {
|
|
// Create one STT_SECTION symbol for each output section we might
|
|
// have a relocation with.
|
|
for (OutputSection *Sec : OutputSections) {
|
|
if (Sec->Sections.empty())
|
|
continue;
|
|
|
|
InputSection *IS = Sec->Sections[0];
|
|
if (isa<SyntheticSection>(IS) || IS->Type == SHT_REL ||
|
|
IS->Type == SHT_RELA)
|
|
continue;
|
|
|
|
auto *Sym =
|
|
make<DefinedRegular>("", /*IsLocal=*/true, /*StOther=*/0, STT_SECTION,
|
|
/*Value=*/0, /*Size=*/0, IS, nullptr);
|
|
In<ELFT>::SymTab->addSymbol(Sym);
|
|
}
|
|
}
|
|
|
|
// 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).
|
|
static int getPPC64SectionRank(StringRef SectionName) {
|
|
return StringSwitch<int>(SectionName)
|
|
.Case(".tocbss", 0)
|
|
.Case(".branch_lt", 2)
|
|
.Case(".toc", 3)
|
|
.Case(".toc1", 4)
|
|
.Case(".opd", 5)
|
|
.Default(1);
|
|
}
|
|
|
|
// All sections with SHF_MIPS_GPREL flag should be grouped together
|
|
// because data in these sections is addressable with a gp relative address.
|
|
static int getMipsSectionRank(const OutputSection *S) {
|
|
if ((S->Flags & SHF_MIPS_GPREL) == 0)
|
|
return 0;
|
|
if (S->Name == ".got")
|
|
return 1;
|
|
return 2;
|
|
}
|
|
|
|
// 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.
|
|
template <class ELFT> bool elf::isRelroSection(const OutputSection *Sec) {
|
|
if (!Config->ZRelro)
|
|
return false;
|
|
|
|
uint64_t Flags = Sec->Flags;
|
|
if (!(Flags & SHF_ALLOC) || !(Flags & SHF_WRITE))
|
|
return false;
|
|
if (Flags & SHF_TLS)
|
|
return true;
|
|
|
|
uint32_t Type = Sec->Type;
|
|
if (Type == SHT_INIT_ARRAY || Type == SHT_FINI_ARRAY ||
|
|
Type == SHT_PREINIT_ARRAY)
|
|
return true;
|
|
|
|
if (Sec == In<ELFT>::GotPlt->OutSec)
|
|
return Config->ZNow;
|
|
if (Sec == In<ELFT>::Dynamic->OutSec)
|
|
return true;
|
|
if (In<ELFT>::Got && Sec == In<ELFT>::Got->OutSec)
|
|
return true;
|
|
if (Sec == In<ELFT>::BssRelRo->OutSec)
|
|
return true;
|
|
|
|
StringRef S = Sec->Name;
|
|
return S == ".data.rel.ro" || S == ".ctors" || S == ".dtors" || S == ".jcr" ||
|
|
S == ".eh_frame" || S == ".openbsd.randomdata";
|
|
}
|
|
|
|
template <class ELFT>
|
|
static bool compareSectionsNonScript(const OutputSection *A,
|
|
const OutputSection *B) {
|
|
// Put .interp first because some loaders want to see that section
|
|
// on the first page of the executable file when loaded into memory.
|
|
bool AIsInterp = A->Name == ".interp";
|
|
bool BIsInterp = B->Name == ".interp";
|
|
if (AIsInterp != BIsInterp)
|
|
return AIsInterp;
|
|
|
|
// Allocatable sections go first to reduce the total PT_LOAD size and
|
|
// so debug info doesn't change addresses in actual code.
|
|
bool AIsAlloc = A->Flags & SHF_ALLOC;
|
|
bool BIsAlloc = B->Flags & SHF_ALLOC;
|
|
if (AIsAlloc != BIsAlloc)
|
|
return AIsAlloc;
|
|
|
|
// We don't have any special requirements for the relative order of two non
|
|
// allocatable sections.
|
|
if (!AIsAlloc)
|
|
return false;
|
|
|
|
// We want to put section specified by -T option first, so we
|
|
// can start assigning VA starting from them later.
|
|
auto AAddrSetI = Config->SectionStartMap.find(A->Name);
|
|
auto BAddrSetI = Config->SectionStartMap.find(B->Name);
|
|
bool AHasAddrSet = AAddrSetI != Config->SectionStartMap.end();
|
|
bool BHasAddrSet = BAddrSetI != Config->SectionStartMap.end();
|
|
if (AHasAddrSet != BHasAddrSet)
|
|
return AHasAddrSet;
|
|
if (AHasAddrSet)
|
|
return AAddrSetI->second < BAddrSetI->second;
|
|
|
|
// We want the read only sections first so that they go in the PT_LOAD
|
|
// covering the program headers at the start of the file.
|
|
bool AIsWritable = A->Flags & SHF_WRITE;
|
|
bool BIsWritable = B->Flags & SHF_WRITE;
|
|
if (AIsWritable != BIsWritable)
|
|
return BIsWritable;
|
|
|
|
if (!Config->SingleRoRx) {
|
|
// For a corresponding reason, put non exec sections first (the program
|
|
// header PT_LOAD is not executable).
|
|
// We only do that if we are not using linker scripts, since with linker
|
|
// scripts ro and rx sections are in the same PT_LOAD, so their relative
|
|
// order is not important. The same applies for -no-rosegment.
|
|
bool AIsExec = A->Flags & SHF_EXECINSTR;
|
|
bool BIsExec = B->Flags & SHF_EXECINSTR;
|
|
if (AIsExec != BIsExec)
|
|
return BIsExec;
|
|
}
|
|
|
|
// If we got here we know that both A and B are in the same PT_LOAD.
|
|
|
|
bool AIsTls = A->Flags & SHF_TLS;
|
|
bool BIsTls = B->Flags & SHF_TLS;
|
|
bool AIsNoBits = A->Type == SHT_NOBITS;
|
|
bool BIsNoBits = B->Type == SHT_NOBITS;
|
|
|
|
// The first requirement we have is to put (non-TLS) nobits sections last. The
|
|
// reason is that the only thing the dynamic linker will see about them is a
|
|
// p_memsz that is larger than p_filesz. Seeing that it zeros the end of the
|
|
// PT_LOAD, so that has to correspond to the nobits sections.
|
|
bool AIsNonTlsNoBits = AIsNoBits && !AIsTls;
|
|
bool BIsNonTlsNoBits = BIsNoBits && !BIsTls;
|
|
if (AIsNonTlsNoBits != BIsNonTlsNoBits)
|
|
return BIsNonTlsNoBits;
|
|
|
|
// We place nobits RelRo sections before plain r/w ones, and non-nobits RelRo
|
|
// sections after r/w ones, so that the RelRo sections are contiguous.
|
|
bool AIsRelRo = isRelroSection<ELFT>(A);
|
|
bool BIsRelRo = isRelroSection<ELFT>(B);
|
|
if (AIsRelRo != BIsRelRo)
|
|
return AIsNonTlsNoBits ? AIsRelRo : BIsRelRo;
|
|
|
|
// 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. The TLS NOBITS sections are placed here as they don't take up
|
|
// virtual address space in the PT_LOAD.
|
|
if (AIsTls != BIsTls)
|
|
return AIsTls;
|
|
|
|
// Within the TLS initialization block, the non-nobits sections need to appear
|
|
// first.
|
|
if (AIsNoBits != BIsNoBits)
|
|
return BIsNoBits;
|
|
|
|
// Some architectures have additional ordering restrictions for sections
|
|
// within the same PT_LOAD.
|
|
if (Config->EMachine == EM_PPC64)
|
|
return getPPC64SectionRank(A->Name) < getPPC64SectionRank(B->Name);
|
|
if (Config->EMachine == EM_MIPS)
|
|
return getMipsSectionRank(A) < getMipsSectionRank(B);
|
|
|
|
return false;
|
|
}
|
|
|
|
// Output section ordering is determined by this function.
|
|
template <class ELFT>
|
|
static bool compareSections(const OutputSection *A, const OutputSection *B) {
|
|
// For now, put sections mentioned in a linker script first.
|
|
int AIndex = Script<ELFT>::X->getSectionIndex(A->Name);
|
|
int BIndex = Script<ELFT>::X->getSectionIndex(B->Name);
|
|
bool AInScript = AIndex != INT_MAX;
|
|
bool BInScript = BIndex != INT_MAX;
|
|
if (AInScript != BInScript)
|
|
return AInScript;
|
|
// If both are in the script, use that order.
|
|
if (AInScript)
|
|
return AIndex < BIndex;
|
|
|
|
return compareSectionsNonScript<ELFT>(A, B);
|
|
}
|
|
|
|
// Program header entry
|
|
PhdrEntry::PhdrEntry(unsigned Type, unsigned Flags) {
|
|
p_type = Type;
|
|
p_flags = Flags;
|
|
}
|
|
|
|
void PhdrEntry::add(OutputSection *Sec) {
|
|
Last = Sec;
|
|
if (!First)
|
|
First = Sec;
|
|
p_align = std::max(p_align, Sec->Addralign);
|
|
if (p_type == PT_LOAD)
|
|
Sec->FirstInPtLoad = First;
|
|
}
|
|
|
|
template <class ELFT>
|
|
static DefinedSynthetic *
|
|
addOptionalSynthetic(StringRef Name, OutputSection *Sec,
|
|
typename ELFT::uint Val, uint8_t StOther = STV_HIDDEN) {
|
|
if (SymbolBody *S = Symtab<ELFT>::X->find(Name))
|
|
if (!S->isInCurrentDSO())
|
|
return cast<DefinedSynthetic>(
|
|
Symtab<ELFT>::X->addSynthetic(Name, Sec, Val, StOther)->body());
|
|
return nullptr;
|
|
}
|
|
|
|
template <class ELFT>
|
|
static Symbol *addRegular(StringRef Name, InputSectionBase *Sec,
|
|
typename ELFT::uint Value) {
|
|
// The linker generated symbols are added as STB_WEAK to allow user defined
|
|
// ones to override them.
|
|
return Symtab<ELFT>::X->addRegular(Name, STV_HIDDEN, STT_NOTYPE, Value,
|
|
/*Size=*/0, STB_WEAK, Sec,
|
|
/*File=*/nullptr);
|
|
}
|
|
|
|
template <class ELFT>
|
|
static Symbol *addOptionalRegular(StringRef Name, InputSectionBase *IS,
|
|
typename ELFT::uint Value) {
|
|
SymbolBody *S = Symtab<ELFT>::X->find(Name);
|
|
if (!S)
|
|
return nullptr;
|
|
if (S->isInCurrentDSO())
|
|
return S->symbol();
|
|
return addRegular<ELFT>(Name, IS, Value);
|
|
}
|
|
|
|
// 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 (In<ELFT>::DynSymTab)
|
|
return;
|
|
StringRef S = Config->Rela ? "__rela_iplt_start" : "__rel_iplt_start";
|
|
addOptionalRegular<ELFT>(S, In<ELFT>::RelaIplt, 0);
|
|
|
|
S = Config->Rela ? "__rela_iplt_end" : "__rel_iplt_end";
|
|
addOptionalRegular<ELFT>(S, In<ELFT>::RelaIplt, -1);
|
|
}
|
|
|
|
// The linker is expected to define some symbols depending on
|
|
// the linking result. This function defines such symbols.
|
|
template <class ELFT> void Writer<ELFT>::addReservedSymbols() {
|
|
if (Config->EMachine == EM_MIPS) {
|
|
// Define _gp for MIPS. st_value of _gp symbol will be updated by Writer
|
|
// so that it points to an absolute address which by default is relative
|
|
// to GOT. Default offset is 0x7ff0.
|
|
// See "Global Data Symbols" in Chapter 6 in the following document:
|
|
// ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
|
|
ElfSym::MipsGp = Symtab<ELFT>::X->addAbsolute("_gp", STV_HIDDEN, STB_LOCAL);
|
|
|
|
// On MIPS O32 ABI, _gp_disp is a magic symbol designates offset between
|
|
// start of function and 'gp' pointer into GOT. To simplify relocation
|
|
// calculation we assign _gp value to it and calculate corresponding
|
|
// relocations as relative to this value.
|
|
if (Symtab<ELFT>::X->find("_gp_disp"))
|
|
ElfSym::MipsGpDisp =
|
|
Symtab<ELFT>::X->addAbsolute("_gp_disp", STV_HIDDEN, STB_LOCAL);
|
|
|
|
// The __gnu_local_gp is a magic symbol equal to the current value of 'gp'
|
|
// pointer. This symbol is used in the code generated by .cpload pseudo-op
|
|
// in case of using -mno-shared option.
|
|
// https://sourceware.org/ml/binutils/2004-12/msg00094.html
|
|
if (Symtab<ELFT>::X->find("__gnu_local_gp"))
|
|
ElfSym::MipsLocalGp =
|
|
Symtab<ELFT>::X->addAbsolute("__gnu_local_gp", STV_HIDDEN, STB_LOCAL);
|
|
}
|
|
|
|
// In the assembly for 32 bit x86 the _GLOBAL_OFFSET_TABLE_ symbol
|
|
// is magical and is used to produce a R_386_GOTPC relocation.
|
|
// The R_386_GOTPC relocation value doesn't actually depend on the
|
|
// symbol value, so it could use an index of STN_UNDEF which, according
|
|
// to the spec, means the symbol value is 0.
|
|
// Unfortunately both gas and MC keep the _GLOBAL_OFFSET_TABLE_ symbol in
|
|
// the object file.
|
|
// The situation is even stranger on x86_64 where the assembly doesn't
|
|
// need the magical symbol, but gas still puts _GLOBAL_OFFSET_TABLE_ as
|
|
// an undefined symbol in the .o files.
|
|
// Given that the symbol is effectively unused, we just create a dummy
|
|
// hidden one to avoid the undefined symbol error.
|
|
Symtab<ELFT>::X->addIgnored("_GLOBAL_OFFSET_TABLE_");
|
|
|
|
// __tls_get_addr is defined by the dynamic linker for dynamic ELFs. For
|
|
// static linking the linker is required to optimize away any references to
|
|
// __tls_get_addr, so it's not defined anywhere. Create a hidden definition
|
|
// to avoid the undefined symbol error. As usual special cases are ARM and
|
|
// MIPS - the libc for these targets defines __tls_get_addr itself because
|
|
// there are no TLS optimizations for these targets.
|
|
if (!In<ELFT>::DynSymTab &&
|
|
(Config->EMachine != EM_MIPS && Config->EMachine != EM_ARM))
|
|
Symtab<ELFT>::X->addIgnored("__tls_get_addr");
|
|
|
|
// If linker script do layout we do not need to create any standart symbols.
|
|
if (ScriptConfig->HasSections)
|
|
return;
|
|
|
|
// __ehdr_start is the location of ELF file headers.
|
|
addOptionalSynthetic<ELFT>("__ehdr_start", Out::ElfHeader, 0);
|
|
|
|
auto Define = [](StringRef S, DefinedSynthetic *&Sym1,
|
|
DefinedSynthetic *&Sym2) {
|
|
Sym1 = addOptionalSynthetic<ELFT>(S, nullptr, 0, STV_DEFAULT);
|
|
assert(S.startswith("_"));
|
|
S = S.substr(1);
|
|
Sym2 = addOptionalSynthetic<ELFT>(S, nullptr, 0, STV_DEFAULT);
|
|
};
|
|
|
|
Define("_end", ElfSym::End, ElfSym::End2);
|
|
Define("_etext", ElfSym::Etext, ElfSym::Etext2);
|
|
Define("_edata", ElfSym::Edata, ElfSym::Edata2);
|
|
}
|
|
|
|
// Sort input sections by section name suffixes for
|
|
// __attribute__((init_priority(N))).
|
|
template <class ELFT> static void sortInitFini(OutputSection *S) {
|
|
if (S)
|
|
reinterpret_cast<OutputSection *>(S)->sortInitFini();
|
|
}
|
|
|
|
// Sort input sections by the special rule for .ctors and .dtors.
|
|
template <class ELFT> static void sortCtorsDtors(OutputSection *S) {
|
|
if (S)
|
|
reinterpret_cast<OutputSection *>(S)->sortCtorsDtors();
|
|
}
|
|
|
|
// Sort input sections using the list provided by --symbol-ordering-file.
|
|
template <class ELFT>
|
|
static void sortBySymbolsOrder(ArrayRef<OutputSection *> OutputSections) {
|
|
if (Config->SymbolOrderingFile.empty())
|
|
return;
|
|
|
|
// 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<StringRef, int> SymbolOrder;
|
|
int Priority = -Config->SymbolOrderingFile.size();
|
|
for (StringRef S : Config->SymbolOrderingFile)
|
|
SymbolOrder.insert({S, Priority++});
|
|
|
|
// Build a map from sections to their priorities.
|
|
DenseMap<InputSectionBase *, int> SectionOrder;
|
|
for (elf::ObjectFile<ELFT> *File : Symtab<ELFT>::X->getObjectFiles()) {
|
|
for (SymbolBody *Body : File->getSymbols()) {
|
|
auto *D = dyn_cast<DefinedRegular>(Body);
|
|
if (!D || !D->Section)
|
|
continue;
|
|
int &Priority = SectionOrder[D->Section];
|
|
Priority = std::min(Priority, SymbolOrder.lookup(D->getName()));
|
|
}
|
|
}
|
|
|
|
// Sort sections by priority.
|
|
for (OutputSection *Base : OutputSections)
|
|
if (auto *Sec = dyn_cast<OutputSection>(Base))
|
|
Sec->sort([&](InputSectionBase *S) { return SectionOrder.lookup(S); });
|
|
}
|
|
|
|
template <class ELFT>
|
|
void Writer<ELFT>::forEachRelSec(std::function<void(InputSectionBase &)> Fn) {
|
|
for (InputSectionBase *IS : InputSections) {
|
|
if (!IS->Live)
|
|
continue;
|
|
// 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.
|
|
if (!(IS->Flags & SHF_ALLOC))
|
|
continue;
|
|
if (isa<InputSection>(IS) || isa<EhInputSection>(IS))
|
|
Fn(*IS);
|
|
}
|
|
}
|
|
|
|
template <class ELFT> void Writer<ELFT>::createSections() {
|
|
for (InputSectionBase *IS : InputSections)
|
|
if (IS)
|
|
Factory.addInputSec<ELFT>(IS, getOutputSectionName(IS->Name));
|
|
|
|
sortBySymbolsOrder<ELFT>(OutputSections);
|
|
sortInitFini<ELFT>(findSection(".init_array"));
|
|
sortInitFini<ELFT>(findSection(".fini_array"));
|
|
sortCtorsDtors<ELFT>(findSection(".ctors"));
|
|
sortCtorsDtors<ELFT>(findSection(".dtors"));
|
|
|
|
for (OutputSection *Sec : OutputSections)
|
|
Sec->assignOffsets<ELFT>();
|
|
}
|
|
|
|
template <class ELFT>
|
|
static bool canSharePtLoad(const OutputSection &S1, const OutputSection &S2) {
|
|
if (!(S1.Flags & SHF_ALLOC) || !(S2.Flags & SHF_ALLOC))
|
|
return false;
|
|
|
|
bool S1IsWrite = S1.Flags & SHF_WRITE;
|
|
bool S2IsWrite = S2.Flags & SHF_WRITE;
|
|
if (S1IsWrite != S2IsWrite)
|
|
return false;
|
|
|
|
if (!S1IsWrite)
|
|
return true; // RO and RX share a PT_LOAD with linker scripts.
|
|
return (S1.Flags & SHF_EXECINSTR) == (S2.Flags & SHF_EXECINSTR);
|
|
}
|
|
|
|
template <class ELFT> void Writer<ELFT>::sortSections() {
|
|
// 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)
|
|
return;
|
|
if (!ScriptConfig->HasSections) {
|
|
std::stable_sort(OutputSections.begin(), OutputSections.end(),
|
|
compareSectionsNonScript<ELFT>);
|
|
return;
|
|
}
|
|
Script<ELFT>::X->adjustSectionsBeforeSorting();
|
|
|
|
// The order of the sections in the script is arbitrary and may not agree with
|
|
// compareSectionsNonScript. 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:
|
|
// * First put script sections at the start and sort the script and
|
|
// non-script sections independently.
|
|
// * Move each non-script section to its preferred position. We try
|
|
// to put each section in the last position where it it can share
|
|
// a PT_LOAD.
|
|
|
|
std::stable_sort(OutputSections.begin(), OutputSections.end(),
|
|
compareSections<ELFT>);
|
|
|
|
auto I = OutputSections.begin();
|
|
auto E = OutputSections.end();
|
|
auto NonScriptI =
|
|
std::find_if(OutputSections.begin(), E, [](OutputSection *S) {
|
|
return Script<ELFT>::X->getSectionIndex(S->Name) == INT_MAX;
|
|
});
|
|
while (NonScriptI != E) {
|
|
auto BestPos = std::max_element(
|
|
I, NonScriptI, [&](OutputSection *&A, OutputSection *&B) {
|
|
bool ACanSharePtLoad = canSharePtLoad<ELFT>(**NonScriptI, *A);
|
|
bool BCanSharePtLoad = canSharePtLoad<ELFT>(**NonScriptI, *B);
|
|
if (ACanSharePtLoad != BCanSharePtLoad)
|
|
return BCanSharePtLoad;
|
|
|
|
bool ACmp = compareSectionsNonScript<ELFT>(*NonScriptI, A);
|
|
bool BCmp = compareSectionsNonScript<ELFT>(*NonScriptI, B);
|
|
if (ACmp != BCmp)
|
|
return BCmp; // FIXME: missing test
|
|
|
|
size_t PosA = &A - &OutputSections[0];
|
|
size_t PosB = &B - &OutputSections[0];
|
|
return ACmp ? PosA > PosB : PosA < PosB;
|
|
});
|
|
|
|
// max_element only returns NonScriptI if the range is empty. If the range
|
|
// is not empty we should consider moving the the element forward one
|
|
// position.
|
|
if (BestPos != NonScriptI &&
|
|
!compareSectionsNonScript<ELFT>(*NonScriptI, *BestPos))
|
|
++BestPos;
|
|
std::rotate(BestPos, NonScriptI, NonScriptI + 1);
|
|
++NonScriptI;
|
|
}
|
|
|
|
Script<ELFT>::X->adjustSectionsAfterSorting();
|
|
}
|
|
|
|
template <class ELFT>
|
|
static void finalizeSynthetic(const std::vector<SyntheticSection *> &Sections) {
|
|
for (SyntheticSection *SS : Sections)
|
|
if (SS && SS->OutSec && !SS->empty()) {
|
|
SS->finalizeContents();
|
|
SS->OutSec->template assignOffsets<ELFT>();
|
|
}
|
|
}
|
|
|
|
// We need to add input synthetic sections early in createSyntheticSections()
|
|
// to make them visible from linkescript side. But not all sections are always
|
|
// required to be in output. For example we don't need dynamic section content
|
|
// sometimes. This function filters out such unused sections from output.
|
|
template <class ELFT>
|
|
static void removeUnusedSyntheticSections(std::vector<OutputSection *> &V) {
|
|
// All input synthetic sections that can be empty are placed after
|
|
// all regular ones. We iterate over them all and exit at first
|
|
// non-synthetic.
|
|
for (InputSectionBase *S : llvm::reverse(InputSections)) {
|
|
SyntheticSection *SS = dyn_cast<SyntheticSection>(S);
|
|
if (!SS)
|
|
return;
|
|
if (!SS->empty() || !SS->OutSec)
|
|
continue;
|
|
|
|
OutputSection *OutSec = cast<OutputSection>(SS->OutSec);
|
|
OutSec->Sections.erase(
|
|
std::find(OutSec->Sections.begin(), OutSec->Sections.end(), SS));
|
|
// If there is no other sections in output section, remove it from output.
|
|
if (OutSec->Sections.empty())
|
|
V.erase(std::find(V.begin(), V.end(), OutSec));
|
|
}
|
|
}
|
|
|
|
// Create output section objects and add them to OutputSections.
|
|
template <class ELFT> void Writer<ELFT>::finalizeSections() {
|
|
Out::DebugInfo = findSection(".debug_info");
|
|
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 (OutputSection *Sec : OutputSections)
|
|
addStartStopSymbols(Sec);
|
|
}
|
|
|
|
// 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 (In<ELFT>::DynSymTab)
|
|
addRegular<ELFT>("_DYNAMIC", In<ELFT>::Dynamic, 0);
|
|
|
|
// Define __rel[a]_iplt_{start,end} symbols if needed.
|
|
addRelIpltSymbols();
|
|
|
|
// This responsible for splitting up .eh_frame section into
|
|
// pieces. The relocation scan uses those peaces, so this has to be
|
|
// earlier.
|
|
finalizeSynthetic<ELFT>({In<ELFT>::EhFrame});
|
|
|
|
// Scan relocations. This must be done after every symbol is declared so that
|
|
// we can correctly decide if a dynamic relocation is needed.
|
|
forEachRelSec(scanRelocations<ELFT>);
|
|
|
|
if (In<ELFT>::Plt && !In<ELFT>::Plt->empty())
|
|
In<ELFT>::Plt->addSymbols();
|
|
if (In<ELFT>::Iplt && !In<ELFT>::Iplt->empty())
|
|
In<ELFT>::Iplt->addSymbols();
|
|
|
|
// Now that we have defined all possible global symbols including linker-
|
|
// synthesized ones. Visit all symbols to give the finishing touches.
|
|
for (Symbol *S : Symtab<ELFT>::X->getSymbols()) {
|
|
SymbolBody *Body = S->body();
|
|
|
|
if (!includeInSymtab<ELFT>(*Body))
|
|
continue;
|
|
if (In<ELFT>::SymTab)
|
|
In<ELFT>::SymTab->addSymbol(Body);
|
|
|
|
if (In<ELFT>::DynSymTab && S->includeInDynsym()) {
|
|
In<ELFT>::DynSymTab->addSymbol(Body);
|
|
if (auto *SS = dyn_cast<SharedSymbol>(Body))
|
|
if (cast<SharedFile<ELFT>>(SS->File)->isNeeded())
|
|
In<ELFT>::VerNeed->addSymbol(SS);
|
|
}
|
|
}
|
|
|
|
// Do not proceed if there was an undefined symbol.
|
|
if (ErrorCount)
|
|
return;
|
|
|
|
// So far we have added sections from input object files.
|
|
// This function adds linker-created Out::* sections.
|
|
addPredefinedSections();
|
|
removeUnusedSyntheticSections<ELFT>(OutputSections);
|
|
|
|
sortSections();
|
|
|
|
// This is a bit of a hack. A value of 0 means undef, so we set it
|
|
// to 1 t make __ehdr_start defined. The section number is not
|
|
// particularly relevant.
|
|
Out::ElfHeader->SectionIndex = 1;
|
|
|
|
unsigned I = 1;
|
|
for (OutputSection *Sec : OutputSections) {
|
|
Sec->SectionIndex = I++;
|
|
Sec->ShName = In<ELFT>::ShStrTab->addString(Sec->Name);
|
|
}
|
|
|
|
// 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) {
|
|
Phdrs = Script<ELFT>::X->hasPhdrsCommands() ? Script<ELFT>::X->createPhdrs()
|
|
: createPhdrs();
|
|
addPtArmExid(Phdrs);
|
|
fixHeaders();
|
|
}
|
|
|
|
// Some architectures use small displacements for jump instructions.
|
|
// It is linker's responsibility to create thunks containing long
|
|
// jump instructions if jump targets are too far. Create thunks.
|
|
if (Target->NeedsThunks)
|
|
createThunks<ELFT>(OutputSections);
|
|
|
|
// 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<ELFT>();
|
|
|
|
// Dynamic section must be the last one in this list and dynamic
|
|
// symbol table section (DynSymTab) must be the first one.
|
|
finalizeSynthetic<ELFT>(
|
|
{In<ELFT>::DynSymTab, In<ELFT>::Bss, In<ELFT>::BssRelRo,
|
|
In<ELFT>::GnuHashTab, In<ELFT>::HashTab, In<ELFT>::SymTab,
|
|
In<ELFT>::ShStrTab, In<ELFT>::StrTab, In<ELFT>::VerDef,
|
|
In<ELFT>::DynStrTab, In<ELFT>::GdbIndex, In<ELFT>::Got,
|
|
In<ELFT>::MipsGot, In<ELFT>::IgotPlt, In<ELFT>::GotPlt,
|
|
In<ELFT>::RelaDyn, In<ELFT>::RelaIplt, In<ELFT>::RelaPlt,
|
|
In<ELFT>::Plt, In<ELFT>::Iplt, In<ELFT>::Plt,
|
|
In<ELFT>::EhFrameHdr, In<ELFT>::VerSym, In<ELFT>::VerNeed,
|
|
In<ELFT>::Dynamic});
|
|
}
|
|
|
|
template <class ELFT> void Writer<ELFT>::addPredefinedSections() {
|
|
// ARM ABI requires .ARM.exidx to be terminated by some piece of data.
|
|
// We have the terminater synthetic section class. Add that at the end.
|
|
auto *OS = dyn_cast_or_null<OutputSection>(findSection(".ARM.exidx"));
|
|
if (OS && !OS->Sections.empty() && !Config->Relocatable)
|
|
OS->addSection(make<ARMExidxSentinelSection<ELFT>>());
|
|
}
|
|
|
|
// 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() {
|
|
auto Define = [&](StringRef Start, StringRef End, OutputSection *OS) {
|
|
// These symbols resolve to the image base if the section does not exist.
|
|
// A special value -1 indicates end of the section.
|
|
addOptionalSynthetic<ELFT>(Start, OS, 0);
|
|
addOptionalSynthetic<ELFT>(End, OS, OS ? -1 : 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 *Sec) {
|
|
StringRef S = Sec->Name;
|
|
if (!isValidCIdentifier(S))
|
|
return;
|
|
addOptionalSynthetic<ELFT>(Saver.save("__start_" + S), Sec, 0, STV_DEFAULT);
|
|
addOptionalSynthetic<ELFT>(Saver.save("__stop_" + S), Sec, -1, STV_DEFAULT);
|
|
}
|
|
|
|
template <class ELFT> OutputSection *Writer<ELFT>::findSection(StringRef Name) {
|
|
for (OutputSection *Sec : OutputSections)
|
|
if (Sec->Name == Name)
|
|
return Sec;
|
|
return nullptr;
|
|
}
|
|
|
|
template <class ELFT> 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.
|
|
template <class ELFT>
|
|
static typename ELFT::uint computeFlags(typename ELFT::uint F) {
|
|
if (Config->Omagic)
|
|
return PF_R | PF_W | PF_X;
|
|
if (Config->SingleRoRx && !(F & PF_W))
|
|
return F | PF_X;
|
|
return F;
|
|
}
|
|
|
|
// Decide which program headers to create and which sections to include in each
|
|
// one.
|
|
template <class ELFT> std::vector<PhdrEntry> Writer<ELFT>::createPhdrs() {
|
|
std::vector<PhdrEntry> Ret;
|
|
auto AddHdr = [&](unsigned Type, unsigned Flags) -> PhdrEntry * {
|
|
Ret.emplace_back(Type, Flags);
|
|
return &Ret.back();
|
|
};
|
|
|
|
// The first phdr entry is PT_PHDR which describes the program header itself.
|
|
AddHdr(PT_PHDR, PF_R)->add(Out::ProgramHeaders);
|
|
|
|
// PT_INTERP must be the second entry if exists.
|
|
if (OutputSection *Sec = findSection(".interp"))
|
|
AddHdr(PT_INTERP, Sec->getPhdrFlags())->add(Sec);
|
|
|
|
// Add the first PT_LOAD segment for regular output sections.
|
|
uintX_t Flags = computeFlags<ELFT>(PF_R);
|
|
PhdrEntry *Load = AddHdr(PT_LOAD, Flags);
|
|
for (OutputSection *Sec : OutputSections) {
|
|
if (!(Sec->Flags & SHF_ALLOC))
|
|
break;
|
|
if (!needsPtLoad<ELFT>(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 using AT linker
|
|
// script command.
|
|
uintX_t NewFlags = computeFlags<ELFT>(Sec->getPhdrFlags());
|
|
if (Script<ELFT>::X->hasLMA(Sec->Name) || Flags != NewFlags) {
|
|
Load = AddHdr(PT_LOAD, NewFlags);
|
|
Flags = NewFlags;
|
|
}
|
|
|
|
Load->add(Sec);
|
|
}
|
|
|
|
// Add a TLS segment if any.
|
|
PhdrEntry TlsHdr(PT_TLS, PF_R);
|
|
for (OutputSection *Sec : OutputSections)
|
|
if (Sec->Flags & SHF_TLS)
|
|
TlsHdr.add(Sec);
|
|
if (TlsHdr.First)
|
|
Ret.push_back(std::move(TlsHdr));
|
|
|
|
// Add an entry for .dynamic.
|
|
if (In<ELFT>::DynSymTab)
|
|
AddHdr(PT_DYNAMIC, In<ELFT>::Dynamic->OutSec->getPhdrFlags())
|
|
->add(In<ELFT>::Dynamic->OutSec);
|
|
|
|
// PT_GNU_RELRO includes all sections that should be marked as
|
|
// read-only by dynamic linker after proccessing relocations.
|
|
PhdrEntry RelRo(PT_GNU_RELRO, PF_R);
|
|
for (OutputSection *Sec : OutputSections)
|
|
if (needsPtLoad<ELFT>(Sec) && isRelroSection<ELFT>(Sec))
|
|
RelRo.add(Sec);
|
|
if (RelRo.First)
|
|
Ret.push_back(std::move(RelRo));
|
|
|
|
// PT_GNU_EH_FRAME is a special section pointing on .eh_frame_hdr.
|
|
if (!In<ELFT>::EhFrame->empty() && In<ELFT>::EhFrameHdr)
|
|
AddHdr(PT_GNU_EH_FRAME, In<ELFT>::EhFrameHdr->OutSec->getPhdrFlags())
|
|
->add(In<ELFT>::EhFrameHdr->OutSec);
|
|
|
|
// PT_OPENBSD_RANDOMIZE specifies the location and size of a part of the
|
|
// memory image of the program that must be filled with random data before any
|
|
// code in the object is executed.
|
|
if (OutputSection *Sec = findSection(".openbsd.randomdata"))
|
|
AddHdr(PT_OPENBSD_RANDOMIZE, Sec->getPhdrFlags())->add(Sec);
|
|
|
|
// 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;
|
|
if (Config->ZExecstack)
|
|
Perm = PF_R | PF_W | PF_X;
|
|
else
|
|
Perm = PF_R | PF_W;
|
|
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);
|
|
|
|
// Create one PT_NOTE per a group of contiguous .note sections.
|
|
PhdrEntry *Note = nullptr;
|
|
for (OutputSection *Sec : OutputSections) {
|
|
if (Sec->Type == SHT_NOTE) {
|
|
if (!Note || Script<ELFT>::X->hasLMA(Sec->Name))
|
|
Note = AddHdr(PT_NOTE, PF_R);
|
|
Note->add(Sec);
|
|
} else {
|
|
Note = nullptr;
|
|
}
|
|
}
|
|
return Ret;
|
|
}
|
|
|
|
template <class ELFT>
|
|
void Writer<ELFT>::addPtArmExid(std::vector<PhdrEntry> &Phdrs) {
|
|
if (Config->EMachine != EM_ARM)
|
|
return;
|
|
auto I = std::find_if(
|
|
OutputSections.begin(), OutputSections.end(),
|
|
[](OutputSection *Sec) { return Sec->Type == SHT_ARM_EXIDX; });
|
|
if (I == OutputSections.end())
|
|
return;
|
|
|
|
// PT_ARM_EXIDX is the ARM EHABI equivalent of PT_GNU_EH_FRAME
|
|
PhdrEntry ARMExidx(PT_ARM_EXIDX, PF_R);
|
|
ARMExidx.add(*I);
|
|
Phdrs.push_back(ARMExidx);
|
|
}
|
|
|
|
// The first section of each PT_LOAD, the first section in PT_GNU_RELRO and the
|
|
// first section after PT_GNU_RELRO have to be page aligned so that the dynamic
|
|
// linker can set the permissions.
|
|
template <class ELFT> void Writer<ELFT>::fixSectionAlignments() {
|
|
for (const PhdrEntry &P : Phdrs)
|
|
if (P.p_type == PT_LOAD && P.First)
|
|
P.First->PageAlign = true;
|
|
|
|
for (const PhdrEntry &P : Phdrs) {
|
|
if (P.p_type != PT_GNU_RELRO)
|
|
continue;
|
|
if (P.First)
|
|
P.First->PageAlign = true;
|
|
// Find the first section after PT_GNU_RELRO. If it is in a PT_LOAD we
|
|
// have to align it to a page.
|
|
auto End = OutputSections.end();
|
|
auto I = std::find(OutputSections.begin(), End, P.Last);
|
|
if (I == End || (I + 1) == End)
|
|
continue;
|
|
OutputSection *Sec = *(I + 1);
|
|
if (needsPtLoad<ELFT>(Sec))
|
|
Sec->PageAlign = true;
|
|
}
|
|
}
|
|
|
|
template <class ELFT>
|
|
bool elf::allocateHeaders(std::vector<PhdrEntry> &Phdrs,
|
|
ArrayRef<OutputSection *> OutputSections,
|
|
uint64_t Min) {
|
|
auto FirstPTLoad =
|
|
std::find_if(Phdrs.begin(), Phdrs.end(),
|
|
[](const PhdrEntry &E) { return E.p_type == PT_LOAD; });
|
|
if (FirstPTLoad == Phdrs.end())
|
|
return false;
|
|
|
|
uint64_t HeaderSize = getHeaderSize<ELFT>();
|
|
if (HeaderSize > Min) {
|
|
auto PhdrI =
|
|
std::find_if(Phdrs.begin(), Phdrs.end(),
|
|
[](const PhdrEntry &E) { return E.p_type == PT_PHDR; });
|
|
if (PhdrI != Phdrs.end())
|
|
Phdrs.erase(PhdrI);
|
|
return false;
|
|
}
|
|
Min = alignDown(Min - HeaderSize, Config->MaxPageSize);
|
|
|
|
if (!ScriptConfig->HasSections)
|
|
Config->ImageBase = Min = std::min(Min, Config->ImageBase);
|
|
|
|
Out::ElfHeader->Addr = Min;
|
|
Out::ProgramHeaders->Addr = Min + Out::ElfHeader->Size;
|
|
|
|
if (Script<ELFT>::X->hasPhdrsCommands())
|
|
return true;
|
|
|
|
if (FirstPTLoad->First)
|
|
for (OutputSection *Sec : OutputSections)
|
|
if (Sec->FirstInPtLoad == FirstPTLoad->First)
|
|
Sec->FirstInPtLoad = Out::ElfHeader;
|
|
FirstPTLoad->First = Out::ElfHeader;
|
|
if (!FirstPTLoad->Last)
|
|
FirstPTLoad->Last = Out::ProgramHeaders;
|
|
return true;
|
|
}
|
|
|
|
// We should set file offsets and VAs for elf header and program headers
|
|
// sections. These are special, we do not include them into output sections
|
|
// list, but have them to simplify the code.
|
|
template <class ELFT> void Writer<ELFT>::fixHeaders() {
|
|
Out::ProgramHeaders->Size = sizeof(Elf_Phdr) * Phdrs.size();
|
|
// If the script has SECTIONS, assignAddresses will compute the values.
|
|
if (ScriptConfig->HasSections)
|
|
return;
|
|
|
|
// When -T<section> option is specified, lower the base to make room for those
|
|
// sections.
|
|
uint64_t Min = -1;
|
|
if (!Config->SectionStartMap.empty())
|
|
for (const auto &P : Config->SectionStartMap)
|
|
Min = std::min(Min, P.second);
|
|
|
|
AllocateHeader = allocateHeaders<ELFT>(Phdrs, OutputSections, Min);
|
|
}
|
|
|
|
// Assign VAs (addresses at run-time) to output sections.
|
|
template <class ELFT> void Writer<ELFT>::assignAddresses() {
|
|
uintX_t VA = Config->ImageBase;
|
|
if (AllocateHeader)
|
|
VA += getHeaderSize<ELFT>();
|
|
uintX_t ThreadBssOffset = 0;
|
|
for (OutputSection *Sec : OutputSections) {
|
|
uintX_t Alignment = Sec->Addralign;
|
|
if (Sec->PageAlign)
|
|
Alignment = std::max<uintX_t>(Alignment, Config->MaxPageSize);
|
|
|
|
auto I = Config->SectionStartMap.find(Sec->Name);
|
|
if (I != Config->SectionStartMap.end())
|
|
VA = I->second;
|
|
|
|
// We only assign VAs to allocated sections.
|
|
if (needsPtLoad<ELFT>(Sec)) {
|
|
VA = alignTo(VA, Alignment);
|
|
Sec->Addr = VA;
|
|
VA += Sec->Size;
|
|
} else if (Sec->Flags & SHF_TLS && Sec->Type == SHT_NOBITS) {
|
|
uintX_t TVA = VA + ThreadBssOffset;
|
|
TVA = alignTo(TVA, Alignment);
|
|
Sec->Addr = TVA;
|
|
ThreadBssOffset = TVA - VA + Sec->Size;
|
|
}
|
|
}
|
|
}
|
|
|
|
// Adjusts the file alignment for a given output section and returns
|
|
// its new file offset. 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.
|
|
template <class ELFT, class uintX_t>
|
|
static uintX_t getFileAlignment(uintX_t Off, OutputSection *Sec) {
|
|
OutputSection *First = Sec->FirstInPtLoad;
|
|
// If the section is not in a PT_LOAD, we just have to align it.
|
|
if (!First)
|
|
return alignTo(Off, Sec->Addralign);
|
|
|
|
// The first section in a PT_LOAD has to have congruent offset and address
|
|
// module the page size.
|
|
if (Sec == First)
|
|
return alignTo(Off, Config->MaxPageSize, Sec->Addr);
|
|
|
|
// If two sections share the same PT_LOAD the file offset is calculated
|
|
// using this formula: Off2 = Off1 + (VA2 - VA1).
|
|
return First->Offset + Sec->Addr - First->Addr;
|
|
}
|
|
|
|
template <class ELFT, class uintX_t>
|
|
static uintX_t setOffset(OutputSection *Sec, uintX_t Off) {
|
|
if (Sec->Type == SHT_NOBITS) {
|
|
Sec->Offset = Off;
|
|
return Off;
|
|
}
|
|
|
|
Off = getFileAlignment<ELFT>(Off, Sec);
|
|
Sec->Offset = Off;
|
|
return Off + Sec->Size;
|
|
}
|
|
|
|
template <class ELFT> void Writer<ELFT>::assignFileOffsetsBinary() {
|
|
uintX_t Off = 0;
|
|
for (OutputSection *Sec : OutputSections)
|
|
if (Sec->Flags & SHF_ALLOC)
|
|
Off = setOffset<ELFT>(Sec, Off);
|
|
FileSize = alignTo(Off, sizeof(uintX_t));
|
|
}
|
|
|
|
// Assign file offsets to output sections.
|
|
template <class ELFT> void Writer<ELFT>::assignFileOffsets() {
|
|
uintX_t Off = 0;
|
|
Off = setOffset<ELFT>(Out::ElfHeader, Off);
|
|
Off = setOffset<ELFT>(Out::ProgramHeaders, Off);
|
|
|
|
for (OutputSection *Sec : OutputSections)
|
|
Off = setOffset<ELFT>(Sec, Off);
|
|
|
|
SectionHeaderOff = alignTo(Off, sizeof(uintX_t));
|
|
FileSize = SectionHeaderOff + (OutputSections.size() + 1) * sizeof(Elf_Shdr);
|
|
}
|
|
|
|
// 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() {
|
|
for (PhdrEntry &P : Phdrs) {
|
|
OutputSection *First = P.First;
|
|
OutputSection *Last = P.Last;
|
|
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;
|
|
if (!P.HasLMA)
|
|
P.p_paddr = First->getLMA();
|
|
}
|
|
if (P.p_type == PT_LOAD)
|
|
P.p_align = Config->MaxPageSize;
|
|
else if (P.p_type == PT_GNU_RELRO) {
|
|
P.p_align = 1;
|
|
// The glibc dynamic loader 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_memsz, Target->PageSize);
|
|
}
|
|
|
|
// The TLS pointer goes after PT_TLS. At least glibc will align it,
|
|
// so round up the size to make sure the offsets are correct.
|
|
if (P.p_type == PT_TLS) {
|
|
Out::TlsPhdr = &P;
|
|
if (P.p_memsz)
|
|
P.p_memsz = alignTo(P.p_memsz, P.p_align);
|
|
}
|
|
}
|
|
}
|
|
|
|
// 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 address of the first byte of the .text section, if present;
|
|
// 5. the address 0.
|
|
template <class ELFT> typename ELFT::uint Writer<ELFT>::getEntryAddr() {
|
|
// Case 1, 2 or 3. As a special case, if the symbol is actually
|
|
// a number, we'll use that number as an address.
|
|
if (SymbolBody *B = Symtab<ELFT>::X->find(Config->Entry))
|
|
return B->getVA<ELFT>();
|
|
uint64_t Addr;
|
|
if (!Config->Entry.getAsInteger(0, Addr))
|
|
return Addr;
|
|
|
|
// Case 4
|
|
if (OutputSection *Sec = findSection(".text")) {
|
|
if (Config->WarnMissingEntry)
|
|
warn("cannot find entry symbol " + Config->Entry + "; defaulting to 0x" +
|
|
utohexstr(Sec->Addr));
|
|
return Sec->Addr;
|
|
}
|
|
|
|
// Case 5
|
|
if (Config->WarnMissingEntry)
|
|
warn("cannot find entry symbol " + Config->Entry +
|
|
"; not setting start address");
|
|
return 0;
|
|
}
|
|
|
|
template <class ELFT> static uint8_t getELFEncoding() {
|
|
if (ELFT::TargetEndianness == llvm::support::little)
|
|
return ELFDATA2LSB;
|
|
return ELFDATA2MSB;
|
|
}
|
|
|
|
static uint16_t getELFType() {
|
|
if (Config->pic())
|
|
return ET_DYN;
|
|
if (Config->Relocatable)
|
|
return ET_REL;
|
|
return ET_EXEC;
|
|
}
|
|
|
|
// This function is called after we have assigned address and size
|
|
// to each section. This function fixes some predefined
|
|
// symbol values that depend on section address and size.
|
|
template <class ELFT> void Writer<ELFT>::fixPredefinedSymbols() {
|
|
auto Set = [](DefinedSynthetic *S1, DefinedSynthetic *S2, OutputSection *Sec,
|
|
uint64_t Value) {
|
|
if (S1) {
|
|
S1->Section = Sec;
|
|
S1->Value = Value;
|
|
}
|
|
if (S2) {
|
|
S2->Section = Sec;
|
|
S2->Value = Value;
|
|
}
|
|
};
|
|
|
|
// _etext is the first location after the last read-only loadable segment.
|
|
// _edata is the first location after the last read-write loadable segment.
|
|
// _end is the first location after the uninitialized data region.
|
|
PhdrEntry *Last = nullptr;
|
|
PhdrEntry *LastRO = nullptr;
|
|
PhdrEntry *LastRW = nullptr;
|
|
for (PhdrEntry &P : Phdrs) {
|
|
if (P.p_type != PT_LOAD)
|
|
continue;
|
|
Last = &P;
|
|
if (P.p_flags & PF_W)
|
|
LastRW = &P;
|
|
else
|
|
LastRO = &P;
|
|
}
|
|
if (Last)
|
|
Set(ElfSym::End, ElfSym::End2, Last->First, Last->p_memsz);
|
|
if (LastRO)
|
|
Set(ElfSym::Etext, ElfSym::Etext2, LastRO->First, LastRO->p_filesz);
|
|
if (LastRW)
|
|
Set(ElfSym::Edata, ElfSym::Edata2, LastRW->First, LastRW->p_filesz);
|
|
|
|
// Setup MIPS _gp_disp/__gnu_local_gp symbols which should
|
|
// be equal to the _gp symbol's value.
|
|
if (Config->EMachine == EM_MIPS) {
|
|
if (!ElfSym::MipsGp->Value) {
|
|
// Find GP-relative section with the lowest address
|
|
// and use this address to calculate default _gp value.
|
|
uintX_t Gp = -1;
|
|
for (const OutputSection *OS : OutputSections)
|
|
if ((OS->Flags & SHF_MIPS_GPREL) && OS->Addr < Gp)
|
|
Gp = OS->Addr;
|
|
if (Gp != (uintX_t)-1)
|
|
ElfSym::MipsGp->Value = Gp + 0x7ff0;
|
|
}
|
|
if (ElfSym::MipsGpDisp)
|
|
ElfSym::MipsGpDisp->Value = ElfSym::MipsGp->Value;
|
|
if (ElfSym::MipsLocalGp)
|
|
ElfSym::MipsLocalGp->Value = ElfSym::MipsGp->Value;
|
|
}
|
|
}
|
|
|
|
template <class ELFT> void Writer<ELFT>::writeHeader() {
|
|
uint8_t *Buf = Buffer->getBufferStart();
|
|
memcpy(Buf, "\177ELF", 4);
|
|
|
|
// Write the ELF header.
|
|
auto *EHdr = reinterpret_cast<Elf_Ehdr *>(Buf);
|
|
EHdr->e_ident[EI_CLASS] = ELFT::Is64Bits ? ELFCLASS64 : ELFCLASS32;
|
|
EHdr->e_ident[EI_DATA] = getELFEncoding<ELFT>();
|
|
EHdr->e_ident[EI_VERSION] = EV_CURRENT;
|
|
EHdr->e_ident[EI_OSABI] = Config->OSABI;
|
|
EHdr->e_type = getELFType();
|
|
EHdr->e_machine = Config->EMachine;
|
|
EHdr->e_version = EV_CURRENT;
|
|
EHdr->e_entry = getEntryAddr();
|
|
EHdr->e_shoff = SectionHeaderOff;
|
|
EHdr->e_ehsize = sizeof(Elf_Ehdr);
|
|
EHdr->e_phnum = Phdrs.size();
|
|
EHdr->e_shentsize = sizeof(Elf_Shdr);
|
|
EHdr->e_shnum = OutputSections.size() + 1;
|
|
EHdr->e_shstrndx = In<ELFT>::ShStrTab->OutSec->SectionIndex;
|
|
|
|
if (Config->EMachine == EM_ARM)
|
|
// We don't currently use any features incompatible with EF_ARM_EABI_VER5,
|
|
// but we don't have any firm guarantees of conformance. Linux AArch64
|
|
// kernels (as of 2016) require an EABI version to be set.
|
|
EHdr->e_flags = EF_ARM_EABI_VER5;
|
|
else if (Config->EMachine == EM_MIPS)
|
|
EHdr->e_flags = getMipsEFlags<ELFT>();
|
|
|
|
if (!Config->Relocatable) {
|
|
EHdr->e_phoff = sizeof(Elf_Ehdr);
|
|
EHdr->e_phentsize = sizeof(Elf_Phdr);
|
|
}
|
|
|
|
// Write the program header table.
|
|
auto *HBuf = reinterpret_cast<Elf_Phdr *>(Buf + EHdr->e_phoff);
|
|
for (PhdrEntry &P : Phdrs) {
|
|
HBuf->p_type = P.p_type;
|
|
HBuf->p_flags = P.p_flags;
|
|
HBuf->p_offset = P.p_offset;
|
|
HBuf->p_vaddr = P.p_vaddr;
|
|
HBuf->p_paddr = P.p_paddr;
|
|
HBuf->p_filesz = P.p_filesz;
|
|
HBuf->p_memsz = P.p_memsz;
|
|
HBuf->p_align = P.p_align;
|
|
++HBuf;
|
|
}
|
|
|
|
// Write the section header table. Note that the first table entry is null.
|
|
auto *SHdrs = reinterpret_cast<Elf_Shdr *>(Buf + EHdr->e_shoff);
|
|
for (OutputSection *Sec : OutputSections)
|
|
Sec->writeHeaderTo<ELFT>(++SHdrs);
|
|
}
|
|
|
|
// Removes a given file asynchronously. This is a performance hack,
|
|
// so remove this when operating systems are improved.
|
|
//
|
|
// On Linux (and probably on other Unix-like systems), unlink(2) is a
|
|
// noticeably slow system call. As of 2016, unlink takes 250
|
|
// milliseconds to remove a 1 GB file on ext4 filesystem on my machine.
|
|
//
|
|
// To create a new result file, we first remove existing file. So, if
|
|
// you repeatedly link a 1 GB program in a regular compile-link-debug
|
|
// cycle, every cycle wastes 250 milliseconds only to remove a file.
|
|
// Since LLD can link a 1 GB binary in about 5 seconds, that waste
|
|
// actually counts.
|
|
//
|
|
// This function spawns a background thread to call unlink.
|
|
// The calling thread returns almost immediately.
|
|
static void unlinkAsync(StringRef Path) {
|
|
if (!Config->Threads || !sys::fs::exists(Config->OutputFile))
|
|
return;
|
|
|
|
// First, rename Path to avoid race condition. We cannot remove
|
|
// Path from a different thread because we are now going to create
|
|
// Path as a new file. If we do that in a different thread, the new
|
|
// thread can remove the new file.
|
|
SmallString<128> TempPath;
|
|
if (sys::fs::createUniqueFile(Path + "tmp%%%%%%%%", TempPath))
|
|
return;
|
|
if (sys::fs::rename(Path, TempPath)) {
|
|
sys::fs::remove(TempPath);
|
|
return;
|
|
}
|
|
|
|
// Remove TempPath in background.
|
|
std::thread([=] { ::remove(TempPath.str().str().c_str()); }).detach();
|
|
}
|
|
|
|
// Open a result file.
|
|
template <class ELFT> void Writer<ELFT>::openFile() {
|
|
unlinkAsync(Config->OutputFile);
|
|
ErrorOr<std::unique_ptr<FileOutputBuffer>> BufferOrErr =
|
|
FileOutputBuffer::create(Config->OutputFile, FileSize,
|
|
FileOutputBuffer::F_executable);
|
|
|
|
if (auto EC = BufferOrErr.getError())
|
|
error("failed to open " + Config->OutputFile + ": " + EC.message());
|
|
else
|
|
Buffer = std::move(*BufferOrErr);
|
|
}
|
|
|
|
template <class ELFT> void Writer<ELFT>::writeSectionsBinary() {
|
|
uint8_t *Buf = Buffer->getBufferStart();
|
|
for (OutputSection *Sec : OutputSections)
|
|
if (Sec->Flags & SHF_ALLOC)
|
|
Sec->writeTo<ELFT>(Buf + Sec->Offset);
|
|
}
|
|
|
|
// Write section contents to a mmap'ed file.
|
|
template <class ELFT> void Writer<ELFT>::writeSections() {
|
|
uint8_t *Buf = Buffer->getBufferStart();
|
|
|
|
// PPC64 needs to process relocations in the .opd section
|
|
// before processing relocations in code-containing sections.
|
|
Out::Opd = findSection(".opd");
|
|
if (Out::Opd) {
|
|
Out::OpdBuf = Buf + Out::Opd->Offset;
|
|
Out::Opd->template writeTo<ELFT>(Buf + Out::Opd->Offset);
|
|
}
|
|
|
|
OutputSection *EhFrameHdr =
|
|
In<ELFT>::EhFrameHdr ? In<ELFT>::EhFrameHdr->OutSec : nullptr;
|
|
|
|
// 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>(Buf + Sec->Offset);
|
|
|
|
for (OutputSection *Sec : OutputSections)
|
|
if (Sec != Out::Opd && Sec != EhFrameHdr && Sec->Type != SHT_REL &&
|
|
Sec->Type != SHT_RELA)
|
|
Sec->writeTo<ELFT>(Buf + Sec->Offset);
|
|
|
|
// The .eh_frame_hdr depends on .eh_frame section contents, therefore
|
|
// it should be written after .eh_frame is written.
|
|
if (EhFrameHdr)
|
|
EhFrameHdr->writeTo<ELFT>(Buf + EhFrameHdr->Offset);
|
|
}
|
|
|
|
template <class ELFT> void Writer<ELFT>::writeBuildId() {
|
|
if (!In<ELFT>::BuildId || !In<ELFT>::BuildId->OutSec)
|
|
return;
|
|
|
|
// Compute a hash of all sections of the output file.
|
|
uint8_t *Start = Buffer->getBufferStart();
|
|
uint8_t *End = Start + FileSize;
|
|
In<ELFT>::BuildId->writeBuildId({Start, End});
|
|
}
|
|
|
|
template void elf::writeResult<ELF32LE>();
|
|
template void elf::writeResult<ELF32BE>();
|
|
template void elf::writeResult<ELF64LE>();
|
|
template void elf::writeResult<ELF64BE>();
|
|
|
|
template bool elf::allocateHeaders<ELF32LE>(std::vector<PhdrEntry> &,
|
|
ArrayRef<OutputSection *>,
|
|
uint64_t);
|
|
template bool elf::allocateHeaders<ELF32BE>(std::vector<PhdrEntry> &,
|
|
ArrayRef<OutputSection *>,
|
|
uint64_t);
|
|
template bool elf::allocateHeaders<ELF64LE>(std::vector<PhdrEntry> &,
|
|
ArrayRef<OutputSection *>,
|
|
uint64_t);
|
|
template bool elf::allocateHeaders<ELF64BE>(std::vector<PhdrEntry> &,
|
|
ArrayRef<OutputSection *>,
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uint64_t);
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template bool elf::isRelroSection<ELF32LE>(const OutputSection *);
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template bool elf::isRelroSection<ELF32BE>(const OutputSection *);
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template bool elf::isRelroSection<ELF64LE>(const OutputSection *);
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template bool elf::isRelroSection<ELF64BE>(const OutputSection *);
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