forked from OSchip/llvm-project
1456 lines
51 KiB
C++
1456 lines
51 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 "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 "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/StringSaver.h"
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#include "llvm/Support/raw_ostream.h"
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#include <climits>
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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 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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typedef PhdrEntry<ELFT> Phdr;
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void copyLocalSymbols();
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void addReservedSymbols();
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void createSections();
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void forEachRelSec(
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std::function<void(InputSectionBase<ELFT> &, const typename ELFT::Shdr &)>
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Fn);
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void sortSections();
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void finalizeSections();
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void addPredefinedSections();
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bool needsGot();
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std::vector<Phdr> createPhdrs();
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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 fixAbsoluteSymbols();
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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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BumpPtrAllocator Alloc;
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std::vector<OutputSectionBase<ELFT> *> OutputSections;
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OutputSectionFactory<ELFT> Factory;
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void addRelIpltSymbols();
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void addStartEndSymbols();
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void addStartStopSymbols(OutputSectionBase<ELFT> *Sec);
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OutputSectionBase<ELFT> *findSection(StringRef Name);
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std::vector<Phdr> Phdrs;
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uintX_t FileSize;
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uintX_t SectionHeaderOff;
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};
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} // anonymous namespace
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template <class ELFT>
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StringRef elf::getOutputSectionName(InputSectionBase<ELFT> *S) {
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StringRef Name = S->Name;
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for (StringRef V :
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{".text.", ".rodata.", ".data.rel.ro.", ".data.", ".bss.",
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".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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return Name;
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}
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template <class ELFT> void elf::reportDiscarded(InputSectionBase<ELFT> *IS) {
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if (!Config->PrintGcSections || !IS || IS == &InputSection<ELFT>::Discarded ||
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IS->Live)
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return;
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errs() << "removing unused section from '" << IS->Name << "' in file '"
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<< IS->getFile()->getName() << "'\n";
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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() {
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typedef typename ELFT::uint uintX_t;
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typedef typename ELFT::Ehdr Elf_Ehdr;
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// Create singleton output sections.
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OutputSection<ELFT> Bss(".bss", SHT_NOBITS, SHF_ALLOC | SHF_WRITE);
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DynamicSection<ELFT> Dynamic;
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EhOutputSection<ELFT> EhFrame;
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GotSection<ELFT> Got;
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PltSection<ELFT> Plt;
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RelocationSection<ELFT> RelaDyn(Config->Rela ? ".rela.dyn" : ".rel.dyn",
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Config->ZCombreloc);
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StringTableSection<ELFT> ShStrTab(".shstrtab", false);
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VersionTableSection<ELFT> VerSym;
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VersionNeedSection<ELFT> VerNeed;
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OutputSectionBase<ELFT> ElfHeader("", 0, SHF_ALLOC);
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ElfHeader.setSize(sizeof(Elf_Ehdr));
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OutputSectionBase<ELFT> ProgramHeaders("", 0, SHF_ALLOC);
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ProgramHeaders.updateAlignment(sizeof(uintX_t));
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// Instantiate optional output sections if they are needed.
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std::unique_ptr<InterpSection<ELFT>> Interp;
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std::unique_ptr<BuildIdSection<ELFT>> BuildId;
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std::unique_ptr<StringTableSection<ELFT>> DynStrTab;
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std::unique_ptr<SymbolTableSection<ELFT>> DynSymTab;
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std::unique_ptr<EhFrameHeader<ELFT>> EhFrameHdr;
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std::unique_ptr<GnuHashTableSection<ELFT>> GnuHashTab;
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std::unique_ptr<GotPltSection<ELFT>> GotPlt;
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std::unique_ptr<HashTableSection<ELFT>> HashTab;
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std::unique_ptr<RelocationSection<ELFT>> RelaPlt;
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std::unique_ptr<StringTableSection<ELFT>> StrTab;
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std::unique_ptr<SymbolTableSection<ELFT>> SymTabSec;
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std::unique_ptr<OutputSection<ELFT>> MipsRldMap;
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std::unique_ptr<VersionDefinitionSection<ELFT>> VerDef;
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if (needsInterpSection<ELFT>())
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Interp.reset(new InterpSection<ELFT>);
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if (Config->BuildId == BuildIdKind::Fast)
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BuildId.reset(new BuildIdFastHash<ELFT>);
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else if (Config->BuildId == BuildIdKind::Md5)
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BuildId.reset(new BuildIdMd5<ELFT>);
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else if (Config->BuildId == BuildIdKind::Sha1)
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BuildId.reset(new BuildIdSha1<ELFT>);
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else if (Config->BuildId == BuildIdKind::Uuid)
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BuildId.reset(new BuildIdUuid<ELFT>);
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else if (Config->BuildId == BuildIdKind::Hexstring)
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BuildId.reset(new BuildIdHexstring<ELFT>);
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if (!Symtab<ELFT>::X->getSharedFiles().empty() || Config->Pic) {
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DynStrTab.reset(new StringTableSection<ELFT>(".dynstr", true));
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DynSymTab.reset(new SymbolTableSection<ELFT>(*DynStrTab));
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}
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if (Config->EhFrameHdr)
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EhFrameHdr.reset(new EhFrameHeader<ELFT>);
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if (Config->GnuHash)
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GnuHashTab.reset(new GnuHashTableSection<ELFT>);
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if (Config->SysvHash)
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HashTab.reset(new HashTableSection<ELFT>);
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StringRef S = Config->Rela ? ".rela.plt" : ".rel.plt";
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GotPlt.reset(new GotPltSection<ELFT>);
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RelaPlt.reset(new RelocationSection<ELFT>(S, false /*Sort*/));
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if (Config->Strip != StripPolicy::All) {
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StrTab.reset(new StringTableSection<ELFT>(".strtab", false));
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SymTabSec.reset(new SymbolTableSection<ELFT>(*StrTab));
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}
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if (Config->EMachine == EM_MIPS && !Config->Shared) {
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// This is a MIPS specific section to hold a space within the data segment
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// of executable file which is pointed to by the DT_MIPS_RLD_MAP entry.
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// See "Dynamic section" in Chapter 5 in the following document:
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// ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
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MipsRldMap.reset(new OutputSection<ELFT>(".rld_map", SHT_PROGBITS,
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SHF_ALLOC | SHF_WRITE));
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MipsRldMap->setSize(sizeof(uintX_t));
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MipsRldMap->updateAlignment(sizeof(uintX_t));
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}
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if (!Config->VersionDefinitions.empty())
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VerDef.reset(new VersionDefinitionSection<ELFT>());
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Out<ELFT>::Bss = &Bss;
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Out<ELFT>::BuildId = BuildId.get();
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Out<ELFT>::DynStrTab = DynStrTab.get();
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Out<ELFT>::DynSymTab = DynSymTab.get();
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Out<ELFT>::Dynamic = &Dynamic;
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Out<ELFT>::EhFrame = &EhFrame;
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Out<ELFT>::EhFrameHdr = EhFrameHdr.get();
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Out<ELFT>::GnuHashTab = GnuHashTab.get();
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Out<ELFT>::Got = &Got;
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Out<ELFT>::GotPlt = GotPlt.get();
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Out<ELFT>::HashTab = HashTab.get();
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Out<ELFT>::Interp = Interp.get();
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Out<ELFT>::Plt = &Plt;
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Out<ELFT>::RelaDyn = &RelaDyn;
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Out<ELFT>::RelaPlt = RelaPlt.get();
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Out<ELFT>::ShStrTab = &ShStrTab;
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Out<ELFT>::StrTab = StrTab.get();
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Out<ELFT>::SymTab = SymTabSec.get();
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Out<ELFT>::VerDef = VerDef.get();
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Out<ELFT>::VerSym = &VerSym;
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Out<ELFT>::VerNeed = &VerNeed;
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Out<ELFT>::MipsRldMap = MipsRldMap.get();
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Out<ELFT>::Opd = nullptr;
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Out<ELFT>::OpdBuf = nullptr;
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Out<ELFT>::TlsPhdr = nullptr;
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Out<ELFT>::ElfHeader = &ElfHeader;
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Out<ELFT>::ProgramHeaders = &ProgramHeaders;
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Out<ELFT>::PreinitArray = nullptr;
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Out<ELFT>::InitArray = nullptr;
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Out<ELFT>::FiniArray = nullptr;
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Writer<ELFT>().run();
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Out<ELFT>::Pool.clear();
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}
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template <class ELFT> static std::vector<DefinedCommon *> getCommonSymbols() {
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std::vector<DefinedCommon *> V;
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for (Symbol *S : Symtab<ELFT>::X->getSymbols())
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if (auto *B = dyn_cast<DefinedCommon>(S->body()))
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V.push_back(B);
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return V;
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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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addReservedSymbols();
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if (Target->NeedsThunks)
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forEachRelSec(createThunks<ELFT>);
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CommonInputSection<ELFT> Common(getCommonSymbols<ELFT>());
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CommonInputSection<ELFT>::X = &Common;
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Script<ELFT>::X->OutputSections = &OutputSections;
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if (ScriptConfig->HasSections) {
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Script<ELFT>::X->createSections(Factory);
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} else {
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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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finalizeSections();
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if (HasError)
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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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Phdrs = Script<ELFT>::X->hasPhdrsCommands() ? Script<ELFT>::X->createPhdrs()
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: createPhdrs();
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fixHeaders();
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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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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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fixAbsoluteSymbols();
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}
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openFile();
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if (HasError)
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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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writeBuildId();
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if (HasError)
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return;
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if (auto EC = Buffer->commit())
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error(EC, "failed to write to the output file");
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}
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template <class ELFT> static void reportUndefined(SymbolBody *Sym) {
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if (Config->UnresolvedSymbols == UnresolvedPolicy::Ignore)
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return;
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if (Config->Shared && Sym->symbol()->Visibility == STV_DEFAULT &&
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Config->UnresolvedSymbols != UnresolvedPolicy::NoUndef)
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return;
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std::string Msg = "undefined symbol: ";
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Msg += Config->Demangle ? demangle(Sym->getName()) : Sym->getName().str();
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if (Sym->File)
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Msg += " in " + getFilename(Sym->File);
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if (Config->UnresolvedSymbols == UnresolvedPolicy::Warn)
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warn(Msg);
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else
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error(Msg);
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}
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template <class ELFT>
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static bool shouldKeepInSymtab(InputSectionBase<ELFT> *Sec, StringRef SymName,
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const SymbolBody &B) {
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if (B.isFile())
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return false;
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// We keep sections in symtab for relocatable output.
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if (B.isSection())
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return Config->Relocatable;
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// If sym references a section in a discarded group, don't keep it.
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if (Sec == &InputSection<ELFT>::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->getSectionHdr()->sh_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<ELFT>>(&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<ELFT>>(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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}
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// Local symbols are not in the linker's symbol table. This function scans
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// each object file's symbol table to copy local symbols to the output.
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template <class ELFT> void Writer<ELFT>::copyLocalSymbols() {
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if (!Out<ELFT>::SymTab)
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return;
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for (elf::ObjectFile<ELFT> *F : Symtab<ELFT>::X->getObjectFiles()) {
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StringRef StrTab = F->getStringTable();
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for (SymbolBody *B : F->getLocalSymbols()) {
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auto *DR = dyn_cast<DefinedRegular<ELFT>>(B);
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// No reason to keep local undefined symbol in symtab.
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if (!DR)
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continue;
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if (!includeInSymtab<ELFT>(*B))
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continue;
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if (B->getNameOffset() >= StrTab.size())
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fatal(getFilename(F) + ": invalid symbol name offset");
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StringRef SymName(StrTab.data() + B->getNameOffset());
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InputSectionBase<ELFT> *Sec = DR->Section;
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if (!shouldKeepInSymtab<ELFT>(Sec, SymName, *B))
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continue;
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++Out<ELFT>::SymTab->NumLocals;
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if (Config->Relocatable)
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B->DynsymIndex = Out<ELFT>::SymTab->NumLocals;
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F->KeptLocalSyms.push_back(
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std::make_pair(DR, Out<ELFT>::SymTab->StrTabSec.addString(SymName)));
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}
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}
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}
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// PPC64 has a number of special SHT_PROGBITS+SHF_ALLOC+SHF_WRITE sections that
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// we would like to make sure appear is a specific order to maximize their
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// coverage by a single signed 16-bit offset from the TOC base pointer.
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// Conversely, the special .tocbss section should be first among all SHT_NOBITS
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// sections. This will put it next to the loaded special PPC64 sections (and,
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// thus, within reach of the TOC base pointer).
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static int getPPC64SectionRank(StringRef SectionName) {
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return StringSwitch<int>(SectionName)
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.Case(".tocbss", 0)
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.Case(".branch_lt", 2)
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.Case(".toc", 3)
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.Case(".toc1", 4)
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.Case(".opd", 5)
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.Default(1);
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}
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template <class ELFT> bool elf::isRelroSection(OutputSectionBase<ELFT> *Sec) {
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if (!Config->ZRelro)
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return false;
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typename ELFT::uint Flags = Sec->getFlags();
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if (!(Flags & SHF_ALLOC) || !(Flags & SHF_WRITE))
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return false;
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if (Flags & SHF_TLS)
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return true;
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uint32_t Type = Sec->getType();
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if (Type == SHT_INIT_ARRAY || Type == SHT_FINI_ARRAY ||
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Type == SHT_PREINIT_ARRAY)
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return true;
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if (Sec == Out<ELFT>::GotPlt)
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return Config->ZNow;
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if (Sec == Out<ELFT>::Dynamic || Sec == Out<ELFT>::Got)
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return true;
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StringRef S = Sec->getName();
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return S == ".data.rel.ro" || S == ".ctors" || S == ".dtors" || S == ".jcr" ||
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S == ".eh_frame";
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}
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template <class ELFT>
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static bool compareSectionsNonScript(OutputSectionBase<ELFT> *A,
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OutputSectionBase<ELFT> *B) {
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typedef typename ELFT::uint uintX_t;
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uintX_t AFlags = A->getFlags();
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uintX_t BFlags = B->getFlags();
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// Allocatable sections go first to reduce the total PT_LOAD size and
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// so debug info doesn't change addresses in actual code.
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bool AIsAlloc = AFlags & SHF_ALLOC;
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bool BIsAlloc = BFlags & SHF_ALLOC;
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if (AIsAlloc != BIsAlloc)
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return AIsAlloc;
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// We don't have any special requirements for the relative order of two non
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// allocatable sections.
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if (!AIsAlloc)
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return false;
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// We want the read only sections first so that they go in the PT_LOAD
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// covering the program headers at the start of the file.
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bool AIsWritable = AFlags & SHF_WRITE;
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bool BIsWritable = BFlags & SHF_WRITE;
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if (AIsWritable != BIsWritable)
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return BIsWritable;
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if (!ScriptConfig->HasSections) {
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// For a corresponding reason, put non exec sections first (the program
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// header PT_LOAD is not executable).
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// We only do that if we are not using linker scripts, since with linker
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// scripts ro and rx sections are in the same PT_LOAD, so their relative
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// order is not important.
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bool AIsExec = AFlags & SHF_EXECINSTR;
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bool BIsExec = BFlags & SHF_EXECINSTR;
|
|
if (AIsExec != BIsExec)
|
|
return BIsExec;
|
|
}
|
|
|
|
// If we got here we know that both A and B are in the same PT_LOAD.
|
|
|
|
// The TLS initialization block needs to be a single contiguous block in a R/W
|
|
// PT_LOAD, so stick TLS sections directly before R/W sections. The TLS NOBITS
|
|
// sections are placed here as they don't take up virtual address space in the
|
|
// PT_LOAD.
|
|
bool AIsTls = AFlags & SHF_TLS;
|
|
bool BIsTls = BFlags & SHF_TLS;
|
|
if (AIsTls != BIsTls)
|
|
return AIsTls;
|
|
|
|
// The next requirement we have is to put 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 AIsNoBits = A->getType() == SHT_NOBITS;
|
|
bool BIsNoBits = B->getType() == SHT_NOBITS;
|
|
if (AIsNoBits != BIsNoBits)
|
|
return BIsNoBits;
|
|
|
|
// We place RelRo section before plain r/w ones.
|
|
bool AIsRelRo = isRelroSection(A);
|
|
bool BIsRelRo = isRelroSection(B);
|
|
if (AIsRelRo != BIsRelRo)
|
|
return AIsRelRo;
|
|
|
|
// Some architectures have additional ordering restrictions for sections
|
|
// within the same PT_LOAD.
|
|
if (Config->EMachine == EM_PPC64)
|
|
return getPPC64SectionRank(A->getName()) <
|
|
getPPC64SectionRank(B->getName());
|
|
|
|
return false;
|
|
}
|
|
|
|
// Output section ordering is determined by this function.
|
|
template <class ELFT>
|
|
static bool compareSections(OutputSectionBase<ELFT> *A,
|
|
OutputSectionBase<ELFT> *B) {
|
|
// For now, put sections mentioned in a linker script first.
|
|
int AIndex = Script<ELFT>::X->getSectionIndex(A->getName());
|
|
int BIndex = Script<ELFT>::X->getSectionIndex(B->getName());
|
|
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(A, B);
|
|
}
|
|
|
|
template <class ELFT> static bool isDiscarded(InputSectionBase<ELFT> *S) {
|
|
return !S || S == &InputSection<ELFT>::Discarded || !S->Live;
|
|
}
|
|
|
|
// Program header entry
|
|
template<class ELFT>
|
|
PhdrEntry<ELFT>::PhdrEntry(unsigned Type, unsigned Flags) {
|
|
H.p_type = Type;
|
|
H.p_flags = Flags;
|
|
}
|
|
|
|
template<class ELFT>
|
|
void PhdrEntry<ELFT>::add(OutputSectionBase<ELFT> *Sec) {
|
|
Last = Sec;
|
|
if (!First)
|
|
First = Sec;
|
|
H.p_align = std::max<typename ELFT::uint>(H.p_align, Sec->getAlignment());
|
|
if (H.p_type == PT_LOAD)
|
|
Sec->FirstInPtLoad = First;
|
|
}
|
|
|
|
template <class ELFT>
|
|
static Symbol *addOptionalSynthetic(StringRef Name,
|
|
OutputSectionBase<ELFT> *Sec,
|
|
typename ELFT::uint Val) {
|
|
SymbolBody *S = Symtab<ELFT>::X->find(Name);
|
|
if (!S)
|
|
return nullptr;
|
|
if (!S->isUndefined() && !S->isShared())
|
|
return S->symbol();
|
|
return Symtab<ELFT>::X->addSynthetic(Name, Sec, Val, STV_HIDDEN);
|
|
}
|
|
|
|
template <class ELFT>
|
|
static void addSynthetic(StringRef Name, OutputSectionBase<ELFT> *Sec,
|
|
typename ELFT::uint Val) {
|
|
SymbolBody *S = Symtab<ELFT>::X->find(Name);
|
|
if (!S || S->isUndefined() || S->isShared())
|
|
Symtab<ELFT>::X->addSynthetic(Name, Sec, Val, STV_HIDDEN);
|
|
}
|
|
|
|
// 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 (Out<ELFT>::DynSymTab || !Out<ELFT>::RelaPlt)
|
|
return;
|
|
StringRef S = Config->Rela ? "__rela_iplt_start" : "__rel_iplt_start";
|
|
addOptionalSynthetic(S, Out<ELFT>::RelaPlt, 0);
|
|
|
|
S = Config->Rela ? "__rela_iplt_end" : "__rel_iplt_end";
|
|
addOptionalSynthetic(S, Out<ELFT>::RelaPlt,
|
|
DefinedSynthetic<ELFT>::SectionEnd);
|
|
}
|
|
|
|
// 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 && !Config->Relocatable) {
|
|
// Define _gp for MIPS. st_value of _gp symbol will be updated by Writer
|
|
// so that it points to an absolute address which is relative to GOT.
|
|
// See "Global Data Symbols" in Chapter 6 in the following document:
|
|
// ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
|
|
Symtab<ELFT>::X->addSynthetic("_gp", Out<ELFT>::Got, MipsGPOffset,
|
|
STV_HIDDEN);
|
|
|
|
// On MIPS O32 ABI, _gp_disp is a magic symbol designates offset between
|
|
// start of function and 'gp' pointer into GOT.
|
|
Symbol *Sym =
|
|
addOptionalSynthetic("_gp_disp", Out<ELFT>::Got, MipsGPOffset);
|
|
if (Sym)
|
|
ElfSym<ELFT>::MipsGpDisp = Sym->body();
|
|
|
|
// 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
|
|
addOptionalSynthetic("__gnu_local_gp", Out<ELFT>::Got, MipsGPOffset);
|
|
}
|
|
|
|
// 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.
|
|
if (!Config->Relocatable)
|
|
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 as special case is MIPS -
|
|
// MIPS libc defines __tls_get_addr itself because there are no TLS
|
|
// optimizations for this target.
|
|
if (!Out<ELFT>::DynSymTab && Config->EMachine != EM_MIPS)
|
|
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;
|
|
|
|
ElfSym<ELFT>::EhdrStart = Symtab<ELFT>::X->addIgnored("__ehdr_start");
|
|
|
|
auto Define = [this](StringRef S, DefinedRegular<ELFT> *&Sym1,
|
|
DefinedRegular<ELFT> *&Sym2) {
|
|
Sym1 = Symtab<ELFT>::X->addIgnored(S, STV_DEFAULT);
|
|
|
|
// The name without the underscore is not a reserved name,
|
|
// so it is defined only when there is a reference against it.
|
|
assert(S.startswith("_"));
|
|
S = S.substr(1);
|
|
if (SymbolBody *B = Symtab<ELFT>::X->find(S))
|
|
if (B->isUndefined())
|
|
Sym2 = Symtab<ELFT>::X->addAbsolute(S, STV_DEFAULT);
|
|
};
|
|
|
|
Define("_end", ElfSym<ELFT>::End, ElfSym<ELFT>::End2);
|
|
Define("_etext", ElfSym<ELFT>::Etext, ElfSym<ELFT>::Etext2);
|
|
Define("_edata", ElfSym<ELFT>::Edata, ElfSym<ELFT>::Edata2);
|
|
}
|
|
|
|
// Sort input sections by section name suffixes for
|
|
// __attribute__((init_priority(N))).
|
|
template <class ELFT> static void sortInitFini(OutputSectionBase<ELFT> *S) {
|
|
if (S)
|
|
reinterpret_cast<OutputSection<ELFT> *>(S)->sortInitFini();
|
|
}
|
|
|
|
// Sort input sections by the special rule for .ctors and .dtors.
|
|
template <class ELFT> static void sortCtorsDtors(OutputSectionBase<ELFT> *S) {
|
|
if (S)
|
|
reinterpret_cast<OutputSection<ELFT> *>(S)->sortCtorsDtors();
|
|
}
|
|
|
|
template <class ELFT>
|
|
void Writer<ELFT>::forEachRelSec(
|
|
std::function<void(InputSectionBase<ELFT> &, const typename ELFT::Shdr &)>
|
|
Fn) {
|
|
for (elf::ObjectFile<ELFT> *F : Symtab<ELFT>::X->getObjectFiles()) {
|
|
for (InputSectionBase<ELFT> *IS : F->getSections()) {
|
|
if (isDiscarded(IS))
|
|
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->getSectionHdr()->sh_flags & SHF_ALLOC))
|
|
continue;
|
|
if (auto *S = dyn_cast<InputSection<ELFT>>(IS)) {
|
|
for (const Elf_Shdr *RelSec : S->RelocSections)
|
|
Fn(*S, *RelSec);
|
|
continue;
|
|
}
|
|
if (auto *S = dyn_cast<EhInputSection<ELFT>>(IS))
|
|
if (S->RelocSection)
|
|
Fn(*S, *S->RelocSection);
|
|
}
|
|
}
|
|
}
|
|
|
|
template <class ELFT> void Writer<ELFT>::createSections() {
|
|
for (elf::ObjectFile<ELFT> *F : Symtab<ELFT>::X->getObjectFiles()) {
|
|
for (InputSectionBase<ELFT> *IS : F->getSections()) {
|
|
if (isDiscarded(IS)) {
|
|
reportDiscarded(IS);
|
|
continue;
|
|
}
|
|
OutputSectionBase<ELFT> *Sec;
|
|
bool IsNew;
|
|
std::tie(Sec, IsNew) = Factory.create(IS, getOutputSectionName(IS));
|
|
if (IsNew)
|
|
OutputSections.push_back(Sec);
|
|
Sec->addSection(IS);
|
|
}
|
|
}
|
|
|
|
sortInitFini(findSection(".init_array"));
|
|
sortInitFini(findSection(".fini_array"));
|
|
sortCtorsDtors(findSection(".ctors"));
|
|
sortCtorsDtors(findSection(".dtors"));
|
|
|
|
for (OutputSectionBase<ELFT> *Sec : OutputSections)
|
|
Sec->assignOffsets();
|
|
}
|
|
|
|
template <class ELFT> void Writer<ELFT>::sortSections() {
|
|
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 the first position where it
|
|
// compareSectionsNonScript less than the successor.
|
|
|
|
std::stable_sort(OutputSections.begin(), OutputSections.end(),
|
|
compareSections<ELFT>);
|
|
|
|
auto I = OutputSections.begin();
|
|
auto E = OutputSections.end();
|
|
auto NonScriptI = std::find_if(I, E, [](OutputSectionBase<ELFT> *S) {
|
|
return Script<ELFT>::X->getSectionIndex(S->getName()) == INT_MAX;
|
|
});
|
|
while (NonScriptI != E) {
|
|
auto FirstGreater =
|
|
std::find_if(I, NonScriptI, [&](OutputSectionBase<ELFT> *S) {
|
|
return compareSectionsNonScript<ELFT>(*NonScriptI, S);
|
|
});
|
|
std::rotate(FirstGreater, NonScriptI, NonScriptI + 1);
|
|
++NonScriptI;
|
|
++I;
|
|
}
|
|
}
|
|
|
|
// Create output section objects and add them to OutputSections.
|
|
template <class ELFT> void Writer<ELFT>::finalizeSections() {
|
|
Out<ELFT>::PreinitArray = findSection(".preinit_array");
|
|
Out<ELFT>::InitArray = findSection(".init_array");
|
|
Out<ELFT>::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 (OutputSectionBase<ELFT> *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 (Out<ELFT>::DynSymTab)
|
|
Symtab<ELFT>::X->addSynthetic("_DYNAMIC", Out<ELFT>::Dynamic, 0,
|
|
STV_HIDDEN);
|
|
|
|
// Define __rel[a]_iplt_{start,end} symbols if needed.
|
|
addRelIpltSymbols();
|
|
|
|
if (!Out<ELFT>::EhFrame->empty()) {
|
|
OutputSections.push_back(Out<ELFT>::EhFrame);
|
|
Out<ELFT>::EhFrame->finalize();
|
|
}
|
|
|
|
// 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>);
|
|
|
|
// Now that we have defined all possible symbols including linker-
|
|
// synthesized ones. Visit all symbols to give the finishing touches.
|
|
for (Symbol *S : Symtab<ELFT>::X->getSymbols()) {
|
|
SymbolBody *Body = S->body();
|
|
|
|
// We only report undefined symbols in regular objects. This means that we
|
|
// will accept an undefined reference in bitcode if it can be optimized out.
|
|
if (S->IsUsedInRegularObj && Body->isUndefined() && !S->isWeak())
|
|
reportUndefined<ELFT>(Body);
|
|
|
|
if (!includeInSymtab<ELFT>(*Body))
|
|
continue;
|
|
if (Out<ELFT>::SymTab)
|
|
Out<ELFT>::SymTab->addSymbol(Body);
|
|
|
|
if (Out<ELFT>::DynSymTab && S->includeInDynsym()) {
|
|
Out<ELFT>::DynSymTab->addSymbol(Body);
|
|
if (auto *SS = dyn_cast<SharedSymbol<ELFT>>(Body))
|
|
if (SS->file()->isNeeded())
|
|
Out<ELFT>::VerNeed->addSymbol(SS);
|
|
}
|
|
}
|
|
|
|
// Do not proceed if there was an undefined symbol.
|
|
if (HasError)
|
|
return;
|
|
|
|
// If linker script processor hasn't added common symbol section yet,
|
|
// then add it to .bss now.
|
|
if (!CommonInputSection<ELFT>::X->OutSec) {
|
|
Out<ELFT>::Bss->addSection(CommonInputSection<ELFT>::X);
|
|
Out<ELFT>::Bss->assignOffsets();
|
|
}
|
|
|
|
// So far we have added sections from input object files.
|
|
// This function adds linker-created Out<ELFT>::* sections.
|
|
addPredefinedSections();
|
|
|
|
sortSections();
|
|
|
|
unsigned I = 1;
|
|
for (OutputSectionBase<ELFT> *Sec : OutputSections) {
|
|
Sec->SectionIndex = I++;
|
|
Sec->setSHName(Out<ELFT>::ShStrTab->addString(Sec->getName()));
|
|
}
|
|
|
|
// Finalizers fix each section's size.
|
|
// .dynsym is finalized early since that may fill up .gnu.hash.
|
|
if (Out<ELFT>::DynSymTab)
|
|
Out<ELFT>::DynSymTab->finalize();
|
|
|
|
// Fill other section headers. The dynamic table is finalized
|
|
// at the end because some tags like RELSZ depend on result
|
|
// of finalizing other sections. The dynamic string table is
|
|
// finalized once the .dynamic finalizer has added a few last
|
|
// strings. See DynamicSection::finalize()
|
|
for (OutputSectionBase<ELFT> *Sec : OutputSections)
|
|
if (Sec != Out<ELFT>::DynStrTab && Sec != Out<ELFT>::Dynamic)
|
|
Sec->finalize();
|
|
|
|
if (Out<ELFT>::DynSymTab)
|
|
Out<ELFT>::Dynamic->finalize();
|
|
|
|
// Now that all output offsets are fixed. Finalize mergeable sections
|
|
// to fix their maps from input offsets to output offsets.
|
|
for (OutputSectionBase<ELFT> *Sec : OutputSections)
|
|
Sec->finalizePieces();
|
|
}
|
|
|
|
template <class ELFT> bool Writer<ELFT>::needsGot() {
|
|
if (!Out<ELFT>::Got->empty())
|
|
return true;
|
|
|
|
// We add the .got section to the result for dynamic MIPS target because
|
|
// its address and properties are mentioned in the .dynamic section.
|
|
if (Config->EMachine == EM_MIPS && !Config->Relocatable)
|
|
return true;
|
|
|
|
// If we have a relocation that is relative to GOT (such as GOTOFFREL),
|
|
// we need to emit a GOT even if it's empty.
|
|
return Out<ELFT>::Got->HasGotOffRel;
|
|
}
|
|
|
|
// This function add Out<ELFT>::* sections to OutputSections.
|
|
template <class ELFT> void Writer<ELFT>::addPredefinedSections() {
|
|
auto Add = [&](OutputSectionBase<ELFT> *OS) {
|
|
if (OS)
|
|
OutputSections.push_back(OS);
|
|
};
|
|
|
|
// A core file does not usually contain unmodified segments except
|
|
// the first page of the executable. Add the build ID section to beginning of
|
|
// the file so that the section is included in the first page.
|
|
if (Out<ELFT>::BuildId)
|
|
OutputSections.insert(OutputSections.begin(), Out<ELFT>::BuildId);
|
|
|
|
// Add .interp at first because some loaders want to see that section
|
|
// on the first page of the executable file when loaded into memory.
|
|
if (Out<ELFT>::Interp)
|
|
OutputSections.insert(OutputSections.begin(), Out<ELFT>::Interp);
|
|
|
|
// This order is not the same as the final output order
|
|
// because we sort the sections using their attributes below.
|
|
Add(Out<ELFT>::SymTab);
|
|
Add(Out<ELFT>::ShStrTab);
|
|
Add(Out<ELFT>::StrTab);
|
|
if (Out<ELFT>::DynSymTab) {
|
|
Add(Out<ELFT>::DynSymTab);
|
|
|
|
bool HasVerNeed = Out<ELFT>::VerNeed->getNeedNum() != 0;
|
|
if (Out<ELFT>::VerDef || HasVerNeed)
|
|
Add(Out<ELFT>::VerSym);
|
|
Add(Out<ELFT>::VerDef);
|
|
if (HasVerNeed)
|
|
Add(Out<ELFT>::VerNeed);
|
|
|
|
Add(Out<ELFT>::GnuHashTab);
|
|
Add(Out<ELFT>::HashTab);
|
|
Add(Out<ELFT>::Dynamic);
|
|
Add(Out<ELFT>::DynStrTab);
|
|
if (Out<ELFT>::RelaDyn->hasRelocs())
|
|
Add(Out<ELFT>::RelaDyn);
|
|
Add(Out<ELFT>::MipsRldMap);
|
|
}
|
|
|
|
// We always need to add rel[a].plt to output if it has entries.
|
|
// Even during static linking it can contain R_[*]_IRELATIVE relocations.
|
|
if (Out<ELFT>::RelaPlt && Out<ELFT>::RelaPlt->hasRelocs())
|
|
Add(Out<ELFT>::RelaPlt);
|
|
|
|
if (needsGot())
|
|
Add(Out<ELFT>::Got);
|
|
if (Out<ELFT>::GotPlt && !Out<ELFT>::GotPlt->empty())
|
|
Add(Out<ELFT>::GotPlt);
|
|
if (!Out<ELFT>::Plt->empty())
|
|
Add(Out<ELFT>::Plt);
|
|
if (!Out<ELFT>::EhFrame->empty())
|
|
Add(Out<ELFT>::EhFrameHdr);
|
|
if (Out<ELFT>::Bss->getSize() > 0)
|
|
Add(Out<ELFT>::Bss);
|
|
}
|
|
|
|
// 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,
|
|
OutputSectionBase<ELFT> *OS) {
|
|
if (OS) {
|
|
addSynthetic(Start, OS, 0);
|
|
addSynthetic(End, OS, DefinedSynthetic<ELFT>::SectionEnd);
|
|
} else {
|
|
addOptionalSynthetic(Start, (OutputSectionBase<ELFT> *)nullptr, 0);
|
|
addOptionalSynthetic(End, (OutputSectionBase<ELFT> *)nullptr, 0);
|
|
}
|
|
};
|
|
|
|
Define("__preinit_array_start", "__preinit_array_end",
|
|
Out<ELFT>::PreinitArray);
|
|
Define("__init_array_start", "__init_array_end", Out<ELFT>::InitArray);
|
|
Define("__fini_array_start", "__fini_array_end", Out<ELFT>::FiniArray);
|
|
}
|
|
|
|
// 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(OutputSectionBase<ELFT> *Sec) {
|
|
StringRef S = Sec->getName();
|
|
if (!isValidCIdentifier(S))
|
|
return;
|
|
StringSaver Saver(Alloc);
|
|
StringRef Start = Saver.save("__start_" + S);
|
|
StringRef Stop = Saver.save("__stop_" + S);
|
|
if (SymbolBody *B = Symtab<ELFT>::X->find(Start))
|
|
if (B->isUndefined())
|
|
Symtab<ELFT>::X->addSynthetic(Start, Sec, 0, B->getVisibility());
|
|
if (SymbolBody *B = Symtab<ELFT>::X->find(Stop))
|
|
if (B->isUndefined())
|
|
Symtab<ELFT>::X->addSynthetic(
|
|
Stop, Sec, DefinedSynthetic<ELFT>::SectionEnd, B->getVisibility());
|
|
}
|
|
|
|
template <class ELFT>
|
|
OutputSectionBase<ELFT> *Writer<ELFT>::findSection(StringRef Name) {
|
|
for (OutputSectionBase<ELFT> *Sec : OutputSections)
|
|
if (Sec->getName() == Name)
|
|
return Sec;
|
|
return nullptr;
|
|
}
|
|
|
|
template <class ELFT> static bool needsPtLoad(OutputSectionBase<ELFT> *Sec) {
|
|
if (!(Sec->getFlags() & 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->getFlags() & SHF_TLS && Sec->getType() == 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 (ScriptConfig->HasSections && !(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<ELFT>> Writer<ELFT>::createPhdrs() {
|
|
std::vector<Phdr> Ret;
|
|
|
|
auto AddHdr = [&](unsigned Type, unsigned Flags) -> Phdr * {
|
|
Ret.emplace_back(Type, Flags);
|
|
return &Ret.back();
|
|
};
|
|
|
|
// The first phdr entry is PT_PHDR which describes the program header itself.
|
|
Phdr &Hdr = *AddHdr(PT_PHDR, PF_R);
|
|
Hdr.add(Out<ELFT>::ProgramHeaders);
|
|
|
|
// PT_INTERP must be the second entry if exists.
|
|
if (Out<ELFT>::Interp) {
|
|
Phdr &Hdr = *AddHdr(PT_INTERP, Out<ELFT>::Interp->getPhdrFlags());
|
|
Hdr.add(Out<ELFT>::Interp);
|
|
}
|
|
|
|
// Add the first PT_LOAD segment for regular output sections.
|
|
uintX_t Flags = computeFlags<ELFT>(PF_R);
|
|
Phdr *Load = AddHdr(PT_LOAD, Flags);
|
|
if (!ScriptConfig->HasSections) {
|
|
Load->add(Out<ELFT>::ElfHeader);
|
|
Load->add(Out<ELFT>::ProgramHeaders);
|
|
}
|
|
|
|
Phdr TlsHdr(PT_TLS, PF_R);
|
|
Phdr RelRo(PT_GNU_RELRO, PF_R);
|
|
Phdr Note(PT_NOTE, PF_R);
|
|
for (OutputSectionBase<ELFT> *Sec : OutputSections) {
|
|
if (!(Sec->getFlags() & SHF_ALLOC))
|
|
break;
|
|
|
|
// If we meet TLS section then we create TLS header
|
|
// and put all TLS sections inside for further use when
|
|
// assign addresses.
|
|
if (Sec->getFlags() & SHF_TLS)
|
|
TlsHdr.add(Sec);
|
|
|
|
if (!needsPtLoad(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->getLma(Sec->getName()) || Flags != NewFlags) {
|
|
Load = AddHdr(PT_LOAD, NewFlags);
|
|
Flags = NewFlags;
|
|
}
|
|
|
|
Load->add(Sec);
|
|
|
|
if (isRelroSection(Sec))
|
|
RelRo.add(Sec);
|
|
if (Sec->getType() == SHT_NOTE)
|
|
Note.add(Sec);
|
|
}
|
|
|
|
// Add the TLS segment unless it's empty.
|
|
if (TlsHdr.First)
|
|
Ret.push_back(std::move(TlsHdr));
|
|
|
|
// Add an entry for .dynamic.
|
|
if (Out<ELFT>::DynSymTab) {
|
|
Phdr &H = *AddHdr(PT_DYNAMIC, Out<ELFT>::Dynamic->getPhdrFlags());
|
|
H.add(Out<ELFT>::Dynamic);
|
|
}
|
|
|
|
// PT_GNU_RELRO includes all sections that should be marked as
|
|
// read-only by dynamic linker after proccessing relocations.
|
|
if (RelRo.First)
|
|
Ret.push_back(std::move(RelRo));
|
|
|
|
// PT_GNU_EH_FRAME is a special section pointing on .eh_frame_hdr.
|
|
if (!Out<ELFT>::EhFrame->empty() && Out<ELFT>::EhFrameHdr) {
|
|
Phdr &Hdr = *AddHdr(PT_GNU_EH_FRAME, Out<ELFT>::EhFrameHdr->getPhdrFlags());
|
|
Hdr.add(Out<ELFT>::EhFrameHdr);
|
|
}
|
|
|
|
// PT_GNU_STACK is a special section to tell the loader to make the
|
|
// pages for the stack non-executable.
|
|
if (!Config->ZExecStack) {
|
|
Phdr &Hdr = *AddHdr(PT_GNU_STACK, PF_R | PF_W);
|
|
if (Config->ZStackSize != uint64_t(-1))
|
|
Hdr.H.p_memsz = Config->ZStackSize;
|
|
}
|
|
|
|
if (Note.First)
|
|
Ret.push_back(std::move(Note));
|
|
return Ret;
|
|
}
|
|
|
|
// The first section of each PT_LOAD 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 Phdr &P : Phdrs)
|
|
if (P.H.p_type == PT_LOAD)
|
|
P.First->PageAlign = true;
|
|
|
|
for (const Phdr &P : Phdrs) {
|
|
if (P.H.p_type != PT_GNU_RELRO)
|
|
continue;
|
|
// 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;
|
|
OutputSectionBase<ELFT> *Sec = *(I + 1);
|
|
if (needsPtLoad(Sec))
|
|
Sec->PageAlign = 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() {
|
|
uintX_t BaseVA = ScriptConfig->HasSections ? 0 : Config->ImageBase;
|
|
Out<ELFT>::ElfHeader->setVA(BaseVA);
|
|
uintX_t Off = Out<ELFT>::ElfHeader->getSize();
|
|
Out<ELFT>::ProgramHeaders->setVA(Off + BaseVA);
|
|
Out<ELFT>::ProgramHeaders->setSize(sizeof(Elf_Phdr) * Phdrs.size());
|
|
}
|
|
|
|
// Assign VAs (addresses at run-time) to output sections.
|
|
template <class ELFT> void Writer<ELFT>::assignAddresses() {
|
|
uintX_t VA = Config->ImageBase + getHeaderSize<ELFT>();
|
|
uintX_t ThreadBssOffset = 0;
|
|
for (OutputSectionBase<ELFT> *Sec : OutputSections) {
|
|
uintX_t Alignment = Sec->getAlignment();
|
|
if (Sec->PageAlign)
|
|
Alignment = std::max<uintX_t>(Alignment, Config->MaxPageSize);
|
|
|
|
auto I = Config->SectionStartMap.find(Sec->getName());
|
|
if (I != Config->SectionStartMap.end())
|
|
VA = I->second;
|
|
|
|
// We only assign VAs to allocated sections.
|
|
if (needsPtLoad(Sec)) {
|
|
VA = alignTo(VA, Alignment);
|
|
Sec->setVA(VA);
|
|
VA += Sec->getSize();
|
|
} else if (Sec->getFlags() & SHF_TLS && Sec->getType() == SHT_NOBITS) {
|
|
uintX_t TVA = VA + ThreadBssOffset;
|
|
TVA = alignTo(TVA, Alignment);
|
|
Sec->setVA(TVA);
|
|
ThreadBssOffset = TVA - VA + Sec->getSize();
|
|
}
|
|
}
|
|
}
|
|
|
|
// 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, OutputSectionBase<ELFT> *Sec) {
|
|
uintX_t Alignment = Sec->getAlignment();
|
|
if (Sec->PageAlign)
|
|
Alignment = std::max<uintX_t>(Alignment, Config->MaxPageSize);
|
|
Off = alignTo(Off, Alignment);
|
|
|
|
OutputSectionBase<ELFT> *First = Sec->FirstInPtLoad;
|
|
// If the section is not in a PT_LOAD, we have no other constraint.
|
|
if (!First)
|
|
return Off;
|
|
|
|
// If two sections share the same PT_LOAD the file offset is calculated using
|
|
// this formula: Off2 = Off1 + (VA2 - VA1).
|
|
if (Sec == First)
|
|
return alignTo(Off, Target->MaxPageSize, Sec->getVA());
|
|
return First->getFileOffset() + Sec->getVA() - First->getVA();
|
|
}
|
|
|
|
template <class ELFT, class uintX_t>
|
|
void setOffset(OutputSectionBase<ELFT> *Sec, uintX_t &Off) {
|
|
if (Sec->getType() == SHT_NOBITS) {
|
|
Sec->setFileOffset(Off);
|
|
return;
|
|
}
|
|
|
|
Off = getFileAlignment<ELFT>(Off, Sec);
|
|
Sec->setFileOffset(Off);
|
|
Off += Sec->getSize();
|
|
}
|
|
|
|
template <class ELFT> void Writer<ELFT>::assignFileOffsetsBinary() {
|
|
uintX_t Off = 0;
|
|
for (OutputSectionBase<ELFT> *Sec : OutputSections)
|
|
if (Sec->getFlags() & SHF_ALLOC)
|
|
setOffset(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;
|
|
setOffset(Out<ELFT>::ElfHeader, Off);
|
|
setOffset(Out<ELFT>::ProgramHeaders, Off);
|
|
|
|
for (OutputSectionBase<ELFT> *Sec : OutputSections)
|
|
setOffset(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 (Phdr &P : Phdrs) {
|
|
Elf_Phdr &H = P.H;
|
|
OutputSectionBase<ELFT> *First = P.First;
|
|
OutputSectionBase<ELFT> *Last = P.Last;
|
|
if (First) {
|
|
H.p_filesz = Last->getFileOff() - First->getFileOff();
|
|
if (Last->getType() != SHT_NOBITS)
|
|
H.p_filesz += Last->getSize();
|
|
H.p_memsz = Last->getVA() + Last->getSize() - First->getVA();
|
|
H.p_offset = First->getFileOff();
|
|
H.p_vaddr = First->getVA();
|
|
}
|
|
if (H.p_type == PT_LOAD)
|
|
H.p_align = Config->MaxPageSize;
|
|
else if (H.p_type == PT_GNU_RELRO)
|
|
H.p_align = 1;
|
|
|
|
if (!P.HasLMA) {
|
|
// The p_paddr field can be set using linker script AT command.
|
|
// By default, it is the same value as p_vaddr.
|
|
H.p_paddr = H.p_vaddr;
|
|
if (H.p_type == PT_LOAD && First)
|
|
if (Expr LmaExpr = Script<ELFT>::X->getLma(First->getName()))
|
|
H.p_paddr = LmaExpr(H.p_vaddr);
|
|
}
|
|
|
|
// 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 (H.p_type == PT_TLS) {
|
|
Out<ELFT>::TlsPhdr = &H;
|
|
if (H.p_memsz)
|
|
H.p_memsz = alignTo(H.p_memsz, H.p_align);
|
|
}
|
|
}
|
|
}
|
|
|
|
template <class ELFT> static typename ELFT::uint getEntryAddr() {
|
|
if (Symbol *S = Config->EntrySym)
|
|
return S->body()->getVA<ELFT>();
|
|
return Config->EntryAddr;
|
|
}
|
|
|
|
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 absolute
|
|
// symbol values that depend on section address and size.
|
|
template <class ELFT> void Writer<ELFT>::fixAbsoluteSymbols() {
|
|
// __ehdr_start is the location of program headers.
|
|
if (ElfSym<ELFT>::EhdrStart)
|
|
ElfSym<ELFT>::EhdrStart->Value = Out<ELFT>::ProgramHeaders->getVA();
|
|
|
|
auto Set = [](DefinedRegular<ELFT> *S1, DefinedRegular<ELFT> *S2, uintX_t V) {
|
|
if (S1)
|
|
S1->Value = V;
|
|
if (S2)
|
|
S2->Value = V;
|
|
};
|
|
|
|
// _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.
|
|
for (Phdr &P : Phdrs) {
|
|
Elf_Phdr &H = P.H;
|
|
if (H.p_type != PT_LOAD)
|
|
continue;
|
|
Set(ElfSym<ELFT>::End, ElfSym<ELFT>::End2, H.p_vaddr + H.p_memsz);
|
|
|
|
uintX_t Val = H.p_vaddr + H.p_filesz;
|
|
if (H.p_flags & PF_W)
|
|
Set(ElfSym<ELFT>::Edata, ElfSym<ELFT>::Edata2, Val);
|
|
else
|
|
Set(ElfSym<ELFT>::Etext, ElfSym<ELFT>::Etext2, Val);
|
|
}
|
|
}
|
|
|
|
template <class ELFT> void Writer<ELFT>::writeHeader() {
|
|
uint8_t *Buf = Buffer->getBufferStart();
|
|
memcpy(Buf, "\177ELF", 4);
|
|
|
|
auto &FirstObj = cast<ELFFileBase<ELFT>>(*Config->FirstElf);
|
|
|
|
// 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] = FirstObj.getOSABI();
|
|
EHdr->e_type = getELFType();
|
|
EHdr->e_machine = FirstObj.EMachine;
|
|
EHdr->e_version = EV_CURRENT;
|
|
EHdr->e_entry = getEntryAddr<ELFT>();
|
|
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 = Out<ELFT>::ShStrTab->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 (Phdr &P : Phdrs)
|
|
*HBuf++ = P.H;
|
|
|
|
// Write the section header table. Note that the first table entry is null.
|
|
auto *SHdrs = reinterpret_cast<Elf_Shdr *>(Buf + EHdr->e_shoff);
|
|
for (OutputSectionBase<ELFT> *Sec : OutputSections)
|
|
Sec->writeHeaderTo(++SHdrs);
|
|
}
|
|
|
|
template <class ELFT> void Writer<ELFT>::openFile() {
|
|
ErrorOr<std::unique_ptr<FileOutputBuffer>> BufferOrErr =
|
|
FileOutputBuffer::create(Config->OutputFile, FileSize,
|
|
FileOutputBuffer::F_executable);
|
|
if (auto EC = BufferOrErr.getError())
|
|
error(EC, "failed to open " + Config->OutputFile);
|
|
else
|
|
Buffer = std::move(*BufferOrErr);
|
|
}
|
|
|
|
template <class ELFT> void Writer<ELFT>::writeSectionsBinary() {
|
|
uint8_t *Buf = Buffer->getBufferStart();
|
|
for (OutputSectionBase<ELFT> *Sec : OutputSections)
|
|
if (Sec->getFlags() & SHF_ALLOC)
|
|
Sec->writeTo(Buf + Sec->getFileOff());
|
|
}
|
|
|
|
// 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<ELFT>::Opd = findSection(".opd");
|
|
if (Out<ELFT>::Opd) {
|
|
Out<ELFT>::OpdBuf = Buf + Out<ELFT>::Opd->getFileOff();
|
|
Out<ELFT>::Opd->writeTo(Buf + Out<ELFT>::Opd->getFileOff());
|
|
}
|
|
|
|
for (OutputSectionBase<ELFT> *Sec : OutputSections)
|
|
if (Sec != Out<ELFT>::Opd && Sec != Out<ELFT>::EhFrameHdr)
|
|
Sec->writeTo(Buf + Sec->getFileOff());
|
|
|
|
// The .eh_frame_hdr depends on .eh_frame section contents, therefore
|
|
// it should be written after .eh_frame is written.
|
|
if (!Out<ELFT>::EhFrame->empty() && Out<ELFT>::EhFrameHdr)
|
|
Out<ELFT>::EhFrameHdr->writeTo(Buf + Out<ELFT>::EhFrameHdr->getFileOff());
|
|
}
|
|
|
|
template <class ELFT> void Writer<ELFT>::writeBuildId() {
|
|
if (!Out<ELFT>::BuildId)
|
|
return;
|
|
|
|
// Compute a hash of all sections of the output file.
|
|
uint8_t *Start = Buffer->getBufferStart();
|
|
uint8_t *End = Start + FileSize;
|
|
Out<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 struct elf::PhdrEntry<ELF32LE>;
|
|
template struct elf::PhdrEntry<ELF32BE>;
|
|
template struct elf::PhdrEntry<ELF64LE>;
|
|
template struct elf::PhdrEntry<ELF64BE>;
|
|
|
|
template bool elf::isRelroSection<ELF32LE>(OutputSectionBase<ELF32LE> *);
|
|
template bool elf::isRelroSection<ELF32BE>(OutputSectionBase<ELF32BE> *);
|
|
template bool elf::isRelroSection<ELF64LE>(OutputSectionBase<ELF64LE> *);
|
|
template bool elf::isRelroSection<ELF64BE>(OutputSectionBase<ELF64BE> *);
|
|
|
|
template StringRef elf::getOutputSectionName<ELF32LE>(InputSectionBase<ELF32LE> *);
|
|
template StringRef elf::getOutputSectionName<ELF32BE>(InputSectionBase<ELF32BE> *);
|
|
template StringRef elf::getOutputSectionName<ELF64LE>(InputSectionBase<ELF64LE> *);
|
|
template StringRef elf::getOutputSectionName<ELF64BE>(InputSectionBase<ELF64BE> *);
|
|
|
|
template void elf::reportDiscarded<ELF32LE>(InputSectionBase<ELF32LE> *);
|
|
template void elf::reportDiscarded<ELF32BE>(InputSectionBase<ELF32BE> *);
|
|
template void elf::reportDiscarded<ELF64LE>(InputSectionBase<ELF64LE> *);
|
|
template void elf::reportDiscarded<ELF64BE>(InputSectionBase<ELF64BE> *);
|