llvm-6502/tools/yaml2obj/yaml2elf.cpp
Sean Silva 068463b714 [yaml2obj][ELF] Make symbol table top-level key.
Although in reality the symbol table in ELF resides in a section, the
standard requires that there be no more than one SHT_SYMTAB. To enforce
this constraint, it is cleaner to group all the symbols under a
top-level `Symbols` key on the object file.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@184627 91177308-0d34-0410-b5e6-96231b3b80d8
2013-06-22 01:38:00 +00:00

399 lines
13 KiB
C++

//===- 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/Object/ELF.h"
#include "llvm/Object/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;
// There is similar code in yaml2coff, but with some slight COFF-specific
// variations like different initial state. Might be able to deduplicate
// some day, but also want to make sure that the Mach-O use case is served.
//
// This class has a deliberately small interface, since a lot of
// implementation variation is possible.
//
// TODO: Use an ordered container with a suffix-based comparison in order
// to deduplicate suffixes. std::map<> with a custom comparator is likely
// to be the simplest implementation, but a suffix trie could be more
// suitable for the job.
namespace {
class StringTableBuilder {
/// \brief Indices of strings currently present in `Buf`.
StringMap<unsigned> StringIndices;
/// \brief The contents of the string table as we build it.
std::string Buf;
public:
StringTableBuilder() {
Buf.push_back('\0');
}
/// \returns Index of string in string table.
unsigned addString(StringRef S) {
StringMapEntry<unsigned> &Entry = StringIndices.GetOrCreateValue(S);
unsigned &I = Entry.getValue();
if (I != 0)
return I;
I = Buf.size();
Buf.append(S.begin(), S.end());
Buf.push_back('\0');
return I;
}
size_t size() const {
return Buf.size();
}
void writeToStream(raw_ostream &OS) {
OS.write(Buf.data(), Buf.size());
}
};
} // end anonymous namespace
// 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) {
uint64_t CurrentOffset = InitialOffset + OS.tell();
uint64_t AlignedOffset = RoundUpToAlignment(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 = 16) {
Offset = padToAlignment(Align);
return OS;
}
void writeBlobToStream(raw_ostream &Out) { Out << OS.str(); }
};
} // end anonymous namespace
// Used to keep track of section names, so that in the YAML file sections
// can be referenced by name instead of by index.
namespace {
class SectionNameToIdxMap {
StringMap<int> Map;
public:
/// \returns true if name is already present in the map.
bool addName(StringRef SecName, unsigned i) {
StringMapEntry<int> &Entry = Map.GetOrCreateValue(SecName, -1);
if (Entry.getValue() != -1)
return true;
Entry.setValue((int)i);
return false;
}
/// \returns true if name is not present in the map
bool lookupSection(StringRef SecName, unsigned &Idx) const {
StringMap<int>::const_iterator I = Map.find(SecName);
if (I == Map.end())
return true;
Idx = I->getValue();
return false;
}
};
} // end anonymous namespace
template <class T>
static size_t vectorDataSize(const std::vector<T> &Vec) {
return Vec.size() * sizeof(T);
}
template <class T>
static void writeVectorData(raw_ostream &OS, const std::vector<T> &Vec) {
OS.write((const char *)Vec.data(), vectorDataSize(Vec));
}
template <class T>
static void zero(T &Obj) {
memset(&Obj, 0, sizeof(Obj));
}
/// \brief Create a string table in `SHeader`, which we assume is already
/// zero'd.
template <class Elf_Shdr>
static void createStringTableSectionHeader(Elf_Shdr &SHeader,
StringTableBuilder &STB,
ContiguousBlobAccumulator &CBA) {
SHeader.sh_type = ELF::SHT_STRTAB;
STB.writeToStream(CBA.getOSAndAlignedOffset(SHeader.sh_offset));
SHeader.sh_size = STB.size();
SHeader.sh_addralign = 1;
}
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 {
/// \brief The future ".strtab" section.
StringTableBuilder DotStrtab;
/// \brief The section number of the ".strtab" section.
unsigned DotStrtabSecNo;
/// \brief The accumulated contents of all sections so far.
ContiguousBlobAccumulator &SectionContentAccum;
typedef typename object::ELFObjectFile<ELFT>::Elf_Ehdr Elf_Ehdr;
/// \brief The ELF file header.
Elf_Ehdr &Header;
SectionNameToIdxMap &SN2I;
public:
ELFState(Elf_Ehdr &Header_, ContiguousBlobAccumulator &Accum,
unsigned DotStrtabSecNo_, SectionNameToIdxMap &SN2I_)
: DotStrtab(), DotStrtabSecNo(DotStrtabSecNo_),
SectionContentAccum(Accum), Header(Header_), SN2I(SN2I_) {}
unsigned getDotStrTabSecNo() const { return DotStrtabSecNo; }
StringTableBuilder &getStringTable() { return DotStrtab; }
ContiguousBlobAccumulator &getSectionContentAccum() {
return SectionContentAccum;
}
SectionNameToIdxMap &getSN2I() { return SN2I; }
};
} // end anonymous namespace
// FIXME: At this point it is fairly clear that we need to refactor these
// static functions into methods of a class sharing some typedefs. These
// ELF type names are insane.
template <class ELFT>
static void
addSymbols(const std::vector<ELFYAML::Symbol> &Symbols, ELFState<ELFT> &State,
std::vector<typename object::ELFObjectFile<ELFT>::Elf_Sym> &Syms,
unsigned SymbolBinding) {
typedef typename object::ELFObjectFile<ELFT>::Elf_Sym Elf_Sym;
for (unsigned i = 0, e = Symbols.size(); i != e; ++i) {
const ELFYAML::Symbol &Sym = Symbols[i];
Elf_Sym Symbol;
zero(Symbol);
if (!Sym.Name.empty())
Symbol.st_name = State.getStringTable().addString(Sym.Name);
Symbol.setBindingAndType(SymbolBinding, Sym.Type);
if (!Sym.Section.empty()) {
unsigned Index;
if (State.getSN2I().lookupSection(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_size = Sym.Size;
Syms.push_back(Symbol);
}
}
template <class ELFT>
static void handleSymtabSectionHeader(
const ELFYAML::LocalGlobalWeakSymbols &Symbols, ELFState<ELFT> &State,
typename object::ELFObjectFile<ELFT>::Elf_Shdr &SHeader) {
typedef typename object::ELFObjectFile<ELFT>::Elf_Sym Elf_Sym;
SHeader.sh_type = ELF::SHT_SYMTAB;
SHeader.sh_link = State.getDotStrTabSecNo();
// One greater than symbol table index of the last local symbol.
SHeader.sh_info = Symbols.Local.size() + 1;
SHeader.sh_entsize = sizeof(Elf_Sym);
std::vector<Elf_Sym> Syms;
{
// Ensure STN_UNDEF is present
Elf_Sym Sym;
zero(Sym);
Syms.push_back(Sym);
}
addSymbols(Symbols.Local, State, Syms, ELF::STB_LOCAL);
addSymbols(Symbols.Global, State, Syms, ELF::STB_GLOBAL);
addSymbols(Symbols.Weak, State, Syms, ELF::STB_WEAK);
ContiguousBlobAccumulator &CBA = State.getSectionContentAccum();
writeVectorData(CBA.getOSAndAlignedOffset(SHeader.sh_offset), Syms);
SHeader.sh_size = vectorDataSize(Syms);
}
template <class ELFT>
static int writeELF(raw_ostream &OS, const ELFYAML::Object &Doc) {
using namespace llvm::ELF;
typedef typename object::ELFObjectFile<ELFT>::Elf_Ehdr Elf_Ehdr;
typedef typename object::ELFObjectFile<ELFT>::Elf_Shdr Elf_Shdr;
const ELFYAML::FileHeader &Hdr = Doc.Header;
Elf_Ehdr Header;
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] = Hdr.OSABI;
Header.e_ident[EI_ABIVERSION] = 0;
Header.e_type = Hdr.Type;
Header.e_machine = Hdr.Machine;
Header.e_version = EV_CURRENT;
Header.e_entry = Hdr.Entry;
Header.e_ehsize = sizeof(Elf_Ehdr);
// TODO: Flesh out section header support.
// TODO: Program headers.
Header.e_shentsize = sizeof(Elf_Shdr);
// Immediately following the ELF header.
Header.e_shoff = sizeof(Header);
const std::vector<ELFYAML::Section> &Sections = Doc.Sections;
// "+ 4" for
// - 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. (placed last)
Header.e_shnum = Sections.size() + 4;
// Place section header string table last.
Header.e_shstrndx = Header.e_shnum - 1;
const unsigned DotStrtabSecNo = Header.e_shnum - 2;
// 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);
SectionNameToIdxMap SN2I;
for (unsigned i = 0, e = Sections.size(); i != e; ++i) {
StringRef Name = 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 1;
}
}
ELFState<ELFT> State(Header, CBA, DotStrtabSecNo, SN2I);
StringTableBuilder SHStrTab;
std::vector<Elf_Shdr> SHeaders;
{
// Ensure SHN_UNDEF entry is present. An all-zero section header is a
// valid SHN_UNDEF entry since SHT_NULL == 0.
Elf_Shdr SHdr;
zero(SHdr);
SHeaders.push_back(SHdr);
}
for (unsigned i = 0, e = Sections.size(); i != e; ++i) {
const ELFYAML::Section &Sec = Sections[i];
Elf_Shdr SHeader;
zero(SHeader);
SHeader.sh_name = SHStrTab.addString(Sec.Name);
SHeader.sh_type = Sec.Type;
SHeader.sh_flags = Sec.Flags;
SHeader.sh_addr = Sec.Address;
Sec.Content.writeAsBinary(CBA.getOSAndAlignedOffset(SHeader.sh_offset));
SHeader.sh_size = Sec.Content.binary_size();
if (!Sec.Link.empty()) {
unsigned Index;
if (SN2I.lookupSection(Sec.Link, Index)) {
errs() << "error: Unknown section referenced: '" << Sec.Link
<< "' at YAML section number " << i << ".\n";
return 1;
}
SHeader.sh_link = Index;
}
SHeader.sh_info = 0;
SHeader.sh_addralign = Sec.AddressAlign;
SHeader.sh_entsize = 0;
SHeaders.push_back(SHeader);
}
// .symtab section.
Elf_Shdr SymtabSHeader;
zero(SymtabSHeader);
SymtabSHeader.sh_name = SHStrTab.addString(StringRef(".symtab"));
handleSymtabSectionHeader<ELFT>(Doc.Symbols, State, SymtabSHeader);
SHeaders.push_back(SymtabSHeader);
// .strtab string table header.
Elf_Shdr DotStrTabSHeader;
zero(DotStrTabSHeader);
DotStrTabSHeader.sh_name = SHStrTab.addString(StringRef(".strtab"));
createStringTableSectionHeader(DotStrTabSHeader, State.getStringTable(), CBA);
SHeaders.push_back(DotStrTabSHeader);
// Section header string table header.
Elf_Shdr SHStrTabSHeader;
zero(SHStrTabSHeader);
createStringTableSectionHeader(SHStrTabSHeader, SHStrTab, CBA);
SHeaders.push_back(SHStrTabSHeader);
OS.write((const char *)&Header, sizeof(Header));
writeVectorData(OS, 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::raw_ostream &Out, llvm::MemoryBuffer *Buf) {
yaml::Input YIn(Buf->getBuffer());
ELFYAML::Object Doc;
YIn >> Doc;
if (YIn.error()) {
errs() << "yaml2obj: Failed to parse YAML file!\n";
return 1;
}
using object::ELFType;
typedef ELFType<support::little, 8, true> LE64;
typedef ELFType<support::big, 8, true> BE64;
typedef ELFType<support::little, 4, false> LE32;
typedef ELFType<support::big, 4, false> BE32;
if (is64Bit(Doc)) {
if (isLittleEndian(Doc))
return writeELF<LE64>(outs(), Doc);
else
return writeELF<BE64>(outs(), Doc);
} else {
if (isLittleEndian(Doc))
return writeELF<LE32>(outs(), Doc);
else
return writeELF<BE32>(outs(), Doc);
}
}