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llvm/lld/ELF/InputSection.cpp
Rui Ueyama 2b6fb80384 Skip scanRelocs for non-alloc sections. 
Relocations against sections with no SHF_ALLOC bit are R_ABS relocations.
Currently we are creating Relocations vector for them, but that is wasteful.
This patch is to skip vector construction and to directly apply relocations
in place.

This patch seems to be pretty effective for large executables with debug info.
r266158 (Rafael's patch to change the way how we apply relocations) caused a
temporary performance degradation for such executables, but this patch makes
it even faster than before.

Time to link clang with debug info (output size is 1070 MB):

  before r266158: 15.312 seconds (0%)
  r266158:        17.301 seconds (+13.0%)
  Head:           16.484 seconds (+7.7%)
  w/patch:        13.166 seconds (-14.0%)

Differential Revision: http://reviews.llvm.org/D19645

llvm-svn: 267917
2016-04-28 18:42:04 +00:00

531 lines
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//===- InputSection.cpp ---------------------------------------------------===//
//
// The LLVM Linker
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#include "InputSection.h"
#include "Config.h"
#include "Error.h"
#include "InputFiles.h"
#include "OutputSections.h"
#include "Target.h"
#include "llvm/Support/Endian.h"
using namespace llvm;
using namespace llvm::ELF;
using namespace llvm::object;
using namespace llvm::support::endian;
using namespace lld;
using namespace lld::elf;
template <class ELFT>
InputSectionBase<ELFT>::InputSectionBase(elf::ObjectFile<ELFT> *File,
const Elf_Shdr *Header,
Kind SectionKind)
: Header(Header), File(File), SectionKind(SectionKind), Repl(this) {
// The garbage collector sets sections' Live bits.
// If GC is disabled, all sections are considered live by default.
Live = !Config->GcSections;
// The ELF spec states that a value of 0 means the section has
// no alignment constraits.
Align = std::max<uintX_t>(Header->sh_addralign, 1);
}
template <class ELFT> size_t InputSectionBase<ELFT>::getSize() const {
if (auto *D = dyn_cast<InputSection<ELFT>>(this))
if (D->getThunksSize() > 0)
return D->getThunkOff() + D->getThunksSize();
return Header->sh_size;
}
template <class ELFT> StringRef InputSectionBase<ELFT>::getSectionName() const {
return check(File->getObj().getSectionName(this->Header));
}
template <class ELFT>
ArrayRef<uint8_t> InputSectionBase<ELFT>::getSectionData() const {
return check(this->File->getObj().getSectionContents(this->Header));
}
template <class ELFT>
typename ELFT::uint InputSectionBase<ELFT>::getOffset(uintX_t Offset) {
switch (SectionKind) {
case Regular:
return cast<InputSection<ELFT>>(this)->OutSecOff + Offset;
case EHFrame:
return cast<EHInputSection<ELFT>>(this)->getOffset(Offset);
case Merge:
return cast<MergeInputSection<ELFT>>(this)->getOffset(Offset);
case MipsReginfo:
// MIPS .reginfo sections are consumed by the linker,
// so it should never be copied to output.
llvm_unreachable("MIPS .reginfo reached writeTo().");
}
llvm_unreachable("invalid section kind");
}
template <class ELFT>
typename ELFT::uint
InputSectionBase<ELFT>::getOffset(const DefinedRegular<ELFT> &Sym) {
return getOffset(Sym.Value);
}
template <class ELFT>
InputSection<ELFT>::InputSection(elf::ObjectFile<ELFT> *F,
const Elf_Shdr *Header)
: InputSectionBase<ELFT>(F, Header, Base::Regular) {}
template <class ELFT>
bool InputSection<ELFT>::classof(const InputSectionBase<ELFT> *S) {
return S->SectionKind == Base::Regular;
}
template <class ELFT>
InputSectionBase<ELFT> *InputSection<ELFT>::getRelocatedSection() {
assert(this->Header->sh_type == SHT_RELA || this->Header->sh_type == SHT_REL);
ArrayRef<InputSectionBase<ELFT> *> Sections = this->File->getSections();
return Sections[this->Header->sh_info];
}
template <class ELFT> void InputSection<ELFT>::addThunk(SymbolBody &Body) {
Body.ThunkIndex = Thunks.size();
Thunks.push_back(&Body);
}
template <class ELFT> uint64_t InputSection<ELFT>::getThunkOff() const {
return this->Header->sh_size;
}
template <class ELFT> uint64_t InputSection<ELFT>::getThunksSize() const {
return Thunks.size() * Target->ThunkSize;
}
// This is used for -r. We can't use memcpy to copy relocations because we need
// to update symbol table offset and section index for each relocation. So we
// copy relocations one by one.
template <class ELFT>
template <class RelTy>
void InputSection<ELFT>::copyRelocations(uint8_t *Buf, ArrayRef<RelTy> Rels) {
InputSectionBase<ELFT> *RelocatedSection = getRelocatedSection();
for (const RelTy &Rel : Rels) {
uint32_t Type = Rel.getType(Config->Mips64EL);
SymbolBody &Body = this->File->getRelocTargetSym(Rel);
RelTy *P = reinterpret_cast<RelTy *>(Buf);
Buf += sizeof(RelTy);
P->r_offset = RelocatedSection->getOffset(Rel.r_offset);
P->setSymbolAndType(Body.DynsymIndex, Type, Config->Mips64EL);
}
}
// Page(Expr) is the page address of the expression Expr, defined
// as (Expr & ~0xFFF). (This applies even if the machine page size
// supported by the platform has a different value.)
static uint64_t getAArch64Page(uint64_t Expr) {
return Expr & (~static_cast<uint64_t>(0xFFF));
}
template <class ELFT>
static typename ELFT::uint
getSymVA(uint32_t Type, typename ELFT::uint A, typename ELFT::uint P,
const SymbolBody &Body, uint8_t *BufLoc,
const elf::ObjectFile<ELFT> &File, RelExpr Expr) {
typedef typename ELFT::uint uintX_t;
switch (Expr) {
case R_TLSLD:
return Out<ELFT>::Got->getTlsIndexOff() + A -
Out<ELFT>::Got->getNumEntries() * sizeof(uintX_t);
case R_TLSLD_PC:
return Out<ELFT>::Got->getTlsIndexVA() + A - P;
case R_THUNK:
return Body.getThunkVA<ELFT>();
case R_PPC_TOC:
return getPPC64TocBase() + A;
case R_TLSGD:
return Out<ELFT>::Got->getGlobalDynOffset(Body) + A -
Out<ELFT>::Got->getNumEntries() * sizeof(uintX_t);
case R_TLSGD_PC:
return Out<ELFT>::Got->getGlobalDynAddr(Body) + A - P;
case R_PLT:
return Body.getPltVA<ELFT>() + A;
case R_PLT_PC:
case R_PPC_PLT_OPD:
return Body.getPltVA<ELFT>() + A - P;
case R_SIZE:
return Body.getSize<ELFT>() + A;
case R_GOTREL:
return Body.getVA<ELFT>(A) - Out<ELFT>::Got->getVA();
case R_GOT_FROM_END:
return Body.getGotOffset<ELFT>() + A -
Out<ELFT>::Got->getNumEntries() * sizeof(uintX_t);
case R_GOT:
case R_RELAX_TLS_GD_TO_IE:
return Body.getGotVA<ELFT>() + A;
case R_GOT_PAGE_PC:
return getAArch64Page(Body.getGotVA<ELFT>() + A) - getAArch64Page(P);
case R_GOT_PC:
case R_RELAX_TLS_GD_TO_IE_PC:
return Body.getGotVA<ELFT>() + A - P;
case R_GOTONLY_PC:
return Out<ELFT>::Got->getVA() + A - P;
case R_TLS:
return Body.getVA<ELFT>(A) - Out<ELFT>::TlsPhdr->p_memsz;
case R_NEG_TLS:
return Out<ELF32LE>::TlsPhdr->p_memsz - Body.getVA<ELFT>(A);
case R_ABS:
case R_RELAX_TLS_GD_TO_LE:
case R_RELAX_TLS_IE_TO_LE:
case R_RELAX_TLS_LD_TO_LE:
return Body.getVA<ELFT>(A);
case R_GOT_OFF:
return Body.getGotOffset<ELFT>() + A;
case R_MIPS_GOT_LOCAL:
// If relocation against MIPS local symbol requires GOT entry, this entry
// should be initialized by 'page address'. This address is high 16-bits
// of sum the symbol's value and the addend.
return Out<ELFT>::Got->getMipsLocalPageOffset(Body.getVA<ELFT>(A));
case R_MIPS_GOT:
// For non-local symbols GOT entries should contain their full
// addresses. But if such symbol cannot be preempted, we do not
// have to put them into the "global" part of GOT and use dynamic
// linker to determine their actual addresses. That is why we
// create GOT entries for them in the "local" part of GOT.
return Out<ELFT>::Got->getMipsLocalEntryOffset(Body.getVA<ELFT>(A));
case R_PPC_OPD: {
uint64_t SymVA = Body.getVA<ELFT>(A);
// If we have an undefined weak symbol, we might get here with a symbol
// address of zero. That could overflow, but the code must be unreachable,
// so don't bother doing anything at all.
if (!SymVA)
return 0;
if (Out<ELF64BE>::Opd) {
// If this is a local call, and we currently have the address of a
// function-descriptor, get the underlying code address instead.
uint64_t OpdStart = Out<ELF64BE>::Opd->getVA();
uint64_t OpdEnd = OpdStart + Out<ELF64BE>::Opd->getSize();
bool InOpd = OpdStart <= SymVA && SymVA < OpdEnd;
if (InOpd)
SymVA = read64be(&Out<ELF64BE>::OpdBuf[SymVA - OpdStart]);
}
return SymVA - P;
}
case R_PC:
return Body.getVA<ELFT>(A) - P;
case R_PAGE_PC:
return getAArch64Page(Body.getVA<ELFT>(A)) - getAArch64Page(P);
}
llvm_unreachable("Invalid expression");
}
// This function applies relocations to sections without SHF_ALLOC bit.
// Such sections are never mapped to memory at runtime. Debug sections are
// an example. Relocations in non-alloc sections are much easier to
// handle than in allocated sections because it will never need complex
// treatement such as GOT or PLT (because at runtime no one refers them).
// So, we handle relocations for non-alloc sections directly in this
// function as a performance optimization.
template <class ELFT>
template <class RelTy>
void InputSection<ELFT>::relocateNonAlloc(uint8_t *Buf, ArrayRef<RelTy> Rels) {
const unsigned Bits = sizeof(uintX_t) * 8;
for (const RelTy &Rel : Rels) {
uint8_t *BufLoc = Buf + Rel.r_offset;
uintX_t AddrLoc = this->OutSec->getVA() + Rel.r_offset;
uint32_t Type = Rel.getType(Config->Mips64EL);
SymbolBody &Sym = this->File->getRelocTargetSym(Rel);
if (Target->getRelExpr(Type, Sym) != R_ABS) {
error(this->getSectionName() + " has non-ABS reloc");
return;
}
uint64_t SymVA = SignExtend64<Bits>(getSymVA<ELFT>(
Type, getAddend<ELFT>(Rel), AddrLoc, Sym, BufLoc, *this->File, R_ABS));
Target->relocateOne(BufLoc, Type, SymVA);
}
}
template <class ELFT>
void InputSectionBase<ELFT>::relocate(uint8_t *Buf, uint8_t *BufEnd) {
// scanReloc function in Writer.cpp constructs Relocations
// vector only for SHF_ALLOC'ed sections. For other sections,
// we handle relocations directly here.
auto *IS = dyn_cast<InputSection<ELFT>>(this);
if (IS && !(IS->Header->sh_flags & SHF_ALLOC)) {
for (const Elf_Shdr *RelSec : IS->RelocSections) {
if (RelSec->sh_type == SHT_RELA)
IS->relocateNonAlloc(Buf, IS->File->getObj().relas(RelSec));
else
IS->relocateNonAlloc(Buf, IS->File->getObj().rels(RelSec));
}
return;
}
const unsigned Bits = sizeof(uintX_t) * 8;
for (const Relocation &Rel : Relocations) {
uintX_t Offset = Rel.Offset;
uint8_t *BufLoc = Buf + Offset;
uint32_t Type = Rel.Type;
uintX_t A = Rel.Addend;
uintX_t AddrLoc = OutSec->getVA() + Offset;
RelExpr Expr = Rel.Expr;
uint64_t SymVA = SignExtend64<Bits>(
getSymVA<ELFT>(Type, A, AddrLoc, *Rel.Sym, BufLoc, *File, Expr));
if (Expr == R_RELAX_TLS_IE_TO_LE) {
Target->relaxTlsIeToLe(BufLoc, Type, SymVA);
continue;
}
if (Expr == R_RELAX_TLS_LD_TO_LE) {
Target->relaxTlsLdToLe(BufLoc, Type, SymVA);
continue;
}
if (Expr == R_RELAX_TLS_GD_TO_LE) {
Target->relaxTlsGdToLe(BufLoc, Type, SymVA);
continue;
}
if (Expr == R_RELAX_TLS_GD_TO_IE_PC || Expr == R_RELAX_TLS_GD_TO_IE) {
Target->relaxTlsGdToIe(BufLoc, Type, SymVA);
continue;
}
if (Expr == R_PPC_PLT_OPD) {
uint32_t Nop = 0x60000000;
if (BufLoc + 8 <= BufEnd && read32be(BufLoc + 4) == Nop)
write32be(BufLoc + 4, 0xe8410028); // ld %r2, 40(%r1)
}
Target->relocateOne(BufLoc, Type, SymVA);
}
}
template <class ELFT> void InputSection<ELFT>::writeTo(uint8_t *Buf) {
if (this->Header->sh_type == SHT_NOBITS)
return;
ELFFile<ELFT> &EObj = this->File->getObj();
// If -r is given, then an InputSection may be a relocation section.
if (this->Header->sh_type == SHT_RELA) {
copyRelocations(Buf + OutSecOff, EObj.relas(this->Header));
return;
}
if (this->Header->sh_type == SHT_REL) {
copyRelocations(Buf + OutSecOff, EObj.rels(this->Header));
return;
}
// Copy section contents from source object file to output file.
ArrayRef<uint8_t> Data = this->getSectionData();
memcpy(Buf + OutSecOff, Data.data(), Data.size());
// Iterate over all relocation sections that apply to this section.
uint8_t *BufEnd = Buf + OutSecOff + Data.size();
this->relocate(Buf, BufEnd);
// The section might have a data/code generated by the linker and need
// to be written after the section. Usually these are thunks - small piece
// of code used to jump between "incompatible" functions like PIC and non-PIC
// or if the jump target too far and its address does not fit to the short
// jump istruction.
if (!Thunks.empty()) {
Buf += OutSecOff + getThunkOff();
for (const SymbolBody *S : Thunks) {
Target->writeThunk(Buf, S->getVA<ELFT>());
Buf += Target->ThunkSize;
}
}
}
template <class ELFT>
void InputSection<ELFT>::replace(InputSection<ELFT> *Other) {
this->Align = std::max(this->Align, Other->Align);
Other->Repl = this->Repl;
Other->Live = false;
}
template <class ELFT>
SplitInputSection<ELFT>::SplitInputSection(
elf::ObjectFile<ELFT> *File, const Elf_Shdr *Header,
typename InputSectionBase<ELFT>::Kind SectionKind)
: InputSectionBase<ELFT>(File, Header, SectionKind) {}
template <class ELFT>
EHInputSection<ELFT>::EHInputSection(elf::ObjectFile<ELFT> *F,
const Elf_Shdr *Header)
: SplitInputSection<ELFT>(F, Header, InputSectionBase<ELFT>::EHFrame) {
// Mark .eh_frame sections as live by default because there are
// usually no relocations that point to .eh_frames. Otherwise,
// the garbage collector would drop all .eh_frame sections.
this->Live = true;
}
template <class ELFT>
bool EHInputSection<ELFT>::classof(const InputSectionBase<ELFT> *S) {
return S->SectionKind == InputSectionBase<ELFT>::EHFrame;
}
template <class ELFT>
typename ELFT::uint EHInputSection<ELFT>::getOffset(uintX_t Offset) {
// The file crtbeginT.o has relocations pointing to the start of an empty
// .eh_frame that is known to be the first in the link. It does that to
// identify the start of the output .eh_frame. Handle this special case.
if (this->getSectionHdr()->sh_size == 0)
return Offset;
std::pair<uintX_t, uintX_t> *I = this->getRangeAndSize(Offset).first;
uintX_t Base = I->second;
if (Base == uintX_t(-1))
return -1; // Not in the output
uintX_t Addend = Offset - I->first;
return Base + Addend;
}
static size_t findNull(StringRef S, size_t EntSize) {
// Optimize the common case.
if (EntSize == 1)
return S.find(0);
for (unsigned I = 0, N = S.size(); I != N; I += EntSize) {
const char *B = S.begin() + I;
if (std::all_of(B, B + EntSize, [](char C) { return C == 0; }))
return I;
}
return StringRef::npos;
}
template <class ELFT>
MergeInputSection<ELFT>::MergeInputSection(elf::ObjectFile<ELFT> *F,
const Elf_Shdr *Header)
: SplitInputSection<ELFT>(F, Header, InputSectionBase<ELFT>::Merge) {
uintX_t EntSize = Header->sh_entsize;
ArrayRef<uint8_t> D = this->getSectionData();
StringRef Data((const char *)D.data(), D.size());
std::vector<std::pair<uintX_t, uintX_t>> &Offsets = this->Offsets;
uintX_t V = Config->GcSections ? -1 : 0;
if (Header->sh_flags & SHF_STRINGS) {
uintX_t Offset = 0;
while (!Data.empty()) {
size_t End = findNull(Data, EntSize);
if (End == StringRef::npos)
fatal("string is not null terminated");
Offsets.push_back(std::make_pair(Offset, V));
uintX_t Size = End + EntSize;
Data = Data.substr(Size);
Offset += Size;
}
return;
}
// If this is not of type string, every entry has the same size.
size_t Size = Data.size();
assert((Size % EntSize) == 0);
for (unsigned I = 0, N = Size; I != N; I += EntSize)
Offsets.push_back(std::make_pair(I, V));
}
template <class ELFT>
bool MergeInputSection<ELFT>::classof(const InputSectionBase<ELFT> *S) {
return S->SectionKind == InputSectionBase<ELFT>::Merge;
}
template <class ELFT>
std::pair<std::pair<typename ELFT::uint, typename ELFT::uint> *,
typename ELFT::uint>
SplitInputSection<ELFT>::getRangeAndSize(uintX_t Offset) {
ArrayRef<uint8_t> D = this->getSectionData();
StringRef Data((const char *)D.data(), D.size());
uintX_t Size = Data.size();
if (Offset >= Size)
fatal("entry is past the end of the section");
// Find the element this offset points to.
auto I = std::upper_bound(
Offsets.begin(), Offsets.end(), Offset,
[](const uintX_t &A, const std::pair<uintX_t, uintX_t> &B) {
return A < B.first;
});
uintX_t End = I == Offsets.end() ? Data.size() : I->first;
--I;
return std::make_pair(&*I, End);
}
template <class ELFT>
typename ELFT::uint MergeInputSection<ELFT>::getOffset(uintX_t Offset) {
std::pair<std::pair<uintX_t, uintX_t> *, uintX_t> T =
this->getRangeAndSize(Offset);
std::pair<uintX_t, uintX_t> *I = T.first;
uintX_t End = T.second;
uintX_t Start = I->first;
// Compute the Addend and if the Base is cached, return.
uintX_t Addend = Offset - Start;
uintX_t &Base = I->second;
if (Base != uintX_t(-1))
return Base + Addend;
// Map the base to the offset in the output section and cache it.
ArrayRef<uint8_t> D = this->getSectionData();
StringRef Data((const char *)D.data(), D.size());
StringRef Entry = Data.substr(Start, End - Start);
Base =
static_cast<MergeOutputSection<ELFT> *>(this->OutSec)->getOffset(Entry);
return Base + Addend;
}
template <class ELFT>
MipsReginfoInputSection<ELFT>::MipsReginfoInputSection(elf::ObjectFile<ELFT> *F,
const Elf_Shdr *Hdr)
: InputSectionBase<ELFT>(F, Hdr, InputSectionBase<ELFT>::MipsReginfo) {
// Initialize this->Reginfo.
ArrayRef<uint8_t> D = this->getSectionData();
if (D.size() != sizeof(Elf_Mips_RegInfo<ELFT>))
fatal("invalid size of .reginfo section");
Reginfo = reinterpret_cast<const Elf_Mips_RegInfo<ELFT> *>(D.data());
}
template <class ELFT>
bool MipsReginfoInputSection<ELFT>::classof(const InputSectionBase<ELFT> *S) {
return S->SectionKind == InputSectionBase<ELFT>::MipsReginfo;
}
template class elf::InputSectionBase<ELF32LE>;
template class elf::InputSectionBase<ELF32BE>;
template class elf::InputSectionBase<ELF64LE>;
template class elf::InputSectionBase<ELF64BE>;
template class elf::InputSection<ELF32LE>;
template class elf::InputSection<ELF32BE>;
template class elf::InputSection<ELF64LE>;
template class elf::InputSection<ELF64BE>;
template class elf::SplitInputSection<ELF32LE>;
template class elf::SplitInputSection<ELF32BE>;
template class elf::SplitInputSection<ELF64LE>;
template class elf::SplitInputSection<ELF64BE>;
template class elf::EHInputSection<ELF32LE>;
template class elf::EHInputSection<ELF32BE>;
template class elf::EHInputSection<ELF64LE>;
template class elf::EHInputSection<ELF64BE>;
template class elf::MergeInputSection<ELF32LE>;
template class elf::MergeInputSection<ELF32BE>;
template class elf::MergeInputSection<ELF64LE>;
template class elf::MergeInputSection<ELF64BE>;
template class elf::MipsReginfoInputSection<ELF32LE>;
template class elf::MipsReginfoInputSection<ELF32BE>;
template class elf::MipsReginfoInputSection<ELF64LE>;
template class elf::MipsReginfoInputSection<ELF64BE>;
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