llvm-project/lld/ELF/OutputSections.cpp

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//===- OutputSections.cpp -------------------------------------------------===//
//
// The LLVM Linker
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#include "OutputSections.h"
#include "Config.h"
#include "SymbolTable.h"
#include "Target.h"
using namespace llvm;
using namespace llvm::object;
using namespace llvm::ELF;
using namespace lld;
using namespace lld::elf2;
template <bool Is64Bits>
OutputSectionBase<Is64Bits>::OutputSectionBase(StringRef Name, uint32_t sh_type,
uintX_t sh_flags)
: Name(Name) {
memset(&Header, 0, sizeof(HeaderT));
Header.sh_type = sh_type;
Header.sh_flags = sh_flags;
}
template <class ELFT>
GotSection<ELFT>::GotSection()
: OutputSectionBase<ELFT::Is64Bits>(".got", llvm::ELF::SHT_PROGBITS,
llvm::ELF::SHF_ALLOC |
llvm::ELF::SHF_WRITE) {
this->Header.sh_addralign = this->getAddrSize();
}
template <class ELFT> void GotSection<ELFT>::addEntry(SymbolBody *Sym) {
Sym->setGotIndex(Entries.size());
Entries.push_back(Sym);
}
template <class ELFT>
typename GotSection<ELFT>::uintX_t
GotSection<ELFT>::getEntryAddr(const SymbolBody &B) const {
return this->getVA() + B.getGotIndex() * this->getAddrSize();
}
template <class ELFT>
PltSection<ELFT>::PltSection(const GotSection<ELFT> &GotSec)
: OutputSectionBase<ELFT::Is64Bits>(".plt", llvm::ELF::SHT_PROGBITS,
llvm::ELF::SHF_ALLOC |
llvm::ELF::SHF_EXECINSTR),
GotSec(GotSec) {
this->Header.sh_addralign = 16;
}
template <class ELFT> void PltSection<ELFT>::writeTo(uint8_t *Buf) {
uintptr_t Start = reinterpret_cast<uintptr_t>(Buf);
for (const SymbolBody *E : Entries) {
uint64_t GotEntryAddr = GotSec.getEntryAddr(*E);
uintptr_t InstPos = reinterpret_cast<uintptr_t>(Buf);
uint64_t PltEntryAddr = (InstPos - Start) + this->getVA();
Target->writePltEntry(Buf, GotEntryAddr, PltEntryAddr);
Buf += 8;
}
}
template <class ELFT> void PltSection<ELFT>::addEntry(SymbolBody *Sym) {
Sym->setPltIndex(Entries.size());
Entries.push_back(Sym);
}
template <class ELFT>
typename PltSection<ELFT>::uintX_t
PltSection<ELFT>::getEntryAddr(const SymbolBody &B) const {
return this->getVA() + B.getPltIndex() * EntrySize;
}
template <class ELFT>
RelocationSection<ELFT>::RelocationSection(SymbolTableSection<ELFT> &DynSymSec,
const GotSection<ELFT> &GotSec,
bool IsRela)
: OutputSectionBase<ELFT::Is64Bits>(IsRela ? ".rela.dyn" : ".rel.dyn",
IsRela ? llvm::ELF::SHT_RELA
: llvm::ELF::SHT_REL,
llvm::ELF::SHF_ALLOC),
DynSymSec(DynSymSec), GotSec(GotSec), IsRela(IsRela) {
this->Header.sh_entsize = IsRela ? sizeof(Elf_Rela) : sizeof(Elf_Rel);
this->Header.sh_addralign = ELFT::Is64Bits ? 8 : 4;
}
template <class ELFT> void RelocationSection<ELFT>::writeTo(uint8_t *Buf) {
const unsigned EntrySize = IsRela ? sizeof(Elf_Rela) : sizeof(Elf_Rel);
bool IsMips64EL = Relocs[0].C.getFile()->getObj().isMips64EL();
for (const DynamicReloc<ELFT> &Rel : Relocs) {
auto *P = reinterpret_cast<Elf_Rel *>(Buf);
Buf += EntrySize;
const InputSection<ELFT> &C = Rel.C;
const Elf_Rel &RI = Rel.RI;
OutputSection<ELFT> *Out = C.getOutputSection();
uint32_t SymIndex = RI.getSymbol(IsMips64EL);
const SymbolBody *Body = C.getFile()->getSymbolBody(SymIndex);
uint32_t Type = RI.getType(IsMips64EL);
if (Target->relocNeedsGot(Type, *Body)) {
P->r_offset = GotSec.getEntryAddr(*Body);
P->setSymbolAndType(Body->getDynamicSymbolTableIndex(),
Target->getGotReloc(), IsMips64EL);
} else {
P->r_offset = RI.r_offset + C.getOutputSectionOff() + Out->getVA();
P->setSymbolAndType(Body->getDynamicSymbolTableIndex(), Type, IsMips64EL);
if (IsRela)
static_cast<Elf_Rela *>(P)->r_addend =
static_cast<const Elf_Rela &>(RI).r_addend;
}
}
}
template <class ELFT> void RelocationSection<ELFT>::finalize() {
this->Header.sh_link = DynSymSec.getSectionIndex();
this->Header.sh_size = Relocs.size() * this->Header.sh_entsize;
}
template <bool Is64Bits>
InterpSection<Is64Bits>::InterpSection()
: OutputSectionBase<Is64Bits>(".interp", llvm::ELF::SHT_PROGBITS,
llvm::ELF::SHF_ALLOC) {
this->Header.sh_size = Config->DynamicLinker.size() + 1;
this->Header.sh_addralign = 1;
}
template <bool Is64Bits>
template <endianness E>
void OutputSectionBase<Is64Bits>::writeHeaderTo(
typename ELFFile<ELFType<E, Is64Bits>>::Elf_Shdr *SHdr) {
SHdr->sh_name = Header.sh_name;
SHdr->sh_type = Header.sh_type;
SHdr->sh_flags = Header.sh_flags;
SHdr->sh_addr = Header.sh_addr;
SHdr->sh_offset = Header.sh_offset;
SHdr->sh_size = Header.sh_size;
SHdr->sh_link = Header.sh_link;
SHdr->sh_info = Header.sh_info;
SHdr->sh_addralign = Header.sh_addralign;
SHdr->sh_entsize = Header.sh_entsize;
}
template <bool Is64Bits> void InterpSection<Is64Bits>::writeTo(uint8_t *Buf) {
memcpy(Buf, Config->DynamicLinker.data(), Config->DynamicLinker.size());
}
template <class ELFT>
HashTableSection<ELFT>::HashTableSection(SymbolTableSection<ELFT> &DynSymSec)
: OutputSectionBase<ELFT::Is64Bits>(".hash", llvm::ELF::SHT_HASH,
llvm::ELF::SHF_ALLOC),
DynSymSec(DynSymSec) {
this->Header.sh_entsize = sizeof(Elf_Word);
this->Header.sh_addralign = sizeof(Elf_Word);
}
template <class ELFT> void HashTableSection<ELFT>::addSymbol(SymbolBody *S) {
StringRef Name = S->getName();
DynSymSec.addSymbol(Name);
Hashes.push_back(hash(Name));
S->setDynamicSymbolTableIndex(Hashes.size());
}
template <class ELFT>
DynamicSection<ELFT>::DynamicSection(SymbolTable &SymTab,
HashTableSection<ELFT> &HashSec,
RelocationSection<ELFT> &RelaDynSec)
: OutputSectionBase<ELFT::Is64Bits>(".dynamic", llvm::ELF::SHT_DYNAMIC,
llvm::ELF::SHF_ALLOC |
llvm::ELF::SHF_WRITE),
HashSec(HashSec), DynSymSec(HashSec.getDynSymSec()),
DynStrSec(DynSymSec.getStrTabSec()), RelaDynSec(RelaDynSec),
SymTab(SymTab) {
typename Base::HeaderT &Header = this->Header;
Header.sh_addralign = ELFT::Is64Bits ? 8 : 4;
Header.sh_entsize = ELFT::Is64Bits ? 16 : 8;
}
template <class ELFT> void DynamicSection<ELFT>::finalize() {
typename Base::HeaderT &Header = this->Header;
Header.sh_link = DynStrSec.getSectionIndex();
unsigned NumEntries = 0;
if (RelaDynSec.hasRelocs()) {
++NumEntries; // DT_RELA / DT_REL
++NumEntries; // DT_RELASZ / DT_RELSZ
++NumEntries; // DT_RELAENT / DT_RELENT
}
++NumEntries; // DT_SYMTAB
++NumEntries; // DT_SYMENT
++NumEntries; // DT_STRTAB
++NumEntries; // DT_STRSZ
++NumEntries; // DT_HASH
StringRef RPath = Config->RPath;
if (!RPath.empty()) {
++NumEntries; // DT_RUNPATH
DynStrSec.add(RPath);
}
const std::vector<std::unique_ptr<SharedFileBase>> &SharedFiles =
SymTab.getSharedFiles();
for (const std::unique_ptr<SharedFileBase> &File : SharedFiles)
DynStrSec.add(File->getName());
NumEntries += SharedFiles.size();
++NumEntries; // DT_NULL
Header.sh_size = NumEntries * Header.sh_entsize;
}
template <class ELFT> void DynamicSection<ELFT>::writeTo(uint8_t *Buf) {
typedef typename std::conditional<ELFT::Is64Bits, Elf64_Dyn, Elf32_Dyn>::type
Elf_Dyn;
auto *P = reinterpret_cast<Elf_Dyn *>(Buf);
if (RelaDynSec.hasRelocs()) {
bool IsRela = RelaDynSec.isRela();
P->d_tag = IsRela ? DT_RELA : DT_REL;
P->d_un.d_ptr = RelaDynSec.getVA();
++P;
P->d_tag = IsRela ? DT_RELASZ : DT_RELSZ;
P->d_un.d_val = RelaDynSec.getSize();
++P;
P->d_tag = IsRela ? DT_RELAENT : DT_RELENT;
P->d_un.d_val = IsRela ? sizeof(Elf_Rela) : sizeof(Elf_Rel);
++P;
}
P->d_tag = DT_SYMTAB;
P->d_un.d_ptr = DynSymSec.getVA();
++P;
P->d_tag = DT_SYMENT;
P->d_un.d_ptr = sizeof(Elf_Sym);
++P;
P->d_tag = DT_STRTAB;
P->d_un.d_ptr = DynStrSec.getVA();
++P;
P->d_tag = DT_STRSZ;
P->d_un.d_val = DynStrSec.data().size();
++P;
P->d_tag = DT_HASH;
P->d_un.d_ptr = HashSec.getVA();
++P;
StringRef RPath = Config->RPath;
if (!RPath.empty()) {
P->d_tag = DT_RUNPATH;
P->d_un.d_val = DynStrSec.getFileOff(RPath);
++P;
}
const std::vector<std::unique_ptr<SharedFileBase>> &SharedFiles =
SymTab.getSharedFiles();
for (const std::unique_ptr<SharedFileBase> &File : SharedFiles) {
P->d_tag = DT_NEEDED;
P->d_un.d_val = DynStrSec.getFileOff(File->getName());
++P;
}
P->d_tag = DT_NULL;
P->d_un.d_val = 0;
++P;
}
template <class ELFT>
OutputSection<ELFT>::OutputSection(const PltSection<ELFT> &PltSec,
const GotSection<ELFT> &GotSec,
const OutputSection<ELFT> &BssSec,
StringRef Name, uint32_t sh_type,
uintX_t sh_flags)
: OutputSectionBase<ELFT::Is64Bits>(Name, sh_type, sh_flags),
PltSec(PltSec), GotSec(GotSec), BssSec(BssSec) {}
template <class ELFT>
void OutputSection<ELFT>::addSection(InputSection<ELFT> *C) {
Sections.push_back(C);
C->setOutputSection(this);
uint32_t Align = C->getAlign();
if (Align > this->Header.sh_addralign)
this->Header.sh_addralign = Align;
uintX_t Off = this->Header.sh_size;
Off = RoundUpToAlignment(Off, Align);
C->setOutputSectionOff(Off);
Off += C->getSize();
this->Header.sh_size = Off;
}
template <class ELFT>
typename ELFFile<ELFT>::uintX_t
lld::elf2::getSymVA(const ELFSymbolBody<ELFT> &S,
const OutputSection<ELFT> &BssSec) {
switch (S.kind()) {
case SymbolBody::DefinedSyntheticKind:
return cast<DefinedSynthetic<ELFT>>(S).Section.getVA() + S.Sym.st_value;
case SymbolBody::DefinedAbsoluteKind:
return S.Sym.st_value;
case SymbolBody::DefinedRegularKind: {
const auto &DR = cast<DefinedRegular<ELFT>>(S);
const InputSection<ELFT> *SC = &DR.Section;
OutputSection<ELFT> *OS = SC->getOutputSection();
return OS->getVA() + SC->getOutputSectionOff() + DR.Sym.st_value;
}
case SymbolBody::DefinedCommonKind:
return BssSec.getVA() + cast<DefinedCommon<ELFT>>(S).OffsetInBSS;
case SymbolBody::SharedKind:
case SymbolBody::UndefinedKind:
return 0;
case SymbolBody::LazyKind:
break;
}
llvm_unreachable("Lazy symbol reached writer");
}
template <class ELFT>
typename ELFFile<ELFT>::uintX_t
lld::elf2::getLocalSymVA(const typename ELFFile<ELFT>::Elf_Sym *Sym,
const ObjectFile<ELFT> &File) {
uint32_t SecIndex = Sym->st_shndx;
if (SecIndex == SHN_XINDEX)
SecIndex = File.getObj().getExtendedSymbolTableIndex(
Sym, File.getSymbolTable(), File.getSymbolTableShndx());
ArrayRef<InputSection<ELFT> *> Sections = File.getSections();
InputSection<ELFT> *Section = Sections[SecIndex];
OutputSection<ELFT> *Out = Section->getOutputSection();
return Out->getVA() + Section->getOutputSectionOff() + Sym->st_value;
}
template <class ELFT> void OutputSection<ELFT>::writeTo(uint8_t *Buf) {
for (InputSection<ELFT> *C : Sections)
C->writeTo(Buf, BssSec, PltSec, GotSec);
}
template <bool Is64Bits>
StringTableSection<Is64Bits>::StringTableSection(bool Dynamic)
: OutputSectionBase<Is64Bits>(Dynamic ? ".dynstr" : ".strtab",
llvm::ELF::SHT_STRTAB,
Dynamic ? (uintX_t)llvm::ELF::SHF_ALLOC : 0),
Dynamic(Dynamic) {
this->Header.sh_addralign = 1;
}
template <bool Is64Bits>
void StringTableSection<Is64Bits>::writeTo(uint8_t *Buf) {
StringRef Data = StrTabBuilder.data();
memcpy(Buf, Data.data(), Data.size());
}
bool lld::elf2::includeInSymtab(const SymbolBody &B) {
if (B.isLazy())
return false;
if (!B.isUsedInRegularObj())
return false;
uint8_t V = B.getMostConstrainingVisibility();
if (V != STV_DEFAULT && V != STV_PROTECTED)
return false;
return true;
}
bool lld::elf2::includeInDynamicSymtab(const SymbolBody &B) {
if (Config->ExportDynamic || Config->Shared)
return true;
return B.isUsedInDynamicReloc();
}
bool lld::elf2::shouldKeepInSymtab(StringRef SymName) {
if (Config->DiscardNone)
return true;
// ELF defines dynamic locals as symbols which name starts with ".L".
return !(Config->DiscardLocals && SymName.startswith(".L"));
}
template <class ELFT>
SymbolTableSection<ELFT>::SymbolTableSection(
SymbolTable &Table, StringTableSection<ELFT::Is64Bits> &StrTabSec,
const OutputSection<ELFT> &BssSec)
: OutputSectionBase<ELFT::Is64Bits>(
StrTabSec.isDynamic() ? ".dynsym" : ".symtab",
StrTabSec.isDynamic() ? llvm::ELF::SHT_DYNSYM : llvm::ELF::SHT_SYMTAB,
StrTabSec.isDynamic() ? (uintX_t)llvm::ELF::SHF_ALLOC : 0),
Table(Table), StrTabSec(StrTabSec), BssSec(BssSec) {
typedef OutputSectionBase<ELFT::Is64Bits> Base;
typename Base::HeaderT &Header = this->Header;
Header.sh_entsize = sizeof(Elf_Sym);
Header.sh_addralign = ELFT::Is64Bits ? 8 : 4;
}
template <class ELFT> void SymbolTableSection<ELFT>::writeTo(uint8_t *Buf) {
Buf += sizeof(Elf_Sym);
// All symbols with STB_LOCAL binding precede the weak and global symbols.
// .dynsym only contains global symbols.
if (!Config->DiscardAll && !StrTabSec.isDynamic())
writeLocalSymbols(Buf);
writeGlobalSymbols(Buf);
}
template <class ELFT>
void SymbolTableSection<ELFT>::writeLocalSymbols(uint8_t *&Buf) {
// Iterate over all input object files to copy their local symbols
// to the output symbol table pointed by Buf.
for (const std::unique_ptr<ObjectFileBase> &FileB : Table.getObjectFiles()) {
auto &File = cast<ObjectFile<ELFT>>(*FileB);
Elf_Sym_Range Syms = File.getLocalSymbols();
for (const Elf_Sym &Sym : Syms) {
ErrorOr<StringRef> SymName = Sym.getName(File.getStringTable());
if (SymName && !shouldKeepInSymtab(*SymName))
continue;
auto *ESym = reinterpret_cast<Elf_Sym *>(Buf);
Buf += sizeof(*ESym);
ESym->st_name = (SymName) ? StrTabSec.getFileOff(*SymName) : 0;
ESym->st_size = Sym.st_size;
ESym->setBindingAndType(Sym.getBinding(), Sym.getType());
uint32_t SecIndex = Sym.st_shndx;
uintX_t VA = Sym.st_value;
if (SecIndex == SHN_ABS) {
ESym->st_shndx = SHN_ABS;
} else {
if (SecIndex == SHN_XINDEX)
SecIndex = File.getObj().getExtendedSymbolTableIndex(
&Sym, File.getSymbolTable(), File.getSymbolTableShndx());
ArrayRef<InputSection<ELFT> *> Sections = File.getSections();
const InputSection<ELFT> *Section = Sections[SecIndex];
const OutputSection<ELFT> *Out = Section->getOutputSection();
ESym->st_shndx = Out->getSectionIndex();
VA += Out->getVA() + Section->getOutputSectionOff();
}
ESym->st_value = VA;
}
}
}
template <class ELFT>
void SymbolTableSection<ELFT>::writeGlobalSymbols(uint8_t *&Buf) {
// Write the internal symbol table contents to the output symbol table
// pointed by Buf.
for (const std::pair<StringRef, Symbol *> &P : Table.getSymbols()) {
StringRef Name = P.first;
Symbol *Sym = P.second;
SymbolBody *Body = Sym->Body;
if (!includeInSymtab(*Body))
continue;
if (StrTabSec.isDynamic() && !includeInDynamicSymtab(*Body))
continue;
const auto &EBody = *cast<ELFSymbolBody<ELFT>>(Body);
const Elf_Sym &InputSym = EBody.Sym;
auto *ESym = reinterpret_cast<Elf_Sym *>(Buf);
Buf += sizeof(*ESym);
ESym->st_name = StrTabSec.getFileOff(Name);
const OutputSection<ELFT> *Out = nullptr;
const InputSection<ELFT> *Section = nullptr;
switch (EBody.kind()) {
case SymbolBody::DefinedSyntheticKind:
Out = &cast<DefinedSynthetic<ELFT>>(Body)->Section;
break;
case SymbolBody::DefinedRegularKind:
Section = &cast<DefinedRegular<ELFT>>(EBody).Section;
break;
case SymbolBody::DefinedCommonKind:
Out = &BssSec;
break;
case SymbolBody::UndefinedKind:
case SymbolBody::DefinedAbsoluteKind:
case SymbolBody::SharedKind:
break;
case SymbolBody::LazyKind:
llvm_unreachable("Lazy symbol got to output symbol table!");
}
ESym->setBindingAndType(InputSym.getBinding(), InputSym.getType());
ESym->st_size = InputSym.st_size;
ESym->setVisibility(EBody.getMostConstrainingVisibility());
if (InputSym.isAbsolute()) {
ESym->st_shndx = SHN_ABS;
ESym->st_value = InputSym.st_value;
}
if (Section)
Out = Section->getOutputSection();
ESym->st_value = getSymVA(EBody, BssSec);
if (Out)
ESym->st_shndx = Out->getSectionIndex();
}
}
namespace lld {
namespace elf2 {
template class OutputSectionBase<false>;
template class OutputSectionBase<true>;
template void OutputSectionBase<false>::writeHeaderTo<support::little>(
ELFFile<ELFType<support::little, false>>::Elf_Shdr *SHdr);
template void OutputSectionBase<true>::writeHeaderTo<support::little>(
ELFFile<ELFType<support::little, true>>::Elf_Shdr *SHdr);
template void OutputSectionBase<false>::writeHeaderTo<support::big>(
ELFFile<ELFType<support::big, false>>::Elf_Shdr *SHdr);
template void OutputSectionBase<true>::writeHeaderTo<support::big>(
ELFFile<ELFType<support::big, true>>::Elf_Shdr *SHdr);
template class GotSection<ELF32LE>;
template class GotSection<ELF32BE>;
template class GotSection<ELF64LE>;
template class GotSection<ELF64BE>;
template class PltSection<ELF32LE>;
template class PltSection<ELF32BE>;
template class PltSection<ELF64LE>;
template class PltSection<ELF64BE>;
template class RelocationSection<ELF32LE>;
template class RelocationSection<ELF32BE>;
template class RelocationSection<ELF64LE>;
template class RelocationSection<ELF64BE>;
template class InterpSection<false>;
template class InterpSection<true>;
template class HashTableSection<ELF32LE>;
template class HashTableSection<ELF32BE>;
template class HashTableSection<ELF64LE>;
template class HashTableSection<ELF64BE>;
template class DynamicSection<ELF32LE>;
template class DynamicSection<ELF32BE>;
template class DynamicSection<ELF64LE>;
template class DynamicSection<ELF64BE>;
template class OutputSection<ELF32LE>;
template class OutputSection<ELF32BE>;
template class OutputSection<ELF64LE>;
template class OutputSection<ELF64BE>;
template class StringTableSection<false>;
template class StringTableSection<true>;
template class SymbolTableSection<ELF32LE>;
template class SymbolTableSection<ELF32BE>;
template class SymbolTableSection<ELF64LE>;
template class SymbolTableSection<ELF64BE>;
template ELFFile<ELF32LE>::uintX_t
getSymVA(const ELFSymbolBody<ELF32LE> &, const OutputSection<ELF32LE> &);
template ELFFile<ELF32BE>::uintX_t
getSymVA(const ELFSymbolBody<ELF32BE> &, const OutputSection<ELF32BE> &);
template ELFFile<ELF64LE>::uintX_t
getSymVA(const ELFSymbolBody<ELF64LE> &, const OutputSection<ELF64LE> &);
template ELFFile<ELF64BE>::uintX_t
getSymVA(const ELFSymbolBody<ELF64BE> &, const OutputSection<ELF64BE> &);
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template ELFFile<ELF32LE>::uintX_t
getLocalSymVA(const ELFFile<ELF32LE>::Elf_Sym *, const ObjectFile<ELF32LE> &);
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template ELFFile<ELF32BE>::uintX_t
getLocalSymVA(const ELFFile<ELF32BE>::Elf_Sym *, const ObjectFile<ELF32BE> &);
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template ELFFile<ELF64LE>::uintX_t
getLocalSymVA(const ELFFile<ELF64LE>::Elf_Sym *, const ObjectFile<ELF64LE> &);
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template ELFFile<ELF64BE>::uintX_t
getLocalSymVA(const ELFFile<ELF64BE>::Elf_Sym *, const ObjectFile<ELF64BE> &);
}
}