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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 "LinkerScript.h"
#include "OutputSections.h"
#include "SymbolTable.h"
#include "Target.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/StringMap.h"
#include "llvm/ADT/StringSwitch.h"
#include "llvm/Support/Endian.h"
#include "llvm/Support/FileOutputBuffer.h"
#include "llvm/Support/StringSaver.h"
#include "llvm/Support/raw_ostream.h"
using namespace llvm;
using namespace llvm::ELF;
using namespace llvm::object;
using namespace llvm::support::endian;
using namespace lld;
using namespace lld::elf;
namespace {
// The writer writes a SymbolTable result to a file.
template <class ELFT> class Writer {
public:
typedef typename ELFT::uint uintX_t;
typedef typename ELFT::Shdr Elf_Shdr;
typedef typename ELFT::Ehdr Elf_Ehdr;
typedef typename ELFT::Phdr Elf_Phdr;
typedef typename ELFT::Sym Elf_Sym;
typedef typename ELFT::SymRange Elf_Sym_Range;
typedef typename ELFT::Rela Elf_Rela;
Writer(SymbolTable<ELFT> &S) : Symtab(S) {}
void run();
private:
// This describes a program header entry.
// Each contains type, access flags and range of output sections that will be
// placed in it.
struct Phdr {
Phdr(unsigned Type, unsigned Flags) {
H.p_type = Type;
H.p_flags = Flags;
}
Elf_Phdr H = {};
OutputSectionBase<ELFT> *First = nullptr;
OutputSectionBase<ELFT> *Last = nullptr;
};
void copyLocalSymbols();
void addReservedSymbols();
void createSections();
void addPredefinedSections();
bool needsGot();
template <class RelTy>
void scanRelocs(InputSectionBase<ELFT> &C, ArrayRef<RelTy> Rels);
void scanRelocs(InputSection<ELFT> &C);
void scanRelocs(InputSectionBase<ELFT> &S, const Elf_Shdr &RelSec);
RelExpr adjustExpr(SymbolBody &S, bool IsWrite, RelExpr Expr, uint32_t Type);
void createPhdrs();
void assignAddresses();
void assignFileOffsets();
void setPhdrs();
void fixHeaders();
void fixSectionAlignments();
void fixAbsoluteSymbols();
void openFile();
void writeHeader();
void writeSections();
void writeBuildId();
bool isDiscarded(InputSectionBase<ELFT> *IS) const;
StringRef getOutputSectionName(InputSectionBase<ELFT> *S) const;
bool needsInterpSection() const {
return !Symtab.getSharedFiles().empty() && !Config->DynamicLinker.empty();
}
bool isOutputDynamic() const {
return !Symtab.getSharedFiles().empty() || Config->Pic;
}
template <class RelTy>
void scanRelocsForThunks(const elf::ObjectFile<ELFT> &File,
ArrayRef<RelTy> Rels);
void ensureBss();
void addCommonSymbols(std::vector<DefinedCommon *> &Syms);
void addCopyRelSymbol(SharedSymbol<ELFT> *Sym);
std::unique_ptr<llvm::FileOutputBuffer> Buffer;
BumpPtrAllocator Alloc;
std::vector<OutputSectionBase<ELFT> *> OutputSections;
std::vector<std::unique_ptr<OutputSectionBase<ELFT>>> OwningSections;
void addRelIpltSymbols();
void addStartEndSymbols();
void addStartStopSymbols(OutputSectionBase<ELFT> *Sec);
SymbolTable<ELFT> &Symtab;
std::vector<Phdr> Phdrs;
uintX_t FileSize;
uintX_t SectionHeaderOff;
// 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> void elf::writeResult(SymbolTable<ELFT> *Symtab) {
typedef typename ELFT::uint uintX_t;
typedef typename ELFT::Ehdr Elf_Ehdr;
// Create singleton output sections.
DynamicSection<ELFT> Dynamic(*Symtab);
EhFrameHeader<ELFT> EhFrameHdr;
GotSection<ELFT> Got;
InterpSection<ELFT> Interp;
PltSection<ELFT> Plt;
RelocationSection<ELFT> RelaDyn(Config->Rela ? ".rela.dyn" : ".rel.dyn");
StringTableSection<ELFT> DynStrTab(".dynstr", true);
StringTableSection<ELFT> ShStrTab(".shstrtab", false);
SymbolTableSection<ELFT> DynSymTab(*Symtab, DynStrTab);
VersionTableSection<ELFT> VerSym;
VersionNeedSection<ELFT> VerNeed;
OutputSectionBase<ELFT> ElfHeader("", 0, SHF_ALLOC);
ElfHeader.setSize(sizeof(Elf_Ehdr));
OutputSectionBase<ELFT> ProgramHeaders("", 0, SHF_ALLOC);
ProgramHeaders.updateAlign(sizeof(uintX_t));
// Instantiate optional output sections if they are needed.
std::unique_ptr<BuildIdSection<ELFT>> BuildId;
std::unique_ptr<GnuHashTableSection<ELFT>> GnuHashTab;
std::unique_ptr<GotPltSection<ELFT>> GotPlt;
std::unique_ptr<HashTableSection<ELFT>> HashTab;
std::unique_ptr<RelocationSection<ELFT>> RelaPlt;
std::unique_ptr<StringTableSection<ELFT>> StrTab;
std::unique_ptr<SymbolTableSection<ELFT>> SymTabSec;
std::unique_ptr<OutputSection<ELFT>> MipsRldMap;
if (Config->BuildId == BuildIdKind::Fnv1)
BuildId.reset(new BuildIdFnv1<ELFT>);
else if (Config->BuildId == BuildIdKind::Md5)
BuildId.reset(new BuildIdMd5<ELFT>);
else if (Config->BuildId == BuildIdKind::Sha1)
BuildId.reset(new BuildIdSha1<ELFT>);
if (Config->GnuHash)
GnuHashTab.reset(new GnuHashTableSection<ELFT>);
if (Config->SysvHash)
HashTab.reset(new HashTableSection<ELFT>);
if (Target->UseLazyBinding) {
StringRef S = Config->Rela ? ".rela.plt" : ".rel.plt";
GotPlt.reset(new GotPltSection<ELFT>);
RelaPlt.reset(new RelocationSection<ELFT>(S));
}
if (!Config->StripAll) {
StrTab.reset(new StringTableSection<ELFT>(".strtab", false));
SymTabSec.reset(new SymbolTableSection<ELFT>(*Symtab, *StrTab));
}
if (Config->EMachine == EM_MIPS && !Config->Shared) {
// 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
MipsRldMap.reset(new OutputSection<ELFT>(".rld_map", SHT_PROGBITS,
SHF_ALLOC | SHF_WRITE));
MipsRldMap->setSize(sizeof(uintX_t));
MipsRldMap->updateAlign(sizeof(uintX_t));
}
Out<ELFT>::BuildId = BuildId.get();
Out<ELFT>::DynStrTab = &DynStrTab;
Out<ELFT>::DynSymTab = &DynSymTab;
Out<ELFT>::Dynamic = &Dynamic;
Out<ELFT>::EhFrameHdr = &EhFrameHdr;
Out<ELFT>::GnuHashTab = GnuHashTab.get();
Out<ELFT>::Got = &Got;
Out<ELFT>::GotPlt = GotPlt.get();
Out<ELFT>::HashTab = HashTab.get();
Out<ELFT>::Interp = &Interp;
Out<ELFT>::Plt = &Plt;
Out<ELFT>::RelaDyn = &RelaDyn;
Out<ELFT>::RelaPlt = RelaPlt.get();
Out<ELFT>::ShStrTab = &ShStrTab;
Out<ELFT>::StrTab = StrTab.get();
Out<ELFT>::SymTab = SymTabSec.get();
Out<ELFT>::VerSym = &VerSym;
Out<ELFT>::VerNeed = &VerNeed;
Out<ELFT>::Bss = nullptr;
Out<ELFT>::MipsRldMap = MipsRldMap.get();
Out<ELFT>::Opd = nullptr;
Out<ELFT>::OpdBuf = nullptr;
Out<ELFT>::TlsPhdr = nullptr;
Out<ELFT>::ElfHeader = &ElfHeader;
Out<ELFT>::ProgramHeaders = &ProgramHeaders;
Writer<ELFT>(*Symtab).run();
}
// The main function of the writer.
template <class ELFT> void Writer<ELFT>::run() {
if (!Config->DiscardAll)
copyLocalSymbols();
addReservedSymbols();
createSections();
if (HasError)
return;
if (Config->Relocatable) {
assignFileOffsets();
} else {
createPhdrs();
fixHeaders();
if (ScriptConfig->DoLayout) {
Script<ELFT>::X->assignAddresses(OutputSections);
} else {
fixSectionAlignments();
assignAddresses();
}
assignFileOffsets();
setPhdrs();
fixAbsoluteSymbols();
}
openFile();
if (HasError)
return;
writeHeader();
writeSections();
writeBuildId();
if (HasError)
return;
check(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 Alignment;
};
}
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.Alignment);
}
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.Alignment == RHS.Alignment;
}
};
}
// Returns the number of relocations processed.
template <class ELFT>
static unsigned handleTlsRelocation(uint32_t Type, SymbolBody &Body,
InputSectionBase<ELFT> &C,
typename ELFT::uint Offset,
typename ELFT::uint Addend, RelExpr Expr) {
if (!(C.getSectionHdr()->sh_flags & SHF_ALLOC))
return 0;
if (!Body.isTls())
return 0;
typedef typename ELFT::uint uintX_t;
if (Expr == R_TLSLD_PC || Expr == R_TLSLD) {
// Local-Dynamic relocs can be relaxed to Local-Exec.
if (!Config->Shared) {
C.Relocations.push_back(
{R_RELAX_TLS_LD_TO_LE, Type, Offset, Addend, &Body});
return 2;
}
if (Out<ELFT>::Got->addTlsIndex())
Out<ELFT>::RelaDyn->addReloc({Target->TlsModuleIndexRel, Out<ELFT>::Got,
Out<ELFT>::Got->getTlsIndexOff(), false,
nullptr, 0});
C.Relocations.push_back({Expr, Type, Offset, Addend, &Body});
return 1;
}
// Local-Dynamic relocs can be relaxed to Local-Exec.
if (Target->isTlsLocalDynamicRel(Type) && !Config->Shared) {
C.Relocations.push_back(
{R_RELAX_TLS_LD_TO_LE, Type, Offset, Addend, &Body});
return 1;
}
if (Target->isTlsGlobalDynamicRel(Type)) {
if (Config->Shared) {
if (Out<ELFT>::Got->addDynTlsEntry(Body)) {
uintX_t Off = Out<ELFT>::Got->getGlobalDynOffset(Body);
Out<ELFT>::RelaDyn->addReloc(
{Target->TlsModuleIndexRel, Out<ELFT>::Got, Off, false, &Body, 0});
Out<ELFT>::RelaDyn->addReloc({Target->TlsOffsetRel, Out<ELFT>::Got,
Off + (uintX_t)sizeof(uintX_t), false,
&Body, 0});
}
C.Relocations.push_back({Expr, Type, Offset, Addend, &Body});
return 1;
}
// Global-Dynamic relocs can be relaxed to Initial-Exec or Local-Exec
// depending on the symbol being locally defined or not.
if (Body.isPreemptible()) {
Expr =
Expr == R_TLSGD_PC ? R_RELAX_TLS_GD_TO_IE_PC : R_RELAX_TLS_GD_TO_IE;
C.Relocations.push_back({Expr, Type, Offset, Addend, &Body});
if (!Body.isInGot()) {
Out<ELFT>::Got->addEntry(Body);
Out<ELFT>::RelaDyn->addReloc({Target->TlsGotRel, Out<ELFT>::Got,
Body.getGotOffset<ELFT>(), false, &Body,
0});
}
return 2;
}
C.Relocations.push_back(
{R_RELAX_TLS_GD_TO_LE, Type, Offset, Addend, &Body});
return Target->TlsGdToLeSkip;
}
// Initial-Exec relocs can be relaxed to Local-Exec if the symbol is locally
// defined.
if (Target->isTlsInitialExecRel(Type) && !Config->Shared &&
!Body.isPreemptible()) {
C.Relocations.push_back(
{R_RELAX_TLS_IE_TO_LE, Type, Offset, Addend, &Body});
return 1;
}
return 0;
}
// Some targets might require creation of thunks for relocations. Now we
// support only MIPS which requires LA25 thunk to call PIC code from non-PIC
// one. Scan relocations to find each one requires thunk.
template <class ELFT>
template <class RelTy>
void Writer<ELFT>::scanRelocsForThunks(const elf::ObjectFile<ELFT> &File,
ArrayRef<RelTy> Rels) {
for (const RelTy &RI : Rels) {
uint32_t Type = RI.getType(Config->Mips64EL);
SymbolBody &Body = File.getRelocTargetSym(RI);
if (Body.hasThunk() || !Target->needsThunk(Type, File, Body))
continue;
auto *D = cast<DefinedRegular<ELFT>>(&Body);
auto *S = cast<InputSection<ELFT>>(D->Section);
S->addThunk(Body);
}
}
template <endianness E> static int16_t readSignedLo16(const uint8_t *Loc) {
return read32<E>(Loc) & 0xffff;
}
template <class RelTy>
static uint32_t getMipsPairType(const RelTy *Rel, const SymbolBody &Sym) {
switch (Rel->getType(Config->Mips64EL)) {
case R_MIPS_HI16:
return R_MIPS_LO16;
case R_MIPS_GOT16:
return Sym.isLocal() ? R_MIPS_LO16 : R_MIPS_NONE;
case R_MIPS_PCHI16:
return R_MIPS_PCLO16;
case R_MICROMIPS_HI16:
return R_MICROMIPS_LO16;
default:
return R_MIPS_NONE;
}
}
template <class ELFT, class RelTy>
static int32_t findMipsPairedAddend(const uint8_t *Buf, const uint8_t *BufLoc,
SymbolBody &Sym, const RelTy *Rel,
const RelTy *End) {
uint32_t SymIndex = Rel->getSymbol(Config->Mips64EL);
uint32_t Type = getMipsPairType(Rel, Sym);
// Some MIPS relocations use addend calculated from addend of the relocation
// itself and addend of paired relocation. ABI requires to compute such
// combined addend in case of REL relocation record format only.
// See p. 4-17 at ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
if (RelTy::IsRela || Type == R_MIPS_NONE)
return 0;
for (const RelTy *RI = Rel; RI != End; ++RI) {
if (RI->getType(Config->Mips64EL) != Type)
continue;
if (RI->getSymbol(Config->Mips64EL) != SymIndex)
continue;
const endianness E = ELFT::TargetEndianness;
return ((read32<E>(BufLoc) & 0xffff) << 16) +
readSignedLo16<E>(Buf + RI->r_offset);
}
unsigned OldType = Rel->getType(Config->Mips64EL);
StringRef OldName = getELFRelocationTypeName(Config->EMachine, OldType);
StringRef NewName = getELFRelocationTypeName(Config->EMachine, Type);
warning("can't find matching " + NewName + " relocation for " + OldName);
return 0;
}
// True if non-preemptable symbol always has the same value regardless of where
// the DSO is loaded.
template <class ELFT> static bool isAbsolute(const SymbolBody &Body) {
if (Body.isUndefined())
return !Body.isLocal() && Body.symbol()->isWeak();
if (const auto *DR = dyn_cast<DefinedRegular<ELFT>>(&Body))
return DR->Section == nullptr; // Absolute symbol.
return false;
}
static bool needsPlt(RelExpr Expr) {
return Expr == R_PLT_PC || Expr == R_PPC_PLT_OPD || Expr == R_PLT;
}
// True if this expression is of the form Sym - X, where X is a position in the
// file (PC, or GOT for example).
static bool isRelExpr(RelExpr Expr) {
return Expr == R_PC || Expr == R_GOTREL || Expr == R_PAGE_PC;
}
template <class ELFT>
static bool isStaticLinkTimeConstant(RelExpr E, uint32_t Type,
const SymbolBody &Body) {
// These expressions always compute a constant
if (E == R_SIZE || E == R_GOT_FROM_END || E == R_GOT_OFF || E == R_MIPS_GOT ||
E == R_MIPS_GOT_LOCAL || E == R_GOT_PAGE_PC || E == R_GOT_PC ||
E == R_PLT_PC || E == R_TLSGD_PC || E == R_TLSGD || E == R_PPC_PLT_OPD)
return true;
// These never do, except if the entire file is position dependent or if
// only the low bits are used.
if (E == R_GOT || E == R_PLT)
return Target->usesOnlyLowPageBits(Type) || !Config->Pic;
if (Body.isPreemptible())
return false;
if (!Config->Pic)
return true;
bool AbsVal = isAbsolute<ELFT>(Body) || Body.isTls();
bool RelE = isRelExpr(E);
if (AbsVal && !RelE)
return true;
if (!AbsVal && RelE)
return true;
// Relative relocation to an absolute value. This is normally unrepresentable,
// but if the relocation refers to a weak undefined symbol, we allow it to
// resolve to the image base. This is a little strange, but it allows us to
// link function calls to such symbols. Normally such a call will be guarded
// with a comparison, which will load a zero from the GOT.
if (AbsVal && RelE) {
if (Body.isUndefined() && !Body.isLocal() && Body.symbol()->isWeak())
return true;
StringRef S = getELFRelocationTypeName(Config->EMachine, Type);
error("relocation " + S + " cannot refer to absolute symbol " +
Body.getName());
return true;
}
return Target->usesOnlyLowPageBits(Type);
}
static RelExpr toPlt(RelExpr Expr) {
if (Expr == R_PPC_OPD)
return R_PPC_PLT_OPD;
if (Expr == R_PC)
return R_PLT_PC;
if (Expr == R_ABS)
return R_PLT;
return Expr;
}
static RelExpr fromPlt(RelExpr Expr) {
// We decided not to use a plt. Optimize a reference to the plt to a
// reference to the symbol itself.
if (Expr == R_PLT_PC)
return R_PC;
if (Expr == R_PPC_PLT_OPD)
return R_PPC_OPD;
if (Expr == R_PLT)
return R_ABS;
return Expr;
}
template <class ELFT>
RelExpr Writer<ELFT>::adjustExpr(SymbolBody &Body, bool IsWrite, RelExpr Expr,
uint32_t Type) {
bool Preemptible = Body.isPreemptible();
if (Body.isGnuIFunc())
Expr = toPlt(Expr);
else if (needsPlt(Expr) && !Preemptible)
Expr = fromPlt(Expr);
if (IsWrite || isStaticLinkTimeConstant<ELFT>(Expr, Type, Body))
return Expr;
// This relocation would require the dynamic linker to write a value to read
// only memory. We can hack around it if we are producing an executable and
// the refered symbol can be preemepted to refer to the executable.
if (Config->Shared || (Config->Pic && !isRelExpr(Expr))) {
StringRef S = getELFRelocationTypeName(Config->EMachine, Type);
error("relocation " + S + " cannot be used when making a shared "
"object; recompile with -fPIC.");
return Expr;
}
if (Body.getVisibility() != STV_DEFAULT) {
error("Cannot preempt symbol");
return Expr;
}
if (Body.isObject()) {
// Produce a copy relocation.
auto *B = cast<SharedSymbol<ELFT>>(&Body);
if (!B->needsCopy())
addCopyRelSymbol(B);
return Expr;
}
if (Body.isFunc()) {
// This handles a non PIC program call to function in a shared library. In
// an ideal world, we could just report an error saying the relocation can
// overflow at runtime. In the real world with glibc, crt1.o has a
// R_X86_64_PC32 pointing to libc.so.
//
// The general idea on how to handle such cases is to create a PLT entry and
// use that as the function value.
//
// For the static linking part, we just return a plt expr and everything
// else will use the the PLT entry as the address.
//
// The remaining problem is making sure pointer equality still works. We
// need the help of the dynamic linker for that. We let it know that we have
// a direct reference to a so symbol by creating an undefined symbol with a
// non zero st_value. Seeing that, the dynamic linker resolves the symbol to
// the value of the symbol we created. This is true even for got entries, so
// pointer equality is maintained. To avoid an infinite loop, the only entry
// that points to the real function is a dedicated got entry used by the
// plt. That is identified by special relocation types (R_X86_64_JUMP_SLOT,
// R_386_JMP_SLOT, etc).
Body.NeedsCopyOrPltAddr = true;
return toPlt(Expr);
}
error("Symbol is missing type");
return Expr;
}
// 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.
// This would have some drawbacks. For example, we would only know if .rela.dyn
// is needed after applying relocations. If it is, it will go after rw and rx
// sections. Given that it is ro, we will need an extra PT_LOAD. This
// complicates things for the dynamic linker and means we would have to reserve
// space for the extra PT_LOAD even if we end up not using it.
template <class ELFT>
template <class RelTy>
void Writer<ELFT>::scanRelocs(InputSectionBase<ELFT> &C, ArrayRef<RelTy> Rels) {
uintX_t Flags = C.getSectionHdr()->sh_flags;
bool IsWrite = Flags & SHF_WRITE;
auto AddDyn = [=](const DynamicReloc<ELFT> &Reloc) {
Out<ELFT>::RelaDyn->addReloc(Reloc);
};
const elf::ObjectFile<ELFT> &File = *C.getFile();
ArrayRef<uint8_t> SectionData = C.getSectionData();
const uint8_t *Buf = SectionData.begin();
for (auto I = Rels.begin(), E = Rels.end(); I != E; ++I) {
const RelTy &RI = *I;
SymbolBody &Body = File.getRelocTargetSym(RI);
uint32_t Type = RI.getType(Config->Mips64EL);
RelExpr Expr = Target->getRelExpr(Type, Body);
// Ignore "hint" relocation because it is for optional code optimization.
if (Expr == R_HINT)
continue;
uintX_t Offset = C.getOffset(RI.r_offset);
if (Offset == (uintX_t)-1)
continue;
bool Preemptible = Body.isPreemptible();
Expr = adjustExpr(Body, IsWrite, Expr, Type);
if (HasError)
continue;
// This relocation does not require got entry, but it is relative to got and
// needs it to be created. Here we request for that.
if (Expr == R_GOTONLY_PC || Expr == R_GOTREL || Expr == R_PPC_TOC)
HasGotOffRel = true;
uintX_t Addend = getAddend<ELFT>(RI);
const uint8_t *BufLoc = Buf + RI.r_offset;
if (!RelTy::IsRela)
Addend += Target->getImplicitAddend(BufLoc, Type);
if (Config->EMachine == EM_MIPS) {
Addend += findMipsPairedAddend<ELFT>(Buf, BufLoc, Body, &RI, E);
if (Type == R_MIPS_LO16 && Expr == R_PC)
// R_MIPS_LO16 expression has R_PC type iif the target is _gp_disp
// symbol. In that case we should use the following formula for
// calculation "AHL + GP - P + 4". Let's add 4 right here.
// For details see p. 4-19 at
// ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
Addend += 4;
}
if (unsigned Processed =
handleTlsRelocation<ELFT>(Type, Body, C, Offset, Addend, Expr)) {
I += (Processed - 1);
continue;
}
if (Expr == R_GOT && !isStaticLinkTimeConstant<ELFT>(Expr, Type, Body) &&
Config->Shared)
AddDyn({Target->RelativeRel, C.OutSec, Offset, true, &Body,
getAddend<ELFT>(RI)});
// If a relocation needs PLT, we create a PLT and a GOT slot
// for the symbol.
if (needsPlt(Expr)) {
C.Relocations.push_back({Expr, Type, Offset, Addend, &Body});
if (Body.isInPlt())
continue;
Out<ELFT>::Plt->addEntry(Body);
uint32_t Rel;
if (Body.isGnuIFunc())
Rel = Preemptible ? Target->PltRel : Target->IRelativeRel;
else
Rel = Target->UseLazyBinding ? Target->PltRel : Target->GotRel;
if (Target->UseLazyBinding) {
Out<ELFT>::GotPlt->addEntry(Body);
Out<ELFT>::RelaPlt->addReloc({Rel, Out<ELFT>::GotPlt,
Body.getGotPltOffset<ELFT>(),
!Preemptible, &Body, 0});
} else {
if (Body.isInGot())
continue;
Out<ELFT>::Got->addEntry(Body);
AddDyn({Rel, Out<ELFT>::Got, Body.getGotOffset<ELFT>(), !Preemptible,
&Body, 0});
}
continue;
}
if (Target->needsThunk(Type, File, Body)) {
C.Relocations.push_back({R_THUNK, Type, Offset, Addend, &Body});
continue;
}
// If a relocation needs GOT, we create a GOT slot for the symbol.
if (refersToGotEntry(Expr)) {
if (Config->EMachine == EM_MIPS && Expr == R_GOT_OFF)
Addend -= MipsGPOffset;
C.Relocations.push_back({Expr, Type, Offset, Addend, &Body});
if (Body.isInGot())
continue;
Out<ELFT>::Got->addEntry(Body);
if (Config->EMachine == EM_MIPS)
// 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
continue;
if (Preemptible || (Config->Pic && !isAbsolute<ELFT>(Body))) {
uint32_t DynType;
if (Body.isTls())
DynType = Target->TlsGotRel;
else if (Preemptible)
DynType = Target->GotRel;
else
DynType = Target->RelativeRel;
AddDyn({DynType, Out<ELFT>::Got, Body.getGotOffset<ELFT>(),
!Preemptible, &Body, 0});
}
continue;
}
if (Body.isPreemptible()) {
// We don't know anything about the finaly symbol. Just ask the dynamic
// linker to handle the relocation for us.
AddDyn({Target->getDynRel(Type), C.OutSec, Offset, false, &Body, Addend});
// MIPS ABI turns using of GOT and dynamic relocations inside out.
// While regular ABI uses dynamic relocations to fill up GOT entries
// MIPS ABI requires dynamic linker to fills up GOT entries using
// specially sorted dynamic symbol table. This affects even dynamic
// relocations against symbols which do not require GOT entries
// creation explicitly, i.e. do not have any GOT-relocations. So if
// a preemptible symbol has a dynamic relocation we anyway have
// to create a GOT entry for it.
// If a non-preemptible symbol has a dynamic relocation against it,
// dynamic linker takes it st_value, adds offset and writes down
// result of the dynamic relocation. In case of preemptible symbol
// dynamic linker performs symbol resolution, writes the symbol value
// to the GOT entry and reads the GOT entry when it needs to perform
// a dynamic relocation.
// ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf p.4-19
if (Config->EMachine == EM_MIPS && !Body.isInGot())
Out<ELFT>::Got->addEntry(Body);
continue;
}
// We know that this is the final symbol. If the program being produced
// is position independent, the final value is still not known.
// If the relocation depends on the symbol value (not the size or distances
// in the output), we still need some help from the dynamic linker.
// We can however do better than just copying the incoming relocation. We
// can process some of it and and just ask the dynamic linker to add the
// load address.
if (!Config->Pic || isStaticLinkTimeConstant<ELFT>(Expr, Type, Body)) {
if (Config->EMachine == EM_MIPS && Expr == R_GOTREL) {
Addend -= MipsGPOffset;
if (Body.isLocal())
Addend += File.getMipsGp0();
}
C.Relocations.push_back({Expr, Type, Offset, Addend, &Body});
continue;
}
if (Config->EMachine == EM_PPC64 && Type == R_PPC64_TOC)
Addend += getPPC64TocBase();
AddDyn({Target->RelativeRel, C.OutSec, Offset, true, &Body, Addend});
C.Relocations.push_back({Expr, Type, Offset, Addend, &Body});
}
// Scan relocations for necessary thunks.
if (Config->EMachine == EM_MIPS)
scanRelocsForThunks(File, Rels);
}
template <class ELFT> void Writer<ELFT>::scanRelocs(InputSection<ELFT> &C) {
// 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::relocateNative.
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->NoUndefined) {
if (Config->Relocatable)
return;
if (Config->Shared)
if (Sym->symbol()->Visibility == STV_DEFAULT)
return;
}
std::string Msg = "undefined symbol: " + Sym->getName().str();
if (InputFile *File = Sym->getSourceFile<ELFT>())
Msg += " in " + File->getName().str();
if (Config->NoinhibitExec)
warning(Msg);
else
error(Msg);
}
template <class ELFT>
static bool shouldKeepInSymtab(InputSectionBase<ELFT> *Sec, StringRef SymName,
const SymbolBody &B) {
if (B.isFile())
return false;
// We keep sections in symtab for relocatable output.
if (B.isSection())
return Config->Relocatable;
// 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);
}
template <class ELFT> static bool includeInSymtab(const SymbolBody &B) {
if (!B.isLocal() && !B.symbol()->IsUsedInRegularObj)
return false;
if (auto *D = dyn_cast<DefinedRegular<ELFT>>(&B)) {
// Always include absolute symbols.
if (!D->Section)
return true;
// Exclude symbols pointing to garbage-collected sections.
if (!D->Section->Live)
return false;
if (auto *S = dyn_cast<MergeInputSection<ELFT>>(D->Section))
if (S->getRangeAndSize(D->Value).first->second ==
MergeInputSection<ELFT>::PieceDead)
return false;
}
return true;
}
// 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<elf::ObjectFile<ELFT>> &F :
Symtab.getObjectFiles()) {
const char *StrTab = F->getStringTable().data();
for (SymbolBody *B : F->getLocalSymbols()) {
auto *DR = dyn_cast<DefinedRegular<ELFT>>(B);
// No reason to keep local undefined symbol in symtab.
if (!DR)
continue;
if (!includeInSymtab<ELFT>(*B))
continue;
StringRef SymName(StrTab + B->getNameOffset());
InputSectionBase<ELFT> *Sec = DR->Section;
if (!shouldKeepInSymtab<ELFT>(Sec, SymName, *B))
continue;
++Out<ELFT>::SymTab->NumLocals;
if (Config->Relocatable)
B->DynsymIndex = Out<ELFT>::SymTab->NumLocals;
F->KeptLocalSyms.push_back(
std::make_pair(DR, 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) {
if (!Config->ZRelro)
return false;
typename ELFT::uint 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 compareSections(OutputSectionBase<ELFT> *A,
OutputSectionBase<ELFT> *B) {
typedef typename ELFT::uint uintX_t;
int Comp = Script<ELFT>::X->compareSections(A->getName(), B->getName());
if (Comp != 0)
return Comp < 0;
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;
}
// The .bss section does not exist if no input file has a .bss section.
// This function creates one if that's the case.
template <class ELFT> void Writer<ELFT>::ensureBss() {
if (Out<ELFT>::Bss)
return;
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);
}
// 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->Alignment > B->Alignment;
});
ensureBss();
uintX_t Off = Out<ELFT>::Bss->getSize();
for (DefinedCommon *C : Syms) {
Off = alignTo(Off, C->Alignment);
Out<ELFT>::Bss->updateAlign(C->Alignment);
C->OffsetInBss = Off;
Off += C->Size;
}
Out<ELFT>::Bss->setSize(Off);
}
template <class ELFT> static uint32_t getAlignment(SharedSymbol<ELFT> *SS) {
typedef typename ELFFile<ELFT>::uintX_t uintX_t;
uintX_t SecAlign = SS->File->getSection(SS->Sym)->sh_addralign;
uintX_t SymValue = SS->Sym.st_value;
int TrailingZeros =
std::min(countTrailingZeros(SecAlign), countTrailingZeros(SymValue));
return 1 << TrailingZeros;
}
// Reserve space in .bss for copy relocation.
template <class ELFT>
void Writer<ELFT>::addCopyRelSymbol(SharedSymbol<ELFT> *SS) {
ensureBss();
uintX_t Align = getAlignment(SS);
uintX_t Off = alignTo(Out<ELFT>::Bss->getSize(), Align);
Out<ELFT>::Bss->setSize(Off + SS->template getSize<ELFT>());
Out<ELFT>::Bss->updateAlign(Align);
uintX_t Shndx = SS->Sym.st_shndx;
uintX_t Value = SS->Sym.st_value;
// Look through the DSO's dynamic symbol table for aliases and create a
// dynamic symbol for each one. This causes the copy relocation to correctly
// interpose any aliases.
for (const Elf_Sym &S : SS->File->getElfSymbols(true)) {
if (S.st_shndx != Shndx || S.st_value != Value)
continue;
auto *Alias = dyn_cast_or_null<SharedSymbol<ELFT>>(
Symtab.find(check(S.getName(SS->File->getStringTable()))));
if (!Alias)
continue;
Alias->OffsetInBss = Off;
Alias->NeedsCopyOrPltAddr = true;
Alias->symbol()->IsUsedInRegularObj = true;
}
Out<ELFT>::RelaDyn->addReloc(
{Target->CopyRel, Out<ELFT>::Bss, SS->OffsetInBss, false, SS, 0});
}
template <class ELFT>
StringRef Writer<ELFT>::getOutputSectionName(InputSectionBase<ELFT> *S) const {
StringRef Dest = Script<ELFT>::X->getOutputSection(S);
if (!Dest.empty())
return Dest;
StringRef Name = S->getSectionName();
for (StringRef V : {".text.", ".rodata.", ".data.rel.ro.", ".data.", ".bss.",
".init_array.", ".fini_array.", ".ctors.", ".dtors.",
".tbss.", ".gcc_except_table.", ".tdata."})
if (Name.startswith(V))
return V.drop_back();
return Name;
}
template <class ELFT>
void reportDiscarded(InputSectionBase<ELFT> *IS,
const std::unique_ptr<elf::ObjectFile<ELFT>> &File) {
if (!Config->PrintGcSections || !IS || IS->Live)
return;
llvm::errs() << "removing unused section from '" << IS->getSectionName()
<< "' in file '" << File->getName() << "'\n";
}
template <class ELFT>
bool Writer<ELFT>::isDiscarded(InputSectionBase<ELFT> *S) const {
return !S || S == &InputSection<ELFT>::Discarded || !S->Live ||
Script<ELFT>::X->isDiscarded(S);
}
template <class ELFT>
static Symbol *addOptionalSynthetic(SymbolTable<ELFT> &Table, StringRef Name,
OutputSectionBase<ELFT> *Sec,
typename ELFT::uint Val) {
SymbolBody *S = Table.find(Name);
if (!S)
return nullptr;
if (!S->isUndefined() && !S->isShared())
return S->symbol();
return Table.addSynthetic(Name, Sec, Val);
}
// 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;
StringRef S = Config->Rela ? "__rela_iplt_start" : "__rel_iplt_start";
addOptionalSynthetic(Symtab, S, Out<ELFT>::RelaPlt, 0);
S = Config->Rela ? "__rela_iplt_end" : "__rel_iplt_end";
addOptionalSynthetic(Symtab, S, Out<ELFT>::RelaPlt,
DefinedSynthetic<ELFT>::SectionEnd);
}
// 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 ELFT::Shdr Elf_Shdr;
typedef typename ELFT::uint 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) {
return Map.lookup({Name, Type, Flags, 0});
}
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,
Key.Alignment);
break;
case InputSectionBase<ELFT>::MipsReginfo:
Sec = new MipsReginfoOutputSection<ELFT>();
break;
case InputSectionBase<ELFT>::MipsOptions:
Sec = new MipsOptionsOutputSection<ELFT>();
break;
}
return {Sec, true};
}
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 alignment.
// This makes each output section simple and keeps a single level mapping from
// input to output.
uintX_t Alignment = 0;
if (isa<MergeInputSection<ELFT>>(C))
Alignment = std::max(H->sh_addralign, H->sh_entsize);
// GNU as can give .eh_frame section 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, Alignment};
}
// The linker is expected to define some symbols depending on
// the linking result. This function defines such symbols.
template <class ELFT> void Writer<ELFT>::addReservedSymbols() {
if (Config->EMachine == EM_MIPS) {
// Define _gp for MIPS. st_value of _gp symbol will be updated by Writer
// so that it points to an absolute address which 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.addSynthetic("_gp", Out<ELFT>::Got, MipsGPOffset);
// On MIPS O32 ABI, _gp_disp is a magic symbol designates offset between
// start of function and 'gp' pointer into GOT.
Symbol *Sym =
addOptionalSynthetic(Symtab, "_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(Symtab, "__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.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.
if (!isOutputDynamic())
Symtab.addIgnored("__tls_get_addr");
auto Define = [this](StringRef S, DefinedRegular<ELFT> *&Sym1,
DefinedRegular<ELFT> *&Sym2) {
Sym1 = Symtab.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.find(S))
if (B->isUndefined())
Sym2 = Symtab.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();
}
// Create output section objects and add them to OutputSections.
template <class ELFT> void 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);
// A core file does not usually contain unmodified segments except
// the first page of the executable. Add the build ID section now
// so that the section is included in the first page.
if (Out<ELFT>::BuildId)
OutputSections.push_back(Out<ELFT>::BuildId);
// Create output sections for input object file sections.
std::vector<OutputSectionBase<ELFT> *> RegularSections;
OutputSectionFactory<ELFT> Factory;
for (const std::unique_ptr<elf::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));
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);
// Sort section contents for __attribute__((init_priority(N)).
sortInitFini(Out<ELFT>::Dynamic->InitArraySec);
sortInitFini(Out<ELFT>::Dynamic->FiniArraySec);
sortCtorsDtors(Factory.lookup(".ctors", SHT_PROGBITS, SHF_WRITE | SHF_ALLOC));
sortCtorsDtors(Factory.lookup(".dtors", SHT_PROGBITS, 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.
if (!Config->Relocatable) {
addStartEndSymbols();
for (OutputSectionBase<ELFT> *Sec : RegularSections)
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 (isOutputDynamic())
Symtab.addSynthetic("_DYNAMIC", Out<ELFT>::Dynamic, 0);
// Define __rel[a]_iplt_{start,end} symbols if needed.
addRelIpltSymbols();
if (Out<ELFT>::EhFrameHdr->Sec)
Out<ELFT>::EhFrameHdr->Sec->finalize();
// Scan relocations. This must be done after every symbol is declared so that
// we can correctly decide if a dynamic relocation is needed.
// Check size() each time to guard against .bss being created.
for (unsigned I = 0; I < OutputSections.size(); ++I) {
OutputSectionBase<ELFT> *Sec = OutputSections[I];
Sec->forEachInputSection([&](InputSectionBase<ELFT> *S) {
if (auto *IS = dyn_cast<InputSection<ELFT>>(S)) {
// Set OutSecOff so that scanRelocs can use it.
uintX_t Off = alignTo(Sec->getSize(), S->Align);
IS->OutSecOff = Off;
scanRelocs(*IS);
// Now that scan relocs possibly changed the size, update the offset.
Sec->setSize(Off + S->getSize());
} else if (auto *EH = dyn_cast<EHInputSection<ELFT>>(S)) {
if (EH->RelocSection)
scanRelocs(*EH, *EH->RelocSection);
}
});
}
// Now that we have defined all possible symbols including linker-
// synthesized ones. Visit all symbols to give the finishing touches.
std::vector<DefinedCommon *> CommonSymbols;
for (Symbol *S : Symtab.getSymbols()) {
SymbolBody *Body = S->body();
// Set "used" bit for --as-needed.
if (S->IsUsedInRegularObj && !S->isWeak())
if (auto *SS = dyn_cast<SharedSymbol<ELFT>>(Body))
SS->File->IsUsed = true;
// 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>(Symtab, Body);
if (auto *C = dyn_cast<DefinedCommon>(Body))
CommonSymbols.push_back(C);
if (!includeInSymtab<ELFT>(*Body))
continue;
if (Out<ELFT>::SymTab)
Out<ELFT>::SymTab->addSymbol(Body);
if (isOutputDynamic() && S->includeInDynsym()) {
Out<ELFT>::DynSymTab->addSymbol(Body);
if (auto *SS = dyn_cast<SharedSymbol<ELFT>>(Body))
Out<ELFT>::VerNeed->addSymbol(SS);
}
}
// Do not proceed if there was an undefined symbol.
if (HasError)
return;
addCommonSymbols(CommonSymbols);
// 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>);
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 (isOutputDynamic())
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 (isOutputDynamic())
Out<ELFT>::Dynamic->finalize();
}
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)
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 HasGotOffRel;
}
// 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);
if (Out<ELFT>::VerNeed->getNeedNum() != 0) {
Add(Out<ELFT>::VerSym);
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);
Out<ELFT>::RelaPlt->Static = !isOutputDynamic();
}
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) {
this->Symtab.addSynthetic(Start, OS, 0);
this->Symtab.addSynthetic(End, OS, DefinedSynthetic<ELFT>::SectionEnd);
} else {
addOptionalSynthetic(this->Symtab, Start,
(OutputSectionBase<ELFT> *)nullptr, 0);
addOptionalSynthetic(this->Symtab, End,
(OutputSectionBase<ELFT> *)nullptr, 0);
}
};
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);
}
// 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, DefinedSynthetic<ELFT>::SectionEnd);
}
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;
}
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;
}
// Decide which program headers to create and which sections to include in each
// one.
template <class ELFT> void Writer<ELFT>::createPhdrs() {
auto AddHdr = [this](unsigned Type, unsigned Flags) {
return &*Phdrs.emplace(Phdrs.end(), Type, Flags);
};
auto AddSec = [](Phdr &Hdr, OutputSectionBase<ELFT> *Sec) {
Hdr.Last = Sec;
if (!Hdr.First)
Hdr.First = Sec;
Hdr.H.p_align = std::max<uintX_t>(Hdr.H.p_align, Sec->getAlign());
};
// The first phdr entry is PT_PHDR which describes the program header itself.
Phdr &Hdr = *AddHdr(PT_PHDR, PF_R);
AddSec(Hdr, Out<ELFT>::ProgramHeaders);
// PT_INTERP must be the second entry if exists.
if (needsInterpSection()) {
Phdr &Hdr = *AddHdr(PT_INTERP, toPhdrFlags(Out<ELFT>::Interp->getFlags()));
AddSec(Hdr, Out<ELFT>::Interp);
}
// Add the first PT_LOAD segment for regular output sections.
uintX_t Flags = PF_R;
Phdr *Load = AddHdr(PT_LOAD, Flags);
AddSec(*Load, Out<ELFT>::ElfHeader);
AddSec(*Load, 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 futher use when
// assign addresses.
if (Sec->getFlags() & SHF_TLS)
AddSec(TlsHdr, Sec);
if (!needsPtLoad<ELFT>(Sec))
continue;
// If flags changed then we want new load segment.
uintX_t NewFlags = toPhdrFlags(Sec->getFlags());
if (Flags != NewFlags) {
Load = AddHdr(PT_LOAD, NewFlags);
Flags = NewFlags;
}
AddSec(*Load, Sec);
if (isRelroSection(Sec))
AddSec(RelRo, Sec);
if (Sec->getType() == SHT_NOTE)
AddSec(Note, Sec);
}
// Add the TLS segment unless it's empty.
if (TlsHdr.First)
Phdrs.push_back(std::move(TlsHdr));
// Add an entry for .dynamic.
if (isOutputDynamic()) {
Phdr &H = *AddHdr(PT_DYNAMIC, toPhdrFlags(Out<ELFT>::Dynamic->getFlags()));
AddSec(H, 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)
Phdrs.push_back(std::move(RelRo));
// PT_GNU_EH_FRAME is a special section pointing on .eh_frame_hdr.
if (Out<ELFT>::EhFrameHdr->Live) {
Phdr &Hdr = *AddHdr(PT_GNU_EH_FRAME,
toPhdrFlags(Out<ELFT>::EhFrameHdr->getFlags()));
AddSec(Hdr, 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)
AddHdr(PT_GNU_STACK, PF_R | PF_W);
if (Note.First)
Phdrs.push_back(std::move(Note));
Out<ELFT>::ProgramHeaders->setSize(sizeof(Elf_Phdr) * Phdrs.size());
}
// 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->DoLayout ? 0 : Target->getVAStart();
Out<ELFT>::ElfHeader->setVA(BaseVA);
Out<ELFT>::ElfHeader->setFileOffset(0);
uintX_t Off = Out<ELFT>::ElfHeader->getSize();
Out<ELFT>::ProgramHeaders->setVA(Off + BaseVA);
Out<ELFT>::ProgramHeaders->setFileOffset(Off);
}
// Assign VAs (addresses at run-time) to output sections.
template <class ELFT> void Writer<ELFT>::assignAddresses() {
uintX_t VA = Target->getVAStart() + Out<ELFT>::ElfHeader->getSize() +
Out<ELFT>::ProgramHeaders->getSize();
uintX_t ThreadBssOffset = 0;
for (OutputSectionBase<ELFT> *Sec : OutputSections) {
uintX_t Align = Sec->getAlign();
if (Sec->PageAlign)
Align = std::max<uintX_t>(Align, Target->PageSize);
// We only assign VAs to allocated sections.
if (needsPtLoad<ELFT>(Sec)) {
VA = alignTo(VA, Align);
Sec->setVA(VA);
VA += Sec->getSize();
} else if (Sec->getFlags() & SHF_TLS && Sec->getType() == SHT_NOBITS) {
uintX_t TVA = VA + ThreadBssOffset;
TVA = alignTo(TVA, Align);
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 Align = Sec->getAlign();
if (Sec->PageAlign)
Align = std::max<uintX_t>(Align, Target->PageSize);
Off = alignTo(Off, Align);
// Relocatable output does not have program headers
// and does not need any other offset adjusting.
if (Config->Relocatable || !(Sec->getFlags() & SHF_ALLOC))
return Off;
return alignTo(Off, Target->PageSize, Sec->getVA());
}
// Assign file offsets to output sections.
template <class ELFT> void Writer<ELFT>::assignFileOffsets() {
uintX_t Off =
Out<ELFT>::ElfHeader->getSize() + Out<ELFT>::ProgramHeaders->getSize();
for (OutputSectionBase<ELFT> *Sec : OutputSections) {
if (Sec->getType() == SHT_NOBITS) {
Sec->setFileOffset(Off);
continue;
}
Off = getFileAlignment<ELFT>(Off, Sec);
Sec->setFileOffset(Off);
Off += Sec->getSize();
}
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 = Target->PageSize;
else if (H.p_type == PT_GNU_RELRO)
H.p_align = 1;
H.p_paddr = 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;
H.p_memsz = alignTo(H.p_memsz, H.p_align);
}
}
}
static uint32_t getMipsEFlags(bool Is64Bits) {
// FIXME: In fact ELF flags depends on ELF flags of input object files
// and selected emulation. For now just use hard coded values.
if (Is64Bits)
return EF_MIPS_CPIC | EF_MIPS_PIC | EF_MIPS_ARCH_64R2;
uint32_t V = EF_MIPS_CPIC | EF_MIPS_ABI_O32 | EF_MIPS_ARCH_32R2;
if (Config->Shared)
V |= EF_MIPS_PIC;
return V;
}
template <class ELFT> static typename ELFT::uint getEntryAddr() {
if (Symbol *S = Config->EntrySym)
return S->body()->getVA<ELFT>();
if (Config->EntryAddr != uint64_t(-1))
return Config->EntryAddr;
return 0;
}
template <class ELFT> static uint8_t getELFEncoding() {
if (ELFT::TargetEndianness == llvm::support::little)
return ELFDATA2LSB;
return ELFDATA2MSB;
}
static uint16_t getELFType() {
if (Config->Pic)
return ET_DYN;
if (Config->Relocatable)
return ET_REL;
return ET_EXEC;
}
// This function is called after we have assigned address and size
// to each section. This function fixes some predefined absolute
// symbol values that depend on section address and size.
template <class ELFT> void Writer<ELFT>::fixAbsoluteSymbols() {
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.getEMachine();
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_MIPS)
EHdr->e_flags = getMipsEFlags(ELFT::Is64Bits);
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 (BufferOrErr)
Buffer = std::move(*BufferOrErr);
else
error(BufferOrErr, "failed to open " + Config->OutputFile);
}
// 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());
}
for (OutputSectionBase<ELFT> *Sec : OutputSections)
if (Sec != Out<ELFT>::Opd)
Sec->writeTo(Buf + Sec->getFileOff());
}
template <class ELFT> void Writer<ELFT>::writeBuildId() {
BuildIdSection<ELFT> *S = Out<ELFT>::BuildId;
if (!S)
return;
// Compute a hash of all sections except .debug_* sections.
// We skip debug sections because they tend to be very large
// and their contents are very likely to be the same as long as
// other sections are the same.
uint8_t *Start = Buffer->getBufferStart();
uint8_t *Last = Start;
std::vector<ArrayRef<uint8_t>> Regions;
for (OutputSectionBase<ELFT> *Sec : OutputSections) {
uint8_t *End = Start + Sec->getFileOff();
if (!Sec->getName().startswith(".debug_"))
Regions.push_back({Last, End});
Last = End;
}
Regions.push_back({Last, Start + FileSize});
S->writeBuildId(Regions);
}
template void elf::writeResult<ELF32LE>(SymbolTable<ELF32LE> *Symtab);
template void elf::writeResult<ELF32BE>(SymbolTable<ELF32BE> *Symtab);
template void elf::writeResult<ELF64LE>(SymbolTable<ELF64LE> *Symtab);
template void elf::writeResult<ELF64BE>(SymbolTable<ELF64BE> *Symtab);
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