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llvm-project/lld/MachO/InputSection.cpp

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//===- InputSection.cpp ---------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include "InputSection.h"
#include "ConcatOutputSection.h"
#include "Config.h"
#include "InputFiles.h"
#include "OutputSegment.h"
#include "Symbols.h"
#include "SyntheticSections.h"
#include "Target.h"
#include "UnwindInfoSection.h"
#include "Writer.h"
#include "lld/Common/Memory.h"
#include "llvm/Support/Endian.h"
#include "llvm/Support/xxhash.h"
using namespace llvm;
using namespace llvm::MachO;
using namespace llvm::support;
using namespace lld;
using namespace lld::macho;
// Verify ConcatInputSection's size on 64-bit builds. The size of std::vector
// can differ based on STL debug levels (e.g. iterator debugging on MSVC's STL),
// so account for that.
static_assert(sizeof(void *) != 8 ||
sizeof(ConcatInputSection) == sizeof(std::vector<Reloc>) + 96,
"Try to minimize ConcatInputSection's size, we create many "
"instances of it");
std::vector<ConcatInputSection *> macho::inputSections;
uint64_t InputSection::getFileSize() const {
return isZeroFill(getFlags()) ? 0 : getSize();
}
uint64_t InputSection::getVA(uint64_t off) const {
return parent->addr + getOffset(off);
}
static uint64_t resolveSymbolVA(const Symbol *sym, uint8_t type) {
const RelocAttrs &relocAttrs = target->getRelocAttrs(type);
if (relocAttrs.hasAttr(RelocAttrBits::BRANCH))
return sym->resolveBranchVA();
if (relocAttrs.hasAttr(RelocAttrBits::GOT))
return sym->resolveGotVA();
if (relocAttrs.hasAttr(RelocAttrBits::TLV))
return sym->resolveTlvVA();
return sym->getVA();
}
std::string InputSection::getLocation(uint64_t off) const {
// First, try to find a symbol that's near the offset. Use it as a reference
// point.
for (size_t i = 0; i < symbols.size(); ++i)
if (symbols[i]->value <= off &&
(i + 1 == symbols.size() || symbols[i + 1]->value > off))
return (toString(getFile()) + ":(symbol " + symbols.front()->getName() +
"+0x" + Twine::utohexstr(off - symbols[i]->value) + ")")
.str();
// If that fails, use the section itself as a reference point.
for (const Subsection &subsec : section.subsections) {
if (subsec.isec == this) {
off += subsec.offset;
break;
}
}
return (toString(getFile()) + ":(" + getName() + "+0x" +
Twine::utohexstr(off) + ")")
.str();
}
// ICF needs to hash any section that might potentially be duplicated so
// that it can match on content rather than identity.
bool ConcatInputSection::isHashableForICF() const {
switch (sectionType(getFlags())) {
case S_REGULAR:
return true;
case S_CSTRING_LITERALS:
case S_4BYTE_LITERALS:
case S_8BYTE_LITERALS:
case S_16BYTE_LITERALS:
case S_LITERAL_POINTERS:
llvm_unreachable("found unexpected literal type in ConcatInputSection");
case S_ZEROFILL:
case S_GB_ZEROFILL:
case S_NON_LAZY_SYMBOL_POINTERS:
case S_LAZY_SYMBOL_POINTERS:
case S_SYMBOL_STUBS:
case S_MOD_INIT_FUNC_POINTERS:
case S_MOD_TERM_FUNC_POINTERS:
case S_COALESCED:
case S_INTERPOSING:
case S_DTRACE_DOF:
case S_LAZY_DYLIB_SYMBOL_POINTERS:
case S_THREAD_LOCAL_REGULAR:
case S_THREAD_LOCAL_ZEROFILL:
case S_THREAD_LOCAL_VARIABLES:
case S_THREAD_LOCAL_VARIABLE_POINTERS:
case S_THREAD_LOCAL_INIT_FUNCTION_POINTERS:
return false;
default:
llvm_unreachable("Section type");
}
}
void ConcatInputSection::hashForICF() {
assert(data.data()); // zeroFill section data has nullptr with non-zero size
assert(icfEqClass[0] == 0); // don't overwrite a unique ID!
// Turn-on the top bit to guarantee that valid hashes have no collisions
// with the small-integer unique IDs for ICF-ineligible sections
icfEqClass[0] = xxHash64(data) | (1ull << 63);
}
void ConcatInputSection::foldIdentical(ConcatInputSection *copy) {
align = std::max(align, copy->align);
copy->live = false;
copy->wasCoalesced = true;
copy->replacement = this;
// Merge the sorted vectors of symbols together.
auto it = symbols.begin();
for (auto copyIt = copy->symbols.begin(); copyIt != copy->symbols.end();) {
if (it == symbols.end()) {
symbols.push_back(*copyIt++);
it = symbols.end();
} else if ((*it)->value > (*copyIt)->value) {
std::swap(*it++, *copyIt);
} else {
++it;
}
}
copy->symbols.clear();
// Remove duplicate compact unwind info for symbols at the same address.
if (symbols.empty())
return;
it = symbols.begin();
uint64_t v = (*it)->value;
for (++it; it != symbols.end(); ++it) {
Defined *d = *it;
if (d->value == v)
d->unwindEntry = nullptr;
else
v = d->value;
}
}
void ConcatInputSection::writeTo(uint8_t *buf) {
assert(!shouldOmitFromOutput());
if (getFileSize() == 0)
return;
memcpy(buf, data.data(), data.size());
for (size_t i = 0; i < relocs.size(); i++) {
const Reloc &r = relocs[i];
uint8_t *loc = buf + r.offset;
uint64_t referentVA = 0;
if (target->hasAttr(r.type, RelocAttrBits::SUBTRAHEND)) {
const Symbol *fromSym = r.referent.get<Symbol *>();
const Reloc &minuend = relocs[++i];
uint64_t minuendVA;
if (const Symbol *toSym = minuend.referent.dyn_cast<Symbol *>())
minuendVA = toSym->getVA() + minuend.addend;
else {
auto *referentIsec = minuend.referent.get<InputSection *>();
assert(!::shouldOmitFromOutput(referentIsec));
minuendVA = referentIsec->getVA(minuend.addend);
}
referentVA = minuendVA - fromSym->getVA();
} else if (auto *referentSym = r.referent.dyn_cast<Symbol *>()) {
if (target->hasAttr(r.type, RelocAttrBits::LOAD) &&
!referentSym->isInGot())
target->relaxGotLoad(loc, r.type);
referentVA = resolveSymbolVA(referentSym, r.type) + r.addend;
if (isThreadLocalVariables(getFlags())) {
// References from thread-local variable sections are treated as offsets
// relative to the start of the thread-local data memory area, which
// is initialized via copying all the TLV data sections (which are all
// contiguous).
if (isa<Defined>(referentSym))
referentVA -= firstTLVDataSection->addr;
}
} else if (auto *referentIsec = r.referent.dyn_cast<InputSection *>()) {
assert(!::shouldOmitFromOutput(referentIsec));
referentVA = referentIsec->getVA(r.addend);
}
target->relocateOne(loc, r, referentVA, getVA() + r.offset);
}
}
ConcatInputSection *macho::makeSyntheticInputSection(StringRef segName,
StringRef sectName,
uint32_t flags,
ArrayRef<uint8_t> data,
uint32_t align) {
Section &section =
*make<Section>(/*file=*/nullptr, segName, sectName, flags, /*addr=*/0);
auto isec = make<ConcatInputSection>(section, data, align);
section.subsections.push_back({0, isec});
return isec;
}
void CStringInputSection::splitIntoPieces() {
size_t off = 0;
StringRef s = toStringRef(data);
while (!s.empty()) {
size_t end = s.find(0);
if (end == StringRef::npos)
fatal(getLocation(off) + ": string is not null terminated");
size_t size = end + 1;
uint32_t hash = config->dedupLiterals ? xxHash64(s.substr(0, size)) : 0;
pieces.emplace_back(off, hash);
s = s.substr(size);
off += size;
}
}
StringPiece &CStringInputSection::getStringPiece(uint64_t off) {
if (off >= data.size())
fatal(toString(this) + ": offset is outside the section");
auto it =
partition_point(pieces, [=](StringPiece p) { return p.inSecOff <= off; });
return it[-1];
}
const StringPiece &CStringInputSection::getStringPiece(uint64_t off) const {
return const_cast<CStringInputSection *>(this)->getStringPiece(off);
}
uint64_t CStringInputSection::getOffset(uint64_t off) const {
const StringPiece &piece = getStringPiece(off);
uint64_t addend = off - piece.inSecOff;
return piece.outSecOff + addend;
}
WordLiteralInputSection::WordLiteralInputSection(const Section &section,
ArrayRef<uint8_t> data,
uint32_t align)
: InputSection(WordLiteralKind, section, data, align) {
switch (sectionType(getFlags())) {
case S_4BYTE_LITERALS:
power2LiteralSize = 2;
break;
case S_8BYTE_LITERALS:
power2LiteralSize = 3;
break;
case S_16BYTE_LITERALS:
power2LiteralSize = 4;
break;
default:
llvm_unreachable("invalid literal section type");
}
live.resize(data.size() >> power2LiteralSize, !config->deadStrip);
}
uint64_t WordLiteralInputSection::getOffset(uint64_t off) const {
auto *osec = cast<WordLiteralSection>(parent);
const uintptr_t buf = reinterpret_cast<uintptr_t>(data.data());
switch (sectionType(getFlags())) {
case S_4BYTE_LITERALS:
return osec->getLiteral4Offset(buf + (off & ~3LLU)) | (off & 3);
case S_8BYTE_LITERALS:
return osec->getLiteral8Offset(buf + (off & ~7LLU)) | (off & 7);
case S_16BYTE_LITERALS:
return osec->getLiteral16Offset(buf + (off & ~15LLU)) | (off & 15);
default:
llvm_unreachable("invalid literal section type");
}
}
bool macho::isCodeSection(const InputSection *isec) {
uint32_t type = sectionType(isec->getFlags());
if (type != S_REGULAR && type != S_COALESCED)
return false;
uint32_t attr = isec->getFlags() & SECTION_ATTRIBUTES_USR;
if (attr == S_ATTR_PURE_INSTRUCTIONS)
return true;
if (isec->getSegName() == segment_names::text)
return StringSwitch<bool>(isec->getName())
.Cases(section_names::textCoalNt, section_names::staticInit, true)
.Default(false);
return false;
}
bool macho::isCfStringSection(const InputSection *isec) {
return isec->getName() == section_names::cfString &&
isec->getSegName() == segment_names::data;
}
std::string lld::toString(const InputSection *isec) {
return (toString(isec->getFile()) + ":(" + isec->getName() + ")").str();
}
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