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llvm-project/llvm/tools/llvm-objcopy/ELF/ELFObjcopy.cpp

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//===- ELFObjcopy.cpp -----------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include "ELFObjcopy.h"
#include "Buffer.h"
#include "CopyConfig.h"
#include "Object.h"
#include "llvm-objcopy.h"
#include "llvm/ADT/BitmaskEnum.h"
#include "llvm/ADT/Optional.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/ADT/Twine.h"
#include "llvm/BinaryFormat/ELF.h"
#include "llvm/MC/MCTargetOptions.h"
#include "llvm/Object/Binary.h"
#include "llvm/Object/ELFObjectFile.h"
#include "llvm/Object/ELFTypes.h"
#include "llvm/Object/Error.h"
#include "llvm/Option/Option.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/Compression.h"
#include "llvm/Support/Errc.h"
#include "llvm/Support/Error.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/ErrorOr.h"
#include "llvm/Support/Memory.h"
#include "llvm/Support/Path.h"
#include "llvm/Support/raw_ostream.h"
#include <algorithm>
#include <cassert>
#include <cstdlib>
#include <functional>
#include <iterator>
#include <memory>
#include <string>
#include <system_error>
#include <utility>
namespace llvm {
namespace objcopy {
namespace elf {
using namespace object;
using namespace ELF;
using SectionPred = std::function<bool(const SectionBase &Sec)>;
static bool isDebugSection(const SectionBase &Sec) {
return StringRef(Sec.Name).startswith(".debug") ||
StringRef(Sec.Name).startswith(".zdebug") || Sec.Name == ".gdb_index";
}
static bool isDWOSection(const SectionBase &Sec) {
return StringRef(Sec.Name).endswith(".dwo");
}
static bool onlyKeepDWOPred(const Object &Obj, const SectionBase &Sec) {
// We can't remove the section header string table.
if (&Sec == Obj.SectionNames)
return false;
// Short of keeping the string table we want to keep everything that is a DWO
// section and remove everything else.
return !isDWOSection(Sec);
}
static uint64_t setSectionFlagsPreserveMask(uint64_t OldFlags,
uint64_t NewFlags) {
// Preserve some flags which should not be dropped when setting flags.
// Also, preserve anything OS/processor dependant.
const uint64_t PreserveMask = ELF::SHF_COMPRESSED | ELF::SHF_EXCLUDE |
ELF::SHF_GROUP | ELF::SHF_LINK_ORDER |
ELF::SHF_MASKOS | ELF::SHF_MASKPROC |
ELF::SHF_TLS | ELF::SHF_INFO_LINK;
return (OldFlags & PreserveMask) | (NewFlags & ~PreserveMask);
}
static ElfType getOutputElfType(const Binary &Bin) {
// Infer output ELF type from the input ELF object
if (isa<ELFObjectFile<ELF32LE>>(Bin))
return ELFT_ELF32LE;
if (isa<ELFObjectFile<ELF64LE>>(Bin))
return ELFT_ELF64LE;
if (isa<ELFObjectFile<ELF32BE>>(Bin))
return ELFT_ELF32BE;
if (isa<ELFObjectFile<ELF64BE>>(Bin))
return ELFT_ELF64BE;
llvm_unreachable("Invalid ELFType");
}
static ElfType getOutputElfType(const MachineInfo &MI) {
// Infer output ELF type from the binary arch specified
if (MI.Is64Bit)
return MI.IsLittleEndian ? ELFT_ELF64LE : ELFT_ELF64BE;
else
return MI.IsLittleEndian ? ELFT_ELF32LE : ELFT_ELF32BE;
}
static std::unique_ptr<Writer> createWriter(const CopyConfig &Config,
Object &Obj, Buffer &Buf,
ElfType OutputElfType) {
if (Config.OutputFormat == "binary") {
return llvm::make_unique<BinaryWriter>(Obj, Buf);
}
// Depending on the initial ELFT and OutputFormat we need a different Writer.
switch (OutputElfType) {
case ELFT_ELF32LE:
return llvm::make_unique<ELFWriter<ELF32LE>>(Obj, Buf,
!Config.StripSections);
case ELFT_ELF64LE:
return llvm::make_unique<ELFWriter<ELF64LE>>(Obj, Buf,
!Config.StripSections);
case ELFT_ELF32BE:
return llvm::make_unique<ELFWriter<ELF32BE>>(Obj, Buf,
!Config.StripSections);
case ELFT_ELF64BE:
return llvm::make_unique<ELFWriter<ELF64BE>>(Obj, Buf,
!Config.StripSections);
}
llvm_unreachable("Invalid output format");
}
template <class ELFT>
static Expected<ArrayRef<uint8_t>>
findBuildID(const object::ELFFile<ELFT> &In) {
for (const auto &Phdr : unwrapOrError(In.program_headers())) {
if (Phdr.p_type != PT_NOTE)
continue;
Error Err = Error::success();
for (const auto &Note : In.notes(Phdr, Err))
if (Note.getType() == NT_GNU_BUILD_ID && Note.getName() == ELF_NOTE_GNU)
return Note.getDesc();
if (Err)
return std::move(Err);
}
return createStringError(llvm::errc::invalid_argument,
"Could not find build ID.");
}
static Expected<ArrayRef<uint8_t>>
findBuildID(const object::ELFObjectFileBase &In) {
if (auto *O = dyn_cast<ELFObjectFile<ELF32LE>>(&In))
return findBuildID(*O->getELFFile());
else if (auto *O = dyn_cast<ELFObjectFile<ELF64LE>>(&In))
return findBuildID(*O->getELFFile());
else if (auto *O = dyn_cast<ELFObjectFile<ELF32BE>>(&In))
return findBuildID(*O->getELFFile());
else if (auto *O = dyn_cast<ELFObjectFile<ELF64BE>>(&In))
return findBuildID(*O->getELFFile());
llvm_unreachable("Bad file format");
}
static void linkToBuildIdDir(const CopyConfig &Config, StringRef ToLink,
StringRef Suffix, ArrayRef<uint8_t> BuildIdBytes) {
SmallString<128> Path = Config.BuildIdLinkDir;
sys::path::append(Path, llvm::toHex(BuildIdBytes[0], /*LowerCase*/ true));
if (auto EC = sys::fs::create_directories(Path))
error("cannot create build ID link directory " + Path + ": " +
EC.message());
sys::path::append(Path,
llvm::toHex(BuildIdBytes.slice(1), /*LowerCase*/ true));
Path += Suffix;
if (auto EC = sys::fs::create_hard_link(ToLink, Path)) {
// Hard linking failed, try to remove the file first if it exists.
if (sys::fs::exists(Path))
sys::fs::remove(Path);
EC = sys::fs::create_hard_link(ToLink, Path);
if (EC)
error("cannot link " + ToLink + " to " + Path + ": " + EC.message());
}
}
static void splitDWOToFile(const CopyConfig &Config, const Reader &Reader,
StringRef File, ElfType OutputElfType) {
auto DWOFile = Reader.create();
DWOFile->removeSections(
[&](const SectionBase &Sec) { return onlyKeepDWOPred(*DWOFile, Sec); });
if (Config.OutputArch)
DWOFile->Machine = Config.OutputArch.getValue().EMachine;
FileBuffer FB(File);
auto Writer = createWriter(Config, *DWOFile, FB, OutputElfType);
if (Error E = Writer->finalize())
error(std::move(E));
if (Error E = Writer->write())
error(std::move(E));
}
static Error dumpSectionToFile(StringRef SecName, StringRef Filename,
Object &Obj) {
for (auto &Sec : Obj.sections()) {
if (Sec.Name == SecName) {
if (Sec.OriginalData.empty())
return createStringError(
object_error::parse_failed,
"Can't dump section \"%s\": it has no contents",
SecName.str().c_str());
Expected<std::unique_ptr<FileOutputBuffer>> BufferOrErr =
FileOutputBuffer::create(Filename, Sec.OriginalData.size());
if (!BufferOrErr)
return BufferOrErr.takeError();
std::unique_ptr<FileOutputBuffer> Buf = std::move(*BufferOrErr);
std::copy(Sec.OriginalData.begin(), Sec.OriginalData.end(),
Buf->getBufferStart());
if (Error E = Buf->commit())
return E;
return Error::success();
}
}
return createStringError(object_error::parse_failed, "Section not found");
}
static bool isCompressed(const SectionBase &Section) {
const char *Magic = "ZLIB";
return StringRef(Section.Name).startswith(".zdebug") ||
(Section.OriginalData.size() > strlen(Magic) &&
!strncmp(reinterpret_cast<const char *>(Section.OriginalData.data()),
Magic, strlen(Magic))) ||
(Section.Flags & ELF::SHF_COMPRESSED);
}
static bool isCompressable(const SectionBase &Section) {
return !isCompressed(Section) && isDebugSection(Section) &&
Section.Name != ".gdb_index";
}
static void replaceDebugSections(
const CopyConfig &Config, Object &Obj, SectionPred &RemovePred,
function_ref<bool(const SectionBase &)> shouldReplace,
function_ref<SectionBase *(const SectionBase *)> addSection) {
SmallVector<SectionBase *, 13> ToReplace;
SmallVector<RelocationSection *, 13> RelocationSections;
for (auto &Sec : Obj.sections()) {
if (RelocationSection *R = dyn_cast<RelocationSection>(&Sec)) {
if (shouldReplace(*R->getSection()))
RelocationSections.push_back(R);
continue;
}
if (shouldReplace(Sec))
ToReplace.push_back(&Sec);
}
for (SectionBase *S : ToReplace) {
SectionBase *NewSection = addSection(S);
for (RelocationSection *RS : RelocationSections) {
if (RS->getSection() == S)
RS->setSection(NewSection);
}
}
RemovePred = [shouldReplace, RemovePred](const SectionBase &Sec) {
return shouldReplace(Sec) || RemovePred(Sec);
};
}
// This function handles the high level operations of GNU objcopy including
// handling command line options. It's important to outline certain properties
// we expect to hold of the command line operations. Any operation that "keeps"
// should keep regardless of a remove. Additionally any removal should respect
// any previous removals. Lastly whether or not something is removed shouldn't
// depend a) on the order the options occur in or b) on some opaque priority
// system. The only priority is that keeps/copies overrule removes.
static void handleArgs(const CopyConfig &Config, Object &Obj,
const Reader &Reader, ElfType OutputElfType) {
if (!Config.SplitDWO.empty()) {
splitDWOToFile(Config, Reader, Config.SplitDWO, OutputElfType);
}
if (Config.OutputArch)
Obj.Machine = Config.OutputArch.getValue().EMachine;
// TODO: update or remove symbols only if there is an option that affects
// them.
if (Obj.SymbolTable) {
Obj.SymbolTable->updateSymbols([&](Symbol &Sym) {
if (!Sym.isCommon() &&
((Config.LocalizeHidden &&
(Sym.Visibility == STV_HIDDEN || Sym.Visibility == STV_INTERNAL)) ||
is_contained(Config.SymbolsToLocalize, Sym.Name)))
Sym.Binding = STB_LOCAL;
// Note: these two globalize flags have very similar names but different
// meanings:
//
// --globalize-symbol: promote a symbol to global
// --keep-global-symbol: all symbols except for these should be made local
//
// If --globalize-symbol is specified for a given symbol, it will be
// global in the output file even if it is not included via
// --keep-global-symbol. Because of that, make sure to check
// --globalize-symbol second.
if (!Config.SymbolsToKeepGlobal.empty() &&
!is_contained(Config.SymbolsToKeepGlobal, Sym.Name) &&
Sym.getShndx() != SHN_UNDEF)
Sym.Binding = STB_LOCAL;
if (is_contained(Config.SymbolsToGlobalize, Sym.Name) &&
Sym.getShndx() != SHN_UNDEF)
Sym.Binding = STB_GLOBAL;
if (is_contained(Config.SymbolsToWeaken, Sym.Name) &&
Sym.Binding == STB_GLOBAL)
Sym.Binding = STB_WEAK;
if (Config.Weaken && Sym.Binding == STB_GLOBAL &&
Sym.getShndx() != SHN_UNDEF)
Sym.Binding = STB_WEAK;
const auto I = Config.SymbolsToRename.find(Sym.Name);
if (I != Config.SymbolsToRename.end())
Sym.Name = I->getValue();
if (!Config.SymbolsPrefix.empty() && Sym.Type != STT_SECTION)
Sym.Name = (Config.SymbolsPrefix + Sym.Name).str();
});
// The purpose of this loop is to mark symbols referenced by sections
// (like GroupSection or RelocationSection). This way, we know which
// symbols are still 'needed' and which are not.
if (Config.StripUnneeded) {
for (auto &Section : Obj.sections())
Section.markSymbols();
}
Obj.removeSymbols([&](const Symbol &Sym) {
if (is_contained(Config.SymbolsToKeep, Sym.Name) ||
(Config.KeepFileSymbols && Sym.Type == STT_FILE))
return false;
if (Config.DiscardAll && Sym.Binding == STB_LOCAL &&
Sym.getShndx() != SHN_UNDEF && Sym.Type != STT_FILE &&
Sym.Type != STT_SECTION)
return true;
if (Config.StripAll || Config.StripAllGNU)
return true;
if (is_contained(Config.SymbolsToRemove, Sym.Name))
return true;
if (Config.StripUnneeded && !Sym.Referenced &&
(Sym.Binding == STB_LOCAL || Sym.getShndx() == SHN_UNDEF) &&
Sym.Type != STT_FILE && Sym.Type != STT_SECTION)
return true;
return false;
});
}
SectionPred RemovePred = [](const SectionBase &) { return false; };
// Removes:
if (!Config.ToRemove.empty()) {
RemovePred = [&Config](const SectionBase &Sec) {
return is_contained(Config.ToRemove, Sec.Name);
};
}
if (Config.StripDWO || !Config.SplitDWO.empty())
RemovePred = [RemovePred](const SectionBase &Sec) {
return isDWOSection(Sec) || RemovePred(Sec);
};
if (Config.ExtractDWO)
RemovePred = [RemovePred, &Obj](const SectionBase &Sec) {
return onlyKeepDWOPred(Obj, Sec) || RemovePred(Sec);
};
if (Config.StripAllGNU)
RemovePred = [RemovePred, &Obj](const SectionBase &Sec) {
if (RemovePred(Sec))
return true;
if ((Sec.Flags & SHF_ALLOC) != 0)
return false;
if (&Sec == Obj.SectionNames)
return false;
switch (Sec.Type) {
case SHT_SYMTAB:
case SHT_REL:
case SHT_RELA:
case SHT_STRTAB:
return true;
}
return isDebugSection(Sec);
};
if (Config.StripSections) {
RemovePred = [RemovePred](const SectionBase &Sec) {
return RemovePred(Sec) || (Sec.Flags & SHF_ALLOC) == 0;
};
}
if (Config.StripDebug) {
RemovePred = [RemovePred](const SectionBase &Sec) {
return RemovePred(Sec) || isDebugSection(Sec);
};
}
if (Config.StripNonAlloc)
RemovePred = [RemovePred, &Obj](const SectionBase &Sec) {
if (RemovePred(Sec))
return true;
if (&Sec == Obj.SectionNames)
return false;
return (Sec.Flags & SHF_ALLOC) == 0;
};
if (Config.StripAll)
RemovePred = [RemovePred, &Obj](const SectionBase &Sec) {
if (RemovePred(Sec))
return true;
if (&Sec == Obj.SectionNames)
return false;
if (StringRef(Sec.Name).startswith(".gnu.warning"))
return false;
return (Sec.Flags & SHF_ALLOC) == 0;
};
// Explicit copies:
if (!Config.OnlySection.empty()) {
RemovePred = [&Config, RemovePred, &Obj](const SectionBase &Sec) {
// Explicitly keep these sections regardless of previous removes.
if (is_contained(Config.OnlySection, Sec.Name))
return false;
// Allow all implicit removes.
if (RemovePred(Sec))
return true;
// Keep special sections.
if (Obj.SectionNames == &Sec)
return false;
if (Obj.SymbolTable == &Sec ||
(Obj.SymbolTable && Obj.SymbolTable->getStrTab() == &Sec))
return false;
// Remove everything else.
return true;
};
}
if (!Config.KeepSection.empty()) {
RemovePred = [&Config, RemovePred](const SectionBase &Sec) {
// Explicitly keep these sections regardless of previous removes.
if (is_contained(Config.KeepSection, Sec.Name))
return false;
// Otherwise defer to RemovePred.
return RemovePred(Sec);
};
}
// This has to be the last predicate assignment.
// If the option --keep-symbol has been specified
// and at least one of those symbols is present
// (equivalently, the updated symbol table is not empty)
// the symbol table and the string table should not be removed.
if ((!Config.SymbolsToKeep.empty() || Config.KeepFileSymbols) &&
Obj.SymbolTable && !Obj.SymbolTable->empty()) {
RemovePred = [&Obj, RemovePred](const SectionBase &Sec) {
if (&Sec == Obj.SymbolTable || &Sec == Obj.SymbolTable->getStrTab())
return false;
return RemovePred(Sec);
};
}
if (Config.CompressionType != DebugCompressionType::None)
replaceDebugSections(Config, Obj, RemovePred, isCompressable,
[&Config, &Obj](const SectionBase *S) {
return &Obj.addSection<CompressedSection>(
*S, Config.CompressionType);
});
else if (Config.DecompressDebugSections)
replaceDebugSections(
Config, Obj, RemovePred,
[](const SectionBase &S) { return isa<CompressedSection>(&S); },
[&Obj](const SectionBase *S) {
auto CS = cast<CompressedSection>(S);
return &Obj.addSection<DecompressedSection>(*CS);
});
Obj.removeSections(RemovePred);
if (!Config.SectionsToRename.empty()) {
for (auto &Sec : Obj.sections()) {
const auto Iter = Config.SectionsToRename.find(Sec.Name);
if (Iter != Config.SectionsToRename.end()) {
const SectionRename &SR = Iter->second;
Sec.Name = SR.NewName;
if (SR.NewFlags.hasValue())
Sec.Flags =
setSectionFlagsPreserveMask(Sec.Flags, SR.NewFlags.getValue());
}
}
}
if (!Config.SetSectionFlags.empty()) {
for (auto &Sec : Obj.sections()) {
const auto Iter = Config.SetSectionFlags.find(Sec.Name);
if (Iter != Config.SetSectionFlags.end()) {
const SectionFlagsUpdate &SFU = Iter->second;
Sec.Flags = setSectionFlagsPreserveMask(Sec.Flags, SFU.NewFlags);
}
}
}
if (!Config.AddSection.empty()) {
for (const auto &Flag : Config.AddSection) {
std::pair<StringRef, StringRef> SecPair = Flag.split("=");
StringRef SecName = SecPair.first;
StringRef File = SecPair.second;
ErrorOr<std::unique_ptr<MemoryBuffer>> BufOrErr =
MemoryBuffer::getFile(File);
if (!BufOrErr)
reportError(File, BufOrErr.getError());
std::unique_ptr<MemoryBuffer> Buf = std::move(*BufOrErr);
ArrayRef<uint8_t> Data(
reinterpret_cast<const uint8_t *>(Buf->getBufferStart()),
Buf->getBufferSize());
OwnedDataSection &NewSection =
Obj.addSection<OwnedDataSection>(SecName, Data);
if (SecName.startswith(".note") && SecName != ".note.GNU-stack")
NewSection.Type = SHT_NOTE;
}
}
if (!Config.DumpSection.empty()) {
for (const auto &Flag : Config.DumpSection) {
std::pair<StringRef, StringRef> SecPair = Flag.split("=");
StringRef SecName = SecPair.first;
StringRef File = SecPair.second;
if (Error E = dumpSectionToFile(SecName, File, Obj))
reportError(Config.InputFilename, std::move(E));
}
}
if (!Config.AddGnuDebugLink.empty())
Obj.addSection<GnuDebugLinkSection>(Config.AddGnuDebugLink);
}
void executeObjcopyOnRawBinary(const CopyConfig &Config, MemoryBuffer &In,
Buffer &Out) {
BinaryReader Reader(Config.BinaryArch, &In);
std::unique_ptr<Object> Obj = Reader.create();
// Prefer OutputArch (-O<format>) if set, otherwise fallback to BinaryArch
// (-B<arch>).
const ElfType OutputElfType = getOutputElfType(
Config.OutputArch ? Config.OutputArch.getValue() : Config.BinaryArch);
handleArgs(Config, *Obj, Reader, OutputElfType);
std::unique_ptr<Writer> Writer =
createWriter(Config, *Obj, Out, OutputElfType);
if (Error E = Writer->finalize())
error(std::move(E));
if (Error E = Writer->write())
error(std::move(E));
}
void executeObjcopyOnBinary(const CopyConfig &Config,
object::ELFObjectFileBase &In, Buffer &Out) {
ELFReader Reader(&In);
std::unique_ptr<Object> Obj = Reader.create();
// Prefer OutputArch (-O<format>) if set, otherwise infer it from the input.
const ElfType OutputElfType =
Config.OutputArch ? getOutputElfType(Config.OutputArch.getValue())
: getOutputElfType(In);
ArrayRef<uint8_t> BuildIdBytes;
if (!Config.BuildIdLinkDir.empty()) {
BuildIdBytes = unwrapOrError(findBuildID(In));
if (BuildIdBytes.size() < 2)
error("build ID in file '" + Config.InputFilename +
"' is smaller than two bytes");
}
if (!Config.BuildIdLinkDir.empty() && Config.BuildIdLinkInput) {
linkToBuildIdDir(Config, Config.InputFilename,
Config.BuildIdLinkInput.getValue(), BuildIdBytes);
}
handleArgs(Config, *Obj, Reader, OutputElfType);
std::unique_ptr<Writer> Writer =
createWriter(Config, *Obj, Out, OutputElfType);
if (Error E = Writer->finalize())
error(std::move(E));
if (Error E = Writer->write())
error(std::move(E));
if (!Config.BuildIdLinkDir.empty() && Config.BuildIdLinkOutput) {
linkToBuildIdDir(Config, Config.OutputFilename,
Config.BuildIdLinkOutput.getValue(), BuildIdBytes);
}
}
} // end namespace elf
} // end namespace objcopy
} // end namespace llvm
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