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llvm-project/llvm/tools/yaml2obj/yaml2elf.cpp

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//===- yaml2elf - Convert YAML to a ELF object file -----------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
///
/// \file
/// \brief The ELF component of yaml2obj.
///
//===----------------------------------------------------------------------===//
#include "yaml2obj.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/MC/StringTableBuilder.h"
#include "llvm/Object/ELFObjectFile.h"
#include "llvm/ObjectYAML/ELFYAML.h"
#include "llvm/Support/ELF.h"
#include "llvm/Support/MemoryBuffer.h"
#include "llvm/Support/YAMLTraits.h"
#include "llvm/Support/raw_ostream.h"
using namespace llvm;
// This class is used to build up a contiguous binary blob while keeping
// track of an offset in the output (which notionally begins at
// `InitialOffset`).
namespace {
class ContiguousBlobAccumulator {
const uint64_t InitialOffset;
SmallVector<char, 128> Buf;
raw_svector_ostream OS;
/// \returns The new offset.
uint64_t padToAlignment(unsigned Align) {
if (Align == 0)
Align = 1;
uint64_t CurrentOffset = InitialOffset + OS.tell();
uint64_t AlignedOffset = alignTo(CurrentOffset, Align);
for (; CurrentOffset != AlignedOffset; ++CurrentOffset)
OS.write('\0');
return AlignedOffset; // == CurrentOffset;
}
public:
ContiguousBlobAccumulator(uint64_t InitialOffset_)
: InitialOffset(InitialOffset_), Buf(), OS(Buf) {}
template <class Integer>
raw_ostream &getOSAndAlignedOffset(Integer &Offset, unsigned Align) {
Offset = padToAlignment(Align);
return OS;
}
void writeBlobToStream(raw_ostream &Out) { Out << OS.str(); }
};
} // end anonymous namespace
// Used to keep track of section and symbol names, so that in the YAML file
// sections and symbols can be referenced by name instead of by index.
namespace {
class NameToIdxMap {
StringMap<int> Map;
public:
/// \returns true if name is already present in the map.
bool addName(StringRef Name, unsigned i) {
return !Map.insert(std::make_pair(Name, (int)i)).second;
}
/// \returns true if name is not present in the map
bool lookup(StringRef Name, unsigned &Idx) const {
StringMap<int>::const_iterator I = Map.find(Name);
if (I == Map.end())
return true;
Idx = I->getValue();
return false;
}
};
} // end anonymous namespace
template <class T>
static size_t arrayDataSize(ArrayRef<T> A) {
return A.size() * sizeof(T);
}
template <class T>
static void writeArrayData(raw_ostream &OS, ArrayRef<T> A) {
OS.write((const char *)A.data(), arrayDataSize(A));
}
template <class T>
static void zero(T &Obj) {
memset(&Obj, 0, sizeof(Obj));
}
namespace {
/// \brief "Single point of truth" for the ELF file construction.
/// TODO: This class still has a ways to go before it is truly a "single
/// point of truth".
template <class ELFT>
class ELFState {
typedef typename object::ELFFile<ELFT>::Elf_Ehdr Elf_Ehdr;
typedef typename object::ELFFile<ELFT>::Elf_Shdr Elf_Shdr;
typedef typename object::ELFFile<ELFT>::Elf_Sym Elf_Sym;
typedef typename object::ELFFile<ELFT>::Elf_Rel Elf_Rel;
typedef typename object::ELFFile<ELFT>::Elf_Rela Elf_Rela;
/// \brief The future ".strtab" section.
StringTableBuilder DotStrtab{StringTableBuilder::ELF};
/// \brief The future ".shstrtab" section.
StringTableBuilder DotShStrtab{StringTableBuilder::ELF};
NameToIdxMap SN2I;
NameToIdxMap SymN2I;
const ELFYAML::Object &Doc;
bool buildSectionIndex();
bool buildSymbolIndex(std::size_t &StartIndex,
const std::vector<ELFYAML::Symbol> &Symbols);
void initELFHeader(Elf_Ehdr &Header);
bool initSectionHeaders(std::vector<Elf_Shdr> &SHeaders,
ContiguousBlobAccumulator &CBA);
void initSymtabSectionHeader(Elf_Shdr &SHeader,
ContiguousBlobAccumulator &CBA);
void initStrtabSectionHeader(Elf_Shdr &SHeader, StringRef Name,
StringTableBuilder &STB,
ContiguousBlobAccumulator &CBA);
void addSymbols(const std::vector<ELFYAML::Symbol> &Symbols,
std::vector<Elf_Sym> &Syms, unsigned SymbolBinding);
void writeSectionContent(Elf_Shdr &SHeader,
const ELFYAML::RawContentSection &Section,
ContiguousBlobAccumulator &CBA);
bool writeSectionContent(Elf_Shdr &SHeader,
const ELFYAML::RelocationSection &Section,
ContiguousBlobAccumulator &CBA);
bool writeSectionContent(Elf_Shdr &SHeader, const ELFYAML::Group &Group,
ContiguousBlobAccumulator &CBA);
bool writeSectionContent(Elf_Shdr &SHeader,
const ELFYAML::MipsABIFlags &Section,
ContiguousBlobAccumulator &CBA);
// - SHT_NULL entry (placed first, i.e. 0'th entry)
// - symbol table (.symtab) (placed third to last)
// - string table (.strtab) (placed second to last)
// - section header string table (.shstrtab) (placed last)
unsigned getDotSymTabSecNo() const { return Doc.Sections.size() + 1; }
unsigned getDotStrTabSecNo() const { return Doc.Sections.size() + 2; }
unsigned getDotShStrTabSecNo() const { return Doc.Sections.size() + 3; }
unsigned getSectionCount() const { return Doc.Sections.size() + 4; }
ELFState(const ELFYAML::Object &D) : Doc(D) {}
public:
static int writeELF(raw_ostream &OS, const ELFYAML::Object &Doc);
};
} // end anonymous namespace
template <class ELFT>
void ELFState<ELFT>::initELFHeader(Elf_Ehdr &Header) {
using namespace llvm::ELF;
zero(Header);
Header.e_ident[EI_MAG0] = 0x7f;
Header.e_ident[EI_MAG1] = 'E';
Header.e_ident[EI_MAG2] = 'L';
Header.e_ident[EI_MAG3] = 'F';
Header.e_ident[EI_CLASS] = ELFT::Is64Bits ? ELFCLASS64 : ELFCLASS32;
bool IsLittleEndian = ELFT::TargetEndianness == support::little;
Header.e_ident[EI_DATA] = IsLittleEndian ? ELFDATA2LSB : ELFDATA2MSB;
Header.e_ident[EI_VERSION] = EV_CURRENT;
Header.e_ident[EI_OSABI] = Doc.Header.OSABI;
Header.e_ident[EI_ABIVERSION] = 0;
Header.e_type = Doc.Header.Type;
Header.e_machine = Doc.Header.Machine;
Header.e_version = EV_CURRENT;
Header.e_entry = Doc.Header.Entry;
Header.e_flags = Doc.Header.Flags;
Header.e_ehsize = sizeof(Elf_Ehdr);
Header.e_shentsize = sizeof(Elf_Shdr);
// Immediately following the ELF header.
Header.e_shoff = sizeof(Header);
Header.e_shnum = getSectionCount();
Header.e_shstrndx = getDotShStrTabSecNo();
}
template <class ELFT>
bool ELFState<ELFT>::initSectionHeaders(std::vector<Elf_Shdr> &SHeaders,
ContiguousBlobAccumulator &CBA) {
// Ensure SHN_UNDEF entry is present. An all-zero section header is a
// valid SHN_UNDEF entry since SHT_NULL == 0.
Elf_Shdr SHeader;
zero(SHeader);
SHeaders.push_back(SHeader);
for (const auto &Sec : Doc.Sections)
DotShStrtab.add(Sec->Name);
DotShStrtab.finalize();
for (const auto &Sec : Doc.Sections) {
zero(SHeader);
SHeader.sh_name = DotShStrtab.getOffset(Sec->Name);
SHeader.sh_type = Sec->Type;
SHeader.sh_flags = Sec->Flags;
SHeader.sh_addr = Sec->Address;
SHeader.sh_addralign = Sec->AddressAlign;
if (!Sec->Link.empty()) {
unsigned Index;
if (SN2I.lookup(Sec->Link, Index)) {
errs() << "error: Unknown section referenced: '" << Sec->Link
<< "' at YAML section '" << Sec->Name << "'.\n";
return false;
}
SHeader.sh_link = Index;
}
if (auto S = dyn_cast<ELFYAML::RawContentSection>(Sec.get()))
writeSectionContent(SHeader, *S, CBA);
else if (auto S = dyn_cast<ELFYAML::RelocationSection>(Sec.get())) {
if (S->Link.empty())
// For relocation section set link to .symtab by default.
SHeader.sh_link = getDotSymTabSecNo();
unsigned Index;
if (SN2I.lookup(S->Info, Index)) {
if (S->Info.getAsInteger(0, Index)) {
errs() << "error: Unknown section referenced: '" << S->Info
<< "' at YAML section '" << S->Name << "'.\n";
return false;
}
}
SHeader.sh_info = Index;
if (!writeSectionContent(SHeader, *S, CBA))
return false;
} else if (auto S = dyn_cast<ELFYAML::Group>(Sec.get())) {
unsigned SymIdx;
if (SymN2I.lookup(S->Info, SymIdx)) {
errs() << "error: Unknown symbol referenced: '" << S->Info
<< "' at YAML section '" << S->Name << "'.\n";
return false;
}
SHeader.sh_info = SymIdx;
if (!writeSectionContent(SHeader, *S, CBA))
return false;
} else if (auto S = dyn_cast<ELFYAML::MipsABIFlags>(Sec.get())) {
if (!writeSectionContent(SHeader, *S, CBA))
return false;
} else if (auto S = dyn_cast<ELFYAML::NoBitsSection>(Sec.get())) {
SHeader.sh_entsize = 0;
SHeader.sh_size = S->Size;
// SHT_NOBITS section does not have content
// so just to setup the section offset.
CBA.getOSAndAlignedOffset(SHeader.sh_offset, SHeader.sh_addralign);
} else
llvm_unreachable("Unknown section type");
SHeaders.push_back(SHeader);
}
return true;
}
template <class ELFT>
void ELFState<ELFT>::initSymtabSectionHeader(Elf_Shdr &SHeader,
ContiguousBlobAccumulator &CBA) {
zero(SHeader);
SHeader.sh_name = DotShStrtab.getOffset(".symtab");
SHeader.sh_type = ELF::SHT_SYMTAB;
SHeader.sh_link = getDotStrTabSecNo();
// One greater than symbol table index of the last local symbol.
SHeader.sh_info = Doc.Symbols.Local.size() + 1;
SHeader.sh_entsize = sizeof(Elf_Sym);
SHeader.sh_addralign = 8;
std::vector<Elf_Sym> Syms;
{
// Ensure STN_UNDEF is present
Elf_Sym Sym;
zero(Sym);
Syms.push_back(Sym);
}
// Add symbol names to .strtab.
for (const auto &Sym : Doc.Symbols.Local)
DotStrtab.add(Sym.Name);
for (const auto &Sym : Doc.Symbols.Global)
DotStrtab.add(Sym.Name);
for (const auto &Sym : Doc.Symbols.Weak)
DotStrtab.add(Sym.Name);
DotStrtab.finalize();
addSymbols(Doc.Symbols.Local, Syms, ELF::STB_LOCAL);
addSymbols(Doc.Symbols.Global, Syms, ELF::STB_GLOBAL);
addSymbols(Doc.Symbols.Weak, Syms, ELF::STB_WEAK);
writeArrayData(
CBA.getOSAndAlignedOffset(SHeader.sh_offset, SHeader.sh_addralign),
makeArrayRef(Syms));
SHeader.sh_size = arrayDataSize(makeArrayRef(Syms));
}
template <class ELFT>
void ELFState<ELFT>::initStrtabSectionHeader(Elf_Shdr &SHeader, StringRef Name,
StringTableBuilder &STB,
ContiguousBlobAccumulator &CBA) {
zero(SHeader);
SHeader.sh_name = DotShStrtab.getOffset(Name);
SHeader.sh_type = ELF::SHT_STRTAB;
STB.write(CBA.getOSAndAlignedOffset(SHeader.sh_offset, SHeader.sh_addralign));
SHeader.sh_size = STB.getSize();
SHeader.sh_addralign = 1;
}
template <class ELFT>
void ELFState<ELFT>::addSymbols(const std::vector<ELFYAML::Symbol> &Symbols,
std::vector<Elf_Sym> &Syms,
unsigned SymbolBinding) {
for (const auto &Sym : Symbols) {
Elf_Sym Symbol;
zero(Symbol);
if (!Sym.Name.empty())
Symbol.st_name = DotStrtab.getOffset(Sym.Name);
Symbol.setBindingAndType(SymbolBinding, Sym.Type);
if (!Sym.Section.empty()) {
unsigned Index;
if (SN2I.lookup(Sym.Section, Index)) {
errs() << "error: Unknown section referenced: '" << Sym.Section
<< "' by YAML symbol " << Sym.Name << ".\n";
exit(1);
}
Symbol.st_shndx = Index;
} // else Symbol.st_shndex == SHN_UNDEF (== 0), since it was zero'd earlier.
Symbol.st_value = Sym.Value;
Symbol.st_other = Sym.Other;
Symbol.st_size = Sym.Size;
Syms.push_back(Symbol);
}
}
template <class ELFT>
void
ELFState<ELFT>::writeSectionContent(Elf_Shdr &SHeader,
const ELFYAML::RawContentSection &Section,
ContiguousBlobAccumulator &CBA) {
assert(Section.Size >= Section.Content.binary_size() &&
"Section size and section content are inconsistent");
raw_ostream &OS =
CBA.getOSAndAlignedOffset(SHeader.sh_offset, SHeader.sh_addralign);
Section.Content.writeAsBinary(OS);
for (auto i = Section.Content.binary_size(); i < Section.Size; ++i)
OS.write(0);
SHeader.sh_entsize = 0;
SHeader.sh_size = Section.Size;
}
static bool isMips64EL(const ELFYAML::Object &Doc) {
return Doc.Header.Machine == ELFYAML::ELF_EM(llvm::ELF::EM_MIPS) &&
Doc.Header.Class == ELFYAML::ELF_ELFCLASS(ELF::ELFCLASS64) &&
Doc.Header.Data == ELFYAML::ELF_ELFDATA(ELF::ELFDATA2LSB);
}
template <class ELFT>
bool
ELFState<ELFT>::writeSectionContent(Elf_Shdr &SHeader,
const ELFYAML::RelocationSection &Section,
ContiguousBlobAccumulator &CBA) {
assert((Section.Type == llvm::ELF::SHT_REL ||
Section.Type == llvm::ELF::SHT_RELA) &&
"Section type is not SHT_REL nor SHT_RELA");
bool IsRela = Section.Type == llvm::ELF::SHT_RELA;
SHeader.sh_entsize = IsRela ? sizeof(Elf_Rela) : sizeof(Elf_Rel);
SHeader.sh_size = SHeader.sh_entsize * Section.Relocations.size();
auto &OS = CBA.getOSAndAlignedOffset(SHeader.sh_offset, SHeader.sh_addralign);
for (const auto &Rel : Section.Relocations) {
unsigned SymIdx = 0;
// Some special relocation, R_ARM_v4BX for instance, does not have
// an external reference. So it ignores the return value of lookup()
// here.
SymN2I.lookup(Rel.Symbol, SymIdx);
if (IsRela) {
Elf_Rela REntry;
zero(REntry);
REntry.r_offset = Rel.Offset;
REntry.r_addend = Rel.Addend;
REntry.setSymbolAndType(SymIdx, Rel.Type, isMips64EL(Doc));
OS.write((const char *)&REntry, sizeof(REntry));
} else {
Elf_Rel REntry;
zero(REntry);
REntry.r_offset = Rel.Offset;
REntry.setSymbolAndType(SymIdx, Rel.Type, isMips64EL(Doc));
OS.write((const char *)&REntry, sizeof(REntry));
}
}
return true;
}
template <class ELFT>
bool ELFState<ELFT>::writeSectionContent(Elf_Shdr &SHeader,
const ELFYAML::Group &Section,
ContiguousBlobAccumulator &CBA) {
typedef typename object::ELFFile<ELFT>::Elf_Word Elf_Word;
assert(Section.Type == llvm::ELF::SHT_GROUP &&
"Section type is not SHT_GROUP");
SHeader.sh_entsize = sizeof(Elf_Word);
SHeader.sh_size = SHeader.sh_entsize * Section.Members.size();
auto &OS = CBA.getOSAndAlignedOffset(SHeader.sh_offset, SHeader.sh_addralign);
for (auto member : Section.Members) {
Elf_Word SIdx;
unsigned int sectionIndex = 0;
if (member.sectionNameOrType == "GRP_COMDAT")
sectionIndex = llvm::ELF::GRP_COMDAT;
else if (SN2I.lookup(member.sectionNameOrType, sectionIndex)) {
errs() << "error: Unknown section referenced: '"
<< member.sectionNameOrType << "' at YAML section' "
<< Section.Name << "\n";
return false;
}
SIdx = sectionIndex;
OS.write((const char *)&SIdx, sizeof(SIdx));
}
return true;
}
template <class ELFT>
bool ELFState<ELFT>::writeSectionContent(Elf_Shdr &SHeader,
const ELFYAML::MipsABIFlags &Section,
ContiguousBlobAccumulator &CBA) {
assert(Section.Type == llvm::ELF::SHT_MIPS_ABIFLAGS &&
"Section type is not SHT_MIPS_ABIFLAGS");
object::Elf_Mips_ABIFlags<ELFT> Flags;
zero(Flags);
SHeader.sh_entsize = sizeof(Flags);
SHeader.sh_size = SHeader.sh_entsize;
auto &OS = CBA.getOSAndAlignedOffset(SHeader.sh_offset, SHeader.sh_addralign);
Flags.version = Section.Version;
Flags.isa_level = Section.ISALevel;
Flags.isa_rev = Section.ISARevision;
Flags.gpr_size = Section.GPRSize;
Flags.cpr1_size = Section.CPR1Size;
Flags.cpr2_size = Section.CPR2Size;
Flags.fp_abi = Section.FpABI;
Flags.isa_ext = Section.ISAExtension;
Flags.ases = Section.ASEs;
Flags.flags1 = Section.Flags1;
Flags.flags2 = Section.Flags2;
OS.write((const char *)&Flags, sizeof(Flags));
return true;
}
template <class ELFT> bool ELFState<ELFT>::buildSectionIndex() {
SN2I.addName(".symtab", getDotSymTabSecNo());
SN2I.addName(".strtab", getDotStrTabSecNo());
SN2I.addName(".shstrtab", getDotShStrTabSecNo());
for (unsigned i = 0, e = Doc.Sections.size(); i != e; ++i) {
StringRef Name = Doc.Sections[i]->Name;
if (Name.empty())
continue;
// "+ 1" to take into account the SHT_NULL entry.
if (SN2I.addName(Name, i + 1)) {
errs() << "error: Repeated section name: '" << Name
<< "' at YAML section number " << i << ".\n";
return false;
}
}
return true;
}
template <class ELFT>
bool
ELFState<ELFT>::buildSymbolIndex(std::size_t &StartIndex,
const std::vector<ELFYAML::Symbol> &Symbols) {
for (const auto &Sym : Symbols) {
++StartIndex;
if (Sym.Name.empty())
continue;
if (SymN2I.addName(Sym.Name, StartIndex)) {
errs() << "error: Repeated symbol name: '" << Sym.Name << "'.\n";
return false;
}
}
return true;
}
template <class ELFT>
int ELFState<ELFT>::writeELF(raw_ostream &OS, const ELFYAML::Object &Doc) {
ELFState<ELFT> State(Doc);
if (!State.buildSectionIndex())
return 1;
std::size_t StartSymIndex = 0;
if (!State.buildSymbolIndex(StartSymIndex, Doc.Symbols.Local) ||
!State.buildSymbolIndex(StartSymIndex, Doc.Symbols.Global) ||
!State.buildSymbolIndex(StartSymIndex, Doc.Symbols.Weak))
return 1;
Elf_Ehdr Header;
State.initELFHeader(Header);
// TODO: Flesh out section header support.
// TODO: Program headers.
// XXX: This offset is tightly coupled with the order that we write
// things to `OS`.
const size_t SectionContentBeginOffset =
Header.e_ehsize + Header.e_shentsize * Header.e_shnum;
ContiguousBlobAccumulator CBA(SectionContentBeginOffset);
// Doc might not contain .symtab, .strtab and .shstrtab sections,
// but we will emit them, so make sure to add them to ShStrTabSHeader.
State.DotShStrtab.add(".symtab");
State.DotShStrtab.add(".strtab");
State.DotShStrtab.add(".shstrtab");
std::vector<Elf_Shdr> SHeaders;
if(!State.initSectionHeaders(SHeaders, CBA))
return 1;
// .symtab section.
Elf_Shdr SymtabSHeader;
State.initSymtabSectionHeader(SymtabSHeader, CBA);
SHeaders.push_back(SymtabSHeader);
// .strtab string table header.
Elf_Shdr DotStrTabSHeader;
State.initStrtabSectionHeader(DotStrTabSHeader, ".strtab", State.DotStrtab,
CBA);
SHeaders.push_back(DotStrTabSHeader);
// .shstrtab string table header.
Elf_Shdr ShStrTabSHeader;
State.initStrtabSectionHeader(ShStrTabSHeader, ".shstrtab", State.DotShStrtab,
CBA);
SHeaders.push_back(ShStrTabSHeader);
OS.write((const char *)&Header, sizeof(Header));
writeArrayData(OS, makeArrayRef(SHeaders));
CBA.writeBlobToStream(OS);
return 0;
}
static bool is64Bit(const ELFYAML::Object &Doc) {
return Doc.Header.Class == ELFYAML::ELF_ELFCLASS(ELF::ELFCLASS64);
}
static bool isLittleEndian(const ELFYAML::Object &Doc) {
return Doc.Header.Data == ELFYAML::ELF_ELFDATA(ELF::ELFDATA2LSB);
}
int yaml2elf(llvm::ELFYAML::Object &Doc, raw_ostream &Out) {
using object::ELFType;
typedef ELFType<support::little, true> LE64;
typedef ELFType<support::big, true> BE64;
typedef ELFType<support::little, false> LE32;
typedef ELFType<support::big, false> BE32;
if (is64Bit(Doc)) {
if (isLittleEndian(Doc))
return ELFState<LE64>::writeELF(Out, Doc);
else
return ELFState<BE64>::writeELF(Out, Doc);
} else {
if (isLittleEndian(Doc))
return ELFState<LE32>::writeELF(Out, Doc);
else
return ELFState<BE32>::writeELF(Out, Doc);
}
}
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