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llvm-project/lld/ELF/InputSection.cpp

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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 "EhFrame.h"
#include "Error.h"
#include "InputFiles.h"
#include "LinkerScript.h"
#include "Memory.h"
#include "OutputSections.h"
#include "Relocations.h"
#include "SyntheticSections.h"
#include "Target.h"
#include "Thunks.h"
#include "llvm/Support/Compression.h"
#include "llvm/Support/Endian.h"
#include <mutex>
using namespace llvm;
using namespace llvm::ELF;
using namespace llvm::object;
using namespace llvm::support;
using namespace llvm::support::endian;
using namespace lld;
using namespace lld::elf;
// Returns a string to construct an error message.
template <class ELFT>
std::string elf::toString(const InputSectionBase<ELFT> *Sec) {
return (Sec->getFile()->getName() + ":(" + Sec->Name + ")").str();
}
template <class ELFT>
static ArrayRef<uint8_t> getSectionContents(elf::ObjectFile<ELFT> *File,
const typename ELFT::Shdr *Hdr) {
if (!File || Hdr->sh_type == SHT_NOBITS)
return makeArrayRef<uint8_t>(nullptr, Hdr->sh_size);
return check(File->getObj().getSectionContents(Hdr));
}
template <class ELFT>
InputSectionBase<ELFT>::InputSectionBase(elf::ObjectFile<ELFT> *File,
uintX_t Flags, uint32_t Type,
uintX_t Entsize, uint32_t Link,
uint32_t Info, uintX_t Addralign,
ArrayRef<uint8_t> Data, StringRef Name,
Kind SectionKind)
: InputSectionData(SectionKind, Name, Data,
!Config->GcSections || !(Flags & SHF_ALLOC)),
File(File), Flags(Flags), Entsize(Entsize), Type(Type), Link(Link),
Info(Info), Repl(this) {
NumRelocations = 0;
AreRelocsRela = false;
// The ELF spec states that a value of 0 means the section has
// no alignment constraits.
uint64_t V = std::max<uint64_t>(Addralign, 1);
if (!isPowerOf2_64(V))
fatal(toString(File) + ": section sh_addralign is not a power of 2");
// We reject object files having insanely large alignments even though
// they are allowed by the spec. I think 4GB is a reasonable limitation.
// We might want to relax this in the future.
if (V > UINT32_MAX)
fatal(toString(File) + ": section sh_addralign is too large");
Alignment = V;
// If it is not a mergeable section, overwrite the flag so that the flag
// is consistent with the class. This inconsistency could occur when
// string merging is disabled using -O0 flag.
if (!Config->Relocatable && !isa<MergeInputSection<ELFT>>(this))
this->Flags &= ~(SHF_MERGE | SHF_STRINGS);
}
template <class ELFT>
InputSectionBase<ELFT>::InputSectionBase(elf::ObjectFile<ELFT> *File,
const Elf_Shdr *Hdr, StringRef Name,
Kind SectionKind)
: InputSectionBase(File, Hdr->sh_flags & ~SHF_INFO_LINK, Hdr->sh_type,
Hdr->sh_entsize, Hdr->sh_link, Hdr->sh_info,
Hdr->sh_addralign, getSectionContents(File, Hdr), Name,
SectionKind) {
this->Offset = Hdr->sh_offset;
}
template <class ELFT> size_t InputSectionBase<ELFT>::getSize() const {
if (auto *S = dyn_cast<SyntheticSection<ELFT>>(this))
return S->getSize();
if (auto *D = dyn_cast<InputSection<ELFT>>(this))
if (D->getThunksSize() > 0)
return D->getThunkOff() + D->getThunksSize();
return Data.size();
}
// Returns a string for an error message.
template <class SectionT> static std::string getName(SectionT *Sec) {
return (Sec->getFile()->getName() + ":(" + Sec->Name + ")").str();
}
template <class ELFT>
typename ELFT::uint InputSectionBase<ELFT>::getOffset(uintX_t Offset) const {
switch (kind()) {
case Regular:
return cast<InputSection<ELFT>>(this)->OutSecOff + Offset;
case Synthetic:
// For synthetic sections we treat offset -1 as the end of the section.
// The same approach is used for synthetic symbols (DefinedSynthetic).
return cast<InputSection<ELFT>>(this)->OutSecOff +
(Offset == uintX_t(-1) ? getSize() : Offset);
case EHFrame:
// 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.
return Offset;
case Merge:
return cast<MergeInputSection<ELFT>>(this)->getOffset(Offset);
}
llvm_unreachable("invalid section kind");
}
template <class ELFT> bool InputSectionBase<ELFT>::isCompressed() const {
return (Flags & SHF_COMPRESSED) || Name.startswith(".zdebug");
}
// Returns compressed data and its size when uncompressed.
template <class ELFT>
std::pair<ArrayRef<uint8_t>, uint64_t>
InputSectionBase<ELFT>::getElfCompressedData(ArrayRef<uint8_t> Data) {
// Compressed section with Elf_Chdr is the ELF standard.
if (Data.size() < sizeof(Elf_Chdr))
fatal(toString(this) + ": corrupted compressed section");
auto *Hdr = reinterpret_cast<const Elf_Chdr *>(Data.data());
if (Hdr->ch_type != ELFCOMPRESS_ZLIB)
fatal(toString(this) + ": unsupported compression type");
return {Data.slice(sizeof(*Hdr)), Hdr->ch_size};
}
// Returns compressed data and its size when uncompressed.
template <class ELFT>
std::pair<ArrayRef<uint8_t>, uint64_t>
InputSectionBase<ELFT>::getRawCompressedData(ArrayRef<uint8_t> Data) {
// Compressed sections without Elf_Chdr header contain this header
// instead. This is a GNU extension.
struct ZlibHeader {
char Magic[4]; // Should be "ZLIB"
char Size[8]; // Uncompressed size in big-endian
};
if (Data.size() < sizeof(ZlibHeader))
fatal(toString(this) + ": corrupted compressed section");
auto *Hdr = reinterpret_cast<const ZlibHeader *>(Data.data());
if (memcmp(Hdr->Magic, "ZLIB", 4))
fatal(toString(this) + ": broken ZLIB-compressed section");
return {Data.slice(sizeof(*Hdr)), read64be(Hdr->Size)};
}
// Uncompress section contents. Note that this function is called
// from parallel_for_each, so it must be thread-safe.
template <class ELFT> void InputSectionBase<ELFT>::uncompress() {
if (!zlib::isAvailable())
fatal(toString(this) +
": build lld with zlib to enable compressed sections support");
// This section is compressed. Here we decompress it. Ideally, all
// compressed sections have SHF_COMPRESSED bit and their contents
// start with headers of Elf_Chdr type. However, sections whose
// names start with ".zdebug_" don't have the bit and contains a raw
// ZLIB-compressed data (which is a bad thing because section names
// shouldn't be significant in ELF.) We need to be able to read both.
ArrayRef<uint8_t> Buf; // Compressed data
size_t Size; // Uncompressed size
if (Flags & SHF_COMPRESSED)
std::tie(Buf, Size) = getElfCompressedData(Data);
else
std::tie(Buf, Size) = getRawCompressedData(Data);
// Uncompress Buf.
char *OutputBuf;
{
static std::mutex Mu;
std::lock_guard<std::mutex> Lock(Mu);
OutputBuf = BAlloc.Allocate<char>(Size);
}
if (zlib::uncompress(toStringRef(Buf), OutputBuf, Size) != zlib::StatusOK)
fatal(toString(this) + ": error while uncompressing section");
Data = ArrayRef<uint8_t>((uint8_t *)OutputBuf, Size);
}
template <class ELFT>
typename ELFT::uint
InputSectionBase<ELFT>::getOffset(const DefinedRegular<ELFT> &Sym) const {
return getOffset(Sym.Value);
}
template <class ELFT>
InputSectionBase<ELFT> *InputSectionBase<ELFT>::getLinkOrderDep() const {
if ((Flags & SHF_LINK_ORDER) && Link != 0)
return getFile()->getSections()[Link];
return nullptr;
}
// Returns a source location string. Used to construct an error message.
template <class ELFT>
std::string InputSectionBase<ELFT>::getLocation(typename ELFT::uint Offset) {
// First check if we can get desired values from debugging information.
std::string LineInfo = File->getLineInfo(this, Offset);
if (!LineInfo.empty())
return LineInfo;
// File->SourceFile contains STT_FILE symbol that contains a
// source file name. If it's missing, we use an object file name.
std::string SrcFile = File->SourceFile;
if (SrcFile.empty())
SrcFile = toString(File);
// Find a function symbol that encloses a given location.
for (SymbolBody *B : File->getSymbols())
if (auto *D = dyn_cast<DefinedRegular<ELFT>>(B))
if (D->Section == this && D->Type == STT_FUNC)
if (D->Value <= Offset && Offset < D->Value + D->Size)
return SrcFile + ":(function " + toString(*D) + ")";
// If there's no symbol, print out the offset in the section.
return (SrcFile + ":(" + Name + "+0x" + utohexstr(Offset) + ")").str();
}
template <class ELFT>
InputSection<ELFT>::InputSection() : InputSectionBase<ELFT>() {}
template <class ELFT>
InputSection<ELFT>::InputSection(uintX_t Flags, uint32_t Type,
uintX_t Addralign, ArrayRef<uint8_t> Data,
StringRef Name, Kind K)
: InputSectionBase<ELFT>(nullptr, Flags, Type,
/*Entsize*/ 0, /*Link*/ 0, /*Info*/ 0, Addralign,
Data, Name, K) {}
template <class ELFT>
InputSection<ELFT>::InputSection(elf::ObjectFile<ELFT> *F,
const Elf_Shdr *Header, StringRef Name)
: InputSectionBase<ELFT>(F, Header, Name, Base::Regular) {}
template <class ELFT>
bool InputSection<ELFT>::classof(const InputSectionData *S) {
return S->kind() == Base::Regular || S->kind() == Base::Synthetic;
}
template <class ELFT>
InputSectionBase<ELFT> *InputSection<ELFT>::getRelocatedSection() {
assert(this->Type == SHT_RELA || this->Type == SHT_REL);
ArrayRef<InputSectionBase<ELFT> *> Sections = this->File->getSections();
return Sections[this->Info];
}
template <class ELFT> void InputSection<ELFT>::addThunk(const Thunk<ELFT> *T) {
Thunks.push_back(T);
}
template <class ELFT> uint64_t InputSection<ELFT>::getThunkOff() const {
return this->Data.size();
}
template <class ELFT> uint64_t InputSection<ELFT>::getThunksSize() const {
uint64_t Total = 0;
for (const Thunk<ELFT> *T : Thunks)
Total += T->size();
return Total;
}
// 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);
Elf_Rela *P = reinterpret_cast<Elf_Rela *>(Buf);
Buf += sizeof(RelTy);
if (Config->Rela)
P->r_addend = getAddend<ELFT>(Rel);
P->r_offset = RelocatedSection->getOffset(Rel.r_offset);
P->setSymbolAndType(Body.DynsymIndex, Type, Config->Mips64EL);
}
}
static uint32_t getARMUndefinedRelativeWeakVA(uint32_t Type, uint32_t A,
uint32_t P) {
switch (Type) {
case R_ARM_THM_JUMP11:
return P + 2;
case R_ARM_CALL:
case R_ARM_JUMP24:
case R_ARM_PC24:
case R_ARM_PLT32:
case R_ARM_PREL31:
case R_ARM_THM_JUMP19:
case R_ARM_THM_JUMP24:
return P + 4;
case R_ARM_THM_CALL:
// We don't want an interworking BLX to ARM
return P + 5;
default:
return A;
}
}
static uint64_t getAArch64UndefinedRelativeWeakVA(uint64_t Type, uint64_t A,
uint64_t P) {
switch (Type) {
case R_AARCH64_CALL26:
case R_AARCH64_CONDBR19:
case R_AARCH64_JUMP26:
case R_AARCH64_TSTBR14:
return P + 4;
default:
return A;
}
}
template <class ELFT>
static typename ELFT::uint
getRelocTargetVA(uint32_t Type, typename ELFT::uint A, typename ELFT::uint P,
const SymbolBody &Body, RelExpr Expr) {
switch (Expr) {
case R_HINT:
case R_TLSDESC_CALL:
llvm_unreachable("cannot relocate hint relocs");
case R_TLSLD:
return In<ELFT>::Got->getTlsIndexOff() + A - In<ELFT>::Got->getSize();
case R_TLSLD_PC:
return In<ELFT>::Got->getTlsIndexVA() + A - P;
case R_THUNK_ABS:
return Body.getThunkVA<ELFT>() + A;
case R_THUNK_PC:
case R_THUNK_PLT_PC:
return Body.getThunkVA<ELFT>() + A - P;
case R_PPC_TOC:
return getPPC64TocBase() + A;
case R_TLSGD:
return In<ELFT>::Got->getGlobalDynOffset(Body) + A -
In<ELFT>::Got->getSize();
case R_TLSGD_PC:
return In<ELFT>::Got->getGlobalDynAddr(Body) + A - P;
case R_TLSDESC:
return In<ELFT>::Got->getGlobalDynAddr(Body) + A;
case R_TLSDESC_PAGE:
return getAArch64Page(In<ELFT>::Got->getGlobalDynAddr(Body) + A) -
getAArch64Page(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) - In<ELFT>::Got->getVA();
case R_GOTREL_FROM_END:
return Body.getVA<ELFT>(A) - In<ELFT>::Got->getVA() -
In<ELFT>::Got->getSize();
case R_RELAX_TLS_GD_TO_IE_END:
case R_GOT_FROM_END:
return Body.getGotOffset<ELFT>() + A - In<ELFT>::Got->getSize();
case R_RELAX_TLS_GD_TO_IE_ABS:
case R_GOT:
return Body.getGotVA<ELFT>() + A;
case R_RELAX_TLS_GD_TO_IE_PAGE_PC:
case R_GOT_PAGE_PC:
return getAArch64Page(Body.getGotVA<ELFT>() + A) - getAArch64Page(P);
case R_RELAX_TLS_GD_TO_IE:
case R_GOT_PC:
return Body.getGotVA<ELFT>() + A - P;
case R_GOTONLY_PC:
return In<ELFT>::Got->getVA() + A - P;
case R_GOTONLY_PC_FROM_END:
return In<ELFT>::Got->getVA() + A - P + In<ELFT>::Got->getSize();
case R_RELAX_TLS_LD_TO_LE:
case R_RELAX_TLS_IE_TO_LE:
case R_RELAX_TLS_GD_TO_LE:
case R_TLS:
// A weak undefined TLS symbol resolves to the base of the TLS
// block, i.e. gets a value of zero. If we pass --gc-sections to
// lld and .tbss is not referenced, it gets reclaimed and we don't
// create a TLS program header. Therefore, we resolve this
// statically to zero.
if (Body.isTls() && (Body.isLazy() || Body.isUndefined()) &&
Body.symbol()->isWeak())
return 0;
if (Target->TcbSize)
return Body.getVA<ELFT>(A) +
alignTo(Target->TcbSize, Out<ELFT>::TlsPhdr->p_align);
return Body.getVA<ELFT>(A) - Out<ELFT>::TlsPhdr->p_memsz;
case R_RELAX_TLS_GD_TO_LE_NEG:
case R_NEG_TLS:
return Out<ELF32LE>::TlsPhdr->p_memsz - Body.getVA<ELFT>(A);
case R_ABS:
case R_RELAX_GOT_PC_NOPIC:
return Body.getVA<ELFT>(A);
case R_GOT_OFF:
return Body.getGotOffset<ELFT>() + A;
case R_MIPS_GOT_LOCAL_PAGE:
// 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 In<ELFT>::MipsGot->getVA() +
In<ELFT>::MipsGot->getPageEntryOffset(Body, A) -
In<ELFT>::MipsGot->getGp();
case R_MIPS_GOT_OFF:
case R_MIPS_GOT_OFF32:
// In case of MIPS if a GOT relocation has non-zero addend this addend
// should be applied to the GOT entry content not to the GOT entry offset.
// That is why we use separate expression type.
return In<ELFT>::MipsGot->getVA() +
In<ELFT>::MipsGot->getBodyEntryOffset(Body, A) -
In<ELFT>::MipsGot->getGp();
case R_MIPS_GOTREL:
return Body.getVA<ELFT>(A) - In<ELFT>::MipsGot->getGp();
case R_MIPS_TLSGD:
return In<ELFT>::MipsGot->getVA() + In<ELFT>::MipsGot->getTlsOffset() +
In<ELFT>::MipsGot->getGlobalDynOffset(Body) -
In<ELFT>::MipsGot->getGp();
case R_MIPS_TLSLD:
return In<ELFT>::MipsGot->getVA() + In<ELFT>::MipsGot->getTlsOffset() +
In<ELFT>::MipsGot->getTlsIndexOff() - In<ELFT>::MipsGot->getGp();
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->Addr;
uint64_t OpdEnd = OpdStart + Out<ELF64BE>::Opd->Size;
bool InOpd = OpdStart <= SymVA && SymVA < OpdEnd;
if (InOpd)
SymVA = read64be(&Out<ELF64BE>::OpdBuf[SymVA - OpdStart]);
}
return SymVA - P;
}
case R_PC:
if (Body.isUndefined() && !Body.isLocal() && Body.symbol()->isWeak()) {
// On ARM and AArch64 a branch to an undefined weak resolves to the
// next instruction, otherwise the place.
if (Config->EMachine == EM_ARM)
return getARMUndefinedRelativeWeakVA(Type, A, P);
if (Config->EMachine == EM_AARCH64)
return getAArch64UndefinedRelativeWeakVA(Type, A, P);
}
case R_RELAX_GOT_PC:
return Body.getVA<ELFT>(A) - P;
case R_PLT_PAGE_PC:
case R_PAGE_PC:
if (Body.isUndefined() && !Body.isLocal() && Body.symbol()->isWeak())
return getAArch64Page(A);
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) {
for (const RelTy &Rel : Rels) {
uint32_t Type = Rel.getType(Config->Mips64EL);
uintX_t Offset = this->getOffset(Rel.r_offset);
uint8_t *BufLoc = Buf + Offset;
uintX_t Addend = getAddend<ELFT>(Rel);
if (!RelTy::IsRela)
Addend += Target->getImplicitAddend(BufLoc, Type);
SymbolBody &Sym = this->File->getRelocTargetSym(Rel);
if (Target->getRelExpr(Type, Sym) != R_ABS) {
error(this->getLocation(Offset) + ": has non-ABS reloc");
return;
}
uintX_t AddrLoc = this->OutSec->Addr + Offset;
uint64_t SymVA = 0;
if (!Sym.isTls() || Out<ELFT>::TlsPhdr)
SymVA = SignExtend64<sizeof(uintX_t) * 8>(
getRelocTargetVA<ELFT>(Type, Addend, AddrLoc, Sym, 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->Flags & SHF_ALLOC)) {
if (IS->AreRelocsRela)
IS->relocateNonAlloc(Buf, IS->relas());
else
IS->relocateNonAlloc(Buf, IS->rels());
return;
}
const unsigned Bits = sizeof(uintX_t) * 8;
for (const Relocation &Rel : Relocations) {
uintX_t Offset = getOffset(Rel.Offset);
uint8_t *BufLoc = Buf + Offset;
uint32_t Type = Rel.Type;
uintX_t A = Rel.Addend;
uintX_t AddrLoc = OutSec->Addr + Offset;
RelExpr Expr = Rel.Expr;
uint64_t TargetVA = SignExtend64<Bits>(
getRelocTargetVA<ELFT>(Type, A, AddrLoc, *Rel.Sym, Expr));
switch (Expr) {
case R_RELAX_GOT_PC:
case R_RELAX_GOT_PC_NOPIC:
Target->relaxGot(BufLoc, TargetVA);
break;
case R_RELAX_TLS_IE_TO_LE:
Target->relaxTlsIeToLe(BufLoc, Type, TargetVA);
break;
case R_RELAX_TLS_LD_TO_LE:
Target->relaxTlsLdToLe(BufLoc, Type, TargetVA);
break;
case R_RELAX_TLS_GD_TO_LE:
case R_RELAX_TLS_GD_TO_LE_NEG:
Target->relaxTlsGdToLe(BufLoc, Type, TargetVA);
break;
case R_RELAX_TLS_GD_TO_IE:
case R_RELAX_TLS_GD_TO_IE_ABS:
case R_RELAX_TLS_GD_TO_IE_PAGE_PC:
case R_RELAX_TLS_GD_TO_IE_END:
Target->relaxTlsGdToIe(BufLoc, Type, TargetVA);
break;
case R_PPC_PLT_OPD:
// Patch a nop (0x60000000) to a ld.
if (BufLoc + 8 <= BufEnd && read32be(BufLoc + 4) == 0x60000000)
write32be(BufLoc + 4, 0xe8410028); // ld %r2, 40(%r1)
// fallthrough
default:
Target->relocateOne(BufLoc, Type, TargetVA);
break;
}
}
}
template <class ELFT> void InputSection<ELFT>::writeTo(uint8_t *Buf) {
if (this->Type == SHT_NOBITS)
return;
if (auto *S = dyn_cast<SyntheticSection<ELFT>>(this)) {
S->writeTo(Buf + OutSecOff);
return;
}
// If -r is given, then an InputSection may be a relocation section.
if (this->Type == SHT_RELA) {
copyRelocations(Buf + OutSecOff, this->template getDataAs<Elf_Rela>());
return;
}
if (this->Type == SHT_REL) {
copyRelocations(Buf + OutSecOff, this->template getDataAs<Elf_Rel>());
return;
}
// Copy section contents from source object file to output file.
ArrayRef<uint8_t> Data = this->Data;
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 Thunk<ELFT> *T : Thunks) {
T->writeTo(Buf);
Buf += T->size();
}
}
}
template <class ELFT>
void InputSection<ELFT>::replace(InputSection<ELFT> *Other) {
this->Alignment = std::max(this->Alignment, Other->Alignment);
Other->Repl = this->Repl;
Other->Live = false;
}
template <class ELFT>
EhInputSection<ELFT>::EhInputSection(elf::ObjectFile<ELFT> *F,
const Elf_Shdr *Header, StringRef Name)
: InputSectionBase<ELFT>(F, Header, Name, 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 InputSectionData *S) {
return S->kind() == InputSectionBase<ELFT>::EHFrame;
}
// Returns the index of the first relocation that points to a region between
// Begin and Begin+Size.
template <class IntTy, class RelTy>
static unsigned getReloc(IntTy Begin, IntTy Size, const ArrayRef<RelTy> &Rels,
unsigned &RelocI) {
// Start search from RelocI for fast access. That works because the
// relocations are sorted in .eh_frame.
for (unsigned N = Rels.size(); RelocI < N; ++RelocI) {
const RelTy &Rel = Rels[RelocI];
if (Rel.r_offset < Begin)
continue;
if (Rel.r_offset < Begin + Size)
return RelocI;
return -1;
}
return -1;
}
// .eh_frame is a sequence of CIE or FDE records.
// This function splits an input section into records and returns them.
template <class ELFT> void EhInputSection<ELFT>::split() {
// Early exit if already split.
if (!this->Pieces.empty())
return;
if (this->NumRelocations) {
if (this->AreRelocsRela)
split(this->relas());
else
split(this->rels());
return;
}
split(makeArrayRef<typename ELFT::Rela>(nullptr, nullptr));
}
template <class ELFT>
template <class RelTy>
void EhInputSection<ELFT>::split(ArrayRef<RelTy> Rels) {
ArrayRef<uint8_t> Data = this->Data;
unsigned RelI = 0;
for (size_t Off = 0, End = Data.size(); Off != End;) {
size_t Size = readEhRecordSize<ELFT>(this, Off);
this->Pieces.emplace_back(Off, this, Size, getReloc(Off, Size, Rels, RelI));
// The empty record is the end marker.
if (Size == 4)
break;
Off += Size;
}
}
static size_t findNull(ArrayRef<uint8_t> A, size_t EntSize) {
// Optimize the common case.
StringRef S((const char *)A.data(), A.size());
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;
}
// Split SHF_STRINGS section. Such section is a sequence of
// null-terminated strings.
template <class ELFT>
void MergeInputSection<ELFT>::splitStrings(ArrayRef<uint8_t> Data,
size_t EntSize) {
size_t Off = 0;
bool IsAlloc = this->Flags & SHF_ALLOC;
while (!Data.empty()) {
size_t End = findNull(Data, EntSize);
if (End == StringRef::npos)
fatal(toString(this) + ": string is not null terminated");
size_t Size = End + EntSize;
Pieces.emplace_back(Off, !IsAlloc);
Hashes.push_back(hash_value(toStringRef(Data.slice(0, Size))));
Data = Data.slice(Size);
Off += Size;
}
}
// Split non-SHF_STRINGS section. Such section is a sequence of
// fixed size records.
template <class ELFT>
void MergeInputSection<ELFT>::splitNonStrings(ArrayRef<uint8_t> Data,
size_t EntSize) {
size_t Size = Data.size();
assert((Size % EntSize) == 0);
bool IsAlloc = this->Flags & SHF_ALLOC;
for (unsigned I = 0, N = Size; I != N; I += EntSize) {
Hashes.push_back(hash_value(toStringRef(Data.slice(I, EntSize))));
Pieces.emplace_back(I, !IsAlloc);
}
}
template <class ELFT>
MergeInputSection<ELFT>::MergeInputSection(elf::ObjectFile<ELFT> *F,
const Elf_Shdr *Header,
StringRef Name)
: InputSectionBase<ELFT>(F, Header, Name, InputSectionBase<ELFT>::Merge) {}
// This function is called after we obtain a complete list of input sections
// that need to be linked. This is responsible to split section contents
// into small chunks for further processing.
//
// Note that this function is called from parallel_for_each. This must be
// thread-safe (i.e. no memory allocation from the pools).
template <class ELFT> void MergeInputSection<ELFT>::splitIntoPieces() {
ArrayRef<uint8_t> Data = this->Data;
uintX_t EntSize = this->Entsize;
if (this->Flags & SHF_STRINGS)
splitStrings(Data, EntSize);
else
splitNonStrings(Data, EntSize);
if (Config->GcSections && (this->Flags & SHF_ALLOC))
for (uintX_t Off : LiveOffsets)
this->getSectionPiece(Off)->Live = true;
}
template <class ELFT>
bool MergeInputSection<ELFT>::classof(const InputSectionData *S) {
return S->kind() == InputSectionBase<ELFT>::Merge;
}
// Do binary search to get a section piece at a given input offset.
template <class ELFT>
SectionPiece *MergeInputSection<ELFT>::getSectionPiece(uintX_t Offset) {
auto *This = static_cast<const MergeInputSection<ELFT> *>(this);
return const_cast<SectionPiece *>(This->getSectionPiece(Offset));
}
template <class It, class T, class Compare>
static It fastUpperBound(It First, It Last, const T &Value, Compare Comp) {
size_t Size = std::distance(First, Last);
assert(Size != 0);
while (Size != 1) {
size_t H = Size / 2;
const It MI = First + H;
Size -= H;
First = Comp(Value, *MI) ? First : First + H;
}
return Comp(Value, *First) ? First : First + 1;
}
template <class ELFT>
const SectionPiece *
MergeInputSection<ELFT>::getSectionPiece(uintX_t Offset) const {
uintX_t Size = this->Data.size();
if (Offset >= Size)
fatal(toString(this) + ": entry is past the end of the section");
// Find the element this offset points to.
auto I = fastUpperBound(
Pieces.begin(), Pieces.end(), Offset,
[](const uintX_t &A, const SectionPiece &B) { return A < B.InputOff; });
--I;
return &*I;
}
// Returns the offset in an output section for a given input offset.
// Because contents of a mergeable section is not contiguous in output,
// it is not just an addition to a base output offset.
template <class ELFT>
typename ELFT::uint MergeInputSection<ELFT>::getOffset(uintX_t Offset) const {
// Initialize OffsetMap lazily.
std::call_once(InitOffsetMap, [&] {
OffsetMap.reserve(Pieces.size());
for (const SectionPiece &Piece : Pieces)
OffsetMap[Piece.InputOff] = Piece.OutputOff;
});
// Find a string starting at a given offset.
auto It = OffsetMap.find(Offset);
if (It != OffsetMap.end())
return It->second;
if (!this->Live)
return 0;
// If Offset is not at beginning of a section piece, it is not in the map.
// In that case we need to search from the original section piece vector.
const SectionPiece &Piece = *this->getSectionPiece(Offset);
if (!Piece.Live)
return 0;
uintX_t Addend = Offset - Piece.InputOff;
return Piece.OutputOff + Addend;
}
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::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 std::string elf::toString(const InputSectionBase<ELF32LE> *);
template std::string elf::toString(const InputSectionBase<ELF32BE> *);
template std::string elf::toString(const InputSectionBase<ELF64LE> *);
template std::string elf::toString(const InputSectionBase<ELF64BE> *);
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