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llvm-project/lld/ELF/Writer.cpp

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//===- Writer.cpp ---------------------------------------------------------===//
//
// The LLVM Linker
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#include "Writer.h"
#include "Config.h"
#include "OutputSections.h"
#include "SymbolTable.h"
#include "Target.h"
#include "llvm/ADT/StringMap.h"
#include "llvm/ADT/StringSwitch.h"
#include "llvm/Support/FileOutputBuffer.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Support/StringSaver.h"
using namespace llvm;
using namespace llvm::ELF;
using namespace llvm::object;
using namespace lld;
using namespace lld::elf2;
namespace {
// The writer writes a SymbolTable result to a file.
template <class ELFT> class Writer {
public:
typedef typename ELFFile<ELFT>::uintX_t uintX_t;
typedef typename ELFFile<ELFT>::Elf_Shdr Elf_Shdr;
typedef typename ELFFile<ELFT>::Elf_Ehdr Elf_Ehdr;
typedef typename ELFFile<ELFT>::Elf_Phdr Elf_Phdr;
typedef typename ELFFile<ELFT>::Elf_Sym Elf_Sym;
typedef typename ELFFile<ELFT>::Elf_Sym_Range Elf_Sym_Range;
typedef typename ELFFile<ELFT>::Elf_Rela Elf_Rela;
Writer(SymbolTable<ELFT> &S) : Symtab(S) {}
void run();
private:
void copyLocalSymbols();
void addReservedSymbols();
bool createSections();
void addPredefinedSections();
template <bool isRela>
void scanRelocs(InputSectionBase<ELFT> &C,
iterator_range<const Elf_Rel_Impl<ELFT, isRela> *> Rels);
void scanRelocs(InputSection<ELFT> &C);
void scanRelocs(InputSectionBase<ELFT> &S, const Elf_Shdr &RelSec);
void updateRelro(Elf_Phdr *Cur, Elf_Phdr *GnuRelroPhdr, uintX_t VA);
void assignAddresses();
void buildSectionMap();
void fixAbsoluteSymbols();
void openFile(StringRef OutputPath);
void writeHeader();
void writeSections();
bool isDiscarded(InputSectionBase<ELFT> *IS) const;
StringRef getOutputSectionName(StringRef S) const;
bool needsInterpSection() const {
return !Symtab.getSharedFiles().empty() && !Config->DynamicLinker.empty();
}
bool isOutputDynamic() const {
return !Symtab.getSharedFiles().empty() || Config->Shared;
}
int getPhdrsNum() const;
OutputSection<ELFT> *getBss();
void addCommonSymbols(std::vector<DefinedCommon *> &Syms);
void addCopyRelSymbols(std::vector<SharedSymbol<ELFT> *> &Syms);
std::unique_ptr<llvm::FileOutputBuffer> Buffer;
BumpPtrAllocator Alloc;
std::vector<OutputSectionBase<ELFT> *> OutputSections;
std::vector<std::unique_ptr<OutputSectionBase<ELFT>>> OwningSections;
unsigned getNumSections() const { return OutputSections.size() + 1; }
void addRelIpltSymbols();
void addStartEndSymbols();
void addStartStopSymbols(OutputSectionBase<ELFT> *Sec);
void setPhdr(Elf_Phdr *PH, uint32_t Type, uint32_t Flags, uintX_t FileOff,
uintX_t VA, uintX_t Size, uintX_t Align);
void copyPhdr(Elf_Phdr *PH, OutputSectionBase<ELFT> *From);
bool HasRelro = false;
SymbolTable<ELFT> &Symtab;
std::vector<Elf_Phdr> Phdrs;
uintX_t FileSize;
uintX_t SectionHeaderOff;
llvm::StringMap<llvm::StringRef> InputToOutputSection;
// Flag to force GOT to be in output if we have relocations
// that relies on its address.
bool HasGotOffRel = false;
};
} // anonymous namespace
template <class ELFT> static bool shouldUseRela() { return ELFT::Is64Bits; }
template <class ELFT> void elf2::writeResult(SymbolTable<ELFT> *Symtab) {
// Initialize output sections that are handled by Writer specially.
// Don't reorder because the order of initialization matters.
InterpSection<ELFT> Interp;
Out<ELFT>::Interp = &Interp;
StringTableSection<ELFT> ShStrTab(".shstrtab", false);
Out<ELFT>::ShStrTab = &ShStrTab;
StringTableSection<ELFT> StrTab(".strtab", false);
if (!Config->StripAll)
Out<ELFT>::StrTab = &StrTab;
StringTableSection<ELFT> DynStrTab(".dynstr", true);
Out<ELFT>::DynStrTab = &DynStrTab;
GotSection<ELFT> Got;
Out<ELFT>::Got = &Got;
GotPltSection<ELFT> GotPlt;
if (Target->UseLazyBinding)
Out<ELFT>::GotPlt = &GotPlt;
PltSection<ELFT> Plt;
Out<ELFT>::Plt = &Plt;
std::unique_ptr<SymbolTableSection<ELFT>> SymTab;
if (!Config->StripAll) {
SymTab.reset(new SymbolTableSection<ELFT>(*Symtab, *Out<ELFT>::StrTab));
Out<ELFT>::SymTab = SymTab.get();
}
SymbolTableSection<ELFT> DynSymTab(*Symtab, *Out<ELFT>::DynStrTab);
Out<ELFT>::DynSymTab = &DynSymTab;
HashTableSection<ELFT> HashTab;
if (Config->SysvHash)
Out<ELFT>::HashTab = &HashTab;
GnuHashTableSection<ELFT> GnuHashTab;
if (Config->GnuHash)
Out<ELFT>::GnuHashTab = &GnuHashTab;
bool IsRela = shouldUseRela<ELFT>();
RelocationSection<ELFT> RelaDyn(IsRela ? ".rela.dyn" : ".rel.dyn", IsRela);
Out<ELFT>::RelaDyn = &RelaDyn;
RelocationSection<ELFT> RelaPlt(IsRela ? ".rela.plt" : ".rel.plt", IsRela);
if (Target->UseLazyBinding)
Out<ELFT>::RelaPlt = &RelaPlt;
DynamicSection<ELFT> Dynamic(*Symtab);
Out<ELFT>::Dynamic = &Dynamic;
EhFrameHeader<ELFT> EhFrameHdr;
Out<ELFT>::EhFrameHdr = &EhFrameHdr;
Writer<ELFT>(*Symtab).run();
}
// The main function of the writer.
template <class ELFT> void Writer<ELFT>::run() {
buildSectionMap();
if (!Config->DiscardAll)
copyLocalSymbols();
addReservedSymbols();
if (!createSections())
return;
assignAddresses();
fixAbsoluteSymbols();
openFile(Config->OutputFile);
writeHeader();
writeSections();
fatal(Buffer->commit());
}
namespace {
template <bool Is64Bits> struct SectionKey {
typedef typename std::conditional<Is64Bits, uint64_t, uint32_t>::type uintX_t;
StringRef Name;
uint32_t Type;
uintX_t Flags;
uintX_t EntSize;
};
}
namespace llvm {
template <bool Is64Bits> struct DenseMapInfo<SectionKey<Is64Bits>> {
static SectionKey<Is64Bits> getEmptyKey() {
return SectionKey<Is64Bits>{DenseMapInfo<StringRef>::getEmptyKey(), 0, 0,
0};
}
static SectionKey<Is64Bits> getTombstoneKey() {
return SectionKey<Is64Bits>{DenseMapInfo<StringRef>::getTombstoneKey(), 0,
0, 0};
}
static unsigned getHashValue(const SectionKey<Is64Bits> &Val) {
return hash_combine(Val.Name, Val.Type, Val.Flags, Val.EntSize);
}
static bool isEqual(const SectionKey<Is64Bits> &LHS,
const SectionKey<Is64Bits> &RHS) {
return DenseMapInfo<StringRef>::isEqual(LHS.Name, RHS.Name) &&
LHS.Type == RHS.Type && LHS.Flags == RHS.Flags &&
LHS.EntSize == RHS.EntSize;
}
};
}
template <class ELFT, class RelT>
static bool handleTlsRelocation(unsigned Type, SymbolBody *Body,
InputSectionBase<ELFT> &C, RelT &RI) {
if (Target->isTlsLocalDynamicRel(Type)) {
if (Target->canRelaxTls(Type, nullptr))
return true;
if (Out<ELFT>::Got->addCurrentModuleTlsIndex())
Out<ELFT>::RelaDyn->addReloc({&C, &RI});
return true;
}
if (!Body || !Body->isTls())
return false;
if (Target->isTlsGlobalDynamicRel(Type)) {
bool Opt = Target->canRelaxTls(Type, Body);
if (!Opt && Out<ELFT>::Got->addDynTlsEntry(Body)) {
Out<ELFT>::RelaDyn->addReloc({&C, &RI});
Out<ELFT>::RelaDyn->addReloc({nullptr, nullptr});
Body->setUsedInDynamicReloc();
return true;
}
if (!canBePreempted(Body, true))
return true;
}
return !Target->isTlsDynRel(Type, *Body);
}
// The reason we have to do this early scan is as follows
// * To mmap the output file, we need to know the size
// * For that, we need to know how many dynamic relocs we will have.
// It might be possible to avoid this by outputting the file with write:
// * Write the allocated output sections, computing addresses.
// * Apply relocations, recording which ones require a dynamic reloc.
// * Write the dynamic relocations.
// * Write the rest of the file.
template <class ELFT>
template <bool isRela>
void Writer<ELFT>::scanRelocs(
InputSectionBase<ELFT> &C,
iterator_range<const Elf_Rel_Impl<ELFT, isRela> *> Rels) {
typedef Elf_Rel_Impl<ELFT, isRela> RelType;
const ObjectFile<ELFT> &File = *C.getFile();
for (const RelType &RI : Rels) {
uint32_t SymIndex = RI.getSymbol(Config->Mips64EL);
SymbolBody *Body = File.getSymbolBody(SymIndex);
uint32_t Type = RI.getType(Config->Mips64EL);
// Ignore "hint" relocation because it is for optional code optimization.
if (Target->isHintRel(Type))
continue;
if (Target->isGotRelative(Type))
HasGotOffRel = true;
// Set "used" bit for --as-needed.
if (Body && Body->isUndefined() && !Body->isWeak())
if (auto *S = dyn_cast<SharedSymbol<ELFT>>(Body->repl()))
S->File->IsUsed = true;
if (Body)
Body = Body->repl();
if (handleTlsRelocation<ELFT>(Type, Body, C, RI))
continue;
if (Target->needsDynRelative(Type)) {
RelType *Rel = new (Alloc) RelType;
Rel->setSymbolAndType(0, Target->RelativeRel, Config->Mips64EL);
Rel->r_offset = RI.r_offset;
Out<ELFT>::RelaDyn->addReloc({&C, Rel});
}
bool NeedsGot = false;
bool NeedsMipsLocalGot = false;
bool NeedsPlt = false;
if (Config->EMachine == EM_MIPS && needsMipsLocalGot(Type, Body)) {
NeedsMipsLocalGot = true;
// FIXME (simon): Do not add so many redundant entries.
Out<ELFT>::Got->addMipsLocalEntry();
} else if (Body) {
if (auto *E = dyn_cast<SharedSymbol<ELFT>>(Body)) {
if (E->NeedsCopy)
continue;
if (Target->needsCopyRel(Type, *Body))
E->NeedsCopy = true;
}
NeedsPlt = Target->needsPlt(Type, *Body);
if (NeedsPlt) {
if (Body->isInPlt())
continue;
Out<ELFT>::Plt->addEntry(Body);
}
NeedsGot = Target->needsGot(Type, *Body);
if (NeedsGot) {
if (NeedsPlt && Target->UseLazyBinding) {
Out<ELFT>::GotPlt->addEntry(Body);
} else {
if (Body->isInGot())
continue;
Out<ELFT>::Got->addEntry(Body);
}
}
}
// An STT_GNU_IFUNC symbol always uses a PLT entry, and all references
// to the symbol go through the PLT. This is true even for a local
// symbol, although local symbols normally do not require PLT entries.
if (Body && isGnuIFunc<ELFT>(*Body)) {
Body->setUsedInDynamicReloc();
Out<ELFT>::RelaPlt->addReloc({&C, &RI});
continue;
}
if (Config->EMachine == EM_MIPS) {
if (Type == R_MIPS_LO16)
// Ignore R_MIPS_LO16 relocation. If it is a pair for R_MIPS_GOT16 we
// already completed all required action (GOT entry allocation) when
// handle R_MIPS_GOT16a. If it is a pair for R_MIPS_HI16 against
// _gp_disp it does not require dynamic relocation. If its a pair for
// R_MIPS_HI16 against a regular symbol it does not require dynamic
// relocation too because that case is possible for executable file
// linking only.
continue;
if (NeedsGot || NeedsMipsLocalGot) {
// MIPS ABI has special rules to process GOT entries
// and doesn't require relocation entries for them.
// See "Global Offset Table" in Chapter 5 in the following document
// for detailed description:
// ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
if (NeedsGot)
Body->setUsedInDynamicReloc();
continue;
}
if (Body == Config->MipsGpDisp)
// MIPS _gp_disp designates offset between start of function and gp
// pointer into GOT therefore any relocations against it do not require
// dynamic relocation.
continue;
}
// Here we are creating a relocation for the dynamic linker based on
// a relocation from an object file, but some relocations need no
// load-time fixup when the final target is known. Skip such relocation.
bool CBP = canBePreempted(Body, NeedsGot);
bool NoDynrel = Target->isRelRelative(Type) || Target->isSizeRel(Type) ||
!Config->Shared;
if (!CBP && NoDynrel)
continue;
if (CBP)
Body->setUsedInDynamicReloc();
if (NeedsPlt && Target->UseLazyBinding)
Out<ELFT>::RelaPlt->addReloc({&C, &RI});
else
Out<ELFT>::RelaDyn->addReloc({&C, &RI});
}
}
template <class ELFT> void Writer<ELFT>::scanRelocs(InputSection<ELFT> &C) {
if (C.getSectionHdr()->sh_flags & SHF_ALLOC)
for (const Elf_Shdr *RelSec : C.RelocSections)
scanRelocs(C, *RelSec);
}
template <class ELFT>
void Writer<ELFT>::scanRelocs(InputSectionBase<ELFT> &S,
const Elf_Shdr &RelSec) {
ELFFile<ELFT> &EObj = S.getFile()->getObj();
if (RelSec.sh_type == SHT_RELA)
scanRelocs(S, EObj.relas(&RelSec));
else
scanRelocs(S, EObj.rels(&RelSec));
}
template <class ELFT>
static void reportUndefined(SymbolTable<ELFT> &Symtab, SymbolBody *Sym) {
if (Config->Shared && !Config->NoUndefined)
return;
std::string Msg = "undefined symbol: " + Sym->getName().str();
if (ELFFileBase<ELFT> *File = Symtab.findFile(Sym))
Msg += " in " + File->getName().str();
if (Config->NoInhibitExec)
warning(Msg);
else
error(Msg);
}
template <class ELFT>
static bool shouldKeepInSymtab(const ObjectFile<ELFT> &File, StringRef SymName,
const typename ELFFile<ELFT>::Elf_Sym &Sym) {
if (Sym.getType() == STT_SECTION || Sym.getType() == STT_FILE)
return false;
InputSectionBase<ELFT> *Sec = File.getSection(Sym);
// If sym references a section in a discarded group, don't keep it.
if (Sec == &InputSection<ELFT>::Discarded)
return false;
if (Config->DiscardNone)
return true;
// In ELF assembly .L symbols are normally discarded by the assembler.
// If the assembler fails to do so, the linker discards them if
// * --discard-locals is used.
// * The symbol is in a SHF_MERGE section, which is normally the reason for
// the assembler keeping the .L symbol.
if (!SymName.startswith(".L") && !SymName.empty())
return true;
if (Config->DiscardLocals)
return false;
return !(Sec->getSectionHdr()->sh_flags & SHF_MERGE);
}
// 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 (!Out<ELFT>::SymTab)
return;
for (const std::unique_ptr<ObjectFile<ELFT>> &F : Symtab.getObjectFiles()) {
for (const Elf_Sym &Sym : F->getLocalSymbols()) {
ErrorOr<StringRef> SymNameOrErr = Sym.getName(F->getStringTable());
fatal(SymNameOrErr);
StringRef SymName = *SymNameOrErr;
if (!shouldKeepInSymtab<ELFT>(*F, SymName, Sym))
continue;
if (Sym.st_shndx != SHN_ABS) {
InputSectionBase<ELFT> *Section = F->getSection(Sym);
if (!Section->isLive())
continue;
}
++Out<ELFT>::SymTab->NumLocals;
F->KeptLocalSyms.push_back(std::make_pair(
&Sym, Out<ELFT>::SymTab->StrTabSec.addString(SymName)));
}
}
}
// 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);
}
template <class ELFT> static bool isRelroSection(OutputSectionBase<ELFT> *Sec) {
typename OutputSectionBase<ELFT>::uintX_t Flags = Sec->getFlags();
if (!(Flags & SHF_ALLOC) || !(Flags & SHF_WRITE))
return false;
if (Flags & SHF_TLS)
return true;
uint32_t Type = Sec->getType();
if (Type == SHT_INIT_ARRAY || Type == SHT_FINI_ARRAY ||
Type == SHT_PREINIT_ARRAY)
return true;
if (Sec == Out<ELFT>::GotPlt)
return Config->ZNow;
if (Sec == Out<ELFT>::Dynamic || Sec == Out<ELFT>::Got)
return true;
StringRef S = Sec->getName();
return S == ".data.rel.ro" || S == ".ctors" || S == ".dtors" || S == ".jcr" ||
S == ".eh_frame";
}
// Output section ordering is determined by this function.
template <class ELFT>
static bool compareOutputSections(OutputSectionBase<ELFT> *A,
OutputSectionBase<ELFT> *B) {
typedef typename ELFFile<ELFT>::uintX_t uintX_t;
uintX_t AFlags = A->getFlags();
uintX_t BFlags = B->getFlags();
// Allocatable sections go first to reduce the total PT_LOAD size and
// so debug info doesn't change addresses in actual code.
bool AIsAlloc = AFlags & SHF_ALLOC;
bool BIsAlloc = BFlags & 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 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 = AFlags & SHF_WRITE;
bool BIsWritable = BFlags & SHF_WRITE;
if (AIsWritable != BIsWritable)
return BIsWritable;
// For a corresponding reason, put non exec sections first (the program
// header PT_LOAD is not executable).
bool AIsExec = AFlags & SHF_EXECINSTR;
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;
}
template <class ELFT> OutputSection<ELFT> *Writer<ELFT>::getBss() {
if (!Out<ELFT>::Bss) {
Out<ELFT>::Bss =
new OutputSection<ELFT>(".bss", SHT_NOBITS, SHF_ALLOC | SHF_WRITE);
OwningSections.emplace_back(Out<ELFT>::Bss);
OutputSections.push_back(Out<ELFT>::Bss);
}
return Out<ELFT>::Bss;
}
// Until this function is called, common symbols do not belong to any section.
// This function adds them to end of BSS section.
template <class ELFT>
void Writer<ELFT>::addCommonSymbols(std::vector<DefinedCommon *> &Syms) {
if (Syms.empty())
return;
// Sort the common symbols by alignment as an heuristic to pack them better.
std::stable_sort(Syms.begin(), Syms.end(),
[](const DefinedCommon *A, const DefinedCommon *B) {
return A->MaxAlignment > B->MaxAlignment;
});
uintX_t Off = getBss()->getSize();
for (DefinedCommon *C : Syms) {
Off = alignTo(Off, C->MaxAlignment);
C->OffsetInBss = Off;
Off += C->Size;
}
Out<ELFT>::Bss->setSize(Off);
}
// Reserve space in .bss for copy relocations.
template <class ELFT>
void Writer<ELFT>::addCopyRelSymbols(std::vector<SharedSymbol<ELFT> *> &Syms) {
if (Syms.empty())
return;
uintX_t Off = getBss()->getSize();
for (SharedSymbol<ELFT> *C : Syms) {
const Elf_Sym &Sym = C->Sym;
const Elf_Shdr *Sec = C->File->getSection(Sym);
uintX_t SecAlign = Sec->sh_addralign;
unsigned TrailingZeros =
std::min(countTrailingZeros(SecAlign),
countTrailingZeros((uintX_t)Sym.st_value));
uintX_t Align = 1 << TrailingZeros;
Out<ELFT>::Bss->updateAlign(Align);
Off = alignTo(Off, Align);
C->OffsetInBss = Off;
Off += Sym.st_size;
}
Out<ELFT>::Bss->setSize(Off);
}
template <class ELFT>
StringRef Writer<ELFT>::getOutputSectionName(StringRef S) const {
auto It = InputToOutputSection.find(S);
if (It != std::end(InputToOutputSection))
return It->second;
if (S.startswith(".text."))
return ".text";
if (S.startswith(".rodata."))
return ".rodata";
if (S.startswith(".data.rel.ro"))
return ".data.rel.ro";
if (S.startswith(".data."))
return ".data";
if (S.startswith(".bss."))
return ".bss";
return S;
}
template <class ELFT>
void reportDiscarded(InputSectionBase<ELFT> *IS,
const std::unique_ptr<ObjectFile<ELFT>> &File) {
if (!Config->PrintGcSections || !IS || IS->isLive())
return;
llvm::errs() << "removing unused section from '" << IS->getSectionName()
<< "' in file '" << File->getName() << "'\n";
}
template <class ELFT>
bool Writer<ELFT>::isDiscarded(InputSectionBase<ELFT> *IS) const {
if (!IS || !IS->isLive() || IS == &InputSection<ELFT>::Discarded)
return true;
return InputToOutputSection.lookup(IS->getSectionName()) == "/DISCARD/";
}
template <class ELFT>
static bool compareSections(OutputSectionBase<ELFT> *A,
OutputSectionBase<ELFT> *B) {
auto ItA = Config->OutputSections.find(A->getName());
auto ItEnd = std::end(Config->OutputSections);
if (ItA == ItEnd)
return compareOutputSections(A, B);
auto ItB = Config->OutputSections.find(B->getName());
if (ItB == ItEnd)
return compareOutputSections(A, B);
return std::distance(ItA, ItB) > 0;
}
// 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 (isOutputDynamic() || !Out<ELFT>::RelaPlt)
return;
bool IsRela = shouldUseRela<ELFT>();
StringRef S = IsRela ? "__rela_iplt_start" : "__rel_iplt_start";
if (Symtab.find(S))
Symtab.addAbsolute(S, ElfSym<ELFT>::RelaIpltStart);
S = IsRela ? "__rela_iplt_end" : "__rel_iplt_end";
if (Symtab.find(S))
Symtab.addAbsolute(S, ElfSym<ELFT>::RelaIpltEnd);
}
template <class ELFT> static bool includeInSymtab(const SymbolBody &B) {
if (!B.isUsedInRegularObj())
return false;
// Don't include synthetic symbols like __init_array_start in every output.
if (auto *U = dyn_cast<DefinedRegular<ELFT>>(&B))
if (&U->Sym == &ElfSym<ELFT>::Ignored)
return false;
return true;
}
static bool includeInDynsym(const SymbolBody &B) {
uint8_t V = B.getVisibility();
if (V != STV_DEFAULT && V != STV_PROTECTED)
return false;
if (Config->ExportDynamic || Config->Shared)
return true;
return B.isUsedInDynamicReloc();
}
// This class knows how to create an output section for a given
// input section. Output section type is determined by various
// factors, including input section's sh_flags, sh_type and
// linker scripts.
namespace {
template <class ELFT> class OutputSectionFactory {
typedef typename ELFFile<ELFT>::Elf_Shdr Elf_Shdr;
typedef typename ELFFile<ELFT>::uintX_t uintX_t;
public:
std::pair<OutputSectionBase<ELFT> *, bool> create(InputSectionBase<ELFT> *C,
StringRef OutsecName);
OutputSectionBase<ELFT> *lookup(StringRef Name, uint32_t Type, uintX_t Flags);
private:
SectionKey<ELFT::Is64Bits> createKey(InputSectionBase<ELFT> *C,
StringRef OutsecName);
SmallDenseMap<SectionKey<ELFT::Is64Bits>, OutputSectionBase<ELFT> *> Map;
};
}
template <class ELFT>
std::pair<OutputSectionBase<ELFT> *, bool>
OutputSectionFactory<ELFT>::create(InputSectionBase<ELFT> *C,
StringRef OutsecName) {
SectionKey<ELFT::Is64Bits> Key = createKey(C, OutsecName);
OutputSectionBase<ELFT> *&Sec = Map[Key];
if (Sec)
return {Sec, false};
switch (C->SectionKind) {
case InputSectionBase<ELFT>::Regular:
Sec = new OutputSection<ELFT>(Key.Name, Key.Type, Key.Flags);
break;
case InputSectionBase<ELFT>::EHFrame:
Sec = new EHOutputSection<ELFT>(Key.Name, Key.Type, Key.Flags);
break;
case InputSectionBase<ELFT>::Merge:
Sec = new MergeOutputSection<ELFT>(Key.Name, Key.Type, Key.Flags);
break;
case InputSectionBase<ELFT>::MipsReginfo:
Sec = new MipsReginfoOutputSection<ELFT>();
break;
}
return {Sec, true};
}
template <class ELFT>
OutputSectionBase<ELFT> *OutputSectionFactory<ELFT>::lookup(StringRef Name,
uint32_t Type,
uintX_t Flags) {
return Map.lookup({Name, Type, Flags, 0});
}
template <class ELFT>
SectionKey<ELFT::Is64Bits>
OutputSectionFactory<ELFT>::createKey(InputSectionBase<ELFT> *C,
StringRef OutsecName) {
const Elf_Shdr *H = C->getSectionHdr();
uintX_t Flags = H->sh_flags & ~SHF_GROUP;
// For SHF_MERGE we create different output sections for each sh_entsize.
// This makes each output section simple and keeps a single level
// mapping from input to output.
uintX_t EntSize = isa<MergeInputSection<ELFT>>(C) ? H->sh_entsize : 0;
// GNU as can give .eh_frame secion type SHT_PROGBITS or SHT_X86_64_UNWIND
// depending on the construct. We want to canonicalize it so that
// there is only one .eh_frame in the end.
uint32_t Type = H->sh_type;
if (Type == SHT_PROGBITS && Config->EMachine == EM_X86_64 &&
isa<EHInputSection<ELFT>>(C))
Type = SHT_X86_64_UNWIND;
return SectionKey<ELFT::Is64Bits>{OutsecName, Type, Flags, EntSize};
}
// 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() {
// __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.
if (!isOutputDynamic())
Symtab.addIgnored("__tls_get_addr");
// If the "_end" symbol is referenced, it is expected to point to the address
// right after the data segment. Usually, this symbol points to the end
// of .bss section or to the end of .data section if .bss section is absent.
// We don't know the final address of _end yet, so just add a symbol here,
// and fix ElfSym<ELFT>::End.st_value later.
if (Symtab.find("_end"))
Symtab.addAbsolute("_end", ElfSym<ELFT>::End);
// Define "end" as an alias to "_end" if it is used but not defined.
// We don't want to define that unconditionally because we don't want to
// break programs that uses "end" as a regular symbol.
if (SymbolBody *B = Symtab.find("end"))
if (B->isUndefined())
Symtab.addAbsolute("end", ElfSym<ELFT>::End);
}
// Create output section objects and add them to OutputSections.
template <class ELFT> bool Writer<ELFT>::createSections() {
// Add .interp first because some loaders want to see that section
// on the first page of the executable file when loaded into memory.
if (needsInterpSection())
OutputSections.push_back(Out<ELFT>::Interp);
// Create output sections for input object file sections.
std::vector<OutputSectionBase<ELFT> *> RegularSections;
OutputSectionFactory<ELFT> Factory;
for (const std::unique_ptr<ObjectFile<ELFT>> &F : Symtab.getObjectFiles()) {
for (InputSectionBase<ELFT> *C : F->getSections()) {
if (isDiscarded(C)) {
reportDiscarded(C, F);
continue;
}
OutputSectionBase<ELFT> *Sec;
bool IsNew;
std::tie(Sec, IsNew) =
Factory.create(C, getOutputSectionName(C->getSectionName()));
if (IsNew) {
OwningSections.emplace_back(Sec);
OutputSections.push_back(Sec);
RegularSections.push_back(Sec);
}
Sec->addSection(C);
}
}
Out<ELFT>::Bss = static_cast<OutputSection<ELFT> *>(
Factory.lookup(".bss", SHT_NOBITS, SHF_ALLOC | SHF_WRITE));
// If we have a .opd section (used under PPC64 for function descriptors),
// store a pointer to it here so that we can use it later when processing
// relocations.
Out<ELFT>::Opd = Factory.lookup(".opd", SHT_PROGBITS, SHF_WRITE | SHF_ALLOC);
Out<ELFT>::Dynamic->PreInitArraySec = Factory.lookup(
".preinit_array", SHT_PREINIT_ARRAY, SHF_WRITE | SHF_ALLOC);
Out<ELFT>::Dynamic->InitArraySec =
Factory.lookup(".init_array", SHT_INIT_ARRAY, SHF_WRITE | SHF_ALLOC);
Out<ELFT>::Dynamic->FiniArraySec =
Factory.lookup(".fini_array", SHT_FINI_ARRAY, SHF_WRITE | SHF_ALLOC);
// 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.
addStartEndSymbols();
for (OutputSectionBase<ELFT> *Sec : RegularSections)
addStartStopSymbols(Sec);
// Scan relocations. This must be done after every symbol is declared so that
// we can correctly decide if a dynamic relocation is needed.
for (const std::unique_ptr<ObjectFile<ELFT>> &F : Symtab.getObjectFiles()) {
for (InputSectionBase<ELFT> *C : F->getSections()) {
if (isDiscarded(C))
continue;
if (auto *S = dyn_cast<InputSection<ELFT>>(C))
scanRelocs(*S);
else if (auto *S = dyn_cast<EHInputSection<ELFT>>(C))
if (S->RelocSection)
scanRelocs(*S, *S->RelocSection);
}
}
// Define __rel[a]_iplt_{start,end} symbols if needed.
addRelIpltSymbols();
// Now that we have defined all possible symbols including linker-
// synthesized ones. Visit all symbols to give the finishing touches.
std::vector<DefinedCommon *> CommonSymbols;
std::vector<SharedSymbol<ELFT> *> CopyRelSymbols;
for (auto &P : Symtab.getSymbols()) {
SymbolBody *Body = P.second->Body;
if (auto *U = dyn_cast<Undefined>(Body))
if (!U->isWeak() && !U->canKeepUndefined())
reportUndefined<ELFT>(Symtab, Body);
if (auto *C = dyn_cast<DefinedCommon>(Body))
CommonSymbols.push_back(C);
if (auto *SC = dyn_cast<SharedSymbol<ELFT>>(Body))
if (SC->NeedsCopy)
CopyRelSymbols.push_back(SC);
if (!includeInSymtab<ELFT>(*Body))
continue;
if (Out<ELFT>::SymTab)
Out<ELFT>::SymTab->addSymbol(Body);
if (isOutputDynamic() && includeInDynsym(*Body))
Out<ELFT>::DynSymTab->addSymbol(Body);
}
// Do not proceed if there was an undefined symbol.
if (HasError)
return false;
addCommonSymbols(CommonSymbols);
addCopyRelSymbols(CopyRelSymbols);
// So far we have added sections from input object files.
// This function adds linker-created Out<ELFT>::* sections.
addPredefinedSections();
std::stable_sort(OutputSections.begin(), OutputSections.end(),
compareSections<ELFT>);
for (unsigned I = 0, N = OutputSections.size(); I < N; ++I) {
OutputSections[I]->SectionIndex = I + 1;
HasRelro |= (Config->ZRelro && isRelroSection(OutputSections[I]));
}
for (OutputSectionBase<ELFT> *Sec : OutputSections)
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 (isOutputDynamic())
Out<ELFT>::DynSymTab->finalize();
// Fill other section headers. The dynamic string table in finalized
// once the .dynamic finalizer has added a few last strings.
for (OutputSectionBase<ELFT> *Sec : OutputSections)
if (Sec != Out<ELFT>::DynStrTab)
Sec->finalize();
return true;
}
// This function add Out<ELFT>::* sections to OutputSections.
template <class ELFT> void Writer<ELFT>::addPredefinedSections() {
auto Add = [&](OutputSectionBase<ELFT> *C) {
if (C)
OutputSections.push_back(C);
};
// 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 (isOutputDynamic()) {
Add(Out<ELFT>::DynSymTab);
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);
// This is a MIPS specific section to hold a space within the data segment
// of executable file which is pointed to by the DT_MIPS_RLD_MAP entry.
// See "Dynamic section" in Chapter 5 in the following document:
// ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
if (Config->EMachine == EM_MIPS && !Config->Shared) {
Out<ELFT>::MipsRldMap = new OutputSection<ELFT>(".rld_map", SHT_PROGBITS,
SHF_ALLOC | SHF_WRITE);
Out<ELFT>::MipsRldMap->setSize(ELFT::Is64Bits ? 8 : 4);
Out<ELFT>::MipsRldMap->updateAlign(ELFT::Is64Bits ? 8 : 4);
OwningSections.emplace_back(Out<ELFT>::MipsRldMap);
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);
Out<ELFT>::RelaPlt->Static = !isOutputDynamic();
}
bool needsGot = !Out<ELFT>::Got->empty();
// 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)
needsGot |= isOutputDynamic();
// If we have a relocation that is relative to GOT (such as GOTOFFREL),
// we need to emit a GOT even if it's empty.
if (HasGotOffRel)
needsGot = true;
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>::EhFrameHdr->Live)
Add(Out<ELFT>::EhFrameHdr);
}
// 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) {
Symtab.addSynthetic(Start, *OS, 0);
Symtab.addSynthetic(End, *OS, OS->getSize());
} else {
Symtab.addIgnored(Start);
Symtab.addIgnored(End);
}
};
Define("__preinit_array_start", "__preinit_array_end",
Out<ELFT>::Dynamic->PreInitArraySec);
Define("__init_array_start", "__init_array_end",
Out<ELFT>::Dynamic->InitArraySec);
Define("__fini_array_start", "__fini_array_end",
Out<ELFT>::Dynamic->FiniArraySec);
}
static bool isAlpha(char C) {
return ('a' <= C && C <= 'z') || ('A' <= C && C <= 'Z') || C == '_';
}
static bool isAlnum(char C) { return isAlpha(C) || ('0' <= C && C <= '9'); }
// Returns true if S is valid as a C language identifier.
static bool isValidCIdentifier(StringRef S) {
if (S.empty() || !isAlpha(S[0]))
return false;
return std::all_of(S.begin() + 1, S.end(), isAlnum);
}
// 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.find(Start))
if (B->isUndefined())
Symtab.addSynthetic(Start, *Sec, 0);
if (SymbolBody *B = Symtab.find(Stop))
if (B->isUndefined())
Symtab.addSynthetic(Stop, *Sec, Sec->getSize());
}
template <class ELFT> static bool needsPhdr(OutputSectionBase<ELFT> *Sec) {
return Sec->getFlags() & SHF_ALLOC;
}
static uint32_t toPhdrFlags(uint64_t Flags) {
uint32_t Ret = PF_R;
if (Flags & SHF_WRITE)
Ret |= PF_W;
if (Flags & SHF_EXECINSTR)
Ret |= PF_X;
return Ret;
}
/// For AMDGPU we need to use custom segment kinds in order to specify which
/// address space data should be loaded into.
template <class ELFT>
static uint32_t getAmdgpuPhdr(OutputSectionBase<ELFT> *Sec) {
uint32_t Flags = Sec->getFlags();
if (Flags & SHF_AMDGPU_HSA_CODE)
return PT_AMDGPU_HSA_LOAD_CODE_AGENT;
if ((Flags & SHF_AMDGPU_HSA_GLOBAL) && !(Flags & SHF_AMDGPU_HSA_AGENT))
return PT_AMDGPU_HSA_LOAD_GLOBAL_PROGRAM;
return PT_LOAD;
}
template <class ELFT>
void Writer<ELFT>::updateRelro(Elf_Phdr *Cur, Elf_Phdr *GnuRelroPhdr,
uintX_t VA) {
if (!GnuRelroPhdr->p_type)
setPhdr(GnuRelroPhdr, PT_GNU_RELRO, PF_R, Cur->p_offset, Cur->p_vaddr,
VA - Cur->p_vaddr, 1 /*p_align*/);
GnuRelroPhdr->p_filesz = VA - Cur->p_vaddr;
GnuRelroPhdr->p_memsz = VA - Cur->p_vaddr;
}
// Visits all sections to create PHDRs and to assign incremental,
// non-overlapping addresses to output sections.
template <class ELFT> void Writer<ELFT>::assignAddresses() {
uintX_t VA = Target->getVAStart() + sizeof(Elf_Ehdr);
uintX_t FileOff = sizeof(Elf_Ehdr);
// Calculate and reserve the space for the program header first so that
// the first section can start right after the program header.
Phdrs.resize(getPhdrsNum());
size_t PhdrSize = sizeof(Elf_Phdr) * Phdrs.size();
// The first phdr entry is PT_PHDR which describes the program header itself.
setPhdr(&Phdrs[0], PT_PHDR, PF_R, FileOff, VA, PhdrSize, /*Align=*/8);
FileOff += PhdrSize;
VA += PhdrSize;
// PT_INTERP must be the second entry if exists.
int PhdrIdx = 0;
Elf_Phdr *Interp = nullptr;
if (needsInterpSection())
Interp = &Phdrs[++PhdrIdx];
// Add the first PT_LOAD segment for regular output sections.
setPhdr(&Phdrs[++PhdrIdx], PT_LOAD, PF_R, 0, Target->getVAStart(), FileOff,
Target->PageSize);
Elf_Phdr GnuRelroPhdr = {};
Elf_Phdr TlsPhdr{};
bool RelroAligned = false;
uintX_t ThreadBssOffset = 0;
// Create phdrs as we assign VAs and file offsets to all output sections.
for (OutputSectionBase<ELFT> *Sec : OutputSections) {
Elf_Phdr *PH = &Phdrs[PhdrIdx];
if (needsPhdr<ELFT>(Sec)) {
uintX_t Flags = toPhdrFlags(Sec->getFlags());
bool InRelRo = Config->ZRelro && (Flags & PF_W) && isRelroSection(Sec);
bool FirstNonRelRo = GnuRelroPhdr.p_type && !InRelRo && !RelroAligned;
if (FirstNonRelRo || PH->p_flags != Flags) {
VA = alignTo(VA, Target->PageSize);
FileOff = alignTo(FileOff, Target->PageSize);
if (FirstNonRelRo)
RelroAligned = true;
}
if (PH->p_flags != Flags) {
// Flags changed. Create a new PT_LOAD.
PH = &Phdrs[++PhdrIdx];
uint32_t PTType = (Config->EMachine != EM_AMDGPU) ? (uint32_t)PT_LOAD
: getAmdgpuPhdr(Sec);
setPhdr(PH, PTType, Flags, FileOff, VA, 0, Target->PageSize);
}
if (Sec->getFlags() & SHF_TLS) {
if (!TlsPhdr.p_vaddr)
setPhdr(&TlsPhdr, PT_TLS, PF_R, FileOff, VA, 0, Sec->getAlign());
if (Sec->getType() != SHT_NOBITS)
VA = alignTo(VA, Sec->getAlign());
uintX_t TVA = alignTo(VA + ThreadBssOffset, Sec->getAlign());
Sec->setVA(TVA);
TlsPhdr.p_memsz += Sec->getSize();
if (Sec->getType() == SHT_NOBITS) {
ThreadBssOffset = TVA - VA + Sec->getSize();
} else {
TlsPhdr.p_filesz += Sec->getSize();
VA += Sec->getSize();
}
TlsPhdr.p_align = std::max<uintX_t>(TlsPhdr.p_align, Sec->getAlign());
} else {
VA = alignTo(VA, Sec->getAlign());
Sec->setVA(VA);
VA += Sec->getSize();
if (InRelRo)
updateRelro(PH, &GnuRelroPhdr, VA);
}
}
FileOff = alignTo(FileOff, Sec->getAlign());
Sec->setFileOffset(FileOff);
if (Sec->getType() != SHT_NOBITS)
FileOff += Sec->getSize();
if (needsPhdr<ELFT>(Sec)) {
PH->p_filesz = FileOff - PH->p_offset;
PH->p_memsz = VA - PH->p_vaddr;
}
}
if (TlsPhdr.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.
TlsPhdr.p_memsz = alignTo(TlsPhdr.p_memsz, TlsPhdr.p_align);
Phdrs[++PhdrIdx] = TlsPhdr;
Out<ELFT>::TlsPhdr = &Phdrs[PhdrIdx];
}
// Add an entry for .dynamic.
if (isOutputDynamic()) {
Elf_Phdr *PH = &Phdrs[++PhdrIdx];
PH->p_type = PT_DYNAMIC;
copyPhdr(PH, Out<ELFT>::Dynamic);
}
if (HasRelro) {
Elf_Phdr *PH = &Phdrs[++PhdrIdx];
*PH = GnuRelroPhdr;
}
if (Out<ELFT>::EhFrameHdr->Live) {
Elf_Phdr *PH = &Phdrs[++PhdrIdx];
PH->p_type = PT_GNU_EH_FRAME;
copyPhdr(PH, 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) {
Elf_Phdr *PH = &Phdrs[++PhdrIdx];
PH->p_type = PT_GNU_STACK;
PH->p_flags = PF_R | PF_W;
}
// Fix up PT_INTERP as we now know the address of .interp section.
if (Interp) {
Interp->p_type = PT_INTERP;
copyPhdr(Interp, Out<ELFT>::Interp);
}
// Add space for section headers.
SectionHeaderOff = alignTo(FileOff, ELFT::Is64Bits ? 8 : 4);
FileSize = SectionHeaderOff + getNumSections() * sizeof(Elf_Shdr);
// Update "_end" and "end" symbols so that they
// point to the end of the data segment.
ElfSym<ELFT>::End.st_value = VA;
}
// Returns the number of PHDR entries.
template <class ELFT> int Writer<ELFT>::getPhdrsNum() const {
bool Tls = false;
int I = 2; // 2 for PT_PHDR and first PT_LOAD
if (needsInterpSection())
++I;
if (isOutputDynamic())
++I;
if (!Config->ZExecStack)
++I;
uintX_t Last = PF_R;
for (OutputSectionBase<ELFT> *Sec : OutputSections) {
if (!needsPhdr<ELFT>(Sec))
continue;
if (Sec->getFlags() & SHF_TLS)
Tls = true;
uintX_t Flags = toPhdrFlags(Sec->getFlags());
if (Last != Flags) {
Last = Flags;
++I;
}
}
if (Tls)
++I;
if (HasRelro)
++I;
if (Out<ELFT>::EhFrameHdr->Live)
++I;
return I;
}
static uint32_t getELFFlags() {
if (Config->EMachine != EM_MIPS)
return 0;
// FIXME: In fact ELF flags depends on ELF flags of input object files
// and selected emulation. For now just use hard coded values.
uint32_t V = EF_MIPS_ABI_O32 | EF_MIPS_CPIC | EF_MIPS_ARCH_32R2;
if (Config->Shared)
V |= EF_MIPS_PIC;
return V;
}
template <class ELFT>
static typename ELFFile<ELFT>::uintX_t getEntryAddr() {
if (Config->EntrySym) {
if (SymbolBody *E = Config->EntrySym->repl())
return getSymVA<ELFT>(*E);
return 0;
}
if (Config->EntryAddr != uint64_t(-1))
return Config->EntryAddr;
return 0;
}
// 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() {
// Update __rel[a]_iplt_{start,end} symbols so that they point
// to beginning or ending of .rela.plt section, respectively.
if (Out<ELFT>::RelaPlt) {
uintX_t Start = Out<ELFT>::RelaPlt->getVA();
ElfSym<ELFT>::RelaIpltStart.st_value = Start;
ElfSym<ELFT>::RelaIpltEnd.st_value = Start + Out<ELFT>::RelaPlt->getSize();
}
// Update MIPS _gp absolute symbol so that it points to the static data.
if (Config->EMachine == EM_MIPS)
ElfSym<ELFT>::MipsGp.st_value = getMipsGpAddr<ELFT>();
}
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] = ELFT::TargetEndianness == llvm::support::little
? ELFDATA2LSB
: ELFDATA2MSB;
EHdr->e_ident[EI_VERSION] = EV_CURRENT;
auto &FirstObj = cast<ELFFileBase<ELFT>>(*Config->FirstElf);
EHdr->e_ident[EI_OSABI] = FirstObj.getOSABI();
EHdr->e_type = Config->Shared ? ET_DYN : ET_EXEC;
EHdr->e_machine = FirstObj.getEMachine();
EHdr->e_version = EV_CURRENT;
EHdr->e_entry = getEntryAddr<ELFT>();
EHdr->e_phoff = sizeof(Elf_Ehdr);
EHdr->e_shoff = SectionHeaderOff;
EHdr->e_flags = getELFFlags();
EHdr->e_ehsize = sizeof(Elf_Ehdr);
EHdr->e_phentsize = sizeof(Elf_Phdr);
EHdr->e_phnum = Phdrs.size();
EHdr->e_shentsize = sizeof(Elf_Shdr);
EHdr->e_shnum = getNumSections();
EHdr->e_shstrndx = Out<ELFT>::ShStrTab->SectionIndex;
// Write the program header table.
memcpy(Buf + EHdr->e_phoff, &Phdrs[0], Phdrs.size() * sizeof(Phdrs[0]));
// 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(StringRef Path) {
ErrorOr<std::unique_ptr<FileOutputBuffer>> BufferOrErr =
FileOutputBuffer::create(Path, FileSize, FileOutputBuffer::F_executable);
fatal(BufferOrErr, "failed to open " + Path);
Buffer = std::move(*BufferOrErr);
}
// 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.
if (OutputSectionBase<ELFT> *Sec = Out<ELFT>::Opd) {
Out<ELFT>::OpdBuf = Buf + Sec->getFileOff();
Sec->writeTo(Buf + Sec->getFileOff());
}
// Write all sections but string table sections. We know the sizes of the
// string tables already, but they may not have actual strings yet (only
// room may be reserved), because writeTo() is allowed to add actual
// strings to the string tables.
for (OutputSectionBase<ELFT> *Sec : OutputSections)
if (Sec != Out<ELFT>::Opd && Sec->getType() != SHT_STRTAB)
Sec->writeTo(Buf + Sec->getFileOff());
// Write string table sections.
for (OutputSectionBase<ELFT> *Sec : OutputSections)
if (Sec != Out<ELFT>::Opd && Sec->getType() == SHT_STRTAB)
Sec->writeTo(Buf + Sec->getFileOff());
}
template <class ELFT>
void Writer<ELFT>::setPhdr(Elf_Phdr *PH, uint32_t Type, uint32_t Flags,
uintX_t FileOff, uintX_t VA, uintX_t Size,
uintX_t Align) {
PH->p_type = Type;
PH->p_flags = Flags;
PH->p_offset = FileOff;
PH->p_vaddr = VA;
PH->p_paddr = VA;
PH->p_filesz = Size;
PH->p_memsz = Size;
PH->p_align = Align;
}
template <class ELFT>
void Writer<ELFT>::copyPhdr(Elf_Phdr *PH, OutputSectionBase<ELFT> *From) {
PH->p_flags = toPhdrFlags(From->getFlags());
PH->p_offset = From->getFileOff();
PH->p_vaddr = From->getVA();
PH->p_paddr = From->getVA();
PH->p_filesz = From->getSize();
PH->p_memsz = From->getSize();
PH->p_align = From->getAlign();
}
template <class ELFT> void Writer<ELFT>::buildSectionMap() {
for (const std::pair<StringRef, std::vector<StringRef>> &OutSec :
Config->OutputSections)
for (StringRef Name : OutSec.second)
InputToOutputSection[Name] = OutSec.first;
}
template void elf2::writeResult<ELF32LE>(SymbolTable<ELF32LE> *Symtab);
template void elf2::writeResult<ELF32BE>(SymbolTable<ELF32BE> *Symtab);
template void elf2::writeResult<ELF64LE>(SymbolTable<ELF64LE> *Symtab);
template void elf2::writeResult<ELF64BE>(SymbolTable<ELF64BE> *Symtab);
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