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llvm-project/lld/MachO/InputFiles.cpp

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//===- InputFiles.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
//
//===----------------------------------------------------------------------===//
//
// This file contains functions to parse Mach-O object files. In this comment,
// we describe the Mach-O file structure and how we parse it.
//
// Mach-O is not very different from ELF or COFF. The notion of symbols,
// sections and relocations exists in Mach-O as it does in ELF and COFF.
//
// Perhaps the notion that is new to those who know ELF/COFF is "subsections".
// In ELF/COFF, sections are an atomic unit of data copied from input files to
// output files. When we merge or garbage-collect sections, we treat each
// section as an atomic unit. In Mach-O, that's not the case. Sections can
// consist of multiple subsections, and subsections are a unit of merging and
// garbage-collecting. Therefore, Mach-O's subsections are more similar to
// ELF/COFF's sections than Mach-O's sections are.
//
// A section can have multiple symbols. A symbol that does not have the
// N_ALT_ENTRY attribute indicates a beginning of a subsection. Therefore, by
// definition, a symbol is always present at the beginning of each subsection. A
// symbol with N_ALT_ENTRY attribute does not start a new subsection and can
// point to a middle of a subsection.
//
// The notion of subsections also affects how relocations are represented in
// Mach-O. All references within a section need to be explicitly represented as
// relocations if they refer to different subsections, because we obviously need
// to fix up addresses if subsections are laid out in an output file differently
// than they were in object files. To represent that, Mach-O relocations can
// refer to an unnamed location via its address. Scattered relocations (those
// with the R_SCATTERED bit set) always refer to unnamed locations.
// Non-scattered relocations refer to an unnamed location if r_extern is not set
// and r_symbolnum is zero.
//
// Without the above differences, I think you can use your knowledge about ELF
// and COFF for Mach-O.
//
//===----------------------------------------------------------------------===//
#include "InputFiles.h"
#include "Config.h"
#include "Driver.h"
#include "Dwarf.h"
#include "ExportTrie.h"
#include "InputSection.h"
#include "MachOStructs.h"
#include "ObjC.h"
#include "OutputSection.h"
#include "OutputSegment.h"
#include "SymbolTable.h"
#include "Symbols.h"
#include "Target.h"
#include "lld/Common/DWARF.h"
#include "lld/Common/ErrorHandler.h"
#include "lld/Common/Memory.h"
#include "lld/Common/Reproduce.h"
#include "llvm/ADT/iterator.h"
#include "llvm/BinaryFormat/MachO.h"
#include "llvm/LTO/LTO.h"
#include "llvm/Support/Endian.h"
#include "llvm/Support/MemoryBuffer.h"
#include "llvm/Support/Path.h"
#include "llvm/Support/TarWriter.h"
#include "llvm/TextAPI/Architecture.h"
#include "llvm/TextAPI/InterfaceFile.h"
using namespace llvm;
using namespace llvm::MachO;
using namespace llvm::support::endian;
using namespace llvm::sys;
using namespace lld;
using namespace lld::macho;
// Returns "<internal>", "foo.a(bar.o)", or "baz.o".
std::string lld::toString(const InputFile *f) {
if (!f)
return "<internal>";
// Multiple dylibs can be defined in one .tbd file.
if (auto dylibFile = dyn_cast<DylibFile>(f))
if (f->getName().endswith(".tbd"))
return (f->getName() + "(" + dylibFile->dylibName + ")").str();
if (f->archiveName.empty())
return std::string(f->getName());
return (f->archiveName + "(" + path::filename(f->getName()) + ")").str();
}
SetVector<InputFile *> macho::inputFiles;
std::unique_ptr<TarWriter> macho::tar;
int InputFile::idCount = 0;
static VersionTuple decodeVersion(uint32_t version) {
unsigned major = version >> 16;
unsigned minor = (version >> 8) & 0xffu;
unsigned subMinor = version & 0xffu;
return VersionTuple(major, minor, subMinor);
}
static std::vector<PlatformInfo> getPlatformInfos(const InputFile *input) {
if (!isa<ObjFile>(input) && !isa<DylibFile>(input))
return {};
const char *hdr = input->mb.getBufferStart();
std::vector<PlatformInfo> platformInfos;
for (auto *cmd : findCommands<build_version_command>(hdr, LC_BUILD_VERSION)) {
PlatformInfo info;
info.target.Platform = static_cast<PlatformKind>(cmd->platform);
info.minimum = decodeVersion(cmd->minos);
platformInfos.emplace_back(std::move(info));
}
for (auto *cmd : findCommands<version_min_command>(
hdr, LC_VERSION_MIN_MACOSX, LC_VERSION_MIN_IPHONEOS,
LC_VERSION_MIN_TVOS, LC_VERSION_MIN_WATCHOS)) {
PlatformInfo info;
switch (cmd->cmd) {
case LC_VERSION_MIN_MACOSX:
info.target.Platform = PlatformKind::macOS;
break;
case LC_VERSION_MIN_IPHONEOS:
info.target.Platform = PlatformKind::iOS;
break;
case LC_VERSION_MIN_TVOS:
info.target.Platform = PlatformKind::tvOS;
break;
case LC_VERSION_MIN_WATCHOS:
info.target.Platform = PlatformKind::watchOS;
break;
}
info.minimum = decodeVersion(cmd->version);
platformInfos.emplace_back(std::move(info));
}
return platformInfos;
}
static PlatformKind removeSimulator(PlatformKind platform) {
// Mapping of platform to simulator and vice-versa.
static const std::map<PlatformKind, PlatformKind> platformMap = {
{PlatformKind::iOSSimulator, PlatformKind::iOS},
{PlatformKind::tvOSSimulator, PlatformKind::tvOS},
{PlatformKind::watchOSSimulator, PlatformKind::watchOS}};
auto iter = platformMap.find(platform);
if (iter == platformMap.end())
return platform;
return iter->second;
}
static bool checkCompatibility(const InputFile *input) {
std::vector<PlatformInfo> platformInfos = getPlatformInfos(input);
if (platformInfos.empty())
return true;
auto it = find_if(platformInfos, [&](const PlatformInfo &info) {
return removeSimulator(info.target.Platform) ==
removeSimulator(config->platform());
});
if (it == platformInfos.end()) {
std::string platformNames;
raw_string_ostream os(platformNames);
interleave(
platformInfos, os,
[&](const PlatformInfo &info) {
os << getPlatformName(info.target.Platform);
},
"/");
error(toString(input) + " has platform " + platformNames +
Twine(", which is different from target platform ") +
getPlatformName(config->platform()));
return false;
}
if (it->minimum <= config->platformInfo.minimum)
return true;
error(toString(input) + " has version " + it->minimum.getAsString() +
", which is newer than target minimum of " +
config->platformInfo.minimum.getAsString());
return false;
}
// Open a given file path and return it as a memory-mapped file.
Optional<MemoryBufferRef> macho::readFile(StringRef path) {
// Open a file.
ErrorOr<std::unique_ptr<MemoryBuffer>> mbOrErr = MemoryBuffer::getFile(path);
if (std::error_code ec = mbOrErr.getError()) {
error("cannot open " + path + ": " + ec.message());
return None;
}
std::unique_ptr<MemoryBuffer> &mb = *mbOrErr;
MemoryBufferRef mbref = mb->getMemBufferRef();
make<std::unique_ptr<MemoryBuffer>>(std::move(mb)); // take mb ownership
// If this is a regular non-fat file, return it.
const char *buf = mbref.getBufferStart();
const auto *hdr = reinterpret_cast<const fat_header *>(buf);
if (mbref.getBufferSize() < sizeof(uint32_t) ||
read32be(&hdr->magic) != FAT_MAGIC) {
if (tar)
tar->append(relativeToRoot(path), mbref.getBuffer());
return mbref;
}
// Object files and archive files may be fat files, which contains
// multiple real files for different CPU ISAs. Here, we search for a
// file that matches with the current link target and returns it as
// a MemoryBufferRef.
const auto *arch = reinterpret_cast<const fat_arch *>(buf + sizeof(*hdr));
for (uint32_t i = 0, n = read32be(&hdr->nfat_arch); i < n; ++i) {
if (reinterpret_cast<const char *>(arch + i + 1) >
buf + mbref.getBufferSize()) {
error(path + ": fat_arch struct extends beyond end of file");
return None;
}
if (read32be(&arch[i].cputype) != target->cpuType ||
read32be(&arch[i].cpusubtype) != target->cpuSubtype)
continue;
uint32_t offset = read32be(&arch[i].offset);
uint32_t size = read32be(&arch[i].size);
if (offset + size > mbref.getBufferSize())
error(path + ": slice extends beyond end of file");
if (tar)
tar->append(relativeToRoot(path), mbref.getBuffer());
return MemoryBufferRef(StringRef(buf + offset, size), path.copy(bAlloc));
}
error("unable to find matching architecture in " + path);
return None;
}
InputFile::InputFile(Kind kind, const InterfaceFile &interface)
: id(idCount++), fileKind(kind), name(saver.save(interface.getPath())) {}
template <class Section>
void ObjFile::parseSections(ArrayRef<Section> sections) {
subsections.reserve(sections.size());
auto *buf = reinterpret_cast<const uint8_t *>(mb.getBufferStart());
for (const Section &sec : sections) {
InputSection *isec = make<InputSection>();
isec->file = this;
isec->name =
StringRef(sec.sectname, strnlen(sec.sectname, sizeof(sec.sectname)));
isec->segname =
StringRef(sec.segname, strnlen(sec.segname, sizeof(sec.segname)));
isec->data = {isZeroFill(sec.flags) ? nullptr : buf + sec.offset,
static_cast<size_t>(sec.size)};
if (sec.align >= 32)
error("alignment " + std::to_string(sec.align) + " of section " +
isec->name + " is too large");
else
isec->align = 1 << sec.align;
isec->flags = sec.flags;
if (!(isDebugSection(isec->flags) &&
isec->segname == segment_names::dwarf)) {
subsections.push_back({{0, isec}});
} else {
// Instead of emitting DWARF sections, we emit STABS symbols to the
// object files that contain them. We filter them out early to avoid
// parsing their relocations unnecessarily. But we must still push an
// empty map to ensure the indices line up for the remaining sections.
subsections.push_back({});
debugSections.push_back(isec);
}
}
}
// Find the subsection corresponding to the greatest section offset that is <=
// that of the given offset.
//
// offset: an offset relative to the start of the original InputSection (before
// any subsection splitting has occurred). It will be updated to represent the
// same location as an offset relative to the start of the containing
// subsection.
static InputSection *findContainingSubsection(SubsectionMap &map,
uint64_t *offset) {
auto it = std::prev(llvm::upper_bound(
map, *offset, [](uint64_t value, SubsectionEntry subsecEntry) {
return value < subsecEntry.offset;
}));
*offset -= it->offset;
return it->isec;
}
template <class Section>
static bool validateRelocationInfo(InputFile *file, const Section &sec,
relocation_info rel) {
const RelocAttrs &relocAttrs = target->getRelocAttrs(rel.r_type);
bool valid = true;
auto message = [relocAttrs, file, sec, rel, &valid](const Twine &diagnostic) {
valid = false;
return (relocAttrs.name + " relocation " + diagnostic + " at offset " +
std::to_string(rel.r_address) + " of " + sec.segname + "," +
sec.sectname + " in " + toString(file))
.str();
};
if (!relocAttrs.hasAttr(RelocAttrBits::LOCAL) && !rel.r_extern)
error(message("must be extern"));
if (relocAttrs.hasAttr(RelocAttrBits::PCREL) != rel.r_pcrel)
error(message(Twine("must ") + (rel.r_pcrel ? "not " : "") +
"be PC-relative"));
if (isThreadLocalVariables(sec.flags) &&
!relocAttrs.hasAttr(RelocAttrBits::UNSIGNED))
error(message("not allowed in thread-local section, must be UNSIGNED"));
if (rel.r_length < 2 || rel.r_length > 3 ||
!relocAttrs.hasAttr(static_cast<RelocAttrBits>(1 << rel.r_length))) {
static SmallVector<StringRef, 4> widths{"0", "4", "8", "4 or 8"};
error(message("has width " + std::to_string(1 << rel.r_length) +
" bytes, but must be " +
widths[(static_cast<int>(relocAttrs.bits) >> 2) & 3] +
" bytes"));
}
return valid;
}
template <class Section>
void ObjFile::parseRelocations(ArrayRef<Section> sectionHeaders,
const Section &sec, SubsectionMap &subsecMap) {
auto *buf = reinterpret_cast<const uint8_t *>(mb.getBufferStart());
ArrayRef<relocation_info> relInfos(
reinterpret_cast<const relocation_info *>(buf + sec.reloff), sec.nreloc);
for (size_t i = 0; i < relInfos.size(); i++) {
// Paired relocations serve as Mach-O's method for attaching a
// supplemental datum to a primary relocation record. ELF does not
// need them because the *_RELOC_RELA records contain the extra
// addend field, vs. *_RELOC_REL which omit the addend.
//
// The {X86_64,ARM64}_RELOC_SUBTRACTOR record holds the subtrahend,
// and the paired *_RELOC_UNSIGNED record holds the minuend. The
// datum for each is a symbolic address. The result is the offset
// between two addresses.
//
// The ARM64_RELOC_ADDEND record holds the addend, and the paired
// ARM64_RELOC_BRANCH26 or ARM64_RELOC_PAGE21/PAGEOFF12 holds the
// base symbolic address.
//
// Note: X86 does not use *_RELOC_ADDEND because it can embed an
// addend into the instruction stream. On X86, a relocatable address
// field always occupies an entire contiguous sequence of byte(s),
// so there is no need to merge opcode bits with address
// bits. Therefore, it's easy and convenient to store addends in the
// instruction-stream bytes that would otherwise contain zeroes. By
// contrast, RISC ISAs such as ARM64 mix opcode bits with with
// address bits so that bitwise arithmetic is necessary to extract
// and insert them. Storing addends in the instruction stream is
// possible, but inconvenient and more costly at link time.
int64_t pairedAddend = 0;
relocation_info relInfo = relInfos[i];
if (target->hasAttr(relInfo.r_type, RelocAttrBits::ADDEND)) {
pairedAddend = SignExtend64<24>(relInfo.r_symbolnum);
relInfo = relInfos[++i];
}
assert(i < relInfos.size());
if (!validateRelocationInfo(this, sec, relInfo))
continue;
if (relInfo.r_address & R_SCATTERED)
fatal("TODO: Scattered relocations not supported");
bool isSubtrahend =
target->hasAttr(relInfo.r_type, RelocAttrBits::SUBTRAHEND);
int64_t embeddedAddend = target->getEmbeddedAddend(mb, sec.offset, relInfo);
assert(!(embeddedAddend && pairedAddend));
int64_t totalAddend = pairedAddend + embeddedAddend;
Reloc r;
r.type = relInfo.r_type;
r.pcrel = relInfo.r_pcrel;
r.length = relInfo.r_length;
r.offset = relInfo.r_address;
if (relInfo.r_extern) {
r.referent = symbols[relInfo.r_symbolnum];
r.addend = isSubtrahend ? 0 : totalAddend;
} else {
assert(!isSubtrahend);
const Section &referentSec = sectionHeaders[relInfo.r_symbolnum - 1];
uint64_t referentOffset;
if (relInfo.r_pcrel) {
// The implicit addend for pcrel section relocations is the pcrel offset
// in terms of the addresses in the input file. Here we adjust it so
// that it describes the offset from the start of the referent section.
// FIXME This logic was written around x86_64 behavior -- ARM64 doesn't
// have pcrel section relocations. We may want to factor this out into
// the arch-specific .cpp file.
assert(target->hasAttr(r.type, RelocAttrBits::BYTE4));
referentOffset =
sec.addr + relInfo.r_address + 4 + totalAddend - referentSec.addr;
} else {
// The addend for a non-pcrel relocation is its absolute address.
referentOffset = totalAddend - referentSec.addr;
}
SubsectionMap &referentSubsecMap = subsections[relInfo.r_symbolnum - 1];
r.referent = findContainingSubsection(referentSubsecMap, &referentOffset);
r.addend = referentOffset;
}
InputSection *subsec = findContainingSubsection(subsecMap, &r.offset);
subsec->relocs.push_back(r);
if (isSubtrahend) {
relocation_info minuendInfo = relInfos[++i];
// SUBTRACTOR relocations should always be followed by an UNSIGNED one
// attached to the same address.
assert(target->hasAttr(minuendInfo.r_type, RelocAttrBits::UNSIGNED) &&
relInfo.r_address == minuendInfo.r_address);
Reloc p;
p.type = minuendInfo.r_type;
if (minuendInfo.r_extern) {
p.referent = symbols[minuendInfo.r_symbolnum];
p.addend = totalAddend;
} else {
uint64_t referentOffset =
totalAddend - sectionHeaders[minuendInfo.r_symbolnum - 1].addr;
SubsectionMap &referentSubsecMap =
subsections[minuendInfo.r_symbolnum - 1];
p.referent =
findContainingSubsection(referentSubsecMap, &referentOffset);
p.addend = referentOffset;
}
subsec->relocs.push_back(p);
}
}
}
template <class NList>
static macho::Symbol *createDefined(const NList &sym, StringRef name,
InputSection *isec, uint64_t value,
uint64_t size) {
// Symbol scope is determined by sym.n_type & (N_EXT | N_PEXT):
// N_EXT: Global symbols. These go in the symbol table during the link,
// and also in the export table of the output so that the dynamic
// linker sees them.
// N_EXT | N_PEXT: Linkage unit (think: dylib) scoped. These go in the
// symbol table during the link so that duplicates are
// either reported (for non-weak symbols) or merged
// (for weak symbols), but they do not go in the export
// table of the output.
// N_PEXT: Does not occur in input files in practice,
// a private extern must be external.
// 0: Translation-unit scoped. These are not in the symbol table during
// link, and not in the export table of the output either.
bool isWeakDefCanBeHidden =
(sym.n_desc & (N_WEAK_DEF | N_WEAK_REF)) == (N_WEAK_DEF | N_WEAK_REF);
if (sym.n_type & (N_EXT | N_PEXT)) {
assert((sym.n_type & N_EXT) && "invalid input");
bool isPrivateExtern = sym.n_type & N_PEXT;
// lld's behavior for merging symbols is slightly different from ld64:
// ld64 picks the winning symbol based on several criteria (see
// pickBetweenRegularAtoms() in ld64's SymbolTable.cpp), while lld
// just merges metadata and keeps the contents of the first symbol
// with that name (see SymbolTable::addDefined). For:
// * inline function F in a TU built with -fvisibility-inlines-hidden
// * and inline function F in another TU built without that flag
// ld64 will pick the one from the file built without
// -fvisibility-inlines-hidden.
// lld will instead pick the one listed first on the link command line and
// give it visibility as if the function was built without
// -fvisibility-inlines-hidden.
// If both functions have the same contents, this will have the same
// behavior. If not, it won't, but the input had an ODR violation in
// that case.
//
// Similarly, merging a symbol
// that's isPrivateExtern and not isWeakDefCanBeHidden with one
// that's not isPrivateExtern but isWeakDefCanBeHidden technically
// should produce one
// that's not isPrivateExtern but isWeakDefCanBeHidden. That matters
// with ld64's semantics, because it means the non-private-extern
// definition will continue to take priority if more private extern
// definitions are encountered. With lld's semantics there's no observable
// difference between a symbol that's isWeakDefCanBeHidden or one that's
// privateExtern -- neither makes it into the dynamic symbol table. So just
// promote isWeakDefCanBeHidden to isPrivateExtern here.
if (isWeakDefCanBeHidden)
isPrivateExtern = true;
return symtab->addDefined(name, isec->file, isec, value, size,
sym.n_desc & N_WEAK_DEF, isPrivateExtern,
sym.n_desc & N_ARM_THUMB_DEF);
}
assert(!isWeakDefCanBeHidden &&
"weak_def_can_be_hidden on already-hidden symbol?");
return make<Defined>(name, isec->file, isec, value, size,
sym.n_desc & N_WEAK_DEF,
/*isExternal=*/false, /*isPrivateExtern=*/false,
sym.n_desc & N_ARM_THUMB_DEF);
}
// Absolute symbols are defined symbols that do not have an associated
// InputSection. They cannot be weak.
template <class NList>
static macho::Symbol *createAbsolute(const NList &sym, InputFile *file,
StringRef name) {
if (sym.n_type & (N_EXT | N_PEXT)) {
assert((sym.n_type & N_EXT) && "invalid input");
return symtab->addDefined(name, file, nullptr, sym.n_value, /*size=*/0,
/*isWeakDef=*/false, sym.n_type & N_PEXT,
sym.n_desc & N_ARM_THUMB_DEF);
}
return make<Defined>(name, file, nullptr, sym.n_value, /*size=*/0,
/*isWeakDef=*/false,
/*isExternal=*/false, /*isPrivateExtern=*/false,
sym.n_desc & N_ARM_THUMB_DEF);
}
template <class NList>
macho::Symbol *ObjFile::parseNonSectionSymbol(const NList &sym,
StringRef name) {
uint8_t type = sym.n_type & N_TYPE;
switch (type) {
case N_UNDF:
return sym.n_value == 0
? symtab->addUndefined(name, this, sym.n_desc & N_WEAK_REF)
: symtab->addCommon(name, this, sym.n_value,
1 << GET_COMM_ALIGN(sym.n_desc),
sym.n_type & N_PEXT);
case N_ABS:
return createAbsolute(sym, this, name);
case N_PBUD:
case N_INDR:
error("TODO: support symbols of type " + std::to_string(type));
return nullptr;
case N_SECT:
llvm_unreachable(
"N_SECT symbols should not be passed to parseNonSectionSymbol");
default:
llvm_unreachable("invalid symbol type");
}
}
template <class LP>
void ObjFile::parseSymbols(ArrayRef<typename LP::section> sectionHeaders,
ArrayRef<typename LP::nlist> nList,
const char *strtab, bool subsectionsViaSymbols) {
using NList = typename LP::nlist;
// Groups indices of the symbols by the sections that contain them.
std::vector<std::vector<uint32_t>> symbolsBySection(subsections.size());
symbols.resize(nList.size());
for (uint32_t i = 0; i < nList.size(); ++i) {
const NList &sym = nList[i];
StringRef name = strtab + sym.n_strx;
if ((sym.n_type & N_TYPE) == N_SECT) {
SubsectionMap &subsecMap = subsections[sym.n_sect - 1];
// parseSections() may have chosen not to parse this section.
if (subsecMap.empty())
continue;
symbolsBySection[sym.n_sect - 1].push_back(i);
} else {
symbols[i] = parseNonSectionSymbol(sym, name);
}
}
// Calculate symbol sizes and create subsections by splitting the sections
// along symbol boundaries.
for (size_t i = 0; i < subsections.size(); ++i) {
SubsectionMap &subsecMap = subsections[i];
if (subsecMap.empty())
continue;
std::vector<uint32_t> &symbolIndices = symbolsBySection[i];
llvm::sort(symbolIndices, [&](uint32_t lhs, uint32_t rhs) {
return nList[lhs].n_value < nList[rhs].n_value;
});
uint64_t sectionAddr = sectionHeaders[i].addr;
// We populate subsecMap by repeatedly splitting the last (highest address)
// subsection.
SubsectionEntry subsecEntry = subsecMap.back();
for (size_t j = 0; j < symbolIndices.size(); ++j) {
uint32_t symIndex = symbolIndices[j];
const NList &sym = nList[symIndex];
StringRef name = strtab + sym.n_strx;
InputSection *isec = subsecEntry.isec;
uint64_t subsecAddr = sectionAddr + subsecEntry.offset;
uint64_t symbolOffset = sym.n_value - subsecAddr;
uint64_t symbolSize =
j + 1 < symbolIndices.size()
? nList[symbolIndices[j + 1]].n_value - sym.n_value
: isec->data.size() - symbolOffset;
// There are 3 cases where we do not need to create a new subsection:
// 1. If the input file does not use subsections-via-symbols.
// 2. Multiple symbols at the same address only induce one subsection.
// (The symbolOffset == 0 check covers both this case as well as
// the first loop iteration.)
// 3. Alternative entry points do not induce new subsections.
if (!subsectionsViaSymbols || symbolOffset == 0 ||
sym.n_desc & N_ALT_ENTRY) {
symbols[symIndex] =
createDefined(sym, name, isec, symbolOffset, symbolSize);
continue;
}
auto *nextIsec = make<InputSection>(*isec);
nextIsec->data = isec->data.slice(symbolOffset);
nextIsec->numRefs = 0;
nextIsec->canOmitFromOutput = false;
isec->data = isec->data.slice(0, symbolOffset);
// By construction, the symbol will be at offset zero in the new
// subsection.
symbols[symIndex] =
createDefined(sym, name, nextIsec, /*value=*/0, symbolSize);
// TODO: ld64 appears to preserve the original alignment as well as each
// subsection's offset from the last aligned address. We should consider
// emulating that behavior.
nextIsec->align = MinAlign(isec->align, sym.n_value);
subsecMap.push_back({sym.n_value - sectionAddr, nextIsec});
subsecEntry = subsecMap.back();
}
}
}
OpaqueFile::OpaqueFile(MemoryBufferRef mb, StringRef segName,
StringRef sectName)
: InputFile(OpaqueKind, mb) {
InputSection *isec = make<InputSection>();
isec->file = this;
isec->name = sectName.take_front(16);
isec->segname = segName.take_front(16);
const auto *buf = reinterpret_cast<const uint8_t *>(mb.getBufferStart());
isec->data = {buf, mb.getBufferSize()};
subsections.push_back({{0, isec}});
}
ObjFile::ObjFile(MemoryBufferRef mb, uint32_t modTime, StringRef archiveName)
: InputFile(ObjKind, mb), modTime(modTime) {
this->archiveName = std::string(archiveName);
if (target->wordSize == 8)
parse<LP64>();
else
parse<ILP32>();
}
template <class LP> void ObjFile::parse() {
using Header = typename LP::mach_header;
using SegmentCommand = typename LP::segment_command;
using Section = typename LP::section;
using NList = typename LP::nlist;
auto *buf = reinterpret_cast<const uint8_t *>(mb.getBufferStart());
auto *hdr = reinterpret_cast<const Header *>(mb.getBufferStart());
Architecture arch = getArchitectureFromCpuType(hdr->cputype, hdr->cpusubtype);
if (arch != config->arch()) {
error(toString(this) + " has architecture " + getArchitectureName(arch) +
" which is incompatible with target architecture " +
getArchitectureName(config->arch()));
return;
}
if (!checkCompatibility(this))
return;
if (const load_command *cmd = findCommand(hdr, LC_LINKER_OPTION)) {
auto *c = reinterpret_cast<const linker_option_command *>(cmd);
StringRef data{reinterpret_cast<const char *>(c + 1),
c->cmdsize - sizeof(linker_option_command)};
parseLCLinkerOption(this, c->count, data);
}
ArrayRef<Section> sectionHeaders;
if (const load_command *cmd = findCommand(hdr, LP::segmentLCType)) {
auto *c = reinterpret_cast<const SegmentCommand *>(cmd);
sectionHeaders =
ArrayRef<Section>{reinterpret_cast<const Section *>(c + 1), c->nsects};
parseSections(sectionHeaders);
}
// TODO: Error on missing LC_SYMTAB?
if (const load_command *cmd = findCommand(hdr, LC_SYMTAB)) {
auto *c = reinterpret_cast<const symtab_command *>(cmd);
ArrayRef<NList> nList(reinterpret_cast<const NList *>(buf + c->symoff),
c->nsyms);
const char *strtab = reinterpret_cast<const char *>(buf) + c->stroff;
bool subsectionsViaSymbols = hdr->flags & MH_SUBSECTIONS_VIA_SYMBOLS;
parseSymbols<LP>(sectionHeaders, nList, strtab, subsectionsViaSymbols);
}
// The relocations may refer to the symbols, so we parse them after we have
// parsed all the symbols.
for (size_t i = 0, n = subsections.size(); i < n; ++i)
if (!subsections[i].empty())
parseRelocations(sectionHeaders, sectionHeaders[i], subsections[i]);
parseDebugInfo();
}
void ObjFile::parseDebugInfo() {
std::unique_ptr<DwarfObject> dObj = DwarfObject::create(this);
if (!dObj)
return;
auto *ctx = make<DWARFContext>(
std::move(dObj), "",
[&](Error err) {
warn(toString(this) + ": " + toString(std::move(err)));
},
[&](Error warning) {
warn(toString(this) + ": " + toString(std::move(warning)));
});
// TODO: Since object files can contain a lot of DWARF info, we should verify
// that we are parsing just the info we need
const DWARFContext::compile_unit_range &units = ctx->compile_units();
// FIXME: There can be more than one compile unit per object file. See
// PR48637.
auto it = units.begin();
compileUnit = it->get();
}
// The path can point to either a dylib or a .tbd file.
static Optional<DylibFile *> loadDylib(StringRef path, DylibFile *umbrella) {
Optional<MemoryBufferRef> mbref = readFile(path);
if (!mbref) {
error("could not read dylib file at " + path);
return {};
}
return loadDylib(*mbref, umbrella);
}
// TBD files are parsed into a series of TAPI documents (InterfaceFiles), with
// the first document storing child pointers to the rest of them. When we are
// processing a given TBD file, we store that top-level document in
// currentTopLevelTapi. When processing re-exports, we search its children for
// potentially matching documents in the same TBD file. Note that the children
// themselves don't point to further documents, i.e. this is a two-level tree.
//
// Re-exports can either refer to on-disk files, or to documents within .tbd
// files.
static Optional<DylibFile *>
findDylib(StringRef path, DylibFile *umbrella,
const InterfaceFile *currentTopLevelTapi) {
if (path::is_absolute(path, path::Style::posix))
for (StringRef root : config->systemLibraryRoots)
if (Optional<std::string> dylibPath =
resolveDylibPath((root + path).str()))
return loadDylib(*dylibPath, umbrella);
// TODO: Expand @loader_path, @executable_path, @rpath etc, handle -dylib_path
if (currentTopLevelTapi) {
for (InterfaceFile &child :
make_pointee_range(currentTopLevelTapi->documents())) {
assert(child.documents().empty());
if (path == child.getInstallName())
return make<DylibFile>(child, umbrella);
}
}
if (Optional<std::string> dylibPath = resolveDylibPath(path))
return loadDylib(*dylibPath, umbrella);
return {};
}
// If a re-exported dylib is public (lives in /usr/lib or
// /System/Library/Frameworks), then it is considered implicitly linked: we
// should bind to its symbols directly instead of via the re-exporting umbrella
// library.
static bool isImplicitlyLinked(StringRef path) {
if (!config->implicitDylibs)
return false;
if (path::parent_path(path) == "/usr/lib")
return true;
// Match /System/Library/Frameworks/$FOO.framework/**/$FOO
if (path.consume_front("/System/Library/Frameworks/")) {
StringRef frameworkName = path.take_until([](char c) { return c == '.'; });
return path::filename(path) == frameworkName;
}
return false;
}
void loadReexport(StringRef path, DylibFile *umbrella,
const InterfaceFile *currentTopLevelTapi) {
Optional<DylibFile *> reexport =
findDylib(path, umbrella, currentTopLevelTapi);
if (!reexport)
error("unable to locate re-export with install name " + path);
else if (isImplicitlyLinked(path))
inputFiles.insert(*reexport);
}
DylibFile::DylibFile(MemoryBufferRef mb, DylibFile *umbrella,
bool isBundleLoader)
: InputFile(DylibKind, mb), refState(RefState::Unreferenced),
isBundleLoader(isBundleLoader) {
assert(!isBundleLoader || !umbrella);
if (umbrella == nullptr)
umbrella = this;
auto *buf = reinterpret_cast<const uint8_t *>(mb.getBufferStart());
auto *hdr = reinterpret_cast<const mach_header *>(mb.getBufferStart());
// Initialize dylibName.
if (const load_command *cmd = findCommand(hdr, LC_ID_DYLIB)) {
auto *c = reinterpret_cast<const dylib_command *>(cmd);
currentVersion = read32le(&c->dylib.current_version);
compatibilityVersion = read32le(&c->dylib.compatibility_version);
dylibName = reinterpret_cast<const char *>(cmd) + read32le(&c->dylib.name);
} else if (!isBundleLoader) {
// macho_executable and macho_bundle don't have LC_ID_DYLIB,
// so it's OK.
error("dylib " + toString(this) + " missing LC_ID_DYLIB load command");
return;
}
if (!checkCompatibility(this))
return;
// Initialize symbols.
DylibFile *exportingFile = isImplicitlyLinked(dylibName) ? this : umbrella;
if (const load_command *cmd = findCommand(hdr, LC_DYLD_INFO_ONLY)) {
auto *c = reinterpret_cast<const dyld_info_command *>(cmd);
parseTrie(buf + c->export_off, c->export_size,
[&](const Twine &name, uint64_t flags) {
bool isWeakDef = flags & EXPORT_SYMBOL_FLAGS_WEAK_DEFINITION;
bool isTlv = flags & EXPORT_SYMBOL_FLAGS_KIND_THREAD_LOCAL;
symbols.push_back(symtab->addDylib(
saver.save(name), exportingFile, isWeakDef, isTlv));
});
} else {
error("LC_DYLD_INFO_ONLY not found in " + toString(this));
return;
}
const uint8_t *p =
reinterpret_cast<const uint8_t *>(hdr) + target->headerSize;
for (uint32_t i = 0, n = hdr->ncmds; i < n; ++i) {
auto *cmd = reinterpret_cast<const load_command *>(p);
p += cmd->cmdsize;
if (!(hdr->flags & MH_NO_REEXPORTED_DYLIBS) &&
cmd->cmd == LC_REEXPORT_DYLIB) {
const auto *c = reinterpret_cast<const dylib_command *>(cmd);
StringRef reexportPath =
reinterpret_cast<const char *>(c) + read32le(&c->dylib.name);
loadReexport(reexportPath, exportingFile, nullptr);
}
// FIXME: What about LC_LOAD_UPWARD_DYLIB, LC_LAZY_LOAD_DYLIB,
// LC_LOAD_WEAK_DYLIB, LC_REEXPORT_DYLIB (..are reexports from dylibs with
// MH_NO_REEXPORTED_DYLIBS loaded for -flat_namespace)?
if (config->namespaceKind == NamespaceKind::flat &&
cmd->cmd == LC_LOAD_DYLIB) {
const auto *c = reinterpret_cast<const dylib_command *>(cmd);
StringRef dylibPath =
reinterpret_cast<const char *>(c) + read32le(&c->dylib.name);
Optional<DylibFile *> dylib = findDylib(dylibPath, umbrella, nullptr);
if (!dylib)
error(Twine("unable to locate library '") + dylibPath +
"' loaded from '" + toString(this) + "' for -flat_namespace");
}
}
}
DylibFile::DylibFile(const InterfaceFile &interface, DylibFile *umbrella,
bool isBundleLoader)
: InputFile(DylibKind, interface), refState(RefState::Unreferenced),
isBundleLoader(isBundleLoader) {
// FIXME: Add test for the missing TBD code path.
if (umbrella == nullptr)
umbrella = this;
dylibName = saver.save(interface.getInstallName());
compatibilityVersion = interface.getCompatibilityVersion().rawValue();
currentVersion = interface.getCurrentVersion().rawValue();
// Some versions of XCode ship with .tbd files that don't have the right
// platform settings.
static constexpr std::array<StringRef, 3> skipPlatformChecks{
"/usr/lib/system/libsystem_kernel.dylib",
"/usr/lib/system/libsystem_platform.dylib",
"/usr/lib/system/libsystem_pthread.dylib"};
if (!is_contained(skipPlatformChecks, dylibName) &&
!is_contained(interface.targets(), config->platformInfo.target)) {
error(toString(this) + " is incompatible with " +
std::string(config->platformInfo.target));
return;
}
DylibFile *exportingFile = isImplicitlyLinked(dylibName) ? this : umbrella;
auto addSymbol = [&](const Twine &name) -> void {
symbols.push_back(symtab->addDylib(saver.save(name), exportingFile,
/*isWeakDef=*/false,
/*isTlv=*/false));
};
// TODO(compnerd) filter out symbols based on the target platform
// TODO: handle weak defs, thread locals
for (const auto *symbol : interface.symbols()) {
if (!symbol->getArchitectures().has(config->arch()))
continue;
switch (symbol->getKind()) {
case SymbolKind::GlobalSymbol:
addSymbol(symbol->getName());
break;
case SymbolKind::ObjectiveCClass:
// XXX ld64 only creates these symbols when -ObjC is passed in. We may
// want to emulate that.
addSymbol(objc::klass + symbol->getName());
addSymbol(objc::metaclass + symbol->getName());
break;
case SymbolKind::ObjectiveCClassEHType:
addSymbol(objc::ehtype + symbol->getName());
break;
case SymbolKind::ObjectiveCInstanceVariable:
addSymbol(objc::ivar + symbol->getName());
break;
}
}
const InterfaceFile *topLevel =
interface.getParent() == nullptr ? &interface : interface.getParent();
for (InterfaceFileRef intfRef : interface.reexportedLibraries()) {
InterfaceFile::const_target_range targets = intfRef.targets();
if (is_contained(skipPlatformChecks, intfRef.getInstallName()) ||
is_contained(targets, config->platformInfo.target))
loadReexport(intfRef.getInstallName(), exportingFile, topLevel);
}
}
ArchiveFile::ArchiveFile(std::unique_ptr<object::Archive> &&f)
: InputFile(ArchiveKind, f->getMemoryBufferRef()), file(std::move(f)) {
for (const object::Archive::Symbol &sym : file->symbols())
symtab->addLazy(sym.getName(), this, sym);
}
void ArchiveFile::fetch(const object::Archive::Symbol &sym) {
object::Archive::Child c =
CHECK(sym.getMember(), toString(this) +
": could not get the member for symbol " +
toMachOString(sym));
if (!seen.insert(c.getChildOffset()).second)
return;
MemoryBufferRef mb =
CHECK(c.getMemoryBufferRef(),
toString(this) +
": could not get the buffer for the member defining symbol " +
toMachOString(sym));
if (tar && c.getParent()->isThin())
tar->append(relativeToRoot(CHECK(c.getFullName(), this)), mb.getBuffer());
uint32_t modTime = toTimeT(
CHECK(c.getLastModified(), toString(this) +
": could not get the modification time "
"for the member defining symbol " +
toMachOString(sym)));
// `sym` is owned by a LazySym, which will be replace<>()d by make<ObjFile>
// and become invalid after that call. Copy it to the stack so we can refer
// to it later.
const object::Archive::Symbol symCopy = sym;
if (Optional<InputFile *> file =
loadArchiveMember(mb, modTime, getName(), /*objCOnly=*/false)) {
inputFiles.insert(*file);
// ld64 doesn't demangle sym here even with -demangle.
// Match that: intentionally don't call toMachOString().
printArchiveMemberLoad(symCopy.getName(), *file);
}
}
static macho::Symbol *createBitcodeSymbol(const lto::InputFile::Symbol &objSym,
BitcodeFile &file) {
StringRef name = saver.save(objSym.getName());
// TODO: support weak references
if (objSym.isUndefined())
return symtab->addUndefined(name, &file, /*isWeakRef=*/false);
assert(!objSym.isCommon() && "TODO: support common symbols in LTO");
// TODO: Write a test demonstrating why computing isPrivateExtern before
// LTO compilation is important.
bool isPrivateExtern = false;
switch (objSym.getVisibility()) {
case GlobalValue::HiddenVisibility:
isPrivateExtern = true;
break;
case GlobalValue::ProtectedVisibility:
error(name + " has protected visibility, which is not supported by Mach-O");
break;
case GlobalValue::DefaultVisibility:
break;
}
return symtab->addDefined(name, &file, /*isec=*/nullptr, /*value=*/0,
/*size=*/0, objSym.isWeak(), isPrivateExtern,
/*isThumb=*/false);
}
BitcodeFile::BitcodeFile(MemoryBufferRef mbref)
: InputFile(BitcodeKind, mbref) {
obj = check(lto::InputFile::create(mbref));
// Convert LTO Symbols to LLD Symbols in order to perform resolution. The
// "winning" symbol will then be marked as Prevailing at LTO compilation
// time.
for (const lto::InputFile::Symbol &objSym : obj->symbols())
symbols.push_back(createBitcodeSymbol(objSym, *this));
}
template void ObjFile::parse<LP64>();
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