/
InputFiles.cpp
1453 lines (1307 loc) · 57.4 KB
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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 "SyntheticSections.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->installName + ")").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 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)
warn(toString(input) + " has version " + it->minimum.getAsString() +
", which is newer than target minimum of " +
config->platformInfo.minimum.getAsString());
return true;
}
// This cache mostly exists to store system libraries (and .tbds) as they're
// loaded, rather than the input archives, which are already cached at a higher
// level, and other files like the filelist that are only read once.
// Theoretically this caching could be more efficient by hoisting it, but that
// would require altering many callers to track the state.
static DenseMap<CachedHashStringRef, MemoryBufferRef> resolvedReads;
// Open a given file path and return it as a memory-mapped file.
Optional<MemoryBufferRef> macho::readFile(StringRef path) {
CachedHashStringRef key(path);
auto entry = resolvedReads.find(key);
if (entry != resolvedReads.end())
return entry->second;
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 resolvedReads[key] = mbref;
}
// Object files and archive files may be fat files, which contain 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) != static_cast<uint32_t>(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 resolvedReads[key] = 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())) {}
// Some sections comprise of fixed-size records, so instead of splitting them at
// symbol boundaries, we split them based on size. Records are distinct from
// literals in that they may contain references to other sections, instead of
// being leaf nodes in the InputSection graph.
//
// Note that "record" is a term I came up with. In contrast, "literal" is a term
// used by the Mach-O format.
static Optional<size_t> getRecordSize(StringRef segname, StringRef name) {
if (name == section_names::cfString) {
if (config->icfLevel != ICFLevel::none && segname == segment_names::data)
return target->wordSize == 8 ? 32 : 16;
} else if (name == section_names::compactUnwind) {
if (segname == segment_names::ld)
return target->wordSize == 8 ? 32 : 20;
}
return {};
}
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) {
StringRef name =
StringRef(sec.sectname, strnlen(sec.sectname, sizeof(sec.sectname)));
StringRef segname =
StringRef(sec.segname, strnlen(sec.segname, sizeof(sec.segname)));
ArrayRef<uint8_t> 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 " + name +
" is too large");
subsections.push_back({});
continue;
}
uint32_t align = 1 << sec.align;
uint32_t flags = sec.flags;
auto splitRecords = [&](int recordSize) -> void {
subsections.push_back({});
if (data.empty())
return;
SubsectionMap &subsecMap = subsections.back();
subsecMap.reserve(data.size() / recordSize);
auto *isec = make<ConcatInputSection>(
segname, name, this, data.slice(0, recordSize), align, flags);
subsecMap.push_back({0, isec});
for (uint64_t off = recordSize; off < data.size(); off += recordSize) {
// Copying requires less memory than constructing a fresh InputSection.
auto *copy = make<ConcatInputSection>(*isec);
copy->data = data.slice(off, recordSize);
subsecMap.push_back({off, copy});
}
};
if (sectionType(sec.flags) == S_CSTRING_LITERALS ||
(config->dedupLiterals && isWordLiteralSection(sec.flags))) {
if (sec.nreloc && config->dedupLiterals)
fatal(toString(this) + " contains relocations in " + sec.segname + "," +
sec.sectname +
", so LLD cannot deduplicate literals. Try re-running without "
"--deduplicate-literals.");
InputSection *isec;
if (sectionType(sec.flags) == S_CSTRING_LITERALS) {
isec =
make<CStringInputSection>(segname, name, this, data, align, flags);
// FIXME: parallelize this?
cast<CStringInputSection>(isec)->splitIntoPieces();
} else {
isec = make<WordLiteralInputSection>(segname, name, this, data, align,
flags);
}
subsections.push_back({{0, isec}});
} else if (auto recordSize = getRecordSize(segname, name)) {
splitRecords(*recordSize);
} else if (segname == segment_names::llvm) {
// ld64 does not appear to emit contents from sections within the __LLVM
// segment. Symbols within those sections point to bitcode metadata
// instead of actual symbols. Global symbols within those sections could
// have the same name without causing duplicate symbol errors. Push an
// empty map to ensure indices line up for the remaining sections.
// TODO: Evaluate whether the bitcode metadata is needed.
subsections.push_back({});
} else {
auto *isec =
make<ConcatInputSection>(segname, name, this, data, align, flags);
if (isDebugSection(isec->getFlags()) &&
isec->getSegName() == segment_names::dwarf) {
// 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);
} else {
subsections.push_back({{0, 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);
auto subsecIt = subsecMap.rbegin();
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;
}
// Find the subsection that this relocation belongs to.
// Though not required by the Mach-O format, clang and gcc seem to emit
// relocations in order, so let's take advantage of it. However, ld64 emits
// unsorted relocations (in `-r` mode), so we have a fallback for that
// uncommon case.
InputSection *subsec;
while (subsecIt != subsecMap.rend() && subsecIt->offset > r.offset)
++subsecIt;
if (subsecIt == subsecMap.rend() ||
subsecIt->offset + subsecIt->isec->getSize() <= r.offset) {
subsec = findContainingSubsection(subsecMap, &r.offset);
// Now that we know the relocs are unsorted, avoid trying the 'fast path'
// for the other relocations.
subsecIt = subsecMap.rend();
} else {
subsec = subsecIt->isec;
r.offset -= subsecIt->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: llvm-mc does not emit these, but `ld -r` (wherein ld64 emits
// object files) may produce them. LLD does not yet support -r.
// These are translation-unit scoped, identical to the `0` case.
// 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) {
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->getFile(), isec, value, size, sym.n_desc & N_WEAK_DEF,
isPrivateExtern, sym.n_desc & N_ARM_THUMB_DEF,
sym.n_desc & REFERENCED_DYNAMICALLY, sym.n_desc & N_NO_DEAD_STRIP);
}
assert(!isWeakDefCanBeHidden &&
"weak_def_can_be_hidden on already-hidden symbol?");
return make<Defined>(
name, isec->getFile(), isec, value, size, sym.n_desc & N_WEAK_DEF,
/*isExternal=*/false, /*isPrivateExtern=*/false,
sym.n_desc & N_ARM_THUMB_DEF, sym.n_desc & REFERENCED_DYNAMICALLY,
sym.n_desc & N_NO_DEAD_STRIP);
}
// 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) {
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,
/*isReferencedDynamically=*/false, sym.n_desc & N_NO_DEAD_STRIP);
}
return make<Defined>(name, file, nullptr, sym.n_value, /*size=*/0,
/*isWeakDef=*/false,
/*isExternal=*/false, /*isPrivateExtern=*/false,
sym.n_desc & N_ARM_THUMB_DEF,
/*isReferencedDynamically=*/false,
sym.n_desc & N_NO_DEAD_STRIP);
}
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 NList> static bool isUndef(const NList &sym) {
return (sym.n_type & N_TYPE) == N_UNDF && sym.n_value == 0;
}
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());
SmallVector<unsigned, 32> undefineds;
for (uint32_t i = 0; i < nList.size(); ++i) {
const NList &sym = nList[i];
// Ignore debug symbols for now.
// FIXME: may need special handling.
if (sym.n_type & N_STAB)
continue;
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 if (isUndef(sym)) {
undefineds.push_back(i);
} else {
symbols[i] = parseNonSectionSymbol(sym, name);
}
}
for (size_t i = 0; i < subsections.size(); ++i) {
SubsectionMap &subsecMap = subsections[i];
if (subsecMap.empty())
continue;
std::vector<uint32_t> &symbolIndices = symbolsBySection[i];
uint64_t sectionAddr = sectionHeaders[i].addr;
uint32_t sectionAlign = 1u << sectionHeaders[i].align;
InputSection *lastIsec = subsecMap.back().isec;
// Record-based sections have already been split into subsections during
// parseSections(), so we simply need to match Symbols to the corresponding
// subsection here.
if (getRecordSize(lastIsec->getSegName(), lastIsec->getName())) {
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;
uint64_t symbolOffset = sym.n_value - sectionAddr;
InputSection *isec = findContainingSubsection(subsecMap, &symbolOffset);
if (symbolOffset != 0) {
error(toString(lastIsec) + ": symbol " + name +
" at misaligned offset");
continue;
}
symbols[symIndex] = createDefined(sym, name, isec, 0, isec->getSize());
}
continue;
}
// Calculate symbol sizes and create subsections by splitting the sections
// along symbol boundaries.
// We populate subsecMap by repeatedly splitting the last (highest address)
// subsection.
llvm::stable_sort(symbolIndices, [&](uint32_t lhs, uint32_t rhs) {
return nList[lhs].n_value < nList[rhs].n_value;
});
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;
size_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 4 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.
// 4. If we have a literal section (e.g. __cstring and __literal4).
if (!subsectionsViaSymbols || symbolOffset == 0 ||
sym.n_desc & N_ALT_ENTRY || !isa<ConcatInputSection>(isec)) {
symbols[symIndex] =
createDefined(sym, name, isec, symbolOffset, symbolSize);
continue;
}
auto *concatIsec = cast<ConcatInputSection>(isec);
auto *nextIsec = make<ConcatInputSection>(*concatIsec);
nextIsec->wasCoalesced = false;
if (isZeroFill(isec->getFlags())) {
// Zero-fill sections have NULL data.data() non-zero data.size()
nextIsec->data = {nullptr, isec->data.size() - symbolOffset};
isec->data = {nullptr, symbolOffset};
} else {
nextIsec->data = isec->data.slice(symbolOffset);
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(sectionAlign, sym.n_value);
subsecMap.push_back({sym.n_value - sectionAddr, nextIsec});
subsecEntry = subsecMap.back();
}
}
// Undefined symbols can trigger recursive fetch from Archives due to
// LazySymbols. Process defined symbols first so that the relative order
// between a defined symbol and an undefined symbol does not change the
// symbol resolution behavior. In addition, a set of interconnected symbols
// will all be resolved to the same file, instead of being resolved to
// different files.
for (unsigned i : undefineds) {
const NList &sym = nList[i];
StringRef name = strtab + sym.n_strx;
symbols[i] = parseNonSectionSymbol(sym, name);
}
}
OpaqueFile::OpaqueFile(MemoryBufferRef mb, StringRef segName,
StringRef sectName)
: InputFile(OpaqueKind, mb) {
const auto *buf = reinterpret_cast<const uint8_t *>(mb.getBufferStart());
ArrayRef<uint8_t> data = {buf, mb.getBufferSize()};
ConcatInputSection *isec =
make<ConcatInputSection>(segName.take_front(16), sectName.take_front(16),
/*file=*/this, data);
isec->live = true;
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()) {
auto msg = config->errorForArchMismatch
? static_cast<void (*)(const Twine &)>(error)
: warn;
msg(toString(this) + " has architecture " + getArchitectureName(arch) +
" which is incompatible with target architecture " +
getArchitectureName(config->arch()));
return;
}
if (!checkCompatibility(this))
return;
for (auto *cmd : findCommands<linker_option_command>(hdr, LC_LINKER_OPTION)) {
StringRef data{reinterpret_cast<const char *>(cmd + 1),
cmd->cmdsize - sizeof(linker_option_command)};
parseLCLinkerOption(this, cmd->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();
if (config->emitDataInCodeInfo)
parseDataInCode();
registerCompactUnwind();
}
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();
}
void ObjFile::parseDataInCode() {
const auto *buf = reinterpret_cast<const uint8_t *>(mb.getBufferStart());
const load_command *cmd = findCommand(buf, LC_DATA_IN_CODE);
if (!cmd)
return;
const auto *c = reinterpret_cast<const linkedit_data_command *>(cmd);
dataInCodeEntries = {
reinterpret_cast<const data_in_code_entry *>(buf + c->dataoff),
c->datasize / sizeof(data_in_code_entry)};
assert(is_sorted(dataInCodeEntries, [](const data_in_code_entry &lhs,
const data_in_code_entry &rhs) {
return lhs.offset < rhs.offset;
}));
}
// Create pointers from symbols to their associated compact unwind entries.
void ObjFile::registerCompactUnwind() {
// First, locate the __compact_unwind section.
SubsectionMap *cuSubsecMap = nullptr;
for (SubsectionMap &map : subsections) {
if (map.empty())
continue;
if (map[0].isec->getSegName() != segment_names::ld)
continue;
cuSubsecMap = ↦
break;
}
if (!cuSubsecMap)
return;
for (SubsectionEntry &entry : *cuSubsecMap) {
ConcatInputSection *isec = cast<ConcatInputSection>(entry.isec);
ConcatInputSection *referentIsec;
for (const Reloc &r : isec->relocs) {
if (r.offset != 0)
continue;
uint64_t add = r.addend;
if (auto *sym = cast_or_null<Defined>(r.referent.dyn_cast<Symbol *>())) {
add += sym->value;
referentIsec = cast<ConcatInputSection>(sym->isec);
} else {
referentIsec =
cast<ConcatInputSection>(r.referent.dyn_cast<InputSection *>());
}
if (referentIsec->getSegName() != segment_names::text)
error("compact unwind references address in " + toString(referentIsec) +
" which is not in segment __TEXT");
// The functionAddress relocations are typically section relocations.
// However, unwind info operates on a per-symbol basis, so we search for
// the function symbol here.
auto it = llvm::lower_bound(
referentIsec->symbols, add,
[](Defined *d, uint64_t add) { return d->value < add; });
// The relocation should point at the exact address of a symbol (with no
// addend).
if (it == referentIsec->symbols.end() || (*it)->value != add) {
assert(referentIsec->wasCoalesced);
continue;
}
(*it)->compactUnwind = isec;
}
}
}
// The path can point to either a dylib or a .tbd file.
static DylibFile *loadDylib(StringRef path, DylibFile *umbrella) {
Optional<MemoryBufferRef> mbref = readFile(path);
if (!mbref) {
error("could not read dylib file at " + path);
return nullptr;
}
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 DylibFile *findDylib(StringRef path, DylibFile *umbrella,
const InterfaceFile *currentTopLevelTapi) {
// Search order:
// 1. Install name basename in -F / -L directories.
{
StringRef stem = path::stem(path);
SmallString<128> frameworkName;
path::append(frameworkName, path::Style::posix, stem + ".framework", stem);
bool isFramework = path.endswith(frameworkName);
if (isFramework) {
for (StringRef dir : config->frameworkSearchPaths) {
SmallString<128> candidate = dir;
path::append(candidate, frameworkName);
if (Optional<StringRef> dylibPath = resolveDylibPath(candidate.str()))
return loadDylib(*dylibPath, umbrella);
}
} else if (Optional<StringRef> dylibPath = findPathCombination(
stem, config->librarySearchPaths, {".tbd", ".dylib"}))
return loadDylib(*dylibPath, umbrella);
}
// 2. As absolute path.
if (path::is_absolute(path, path::Style::posix))
for (StringRef root : config->systemLibraryRoots)
if (Optional<StringRef> dylibPath = resolveDylibPath((root + path).str()))
return loadDylib(*dylibPath, umbrella);
// 3. As relative path.
// TODO: Handle -dylib_file
// Replace @executable_path, @loader_path, @rpath prefixes in install name.
SmallString<128> newPath;
if (config->outputType == MH_EXECUTE &&
path.consume_front("@executable_path/")) {
// ld64 allows overriding this with the undocumented flag -executable_path.
// lld doesn't currently implement that flag.
// FIXME: Consider using finalOutput instead of outputFile.
path::append(newPath, path::parent_path(config->outputFile), path);
path = newPath;
} else if (path.consume_front("@loader_path/")) {
fs::real_path(umbrella->getName(), newPath);
path::remove_filename(newPath);