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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 "EhFrame.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/CommonLinkerContext.h"
#include "lld/Common/DWARF.h"
#include "lld/Common/Reproduce.h"
#include "llvm/ADT/iterator.h"
#include "llvm/BinaryFormat/MachO.h"
#include "llvm/LTO/LTO.h"
#include "llvm/Support/BinaryStreamReader.h"
#include "llvm/Support/Endian.h"
#include "llvm/Support/LEB128.h"
#include "llvm/Support/MemoryBuffer.h"
#include "llvm/Support/Path.h"
#include "llvm/Support/TarWriter.h"
#include "llvm/Support/TimeProfiler.h"
#include "llvm/TextAPI/Architecture.h"
#include "llvm/TextAPI/InterfaceFile.h"
#include <type_traits>
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();
}
std::string lld::toString(const Section &sec) {
return (toString(sec.file) + ":(" + sec.name + ")").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();
// "Zippered" object files can have multiple LC_BUILD_VERSION load commands.
std::vector<PlatformInfo> platformInfos;
for (auto *cmd : findCommands<build_version_command>(hdr, LC_BUILD_VERSION)) {
PlatformInfo info;
info.target.Platform = static_cast<PlatformType>(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 = PLATFORM_MACOS;
break;
case LC_VERSION_MIN_IPHONEOS:
info.target.Platform = PLATFORM_IOS;
break;
case LC_VERSION_MIN_TVOS:
info.target.Platform = PLATFORM_TVOS;
break;
case LC_VERSION_MIN_WATCHOS:
info.target.Platform = PLATFORM_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.
DenseMap<CachedHashStringRef, MemoryBufferRef> macho::cachedReads;
// Open a given file path and return it as a memory-mapped file.
Optional<MemoryBufferRef> macho::readFile(StringRef path) {
CachedHashStringRef key(path);
auto entry = cachedReads.find(key);
if (entry != cachedReads.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 cachedReads[key] = mbref;
}
llvm::BumpPtrAllocator &bAlloc = lld::bAlloc();
// 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 cachedReads[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::compactUnwind) {
if (segname == segment_names::ld)
return target->wordSize == 8 ? 32 : 20;
}
if (!config->dedupLiterals)
return {};
if (name == section_names::cfString && segname == segment_names::data)
return target->wordSize == 8 ? 32 : 16;
if (config->icfLevel == ICFLevel::none)
return {};
if (name == section_names::objcClassRefs && segname == segment_names::data)
return target->wordSize;
return {};
}
static Error parseCallGraph(ArrayRef<uint8_t> data,
std::vector<CallGraphEntry> &callGraph) {
TimeTraceScope timeScope("Parsing call graph section");
BinaryStreamReader reader(data, support::little);
while (!reader.empty()) {
uint32_t fromIndex, toIndex;
uint64_t count;
if (Error err = reader.readInteger(fromIndex))
return err;
if (Error err = reader.readInteger(toIndex))
return err;
if (Error err = reader.readInteger(count))
return err;
callGraph.emplace_back(fromIndex, toIndex, count);
}
return Error::success();
}
// Parse the sequence of sections within a single LC_SEGMENT(_64).
// Split each section into subsections.
template <class SectionHeader>
void ObjFile::parseSections(ArrayRef<SectionHeader> sectionHeaders) {
sections.reserve(sectionHeaders.size());
auto *buf = reinterpret_cast<const uint8_t *>(mb.getBufferStart());
for (const SectionHeader &sec : sectionHeaders) {
StringRef name =
StringRef(sec.sectname, strnlen(sec.sectname, sizeof(sec.sectname)));
StringRef segname =
StringRef(sec.segname, strnlen(sec.segname, sizeof(sec.segname)));
sections.push_back(make<Section>(this, segname, name, sec.flags, sec.addr));
if (sec.align >= 32) {
error("alignment " + std::to_string(sec.align) + " of section " + name +
" is too large");
continue;
}
Section &section = *sections.back();
uint32_t align = 1 << sec.align;
ArrayRef<uint8_t> data = {isZeroFill(sec.flags) ? nullptr
: buf + sec.offset,
static_cast<size_t>(sec.size)};
auto splitRecords = [&](int recordSize) -> void {
if (data.empty())
return;
Subsections &subsections = section.subsections;
subsections.reserve(data.size() / recordSize);
for (uint64_t off = 0; off < data.size(); off += recordSize) {
auto *isec = make<ConcatInputSection>(
section, data.slice(off, recordSize), align);
subsections.push_back({off, isec});
}
section.doneSplitting = true;
};
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>(section, data, align,
/*dedupLiterals=*/name ==
section_names::objcMethname ||
config->dedupLiterals);
// FIXME: parallelize this?
cast<CStringInputSection>(isec)->splitIntoPieces();
} else {
isec = make<WordLiteralInputSection>(section, data, align);
}
section.subsections.push_back({0, isec});
} else if (auto recordSize = getRecordSize(segname, name)) {
splitRecords(*recordSize);
} else if (name == section_names::ehFrame &&
segname == segment_names::text) {
splitEhFrames(data, *sections.back());
} else if (segname == segment_names::llvm) {
if (config->callGraphProfileSort && name == section_names::cgProfile)
checkError(parseCallGraph(data, callGraph));
// 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. To avoid
// spurious duplicate symbol errors, we do not parse these sections.
// TODO: Evaluate whether the bitcode metadata is needed.
} else if (name == section_names::objCImageInfo &&
segname == segment_names::data) {
objCImageInfo = data;
} else {
if (name == section_names::addrSig)
addrSigSection = sections.back();
auto *isec = make<ConcatInputSection>(section, data, align);
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.
debugSections.push_back(isec);
} else {
section.subsections.push_back({0, isec});
}
}
}
}
void ObjFile::splitEhFrames(ArrayRef<uint8_t> data, Section &ehFrameSection) {
EhReader reader(this, data, /*dataOff=*/0);
size_t off = 0;
while (off < reader.size()) {
uint64_t frameOff = off;
uint64_t length = reader.readLength(&off);
if (length == 0)
break;
uint64_t fullLength = length + (off - frameOff);
off += length;
// We hard-code an alignment of 1 here because we don't actually want our
// EH frames to be aligned to the section alignment. EH frame decoders don't
// expect this alignment. Moreover, each EH frame must start where the
// previous one ends, and where it ends is indicated by the length field.
// Unless we update the length field (troublesome), we should keep the
// alignment to 1.
// Note that we still want to preserve the alignment of the overall section,
// just not of the individual EH frames.
ehFrameSection.subsections.push_back(
{frameOff, make<ConcatInputSection>(ehFrameSection,
data.slice(frameOff, fullLength),
/*align=*/1)});
}
ehFrameSection.doneSplitting = true;
}
template <class T>
static Section *findContainingSection(const std::vector<Section *> &sections,
T *offset) {
static_assert(std::is_same<uint64_t, T>::value ||
std::is_same<uint32_t, T>::value,
"unexpected type for offset");
auto it = std::prev(llvm::upper_bound(
sections, *offset,
[](uint64_t value, const Section *sec) { return value < sec->addr; }));
*offset -= (*it)->addr;
return *it;
}
// 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.
template <class T>
static InputSection *findContainingSubsection(const Section &section,
T *offset) {
static_assert(std::is_same<uint64_t, T>::value ||
std::is_same<uint32_t, T>::value,
"unexpected type for offset");
auto it = std::prev(llvm::upper_bound(
section.subsections, *offset,
[](uint64_t value, Subsection subsec) { return value < subsec.offset; }));
*offset -= it->offset;
return it->isec;
}
// Find a symbol at offset `off` within `isec`.
static Defined *findSymbolAtOffset(const ConcatInputSection *isec,
uint64_t off) {
auto it = llvm::lower_bound(isec->symbols, off, [](Defined *d, uint64_t off) {
return d->value < off;
});
// The offset should point at the exact address of a symbol (with no addend.)
if (it == isec->symbols.end() || (*it)->value != off) {
assert(isec->wasCoalesced);
return nullptr;
}
return *it;
}
// Linker optimization hints mark a sequence of instructions used for
// synthesizing an address which that be transformed into a faster sequence. The
// transformations depend on conditions that are determined at link time, like
// the distance to the referenced symbol or its alignment.
//
// Each hint has a type and refers to 2 or 3 instructions. Each of those
// instructions must have a corresponding relocation. After addresses have been
// finalized and relocations have been performed, we check if the requirements
// hold, and perform the optimizations if they do.
//
// Similar linker relaxations exist for ELF as well, with the difference being
// that the explicit marking allows for the relaxation of non-consecutive
// relocations too.
//
// The specific types of hints are documented in Arch/ARM64.cpp
void ObjFile::parseOptimizationHints(ArrayRef<uint8_t> data) {
auto expectedArgCount = [](uint8_t type) {
switch (type) {
case LOH_ARM64_ADRP_ADRP:
case LOH_ARM64_ADRP_LDR:
case LOH_ARM64_ADRP_ADD:
case LOH_ARM64_ADRP_LDR_GOT:
return 2;
case LOH_ARM64_ADRP_ADD_LDR:
case LOH_ARM64_ADRP_ADD_STR:
case LOH_ARM64_ADRP_LDR_GOT_LDR:
case LOH_ARM64_ADRP_LDR_GOT_STR:
return 3;
}
return -1;
};
// Each hint contains at least 4 ULEB128-encoded fields, so in the worst case,
// there are data.size() / 4 LOHs. It's a huge overestimation though, as
// offsets are unlikely to fall in the 0-127 byte range, so we pre-allocate
// half as much.
optimizationHints.reserve(data.size() / 8);
for (const uint8_t *p = data.begin(); p < data.end();) {
const ptrdiff_t inputOffset = p - data.begin();
unsigned int n = 0;
uint8_t type = decodeULEB128(p, &n, data.end());
p += n;
// An entry of type 0 terminates the list.
if (type == 0)
break;
int expectedCount = expectedArgCount(type);
if (LLVM_UNLIKELY(expectedCount == -1)) {
error("Linker optimization hint at offset " + Twine(inputOffset) +
" has unknown type " + Twine(type));
return;
}
uint8_t argCount = decodeULEB128(p, &n, data.end());
p += n;
if (LLVM_UNLIKELY(argCount != expectedCount)) {
error("Linker optimization hint at offset " + Twine(inputOffset) +
" has " + Twine(argCount) + " arguments instead of the expected " +
Twine(expectedCount));
return;
}
uint64_t offset0 = decodeULEB128(p, &n, data.end());
p += n;
int16_t delta[2];
for (int i = 0; i < argCount - 1; ++i) {
uint64_t address = decodeULEB128(p, &n, data.end());
p += n;
int64_t d = address - offset0;
if (LLVM_UNLIKELY(d > std::numeric_limits<int16_t>::max() ||
d < std::numeric_limits<int16_t>::min())) {
error("Linker optimization hint at offset " + Twine(inputOffset) +
" has addresses too far apart");
return;
}
delta[i] = d;
}
optimizationHints.push_back({offset0, {delta[0], delta[1]}, type});
}
// We sort the per-object vector of optimization hints so each section only
// needs to hold an ArrayRef to a contiguous range of hints.
llvm::sort(optimizationHints,
[](const OptimizationHint &a, const OptimizationHint &b) {
return a.offset0 < b.offset0;
});
auto section = sections.begin();
auto subsection = (*section)->subsections.begin();
uint64_t subsectionBase = 0;
uint64_t subsectionEnd = 0;
auto updateAddr = [&]() {
subsectionBase = (*section)->addr + subsection->offset;
subsectionEnd = subsectionBase + subsection->isec->getSize();
};
auto advanceSubsection = [&]() {
if (section == sections.end())
return;
++subsection;
while (subsection == (*section)->subsections.end()) {
++section;
if (section == sections.end())
return;
subsection = (*section)->subsections.begin();
}
};
updateAddr();
auto hintStart = optimizationHints.begin();
for (auto hintEnd = hintStart, end = optimizationHints.end(); hintEnd != end;
++hintEnd) {
if (hintEnd->offset0 >= subsectionEnd) {
subsection->isec->optimizationHints =
ArrayRef<OptimizationHint>(&*hintStart, hintEnd - hintStart);
hintStart = hintEnd;
while (hintStart->offset0 >= subsectionEnd) {
advanceSubsection();
if (section == sections.end())
break;
updateAddr();
assert(hintStart->offset0 >= subsectionBase);
}
}
hintEnd->offset0 -= subsectionBase;
for (int i = 0, count = expectedArgCount(hintEnd->type); i < count - 1;
++i) {
if (LLVM_UNLIKELY(
hintEnd->delta[i] < -static_cast<int64_t>(hintEnd->offset0) ||
hintEnd->delta[i] >=
static_cast<int64_t>(subsectionEnd - hintEnd->offset0))) {
error("Linker optimization hint spans multiple sections");
return;
}
}
}
if (section != sections.end())
subsection->isec->optimizationHints = ArrayRef<OptimizationHint>(
&*hintStart, optimizationHints.end() - hintStart);
}
template <class SectionHeader>
static bool validateRelocationInfo(InputFile *file, const SectionHeader &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 SectionHeader>
void ObjFile::parseRelocations(ArrayRef<SectionHeader> sectionHeaders,
const SectionHeader &sec, Section &section) {
auto *buf = reinterpret_cast<const uint8_t *>(mb.getBufferStart());
ArrayRef<relocation_info> relInfos(
reinterpret_cast<const relocation_info *>(buf + sec.reloff), sec.nreloc);
Subsections &subsections = section.subsections;
auto subsecIt = subsections.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.
relocation_info relInfo = relInfos[i];
bool isSubtrahend =
target->hasAttr(relInfo.r_type, RelocAttrBits::SUBTRAHEND);
int64_t pairedAddend = 0;
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");
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 SectionHeader &referentSecHead =
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 -
referentSecHead.addr;
} else {
// The addend for a non-pcrel relocation is its absolute address.
referentOffset = totalAddend - referentSecHead.addr;
}
r.referent = findContainingSubsection(*sections[relInfo.r_symbolnum - 1],
&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 != subsections.rend() && subsecIt->offset > r.offset)
++subsecIt;
if (subsecIt == subsections.rend() ||
subsecIt->offset + subsecIt->isec->getSize() <= r.offset) {
subsec = findContainingSubsection(section, &r.offset);
// Now that we know the relocs are unsorted, avoid trying the 'fast path'
// for the other relocations.
subsecIt = subsections.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;
p.referent = findContainingSubsection(
*sections[minuendInfo.r_symbolnum - 1], &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, bool forceHidden) {
// 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) {
// -load_hidden makes us treat global symbols as linkage unit scoped.
// Duplicates are reported but the symbol does not go in the export trie.
bool isPrivateExtern = sym.n_type & N_PEXT || forceHidden;
// 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(autohide) or one
// that's privateExtern -- neither makes it into the dynamic symbol table,
// unless the autohide symbol is explicitly exported.
// But if a symbol is both privateExtern and autohide then it can't
// be exported.
// So we nullify the autohide flag when privateExtern is present
// and promote the symbol to privateExtern when it is not already.
if (isWeakDefCanBeHidden && isPrivateExtern)
isWeakDefCanBeHidden = false;
else 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,
isWeakDefCanBeHidden);
}
assert(!isWeakDefCanBeHidden &&
"weak_def_can_be_hidden on already-hidden symbol?");
bool includeInSymtab =
!name.startswith("l") && !name.startswith("L") && !isEhFrameSection(isec);
return make<Defined>(
name, isec->getFile(), isec, value, size, sym.n_desc & N_WEAK_DEF,
/*isExternal=*/false, /*isPrivateExtern=*/false, includeInSymtab,
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, bool forceHidden) {
if (sym.n_type & N_EXT) {
bool isPrivateExtern = sym.n_type & N_PEXT || forceHidden;
return symtab->addDefined(
name, file, nullptr, sym.n_value, /*size=*/0,
/*isWeakDef=*/false, isPrivateExtern, sym.n_desc & N_ARM_THUMB_DEF,
/*isReferencedDynamically=*/false, sym.n_desc & N_NO_DEAD_STRIP,
/*isWeakDefCanBeHidden=*/false);
}
return make<Defined>(name, file, nullptr, sym.n_value, /*size=*/0,
/*isWeakDef=*/false,
/*isExternal=*/false, /*isPrivateExtern=*/false,
/*includeInSymtab=*/true, 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;
bool isPrivateExtern = sym.n_type & N_PEXT || forceHidden;
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),
isPrivateExtern);
case N_ABS:
return createAbsolute(sym, this, name, forceHidden);
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(sections.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;
if ((sym.n_type & N_TYPE) == N_SECT) {
Subsections &subsections = sections[sym.n_sect - 1]->subsections;
// parseSections() may have chosen not to parse this section.
if (subsections.empty())
continue;
symbolsBySection[sym.n_sect - 1].push_back(i);
} else if (isUndef(sym)) {
undefineds.push_back(i);
} else {
symbols[i] = parseNonSectionSymbol(sym, StringRef(strtab + sym.n_strx));
}
}
for (size_t i = 0; i < sections.size(); ++i) {
Subsections &subsections = sections[i]->subsections;
if (subsections.empty())
continue;
std::vector<uint32_t> &symbolIndices = symbolsBySection[i];
uint64_t sectionAddr = sectionHeaders[i].addr;
uint32_t sectionAlign = 1u << sectionHeaders[i].align;
// Some sections have already been split into subsections during
// parseSections(), so we simply need to match Symbols to the corresponding
// subsection here.
if (sections[i]->doneSplitting) {
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(*sections[i], &symbolOffset);
if (symbolOffset != 0) {
error(toString(*sections[i]) + ": symbol " + name +
" at misaligned offset");
continue;
}
symbols[symIndex] =
createDefined(sym, name, isec, 0, isec->getSize(), forceHidden);
}
continue;
}
sections[i]->doneSplitting = true;
// Calculate symbol sizes and create subsections by splitting the sections
// along symbol boundaries.
// We populate subsections 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;
});
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;
Subsection &subsec = subsections.back();
InputSection *isec = subsec.isec;
uint64_t subsecAddr = sectionAddr + subsec.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, forceHidden);
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, forceHidden);
// 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);
subsections.push_back({sym.n_value - sectionAddr, nextIsec});
}
}
// 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()};
sections.push_back(make<Section>(/*file=*/this, segName.take_front(16),
sectName.take_front(16),
/*flags=*/0, /*addr=*/0));
Section &section = *sections.back();
ConcatInputSection *isec = make<ConcatInputSection>(section, data);
isec->live = true;
section.subsections.push_back({0, isec});
}
ObjFile::ObjFile(MemoryBufferRef mb, uint32_t modTime, StringRef archiveName,
bool lazy, bool forceHidden)
: InputFile(ObjKind, mb, lazy), modTime(modTime), forceHidden(forceHidden) {
this->archiveName = std::string(archiveName);
if (lazy) {
if (target->wordSize == 8)
parseLazy<LP64>();
else
parseLazy<ILP32>();
} else {
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 SectionHeader = 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());
uint32_t cpuType;
std::tie(cpuType, std::ignore) = getCPUTypeFromArchitecture(config->arch());
if (hdr->cputype != cpuType) {
Architecture arch =
getArchitectureFromCpuType(hdr->cputype, hdr->cpusubtype);
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<SectionHeader> sectionHeaders;
if (const load_command *cmd = findCommand(hdr, LP::segmentLCType)) {
auto *c = reinterpret_cast<const SegmentCommand *>(cmd);
sectionHeaders = ArrayRef<SectionHeader>{
reinterpret_cast<const SectionHeader *>(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 = sections.size(); i < n; ++i)
if (!sections[i]->subsections.empty())
parseRelocations(sectionHeaders, sectionHeaders[i], *sections[i]);
if (!config->ignoreOptimizationHints)
if (auto *cmd = findCommand<linkedit_data_command>(
hdr, LC_LINKER_OPTIMIZATION_HINT))
parseOptimizationHints({buf + cmd->dataoff, cmd->datasize});
parseDebugInfo();
Section *ehFrameSection = nullptr;
Section *compactUnwindSection = nullptr;
for (Section *sec : sections) {
Section **s = StringSwitch<Section **>(sec->name)
.Case(section_names::compactUnwind, &compactUnwindSection)
.Case(section_names::ehFrame, &ehFrameSection)
.Default(nullptr);
if (s)
*s = sec;
}
if (compactUnwindSection)
registerCompactUnwind(*compactUnwindSection);
if (ehFrameSection)
registerEhFrames(*ehFrameSection);
}
template <class LP> void ObjFile::parseLazy() {
using Header = typename LP::mach_header;
using NList = typename LP::nlist;
auto *buf = reinterpret_cast<const uint8_t *>(mb.getBufferStart());
auto *hdr = reinterpret_cast<const Header *>(mb.getBufferStart());
const load_command *cmd = findCommand(hdr, LC_SYMTAB);
if (!cmd)
return;
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;
symbols.resize(nList.size());
for (auto it : llvm::enumerate(nList)) {
const NList &sym = it.value();
if ((sym.n_type & N_EXT) && !isUndef(sym)) {
// TODO: Bound checking
StringRef name = strtab + sym.n_strx;
symbols[it.index()] = symtab->addLazyObject(name, *this);
if (!lazy)
break;
}
}
}
void ObjFile::parseDebugInfo() {
std::unique_ptr<DwarfObject> dObj = DwarfObject::create(this);
if (!dObj)
return;
// We do not re-use the context from getDwarf() here as that function
// constructs an expensive DWARFCache object.
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 != units.end() ? it->get() : nullptr;
}
ArrayRef<data_in_code_entry> ObjFile::getDataInCode() const {
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);
return {reinterpret_cast<const data_in_code_entry *>(buf + c->dataoff),
c->datasize / sizeof(data_in_code_entry)};
}
// Create pointers from symbols to their associated compact unwind entries.
void ObjFile::registerCompactUnwind(Section &compactUnwindSection) {
for (const Subsection &subsection : compactUnwindSection.subsections) {
ConcatInputSection *isec = cast<ConcatInputSection>(subsection.isec);
// Hack!! Each compact unwind entry (CUE) has its UNSIGNED relocations embed
// their addends in its data. Thus if ICF operated naively and compared the
// entire contents of each CUE, entries with identical unwind info but e.g.
// belonging to different functions would never be considered equivalent. To
// work around this problem, we remove some parts of the data containing the
// embedded addends. In particular, we remove the function address and LSDA
// pointers. Since these locations are at the start and end of the entry,
// we can do this using a simple, efficient slice rather than performing a
// copy. We are not losing any information here because the embedded
// addends have already been parsed in the corresponding Reloc structs.
//
// Removing these pointers would not be safe if they were pointers to
// absolute symbols. In that case, there would be no corresponding
// relocation. However, (AFAIK) MC cannot emit references to absolute
// symbols for either the function address or the LSDA. However, it *can* do
// so for the personality pointer, so we are not slicing that field away.
//
// Note that we do not adjust the offsets of the corresponding relocations;
// instead, we rely on `relocateCompactUnwind()` to correctly handle these
// truncated input sections.
isec->data = isec->data.slice(target->wordSize, 8 + target->wordSize);
uint32_t encoding = read32le(isec->data.data() + sizeof(uint32_t));
// llvm-mc omits CU entries for functions that need DWARF encoding, but
// `ld -r` doesn't. We can ignore them because we will re-synthesize these
// CU entries from the DWARF info during the output phase.
if ((encoding & target->modeDwarfEncoding) == target->modeDwarfEncoding)
continue;
ConcatInputSection *referentIsec;
for (auto it = isec->relocs.begin(); it != isec->relocs.end();) {
Reloc &r = *it;
// CUE::functionAddress is at offset 0. Skip personality & LSDA relocs.
if (r.offset != 0) {
++it;
continue;
}
uint64_t add = r.addend;
if (auto *sym = cast_or_null<Defined>(r.referent.dyn_cast<Symbol *>())) {
// Check whether the symbol defined in this file is the prevailing one.
// Skip if it is e.g. a weak def that didn't prevail.
if (sym->getFile() != this) {
++it;
continue;
}
add += sym->value;
referentIsec = cast<ConcatInputSection>(sym->isec);
} else {
referentIsec =
cast<ConcatInputSection>(r.referent.dyn_cast<InputSection *>());
}
// Unwind info lives in __DATA, and finalization of __TEXT will occur
// before finalization of __DATA. Moreover, the finalization of unwind
// info depends on the exact addresses that it references. So it is safe
// for compact unwind to reference addresses in __TEXT, but not addresses
// in any other segment.
if (referentIsec->getSegName() != segment_names::text)
error(isec->getLocation(r.offset) + " references section " +
referentIsec->getName() + " 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.
Defined *d = findSymbolAtOffset(referentIsec, add);
if (!d) {
++it;
continue;
}
d->unwindEntry = isec;
// Now that the symbol points to the unwind entry, we can remove the reloc
// that points from the unwind entry back to the symbol.
//
// First, the symbol keeps the unwind entry alive (and not vice versa), so
// this keeps dead-stripping simple.
//
// Moreover, it reduces the work that ICF needs to do to figure out if
// functions with unwind info are foldable.
//
// However, this does make it possible for ICF to fold CUEs that point to
// distinct functions (if the CUEs are otherwise identical).
// UnwindInfoSection takes care of this by re-duplicating the CUEs so that
// each one can hold a distinct functionAddress value.
//
// Given that clang emits relocations in reverse order of address, this
// relocation should be at the end of the vector for most of our input
// object files, so this erase() is typically an O(1) operation.
it = isec->relocs.erase(it);
}
}
}
struct CIE {
macho::Symbol *personalitySymbol = nullptr;
bool fdesHaveAug = false;
uint8_t lsdaPtrSize = 0; // 0 => no LSDA
uint8_t funcPtrSize = 0;
};
static uint8_t pointerEncodingToSize(uint8_t enc) {
switch (enc & 0xf) {
case dwarf::DW_EH_PE_absptr:
return target->wordSize;
case dwarf::DW_EH_PE_sdata4:
return 4;
case dwarf::DW_EH_PE_sdata8:
// ld64 doesn't actually support sdata8, but this seems simple enough...
return 8;
default:
return 0;
};
}
static CIE parseCIE(const InputSection *isec, const EhReader &reader,
size_t off) {
// Handling the full generality of possible DWARF encodings would be a major
// pain. We instead take advantage of our knowledge of how llvm-mc encodes
// DWARF and handle just that.
constexpr uint8_t expectedPersonalityEnc =
dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_sdata4;
CIE cie;
uint8_t version = reader.readByte(&off);
if (version != 1 && version != 3)
fatal("Expected CIE version of 1 or 3, got " + Twine(version));
StringRef aug = reader.readString(&off);
reader.skipLeb128(&off); // skip code alignment
reader.skipLeb128(&off); // skip data alignment
reader.skipLeb128(&off); // skip return address register
reader.skipLeb128(&off); // skip aug data length
uint64_t personalityAddrOff = 0;
for (char c : aug) {
switch (c) {
case 'z':
cie.fdesHaveAug = true;
break;
case 'P': {
uint8_t personalityEnc = reader.readByte(&off);
if (personalityEnc != expectedPersonalityEnc)
reader.failOn(off, "unexpected personality encoding 0x" +
Twine::utohexstr(personalityEnc));
personalityAddrOff = off;
off += 4;
break;
}
case 'L': {
uint8_t lsdaEnc = reader.readByte(&off);
cie.lsdaPtrSize = pointerEncodingToSize(lsdaEnc);
if (cie.lsdaPtrSize == 0)
reader.failOn(off, "unexpected LSDA encoding 0x" +
Twine::utohexstr(lsdaEnc));
break;
}
case 'R': {
uint8_t pointerEnc = reader.readByte(&off);
cie.funcPtrSize = pointerEncodingToSize(pointerEnc);
if (cie.funcPtrSize == 0 || !(pointerEnc & dwarf::DW_EH_PE_pcrel))
reader.failOn(off, "unexpected pointer encoding 0x" +
Twine::utohexstr(pointerEnc));
break;
}
default:
break;
}
}
if (personalityAddrOff != 0) {
auto personalityRelocIt =
llvm::find_if(isec->relocs, [=](const macho::Reloc &r) {
return r.offset == personalityAddrOff;
});
if (personalityRelocIt == isec->relocs.end())
reader.failOn(off, "Failed to locate relocation for personality symbol");
cie.personalitySymbol = personalityRelocIt->referent.get<macho::Symbol *>();
}
return cie;
}
// EH frame target addresses may be encoded as pcrel offsets. However, instead
// of using an actual pcrel reloc, ld64 emits subtractor relocations instead.
// This function recovers the target address from the subtractors, essentially
// performing the inverse operation of EhRelocator.
//
// Concretely, we expect our relocations to write the value of `PC -
// target_addr` to `PC`. `PC` itself is denoted by a minuend relocation that
// points to a symbol plus an addend.
//
// It is important that the minuend relocation point to a symbol within the
// same section as the fixup value, since sections may get moved around.
//
// For example, for arm64, llvm-mc emits relocations for the target function
// address like so:
//
// ltmp:
// <CIE start>
// ...
// <CIE end>
// ... multiple FDEs ...
// <FDE start>
// <target function address - (ltmp + pcrel offset)>
// ...
//
// If any of the FDEs in `multiple FDEs` get dead-stripped, then `FDE start`
// will move to an earlier address, and `ltmp + pcrel offset` will no longer
// reflect an accurate pcrel value. To avoid this problem, we "canonicalize"
// our relocation by adding an `EH_Frame` symbol at `FDE start`, and updating
// the reloc to be `target function address - (EH_Frame + new pcrel offset)`.
//
// If `Invert` is set, then we instead expect `target_addr - PC` to be written
// to `PC`.
template <bool Invert = false>
Defined *
targetSymFromCanonicalSubtractor(const InputSection *isec,
std::vector<macho::Reloc>::iterator relocIt) {
macho::Reloc &subtrahend = *relocIt;
macho::Reloc &minuend = *std::next(relocIt);
assert(target->hasAttr(subtrahend.type, RelocAttrBits::SUBTRAHEND));
assert(target->hasAttr(minuend.type, RelocAttrBits::UNSIGNED));
// Note: pcSym may *not* be exactly at the PC; there's usually a non-zero
// addend.
auto *pcSym = cast<Defined>(subtrahend.referent.get<macho::Symbol *>());
Defined *target =
cast_or_null<Defined>(minuend.referent.dyn_cast<macho::Symbol *>());
if (!pcSym) {
auto *targetIsec =
cast<ConcatInputSection>(minuend.referent.get<InputSection *>());
target = findSymbolAtOffset(targetIsec, minuend.addend);
}
if (Invert)
std::swap(pcSym, target);
if (pcSym->isec == isec) {
if (pcSym->value - (Invert ? -1 : 1) * minuend.addend != subtrahend.offset)
fatal("invalid FDE relocation in __eh_frame");
} else {
// Ensure the pcReloc points to a symbol within the current EH frame.
// HACK: we should really verify that the original relocation's semantics
// are preserved. In particular, we should have
// `oldSym->value + oldOffset == newSym + newOffset`. However, we don't
// have an easy way to access the offsets from this point in the code; some
// refactoring is needed for that.
macho::Reloc &pcReloc = Invert ? minuend : subtrahend;
pcReloc.referent = isec->symbols[0];
assert(isec->symbols[0]->value == 0);
minuend.addend = pcReloc.offset * (Invert ? 1LL : -1LL);
}
return target;
}
Defined *findSymbolAtAddress(const std::vector<Section *> &sections,
uint64_t addr) {
Section *sec = findContainingSection(sections, &addr);
auto *isec = cast<ConcatInputSection>(findContainingSubsection(*sec, &addr));
return findSymbolAtOffset(isec, addr);
}
// For symbols that don't have compact unwind info, associate them with the more
// general-purpose (and verbose) DWARF unwind info found in __eh_frame.
//
// This requires us to parse the contents of __eh_frame. See EhFrame.h for a
// description of its format.
//
// While parsing, we also look for what MC calls "abs-ified" relocations -- they
// are relocations which are implicitly encoded as offsets in the section data.
// We convert them into explicit Reloc structs so that the EH frames can be
// handled just like a regular ConcatInputSection later in our output phase.
//
// We also need to handle the case where our input object file has explicit
// relocations. This is the case when e.g. it's the output of `ld -r`. We only
// look for the "abs-ified" relocation if an explicit relocation is absent.
void ObjFile::registerEhFrames(Section &ehFrameSection) {
DenseMap<const InputSection *, CIE> cieMap;
for (const Subsection &subsec : ehFrameSection.subsections) {
auto *isec = cast<ConcatInputSection>(subsec.isec);
uint64_t isecOff = subsec.offset;
// Subtractor relocs require the subtrahend to be a symbol reloc. Ensure
// that all EH frames have an associated symbol so that we can generate
// subtractor relocs that reference them.
if (isec->symbols.size() == 0)
isec->symbols.push_back(make<Defined>(
"EH_Frame", isec->getFile(), isec, /*value=*/0, /*size=*/0,
/*isWeakDef=*/false, /*isExternal=*/false, /*isPrivateExtern=*/false,
/*includeInSymtab=*/false, /*isThumb=*/false,
/*isReferencedDynamically=*/false, /*noDeadStrip=*/false));
else if (isec->symbols[0]->value != 0)
fatal("found symbol at unexpected offset in __eh_frame");
EhReader reader(this, isec->data, subsec.offset);
size_t dataOff = 0; // Offset from the start of the EH frame.
reader.skipValidLength(&dataOff); // readLength() already validated this.
// cieOffOff is the offset from the start of the EH frame to the cieOff
// value, which is itself an offset from the current PC to a CIE.
const size_t cieOffOff = dataOff;
EhRelocator ehRelocator(isec);
auto cieOffRelocIt = llvm::find_if(
isec->relocs, [=](const Reloc &r) { return r.offset == cieOffOff; });
InputSection *cieIsec = nullptr;
if (cieOffRelocIt != isec->relocs.end()) {
// We already have an explicit relocation for the CIE offset.
cieIsec =
targetSymFromCanonicalSubtractor</*Invert=*/true>(isec, cieOffRelocIt)
->isec;
dataOff += sizeof(uint32_t);
} else {
// If we haven't found a relocation, then the CIE offset is most likely
// embedded in the section data (AKA an "abs-ified" reloc.). Parse that
// and generate a Reloc struct.
uint32_t cieMinuend = reader.readU32(&dataOff);
if (cieMinuend == 0) {
cieIsec = isec;
} else {
uint32_t cieOff = isecOff + dataOff - cieMinuend;
cieIsec = findContainingSubsection(ehFrameSection, &cieOff);
if (cieIsec == nullptr)
fatal("failed to find CIE");
}
if (cieIsec != isec)
ehRelocator.makeNegativePcRel(cieOffOff, cieIsec->symbols[0],
/*length=*/2);
}
if (cieIsec == isec) {
cieMap[cieIsec] = parseCIE(isec, reader, dataOff);
continue;
}
assert(cieMap.count(cieIsec));
const CIE &cie = cieMap[cieIsec];
// Offset of the function address within the EH frame.
const size_t funcAddrOff = dataOff;
uint64_t funcAddr = reader.readPointer(&dataOff, cie.funcPtrSize) +
ehFrameSection.addr + isecOff + funcAddrOff;
uint32_t funcLength = reader.readPointer(&dataOff, cie.funcPtrSize);
size_t lsdaAddrOff = 0; // Offset of the LSDA address within the EH frame.
Optional<uint64_t> lsdaAddrOpt;
if (cie.fdesHaveAug) {
reader.skipLeb128(&dataOff);
lsdaAddrOff = dataOff;
if (cie.lsdaPtrSize != 0) {
uint64_t lsdaOff = reader.readPointer(&dataOff, cie.lsdaPtrSize);
if (lsdaOff != 0) // FIXME possible to test this?
lsdaAddrOpt = ehFrameSection.addr + isecOff + lsdaAddrOff + lsdaOff;
}
}
auto funcAddrRelocIt = isec->relocs.end();
auto lsdaAddrRelocIt = isec->relocs.end();
for (auto it = isec->relocs.begin(); it != isec->relocs.end(); ++it) {
if (it->offset == funcAddrOff)
funcAddrRelocIt = it++; // Found subtrahend; skip over minuend reloc
else if (lsdaAddrOpt && it->offset == lsdaAddrOff)
lsdaAddrRelocIt = it++; // Found subtrahend; skip over minuend reloc
}
Defined *funcSym;
if (funcAddrRelocIt != isec->relocs.end()) {
funcSym = targetSymFromCanonicalSubtractor(isec, funcAddrRelocIt);
// Canonicalize the symbol. If there are multiple symbols at the same
// address, we want both `registerEhFrame` and `registerCompactUnwind`
// to register the unwind entry under same symbol.
// This is not particularly efficient, but we should run into this case
// infrequently (only when handling the output of `ld -r`).
if (funcSym->isec)
funcSym = findSymbolAtOffset(cast<ConcatInputSection>(funcSym->isec),
funcSym->value);
} else {
funcSym = findSymbolAtAddress(sections, funcAddr);
ehRelocator.makePcRel(funcAddrOff, funcSym, target->p2WordSize);
}
// The symbol has been coalesced, or already has a compact unwind entry.
if (!funcSym || funcSym->getFile() != this || funcSym->unwindEntry) {
// We must prune unused FDEs for correctness, so we cannot rely on
// -dead_strip being enabled.
isec->live = false;
continue;
}
InputSection *lsdaIsec = nullptr;
if (lsdaAddrRelocIt != isec->relocs.end()) {
lsdaIsec = targetSymFromCanonicalSubtractor(isec, lsdaAddrRelocIt)->isec;
} else if (lsdaAddrOpt) {
uint64_t lsdaAddr = *lsdaAddrOpt;
Section *sec = findContainingSection(sections, &lsdaAddr);
lsdaIsec =
cast<ConcatInputSection>(findContainingSubsection(*sec, &lsdaAddr));
ehRelocator.makePcRel(lsdaAddrOff, lsdaIsec, target->p2WordSize);
}
fdes[isec] = {funcLength, cie.personalitySymbol, lsdaIsec};
funcSym->unwindEntry = isec;
ehRelocator.commit();
}
}
std::string ObjFile::sourceFile() const {
SmallString<261> dir(compileUnit->getCompilationDir());
StringRef sep = sys::path::get_separator();
// We don't use `path::append` here because we want an empty `dir` to result
// in an absolute path. `append` would give us a relative path for that case.
if (!dir.endswith(sep))
dir += sep;
return (dir + compileUnit->getUnitDIE().getShortName()).str();
}
lld::DWARFCache *ObjFile::getDwarf() {
llvm::call_once(initDwarf, [this]() {
auto dwObj = DwarfObject::create(this);
if (!dwObj)
return;
dwarfCache = std::make_unique<DWARFCache>(std::make_unique<DWARFContext>(
std::move(dwObj), "",
[&](Error err) { warn(getName() + ": " + toString(std::move(err))); },
[&](Error warning) {
warn(getName() + ": " + toString(std::move(warning)));
}));
});
return dwarfCache.get();
}
// 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);
path::append(newPath, path);
path = newPath;
} else if (path.startswith("@rpath/")) {
for (StringRef rpath : umbrella->rpaths) {
newPath.clear();
if (rpath.consume_front("@loader_path/")) {
fs::real_path(umbrella->getName(), newPath);
path::remove_filename(newPath);
}
path::append(newPath, rpath, path.drop_front(strlen("@rpath/")));
if (Optional<StringRef> dylibPath = resolveDylibPath(newPath.str()))
return loadDylib(*dylibPath, umbrella);
}
}
// FIXME: Should this be further up?
if (currentTopLevelTapi) {
for (InterfaceFile &child :
make_pointee_range(currentTopLevelTapi->documents())) {
assert(child.documents().empty());
if (path == child.getInstallName()) {
auto file = make<DylibFile>(child, umbrella, /*isBundleLoader=*/false,
/*explicitlyLinked=*/false);
file->parseReexports(child);
return file;
}
}
}
if (Optional<StringRef> dylibPath = resolveDylibPath(path))
return loadDylib(*dylibPath, umbrella);
return nullptr;
}
// 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;
}
static void loadReexport(StringRef path, DylibFile *umbrella,
const InterfaceFile *currentTopLevelTapi) {
DylibFile *reexport = findDylib(path, umbrella, currentTopLevelTapi);
if (!reexport)
error("unable to locate re-export with install name " + path);
}
DylibFile::DylibFile(MemoryBufferRef mb, DylibFile *umbrella,
bool isBundleLoader, bool explicitlyLinked)
: InputFile(DylibKind, mb), refState(RefState::Unreferenced),
explicitlyLinked(explicitlyLinked), isBundleLoader(isBundleLoader) {
assert(!isBundleLoader || !umbrella);
if (umbrella == nullptr)
umbrella = this;
this->umbrella = umbrella;
auto *hdr = reinterpret_cast<const mach_header *>(mb.getBufferStart());
// Initialize installName.
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);
installName =
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 (config->printEachFile)
message(toString(this));
inputFiles.insert(this);
deadStrippable = hdr->flags & MH_DEAD_STRIPPABLE_DYLIB;
if (!checkCompatibility(this))
return;
checkAppExtensionSafety(hdr->flags & MH_APP_EXTENSION_SAFE);
for (auto *cmd : findCommands<rpath_command>(hdr, LC_RPATH)) {
StringRef rpath{reinterpret_cast<const char *>(cmd) + cmd->path};
rpaths.push_back(rpath);
}
// Initialize symbols.
exportingFile = isImplicitlyLinked(installName) ? this : this->umbrella;
const auto *dyldInfo = findCommand<dyld_info_command>(hdr, LC_DYLD_INFO_ONLY);
const auto *exportsTrie =
findCommand<linkedit_data_command>(hdr, LC_DYLD_EXPORTS_TRIE);
if (dyldInfo && exportsTrie) {
// It's unclear what should happen in this case. Maybe we should only error
// out if the two load commands refer to different data?
error("dylib " + toString(this) +
" has both LC_DYLD_INFO_ONLY and LC_DYLD_EXPORTS_TRIE");
return;
} else if (dyldInfo) {
parseExportedSymbols(dyldInfo->export_off, dyldInfo->export_size);
} else if (exportsTrie) {
parseExportedSymbols(exportsTrie->dataoff, exportsTrie->datasize);
} else {
error("No LC_DYLD_INFO_ONLY or LC_DYLD_EXPORTS_TRIE found in " +
toString(this));
return;
}
}
void DylibFile::parseExportedSymbols(uint32_t offset, uint32_t size) {
struct TrieEntry {
StringRef name;
uint64_t flags;
};
auto *buf = reinterpret_cast<const uint8_t *>(mb.getBufferStart());
std::vector<TrieEntry> entries;
// Find all the $ld$* symbols to process first.
parseTrie(buf + offset, size, [&](const Twine &name, uint64_t flags) {
StringRef savedName = saver().save(name);
if (handleLDSymbol(savedName))
return;
entries.push_back({savedName, flags});
});
// Process the "normal" symbols.
for (TrieEntry &entry : entries) {
if (exportingFile->hiddenSymbols.contains(CachedHashStringRef(entry.name)))
continue;
bool isWeakDef = entry.flags & EXPORT_SYMBOL_FLAGS_WEAK_DEFINITION;
bool isTlv = entry.flags & EXPORT_SYMBOL_FLAGS_KIND_THREAD_LOCAL;
symbols.push_back(
symtab->addDylib(entry.name, exportingFile, isWeakDef, isTlv));
}
}
void DylibFile::parseLoadCommands(MemoryBufferRef mb) {
auto *hdr = reinterpret_cast<const mach_header *>(mb.getBufferStart());
const uint8_t *p = reinterpret_cast<const uint8_t *>(mb.getBufferStart()) +
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);
DylibFile *dylib = findDylib(dylibPath, umbrella, nullptr);
if (!dylib)
error(Twine("unable to locate library '") + dylibPath +
"' loaded from '" + toString(this) + "' for -flat_namespace");
}
}
}
// Some versions of Xcode ship with .tbd files that don't have the right
// platform settings.
constexpr std::array<StringRef, 3> skipPlatformChecks{
"/usr/lib/system/libsystem_kernel.dylib",
"/usr/lib/system/libsystem_platform.dylib",
"/usr/lib/system/libsystem_pthread.dylib"};
static bool skipPlatformCheckForCatalyst(const InterfaceFile &interface,
bool explicitlyLinked) {
// Catalyst outputs can link against implicitly linked macOS-only libraries.
if (config->platform() != PLATFORM_MACCATALYST || explicitlyLinked)
return false;
return is_contained(interface.targets(),
MachO::Target(config->arch(), PLATFORM_MACOS));
}
static bool isArchABICompatible(ArchitectureSet archSet,
Architecture targetArch) {
uint32_t cpuType;
uint32_t targetCpuType;
std::tie(targetCpuType, std::ignore) = getCPUTypeFromArchitecture(targetArch);
return llvm::any_of(archSet, [&](const auto &p) {
std::tie(cpuType, std::ignore) = getCPUTypeFromArchitecture(p);
return cpuType == targetCpuType;
});
}
static bool isTargetPlatformArchCompatible(
InterfaceFile::const_target_range interfaceTargets, Target target) {
if (is_contained(interfaceTargets, target))
return true;
if (config->forceExactCpuSubtypeMatch)
return false;
ArchitectureSet archSet;
for (const auto &p : interfaceTargets)
if (p.Platform == target.Platform)
archSet.set(p.Arch);
if (archSet.empty())
return false;
return isArchABICompatible(archSet, target.Arch);
}
DylibFile::DylibFile(const InterfaceFile &interface, DylibFile *umbrella,
bool isBundleLoader, bool explicitlyLinked)
: InputFile(DylibKind, interface), refState(RefState::Unreferenced),
explicitlyLinked(explicitlyLinked), isBundleLoader(isBundleLoader) {
// FIXME: Add test for the missing TBD code path.
if (umbrella == nullptr)
umbrella = this;
this->umbrella = umbrella;
installName = saver().save(interface.getInstallName());
compatibilityVersion = interface.getCompatibilityVersion().rawValue();
currentVersion = interface.getCurrentVersion().rawValue();
if (config->printEachFile)
message(toString(this));
inputFiles.insert(this);
if (!is_contained(skipPlatformChecks, installName) &&
!isTargetPlatformArchCompatible(interface.targets(),
config->platformInfo.target) &&
!skipPlatformCheckForCatalyst(interface, explicitlyLinked)) {
error(toString(this) + " is incompatible with " +
std::string(config->platformInfo.target));
return;
}
checkAppExtensionSafety(interface.isApplicationExtensionSafe());
exportingFile = isImplicitlyLinked(installName) ? this : umbrella;
auto addSymbol = [&](const llvm::MachO::Symbol &symbol,
const Twine &name) -> void {
StringRef savedName = saver().save(name);
if (exportingFile->hiddenSymbols.contains(CachedHashStringRef(savedName)))
return;
symbols.push_back(symtab->addDylib(savedName, exportingFile,
symbol.isWeakDefined(),
symbol.isThreadLocalValue()));
};
std::vector<const llvm::MachO::Symbol *> normalSymbols;
normalSymbols.reserve(interface.symbolsCount());
for (const auto *symbol : interface.symbols()) {
if (!isArchABICompatible(symbol->getArchitectures(), config->arch()))
continue;
if (handleLDSymbol(symbol->getName()))
continue;
switch (symbol->getKind()) {
case SymbolKind::GlobalSymbol:
case SymbolKind::ObjectiveCClass:
case SymbolKind::ObjectiveCClassEHType:
case SymbolKind::ObjectiveCInstanceVariable:
normalSymbols.push_back(symbol);
}
}
// TODO(compnerd) filter out symbols based on the target platform
for (const auto *symbol : normalSymbols) {
switch (symbol->getKind()) {
case SymbolKind::GlobalSymbol:
addSymbol(*symbol, symbol->getName());
break;
case SymbolKind::ObjectiveCClass:
// XXX ld64 only creates these symbols when -ObjC is passed in. We may
// want to emulate that.
addSymbol(*symbol, objc::klass + symbol->getName());
addSymbol(*symbol, objc::metaclass + symbol->getName());
break;
case SymbolKind::ObjectiveCClassEHType:
addSymbol(*symbol, objc::ehtype + symbol->getName());
break;
case SymbolKind::ObjectiveCInstanceVariable:
addSymbol(*symbol, objc::ivar + symbol->getName());
break;
}
}
}
DylibFile::DylibFile(DylibFile *umbrella)
: InputFile(DylibKind, MemoryBufferRef{}), refState(RefState::Unreferenced),
explicitlyLinked(false), isBundleLoader(false) {
if (umbrella == nullptr)
umbrella = this;
this->umbrella = umbrella;
}
void DylibFile::parseReexports(const InterfaceFile &interface) {
const InterfaceFile *topLevel =
interface.getParent() == nullptr ? &interface : interface.getParent();
for (const InterfaceFileRef &intfRef : interface.reexportedLibraries()) {
InterfaceFile::const_target_range targets = intfRef.targets();
if (is_contained(skipPlatformChecks, intfRef.getInstallName()) ||
isTargetPlatformArchCompatible(targets, config->platformInfo.target))
loadReexport(intfRef.getInstallName(), exportingFile, topLevel);
}
}
bool DylibFile::isExplicitlyLinked() const {
if (!explicitlyLinked)
return false;
// If this dylib was explicitly linked, but at least one of the symbols
// of the synthetic dylibs it created via $ld$previous symbols is
// referenced, then that synthetic dylib fulfils the explicit linkedness
// and we can deadstrip this dylib if it's unreferenced.
for (const auto *dylib : extraDylibs)
if (dylib->isReferenced())
return false;
return true;
}
DylibFile *DylibFile::getSyntheticDylib(StringRef installName,
uint32_t currentVersion,
uint32_t compatVersion) {
for (DylibFile *dylib : extraDylibs)
if (dylib->installName == installName) {
// FIXME: Check what to do if different $ld$previous symbols
// request the same dylib, but with different versions.
return dylib;
}
auto *dylib = make<DylibFile>(umbrella == this ? nullptr : umbrella);
dylib->installName = saver().save(installName);
dylib->currentVersion = currentVersion;
dylib->compatibilityVersion = compatVersion;
extraDylibs.push_back(dylib);
return dylib;
}
// $ld$ symbols modify the properties/behavior of the library (e.g. its install
// name, compatibility version or hide/add symbols) for specific target
// versions.
bool DylibFile::handleLDSymbol(StringRef originalName) {
if (!originalName.startswith("$ld$"))
return false;
StringRef action;
StringRef name;
std::tie(action, name) = originalName.drop_front(strlen("$ld$")).split('$');
if (action == "previous")
handleLDPreviousSymbol(name, originalName);
else if (action == "install_name")
handleLDInstallNameSymbol(name, originalName);
else if (action == "hide")
handleLDHideSymbol(name, originalName);
return true;
}
void DylibFile::handleLDPreviousSymbol(StringRef name, StringRef originalName) {
// originalName: $ld$ previous $ <installname> $ <compatversion> $
// <platformstr> $ <startversion> $ <endversion> $ <symbol-name> $
StringRef installName;
StringRef compatVersion;
StringRef platformStr;
StringRef startVersion;
StringRef endVersion;
StringRef symbolName;
StringRef rest;
std::tie(installName, name) = name.split('$');
std::tie(compatVersion, name) = name.split('$');
std::tie(platformStr, name) = name.split('$');
std::tie(startVersion, name) = name.split('$');
std::tie(endVersion, name) = name.split('$');
std::tie(symbolName, rest) = name.rsplit('$');
// FIXME: Does this do the right thing for zippered files?
unsigned platform;
if (platformStr.getAsInteger(10, platform) ||
platform != static_cast<unsigned>(config->platform()))
return;
VersionTuple start;
if (start.tryParse(startVersion)) {
warn("failed to parse start version, symbol '" + originalName +
"' ignored");
return;
}
VersionTuple end;
if (end.tryParse(endVersion)) {
warn("failed to parse end version, symbol '" + originalName + "' ignored");
return;
}
if (config->platformInfo.minimum < start ||
config->platformInfo.minimum >= end)
return;
// Initialized to compatibilityVersion for the symbolName branch below.
uint32_t newCompatibilityVersion = compatibilityVersion;
uint32_t newCurrentVersionForSymbol = currentVersion;
if (!compatVersion.empty()) {
VersionTuple cVersion;
if (cVersion.tryParse(compatVersion)) {
warn("failed to parse compatibility version, symbol '" + originalName +
"' ignored");
return;
}
newCompatibilityVersion = encodeVersion(cVersion);
newCurrentVersionForSymbol = newCompatibilityVersion;
}
if (!symbolName.empty()) {
// A $ld$previous$ symbol with symbol name adds a symbol with that name to
// a dylib with given name and version.
auto *dylib = getSyntheticDylib(installName, newCurrentVersionForSymbol,
newCompatibilityVersion);
// The tbd file usually contains the $ld$previous symbol for an old version,
// and then the symbol itself later, for newer deployment targets, like so:
// symbols: [
// '$ld$previous$/Another$$1$3.0$14.0$_zzz$',
// _zzz,
// ]
// Since the symbols are sorted, adding them to the symtab in the given
// order means the $ld$previous version of _zzz will prevail, as desired.
dylib->symbols.push_back(symtab->addDylib(
saver().save(symbolName), dylib, /*isWeakDef=*/false, /*isTlv=*/false));
return;
}
// A $ld$previous$ symbol without symbol name modifies the dylib it's in.
this->installName = saver().save(installName);
this->compatibilityVersion = newCompatibilityVersion;
}
void DylibFile::handleLDInstallNameSymbol(StringRef name,
StringRef originalName) {
// originalName: $ld$ install_name $ os<version> $ install_name
StringRef condition, installName;
std::tie(condition, installName) = name.split('$');
VersionTuple version;
if (!condition.consume_front("os") || version.tryParse(condition))
warn("failed to parse os version, symbol '" + originalName + "' ignored");
else if (version == config->platformInfo.minimum)
this->installName = saver().save(installName);
}
void DylibFile::handleLDHideSymbol(StringRef name, StringRef originalName) {
StringRef symbolName;
bool shouldHide = true;
if (name.startswith("os")) {
// If it's hidden based on versions.
name = name.drop_front(2);
StringRef minVersion;
std::tie(minVersion, symbolName) = name.split('$');
VersionTuple versionTup;
if (versionTup.tryParse(minVersion)) {
warn("Failed to parse hidden version, symbol `" + originalName +
"` ignored.");
return;
}
shouldHide = versionTup == config->platformInfo.minimum;
} else {
symbolName = name;
}
if (shouldHide)
exportingFile->hiddenSymbols.insert(CachedHashStringRef(symbolName));
}
void DylibFile::checkAppExtensionSafety(bool dylibIsAppExtensionSafe) const {
if (config->applicationExtension && !dylibIsAppExtensionSafe)
warn("using '-application_extension' with unsafe dylib: " + toString(this));
}
ArchiveFile::ArchiveFile(std::unique_ptr<object::Archive> &&f, bool forceHidden)
: InputFile(ArchiveKind, f->getMemoryBufferRef()), file(std::move(f)),
forceHidden(forceHidden) {}
void ArchiveFile::addLazySymbols() {
for (const object::Archive::Symbol &sym : file->symbols())
symtab->addLazyArchive(sym.getName(), this, sym);
}
static Expected<InputFile *>
loadArchiveMember(MemoryBufferRef mb, uint32_t modTime, StringRef archiveName,
uint64_t offsetInArchive, bool forceHidden) {
if (config->zeroModTime)
modTime = 0;
switch (identify_magic(mb.getBuffer())) {
case file_magic::macho_object:
return make<ObjFile>(mb, modTime, archiveName, /*lazy=*/false, forceHidden);
case file_magic::bitcode:
return make<BitcodeFile>(mb, archiveName, offsetInArchive, /*lazy=*/false,
forceHidden);
default:
return createStringError(inconvertibleErrorCode(),
mb.getBufferIdentifier() +
" has unhandled file type");
}
}
Error ArchiveFile::fetch(const object::Archive::Child &c, StringRef reason) {
if (!seen.insert(c.getChildOffset()).second)
return Error::success();
Expected<MemoryBufferRef> mb = c.getMemoryBufferRef();
if (!mb)
return mb.takeError();
// Thin archives refer to .o files, so --reproduce needs the .o files too.
if (tar && c.getParent()->isThin())
tar->append(relativeToRoot(CHECK(c.getFullName(), this)), mb->getBuffer());
Expected<TimePoint<std::chrono::seconds>> modTime = c.getLastModified();
if (!modTime)
return modTime.takeError();
Expected<InputFile *> file = loadArchiveMember(
*mb, toTimeT(*modTime), getName(), c.getChildOffset(), forceHidden);
if (!file)
return file.takeError();
inputFiles.insert(*file);
printArchiveMemberLoad(reason, *file);
return Error::success();
}
void ArchiveFile::fetch(const object::Archive::Symbol &sym) {
object::Archive::Child c =
CHECK(sym.getMember(), toString(this) +
": could not get 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;
// ld64 doesn't demangle sym here even with -demangle.
// Match that: intentionally don't call toMachOString().
if (Error e = fetch(c, symCopy.getName()))
error(toString(this) + ": could not get the member defining symbol " +
toMachOString(symCopy) + ": " + toString(std::move(e)));
}
static macho::Symbol *createBitcodeSymbol(const lto::InputFile::Symbol &objSym,
BitcodeFile &file) {
StringRef name = saver().save(objSym.getName());
if (objSym.isUndefined())
return symtab->addUndefined(name, &file, /*isWeakRef=*/objSym.isWeak());
// 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;
}
isPrivateExtern = isPrivateExtern || objSym.canBeOmittedFromSymbolTable() ||
file.forceHidden;
if (objSym.isCommon())
return symtab->addCommon(name, &file, objSym.getCommonSize(),
objSym.getCommonAlignment(), isPrivateExtern);
return symtab->addDefined(name, &file, /*isec=*/nullptr, /*value=*/0,
/*size=*/0, objSym.isWeak(), isPrivateExtern,
/*isThumb=*/false,
/*isReferencedDynamically=*/false,
/*noDeadStrip=*/false,
/*isWeakDefCanBeHidden=*/false);
}
BitcodeFile::BitcodeFile(MemoryBufferRef mb, StringRef archiveName,
uint64_t offsetInArchive, bool lazy, bool forceHidden)
: InputFile(BitcodeKind, mb, lazy), forceHidden(forceHidden) {
this->archiveName = std::string(archiveName);
std::string path = mb.getBufferIdentifier().str();
// ThinLTO assumes that all MemoryBufferRefs given to it have a unique
// name. If two members with the same name are provided, this causes a
// collision and ThinLTO can't proceed.
// So, we append the archive name to disambiguate two members with the same
// name from multiple different archives, and offset within the archive to
// disambiguate two members of the same name from a single archive.
MemoryBufferRef mbref(mb.getBuffer(),
saver().save(archiveName.empty()
? path
: archiveName +
sys::path::filename(path) +
utostr(offsetInArchive)));
obj = check(lto::InputFile::create(mbref));
if (lazy)
parseLazy();
else
parse();
}
void BitcodeFile::parse() {
// Convert LTO Symbols to LLD Symbols in order to perform resolution. The
// "winning" symbol will then be marked as Prevailing at LTO compilation
// time.
symbols.clear();
for (const lto::InputFile::Symbol &objSym : obj->symbols())
symbols.push_back(createBitcodeSymbol(objSym, *this));
}
void BitcodeFile::parseLazy() {
symbols.resize(obj->symbols().size());
for (auto it : llvm::enumerate(obj->symbols())) {
const lto::InputFile::Symbol &objSym = it.value();
if (!objSym.isUndefined()) {
symbols[it.index()] =
symtab->addLazyObject(saver().save(objSym.getName()), *this);
if (!lazy)
break;
}
}
}
void macho::extract(InputFile &file, StringRef reason) {
assert(file.lazy);
file.lazy = false;
printArchiveMemberLoad(reason, &file);
if (auto *bitcode = dyn_cast<BitcodeFile>(&file)) {
bitcode->parse();
} else {
auto &f = cast<ObjFile>(file);
if (target->wordSize == 8)
f.parse<LP64>();
else
f.parse<ILP32>();
}
}
template void ObjFile::parse<LP64>();
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