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llvm-project/lld/COFF/Writer.cpp

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//===- Writer.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 "Writer.h"
#include "Config.h"
#include "DLL.h"
#include "InputFiles.h"
#include "MapFile.h"
#include "PDB.h"
#include "SymbolTable.h"
#include "Symbols.h"
#include "lld/Common/ErrorHandler.h"
#include "lld/Common/Memory.h"
#include "lld/Common/Threads.h"
#include "lld/Common/Timer.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/StringSwitch.h"
#include "llvm/Support/BinaryStreamReader.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/Endian.h"
#include "llvm/Support/FileOutputBuffer.h"
#include "llvm/Support/Parallel.h"
#include "llvm/Support/Path.h"
#include "llvm/Support/RandomNumberGenerator.h"
#include "llvm/Support/xxhash.h"
#include <algorithm>
#include <cstdio>
#include <map>
#include <memory>
#include <utility>
using namespace llvm;
using namespace llvm::COFF;
using namespace llvm::object;
using namespace llvm::support;
using namespace llvm::support::endian;
using namespace lld;
using namespace lld::coff;
/* To re-generate DOSProgram:
$ cat > /tmp/DOSProgram.asm
org 0
; Copy cs to ds.
push cs
pop ds
; Point ds:dx at the $-terminated string.
mov dx, str
; Int 21/AH=09h: Write string to standard output.
mov ah, 0x9
int 0x21
; Int 21/AH=4Ch: Exit with return code (in AL).
mov ax, 0x4C01
int 0x21
str:
db 'This program cannot be run in DOS mode.$'
align 8, db 0
$ nasm -fbin /tmp/DOSProgram.asm -o /tmp/DOSProgram.bin
$ xxd -i /tmp/DOSProgram.bin
*/
static unsigned char dosProgram[] = {
0x0e, 0x1f, 0xba, 0x0e, 0x00, 0xb4, 0x09, 0xcd, 0x21, 0xb8, 0x01, 0x4c,
0xcd, 0x21, 0x54, 0x68, 0x69, 0x73, 0x20, 0x70, 0x72, 0x6f, 0x67, 0x72,
0x61, 0x6d, 0x20, 0x63, 0x61, 0x6e, 0x6e, 0x6f, 0x74, 0x20, 0x62, 0x65,
0x20, 0x72, 0x75, 0x6e, 0x20, 0x69, 0x6e, 0x20, 0x44, 0x4f, 0x53, 0x20,
0x6d, 0x6f, 0x64, 0x65, 0x2e, 0x24, 0x00, 0x00
};
static_assert(sizeof(dosProgram) % 8 == 0,
"DOSProgram size must be multiple of 8");
static const int dosStubSize = sizeof(dos_header) + sizeof(dosProgram);
static_assert(dosStubSize % 8 == 0, "DOSStub size must be multiple of 8");
static const int numberOfDataDirectory = 16;
// Global vector of all output sections. After output sections are finalized,
// this can be indexed by Chunk::getOutputSection.
static std::vector<OutputSection *> outputSections;
OutputSection *Chunk::getOutputSection() const {
return osidx == 0 ? nullptr : outputSections[osidx - 1];
}
namespace {
class DebugDirectoryChunk : public NonSectionChunk {
public:
DebugDirectoryChunk(const std::vector<Chunk *> &r, bool writeRepro)
: records(r), writeRepro(writeRepro) {}
size_t getSize() const override {
return (records.size() + int(writeRepro)) * sizeof(debug_directory);
}
void writeTo(uint8_t *b) const override {
auto *d = reinterpret_cast<debug_directory *>(b);
for (const Chunk *record : records) {
OutputSection *os = record->getOutputSection();
uint64_t offs = os->getFileOff() + (record->getRVA() - os->getRVA());
fillEntry(d, COFF::IMAGE_DEBUG_TYPE_CODEVIEW, record->getSize(),
record->getRVA(), offs);
++d;
}
if (writeRepro) {
// FIXME: The COFF spec allows either a 0-sized entry to just say
// "the timestamp field is really a hash", or a 4-byte size field
// followed by that many bytes containing a longer hash (with the
// lowest 4 bytes usually being the timestamp in little-endian order).
// Consider storing the full 8 bytes computed by xxHash64 here.
fillEntry(d, COFF::IMAGE_DEBUG_TYPE_REPRO, 0, 0, 0);
}
}
void setTimeDateStamp(uint32_t timeDateStamp) {
for (support::ulittle32_t *tds : timeDateStamps)
*tds = timeDateStamp;
}
private:
void fillEntry(debug_directory *d, COFF::DebugType debugType, size_t size,
uint64_t rva, uint64_t offs) const {
d->Characteristics = 0;
d->TimeDateStamp = 0;
d->MajorVersion = 0;
d->MinorVersion = 0;
d->Type = debugType;
d->SizeOfData = size;
d->AddressOfRawData = rva;
d->PointerToRawData = offs;
timeDateStamps.push_back(&d->TimeDateStamp);
}
mutable std::vector<support::ulittle32_t *> timeDateStamps;
const std::vector<Chunk *> &records;
bool writeRepro;
};
class CVDebugRecordChunk : public NonSectionChunk {
public:
size_t getSize() const override {
return sizeof(codeview::DebugInfo) + config->pdbAltPath.size() + 1;
}
void writeTo(uint8_t *b) const override {
// Save off the DebugInfo entry to backfill the file signature (build id)
// in Writer::writeBuildId
buildId = reinterpret_cast<codeview::DebugInfo *>(b);
// variable sized field (PDB Path)
char *p = reinterpret_cast<char *>(b + sizeof(*buildId));
if (!config->pdbAltPath.empty())
memcpy(p, config->pdbAltPath.data(), config->pdbAltPath.size());
p[config->pdbAltPath.size()] = '\0';
}
mutable codeview::DebugInfo *buildId = nullptr;
};
// PartialSection represents a group of chunks that contribute to an
// OutputSection. Collating a collection of PartialSections of same name and
// characteristics constitutes the OutputSection.
class PartialSectionKey {
public:
StringRef name;
unsigned characteristics;
bool operator<(const PartialSectionKey &other) const {
int c = name.compare(other.name);
if (c == 1)
return false;
if (c == 0)
return characteristics < other.characteristics;
return true;
}
};
// The writer writes a SymbolTable result to a file.
class Writer {
public:
Writer() : buffer(errorHandler().outputBuffer) {}
void run();
private:
void createSections();
void createMiscChunks();
void createImportTables();
void appendImportThunks();
void locateImportTables();
void createExportTable();
void mergeSections();
void removeUnusedSections();
void assignAddresses();
void finalizeAddresses();
void removeEmptySections();
void assignOutputSectionIndices();
void createSymbolAndStringTable();
void openFile(StringRef outputPath);
template <typename PEHeaderTy> void writeHeader();
void createSEHTable();
void createRuntimePseudoRelocs();
void insertCtorDtorSymbols();
void createGuardCFTables();
void markSymbolsForRVATable(ObjFile *file,
ArrayRef<SectionChunk *> symIdxChunks,
SymbolRVASet &tableSymbols);
void maybeAddRVATable(SymbolRVASet tableSymbols, StringRef tableSym,
StringRef countSym);
void setSectionPermissions();
void writeSections();
void writeBuildId();
void sortExceptionTable();
void sortCRTSectionChunks(std::vector<Chunk *> &chunks);
void addSyntheticIdata();
void fixPartialSectionChars(StringRef name, uint32_t chars);
bool fixGnuImportChunks();
PartialSection *createPartialSection(StringRef name, uint32_t outChars);
PartialSection *findPartialSection(StringRef name, uint32_t outChars);
llvm::Optional<coff_symbol16> createSymbol(Defined *d);
size_t addEntryToStringTable(StringRef str);
OutputSection *findSection(StringRef name);
void addBaserels();
void addBaserelBlocks(std::vector<Baserel> &v);
uint32_t getSizeOfInitializedData();
std::unique_ptr<FileOutputBuffer> &buffer;
std::map<PartialSectionKey, PartialSection *> partialSections;
std::vector<char> strtab;
std::vector<llvm::object::coff_symbol16> outputSymtab;
IdataContents idata;
Chunk *importTableStart = nullptr;
uint64_t importTableSize = 0;
Chunk *edataStart = nullptr;
Chunk *edataEnd = nullptr;
Chunk *iatStart = nullptr;
uint64_t iatSize = 0;
DelayLoadContents delayIdata;
EdataContents edata;
bool setNoSEHCharacteristic = false;
DebugDirectoryChunk *debugDirectory = nullptr;
std::vector<Chunk *> debugRecords;
CVDebugRecordChunk *buildId = nullptr;
ArrayRef<uint8_t> sectionTable;
uint64_t fileSize;
uint32_t pointerToSymbolTable = 0;
uint64_t sizeOfImage;
uint64_t sizeOfHeaders;
OutputSection *textSec;
OutputSection *rdataSec;
OutputSection *buildidSec;
OutputSection *dataSec;
OutputSection *pdataSec;
OutputSection *idataSec;
OutputSection *edataSec;
OutputSection *didatSec;
OutputSection *rsrcSec;
OutputSection *relocSec;
OutputSection *ctorsSec;
OutputSection *dtorsSec;
// The first and last .pdata sections in the output file.
//
// We need to keep track of the location of .pdata in whichever section it
// gets merged into so that we can sort its contents and emit a correct data
// directory entry for the exception table. This is also the case for some
// other sections (such as .edata) but because the contents of those sections
// are entirely linker-generated we can keep track of their locations using
// the chunks that the linker creates. All .pdata chunks come from input
// files, so we need to keep track of them separately.
Chunk *firstPdata = nullptr;
Chunk *lastPdata;
};
} // anonymous namespace
namespace lld {
namespace coff {
static Timer codeLayoutTimer("Code Layout", Timer::root());
static Timer diskCommitTimer("Commit Output File", Timer::root());
void writeResult() { Writer().run(); }
void OutputSection::addChunk(Chunk *c) {
chunks.push_back(c);
}
void OutputSection::insertChunkAtStart(Chunk *c) {
chunks.insert(chunks.begin(), c);
}
void OutputSection::setPermissions(uint32_t c) {
header.Characteristics &= ~permMask;
header.Characteristics |= c;
}
void OutputSection::merge(OutputSection *other) {
chunks.insert(chunks.end(), other->chunks.begin(), other->chunks.end());
other->chunks.clear();
contribSections.insert(contribSections.end(), other->contribSections.begin(),
other->contribSections.end());
other->contribSections.clear();
}
// Write the section header to a given buffer.
void OutputSection::writeHeaderTo(uint8_t *buf) {
auto *hdr = reinterpret_cast<coff_section *>(buf);
*hdr = header;
if (stringTableOff) {
// If name is too long, write offset into the string table as a name.
sprintf(hdr->Name, "/%d", stringTableOff);
} else {
assert(!config->debug || name.size() <= COFF::NameSize ||
(hdr->Characteristics & IMAGE_SCN_MEM_DISCARDABLE) == 0);
strncpy(hdr->Name, name.data(),
std::min(name.size(), (size_t)COFF::NameSize));
}
}
void OutputSection::addContributingPartialSection(PartialSection *sec) {
contribSections.push_back(sec);
}
} // namespace coff
} // namespace lld
// Check whether the target address S is in range from a relocation
// of type relType at address P.
static bool isInRange(uint16_t relType, uint64_t s, uint64_t p, int margin) {
if (config->machine == ARMNT) {
int64_t diff = AbsoluteDifference(s, p + 4) + margin;
switch (relType) {
case IMAGE_REL_ARM_BRANCH20T:
return isInt<21>(diff);
case IMAGE_REL_ARM_BRANCH24T:
case IMAGE_REL_ARM_BLX23T:
return isInt<25>(diff);
default:
return true;
}
} else if (config->machine == ARM64) {
int64_t diff = AbsoluteDifference(s, p) + margin;
switch (relType) {
case IMAGE_REL_ARM64_BRANCH26:
return isInt<28>(diff);
case IMAGE_REL_ARM64_BRANCH19:
return isInt<21>(diff);
case IMAGE_REL_ARM64_BRANCH14:
return isInt<16>(diff);
default:
return true;
}
} else {
llvm_unreachable("Unexpected architecture");
}
}
// Return the last thunk for the given target if it is in range,
// or create a new one.
static std::pair<Defined *, bool>
getThunk(DenseMap<uint64_t, Defined *> &lastThunks, Defined *target, uint64_t p,
uint16_t type, int margin) {
Defined *&lastThunk = lastThunks[target->getRVA()];
if (lastThunk && isInRange(type, lastThunk->getRVA(), p, margin))
return {lastThunk, false};
Chunk *c;
switch (config->machine) {
case ARMNT:
c = make<RangeExtensionThunkARM>(target);
break;
case ARM64:
c = make<RangeExtensionThunkARM64>(target);
break;
default:
llvm_unreachable("Unexpected architecture");
}
Defined *d = make<DefinedSynthetic>("", c);
lastThunk = d;
return {d, true};
}
// This checks all relocations, and for any relocation which isn't in range
// it adds a thunk after the section chunk that contains the relocation.
// If the latest thunk for the specific target is in range, that is used
// instead of creating a new thunk. All range checks are done with the
// specified margin, to make sure that relocations that originally are in
// range, but only barely, also get thunks - in case other added thunks makes
// the target go out of range.
//
// After adding thunks, we verify that all relocations are in range (with
// no extra margin requirements). If this failed, we restart (throwing away
// the previously created thunks) and retry with a wider margin.
static bool createThunks(OutputSection *os, int margin) {
bool addressesChanged = false;
DenseMap<uint64_t, Defined *> lastThunks;
DenseMap<std::pair<ObjFile *, Defined *>, uint32_t> thunkSymtabIndices;
size_t thunksSize = 0;
// Recheck Chunks.size() each iteration, since we can insert more
// elements into it.
for (size_t i = 0; i != os->chunks.size(); ++i) {
SectionChunk *sc = dyn_cast_or_null<SectionChunk>(os->chunks[i]);
if (!sc)
continue;
size_t thunkInsertionSpot = i + 1;
// Try to get a good enough estimate of where new thunks will be placed.
// Offset this by the size of the new thunks added so far, to make the
// estimate slightly better.
size_t thunkInsertionRVA = sc->getRVA() + sc->getSize() + thunksSize;
ObjFile *file = sc->file;
std::vector<std::pair<uint32_t, uint32_t>> relocReplacements;
ArrayRef<coff_relocation> originalRelocs =
file->getCOFFObj()->getRelocations(sc->header);
for (size_t j = 0, e = originalRelocs.size(); j < e; ++j) {
const coff_relocation &rel = originalRelocs[j];
Symbol *relocTarget = file->getSymbol(rel.SymbolTableIndex);
// The estimate of the source address P should be pretty accurate,
// but we don't know whether the target Symbol address should be
// offset by thunksSize or not (or by some of thunksSize but not all of
// it), giving us some uncertainty once we have added one thunk.
uint64_t p = sc->getRVA() + rel.VirtualAddress + thunksSize;
Defined *sym = dyn_cast_or_null<Defined>(relocTarget);
if (!sym)
continue;
uint64_t s = sym->getRVA();
if (isInRange(rel.Type, s, p, margin))
continue;
// If the target isn't in range, hook it up to an existing or new
// thunk.
Defined *thunk;
bool wasNew;
std::tie(thunk, wasNew) = getThunk(lastThunks, sym, p, rel.Type, margin);
if (wasNew) {
Chunk *thunkChunk = thunk->getChunk();
thunkChunk->setRVA(
thunkInsertionRVA); // Estimate of where it will be located.
os->chunks.insert(os->chunks.begin() + thunkInsertionSpot, thunkChunk);
thunkInsertionSpot++;
thunksSize += thunkChunk->getSize();
thunkInsertionRVA += thunkChunk->getSize();
addressesChanged = true;
}
// To redirect the relocation, add a symbol to the parent object file's
// symbol table, and replace the relocation symbol table index with the
// new index.
auto insertion = thunkSymtabIndices.insert({{file, thunk}, ~0U});
uint32_t &thunkSymbolIndex = insertion.first->second;
if (insertion.second)
thunkSymbolIndex = file->addRangeThunkSymbol(thunk);
relocReplacements.push_back({j, thunkSymbolIndex});
}
// Get a writable copy of this section's relocations so they can be
// modified. If the relocations point into the object file, allocate new
// memory. Otherwise, this must be previously allocated memory that can be
// modified in place.
ArrayRef<coff_relocation> curRelocs = sc->getRelocs();
MutableArrayRef<coff_relocation> newRelocs;
if (originalRelocs.data() == curRelocs.data()) {
newRelocs = makeMutableArrayRef(
bAlloc.Allocate<coff_relocation>(originalRelocs.size()),
originalRelocs.size());
} else {
newRelocs = makeMutableArrayRef(
const_cast<coff_relocation *>(curRelocs.data()), curRelocs.size());
}
// Copy each relocation, but replace the symbol table indices which need
// thunks.
auto nextReplacement = relocReplacements.begin();
auto endReplacement = relocReplacements.end();
for (size_t i = 0, e = originalRelocs.size(); i != e; ++i) {
newRelocs[i] = originalRelocs[i];
if (nextReplacement != endReplacement && nextReplacement->first == i) {
newRelocs[i].SymbolTableIndex = nextReplacement->second;
++nextReplacement;
}
}
sc->setRelocs(newRelocs);
}
return addressesChanged;
}
// Verify that all relocations are in range, with no extra margin requirements.
static bool verifyRanges(const std::vector<Chunk *> chunks) {
for (Chunk *c : chunks) {
SectionChunk *sc = dyn_cast_or_null<SectionChunk>(c);
if (!sc)
continue;
ArrayRef<coff_relocation> relocs = sc->getRelocs();
for (size_t j = 0, e = relocs.size(); j < e; ++j) {
const coff_relocation &rel = relocs[j];
Symbol *relocTarget = sc->file->getSymbol(rel.SymbolTableIndex);
Defined *sym = dyn_cast_or_null<Defined>(relocTarget);
if (!sym)
continue;
uint64_t p = sc->getRVA() + rel.VirtualAddress;
uint64_t s = sym->getRVA();
if (!isInRange(rel.Type, s, p, 0))
return false;
}
}
return true;
}
// Assign addresses and add thunks if necessary.
void Writer::finalizeAddresses() {
assignAddresses();
if (config->machine != ARMNT && config->machine != ARM64)
return;
size_t origNumChunks = 0;
for (OutputSection *sec : outputSections) {
sec->origChunks = sec->chunks;
origNumChunks += sec->chunks.size();
}
int pass = 0;
int margin = 1024 * 100;
while (true) {
// First check whether we need thunks at all, or if the previous pass of
// adding them turned out ok.
bool rangesOk = true;
size_t numChunks = 0;
for (OutputSection *sec : outputSections) {
if (!verifyRanges(sec->chunks)) {
rangesOk = false;
break;
}
numChunks += sec->chunks.size();
}
if (rangesOk) {
if (pass > 0)
log("Added " + Twine(numChunks - origNumChunks) + " thunks with " +
"margin " + Twine(margin) + " in " + Twine(pass) + " passes");
return;
}
if (pass >= 10)
fatal("adding thunks hasn't converged after " + Twine(pass) + " passes");
if (pass > 0) {
// If the previous pass didn't work out, reset everything back to the
// original conditions before retrying with a wider margin. This should
// ideally never happen under real circumstances.
for (OutputSection *sec : outputSections)
sec->chunks = sec->origChunks;
margin *= 2;
}
// Try adding thunks everywhere where it is needed, with a margin
// to avoid things going out of range due to the added thunks.
bool addressesChanged = false;
for (OutputSection *sec : outputSections)
addressesChanged |= createThunks(sec, margin);
// If the verification above thought we needed thunks, we should have
// added some.
assert(addressesChanged);
// Recalculate the layout for the whole image (and verify the ranges at
// the start of the next round).
assignAddresses();
pass++;
}
}
// The main function of the writer.
void Writer::run() {
ScopedTimer t1(codeLayoutTimer);
createImportTables();
createSections();
createMiscChunks();
appendImportThunks();
createExportTable();
mergeSections();
removeUnusedSections();
finalizeAddresses();
removeEmptySections();
assignOutputSectionIndices();
setSectionPermissions();
createSymbolAndStringTable();
if (fileSize > UINT32_MAX)
fatal("image size (" + Twine(fileSize) + ") " +
"exceeds maximum allowable size (" + Twine(UINT32_MAX) + ")");
openFile(config->outputFile);
if (config->is64()) {
writeHeader<pe32plus_header>();
} else {
writeHeader<pe32_header>();
}
writeSections();
sortExceptionTable();
t1.stop();
if (!config->pdbPath.empty() && config->debug) {
assert(buildId);
createPDB(symtab, outputSections, sectionTable, buildId->buildId);
}
writeBuildId();
writeMapFile(outputSections);
if (errorCount())
return;
ScopedTimer t2(diskCommitTimer);
if (auto e = buffer->commit())
fatal("failed to write the output file: " + toString(std::move(e)));
}
static StringRef getOutputSectionName(StringRef name) {
StringRef s = name.split('$').first;
// Treat a later period as a separator for MinGW, for sections like
// ".ctors.01234".
return s.substr(0, s.find('.', 1));
}
// For /order.
static void sortBySectionOrder(std::vector<Chunk *> &chunks) {
auto getPriority = [](const Chunk *c) {
if (auto *sec = dyn_cast<SectionChunk>(c))
if (sec->sym)
return config->order.lookup(sec->sym->getName());
return 0;
};
llvm::stable_sort(chunks, [=](const Chunk *a, const Chunk *b) {
return getPriority(a) < getPriority(b);
});
}
// Change the characteristics of existing PartialSections that belong to the
// section Name to Chars.
void Writer::fixPartialSectionChars(StringRef name, uint32_t chars) {
for (auto it : partialSections) {
PartialSection *pSec = it.second;
StringRef curName = pSec->name;
if (!curName.consume_front(name) ||
(!curName.empty() && !curName.startswith("$")))
continue;
if (pSec->characteristics == chars)
continue;
PartialSection *destSec = createPartialSection(pSec->name, chars);
destSec->chunks.insert(destSec->chunks.end(), pSec->chunks.begin(),
pSec->chunks.end());
pSec->chunks.clear();
}
}
// Sort concrete section chunks from GNU import libraries.
//
// GNU binutils doesn't use short import files, but instead produces import
// libraries that consist of object files, with section chunks for the .idata$*
// sections. These are linked just as regular static libraries. Each import
// library consists of one header object, one object file for every imported
// symbol, and one trailer object. In order for the .idata tables/lists to
// be formed correctly, the section chunks within each .idata$* section need
// to be grouped by library, and sorted alphabetically within each library
// (which makes sure the header comes first and the trailer last).
bool Writer::fixGnuImportChunks() {
uint32_t rdata = IMAGE_SCN_CNT_INITIALIZED_DATA | IMAGE_SCN_MEM_READ;
// Make sure all .idata$* section chunks are mapped as RDATA in order to
// be sorted into the same sections as our own synthesized .idata chunks.
fixPartialSectionChars(".idata", rdata);
bool hasIdata = false;
// Sort all .idata$* chunks, grouping chunks from the same library,
// with alphabetical ordering of the object fils within a library.
for (auto it : partialSections) {
PartialSection *pSec = it.second;
if (!pSec->name.startswith(".idata"))
continue;
if (!pSec->chunks.empty())
hasIdata = true;
llvm::stable_sort(pSec->chunks, [&](Chunk *s, Chunk *t) {
SectionChunk *sc1 = dyn_cast_or_null<SectionChunk>(s);
SectionChunk *sc2 = dyn_cast_or_null<SectionChunk>(t);
if (!sc1 || !sc2) {
// if SC1, order them ascending. If SC2 or both null,
// S is not less than T.
return sc1 != nullptr;
}
// Make a string with "libraryname/objectfile" for sorting, achieving
// both grouping by library and sorting of objects within a library,
// at once.
std::string key1 =
(sc1->file->parentName + "/" + sc1->file->getName()).str();
std::string key2 =
(sc2->file->parentName + "/" + sc2->file->getName()).str();
return key1 < key2;
});
}
return hasIdata;
}
// Add generated idata chunks, for imported symbols and DLLs, and a
// terminator in .idata$2.
void Writer::addSyntheticIdata() {
uint32_t rdata = IMAGE_SCN_CNT_INITIALIZED_DATA | IMAGE_SCN_MEM_READ;
idata.create();
// Add the .idata content in the right section groups, to allow
// chunks from other linked in object files to be grouped together.
// See Microsoft PE/COFF spec 5.4 for details.
auto add = [&](StringRef n, std::vector<Chunk *> &v) {
PartialSection *pSec = createPartialSection(n, rdata);
pSec->chunks.insert(pSec->chunks.end(), v.begin(), v.end());
};
// The loader assumes a specific order of data.
// Add each type in the correct order.
add(".idata$2", idata.dirs);
add(".idata$4", idata.lookups);
add(".idata$5", idata.addresses);
add(".idata$6", idata.hints);
add(".idata$7", idata.dllNames);
}
// Locate the first Chunk and size of the import directory list and the
// IAT.
void Writer::locateImportTables() {
uint32_t rdata = IMAGE_SCN_CNT_INITIALIZED_DATA | IMAGE_SCN_MEM_READ;
if (PartialSection *importDirs = findPartialSection(".idata$2", rdata)) {
if (!importDirs->chunks.empty())
importTableStart = importDirs->chunks.front();
for (Chunk *c : importDirs->chunks)
importTableSize += c->getSize();
}
if (PartialSection *importAddresses = findPartialSection(".idata$5", rdata)) {
if (!importAddresses->chunks.empty())
iatStart = importAddresses->chunks.front();
for (Chunk *c : importAddresses->chunks)
iatSize += c->getSize();
}
}
// Return whether a SectionChunk's suffix (the dollar and any trailing
// suffix) should be removed and sorted into the main suffixless
// PartialSection.
static bool shouldStripSectionSuffix(SectionChunk *sc, StringRef name) {
// On MinGW, comdat groups are formed by putting the comdat group name
// after the '$' in the section name. For .eh_frame$<symbol>, that must
// still be sorted before the .eh_frame trailer from crtend.o, thus just
// strip the section name trailer. For other sections, such as
// .tls$$<symbol> (where non-comdat .tls symbols are otherwise stored in
// ".tls$"), they must be strictly sorted after .tls. And for the
// hypothetical case of comdat .CRT$XCU, we definitely need to keep the
// suffix for sorting. Thus, to play it safe, only strip the suffix for
// the standard sections.
if (!config->mingw)
return false;
if (!sc || !sc->isCOMDAT())
return false;
return name.startswith(".text$") || name.startswith(".data$") ||
name.startswith(".rdata$") || name.startswith(".pdata$") ||
name.startswith(".xdata$") || name.startswith(".eh_frame$");
}
// Create output section objects and add them to OutputSections.
void Writer::createSections() {
// First, create the builtin sections.
const uint32_t data = IMAGE_SCN_CNT_INITIALIZED_DATA;
const uint32_t bss = IMAGE_SCN_CNT_UNINITIALIZED_DATA;
const uint32_t code = IMAGE_SCN_CNT_CODE;
const uint32_t discardable = IMAGE_SCN_MEM_DISCARDABLE;
const uint32_t r = IMAGE_SCN_MEM_READ;
const uint32_t w = IMAGE_SCN_MEM_WRITE;
const uint32_t x = IMAGE_SCN_MEM_EXECUTE;
SmallDenseMap<std::pair<StringRef, uint32_t>, OutputSection *> sections;
auto createSection = [&](StringRef name, uint32_t outChars) {
OutputSection *&sec = sections[{name, outChars}];
if (!sec) {
sec = make<OutputSection>(name, outChars);
outputSections.push_back(sec);
}
return sec;
};
// Try to match the section order used by link.exe.
textSec = createSection(".text", code | r | x);
createSection(".bss", bss | r | w);
rdataSec = createSection(".rdata", data | r);
buildidSec = createSection(".buildid", data | r);
dataSec = createSection(".data", data | r | w);
pdataSec = createSection(".pdata", data | r);
idataSec = createSection(".idata", data | r);
edataSec = createSection(".edata", data | r);
didatSec = createSection(".didat", data | r);
rsrcSec = createSection(".rsrc", data | r);
relocSec = createSection(".reloc", data | discardable | r);
ctorsSec = createSection(".ctors", data | r | w);
dtorsSec = createSection(".dtors", data | r | w);
// Then bin chunks by name and output characteristics.
for (Chunk *c : symtab->getChunks()) {
auto *sc = dyn_cast<SectionChunk>(c);
if (sc && !sc->live) {
if (config->verbose)
sc->printDiscardedMessage();
continue;
}
StringRef name = c->getSectionName();
if (shouldStripSectionSuffix(sc, name))
name = name.split('$').first;
PartialSection *pSec = createPartialSection(name,
c->getOutputCharacteristics());
pSec->chunks.push_back(c);
}
fixPartialSectionChars(".rsrc", data | r);
fixPartialSectionChars(".edata", data | r);
// Even in non MinGW cases, we might need to link against GNU import
// libraries.
bool hasIdata = fixGnuImportChunks();
if (!idata.empty())
hasIdata = true;
if (hasIdata)
addSyntheticIdata();
// Process an /order option.
if (!config->order.empty())
for (auto it : partialSections)
sortBySectionOrder(it.second->chunks);
if (hasIdata)
locateImportTables();
// Then create an OutputSection for each section.
// '$' and all following characters in input section names are
// discarded when determining output section. So, .text$foo
// contributes to .text, for example. See PE/COFF spec 3.2.
for (auto it : partialSections) {
PartialSection *pSec = it.second;
StringRef name = getOutputSectionName(pSec->name);
uint32_t outChars = pSec->characteristics;
if (name == ".CRT") {
// In link.exe, there is a special case for the I386 target where .CRT
// sections are treated as if they have output characteristics DATA | R if
// their characteristics are DATA | R | W. This implements the same
// special case for all architectures.
outChars = data | r;
log("Processing section " + pSec->name + " -> " + name);
sortCRTSectionChunks(pSec->chunks);
}
OutputSection *sec = createSection(name, outChars);
for (Chunk *c : pSec->chunks)
sec->addChunk(c);
sec->addContributingPartialSection(pSec);
}
// Finally, move some output sections to the end.
auto sectionOrder = [&](const OutputSection *s) {
// Move DISCARDABLE (or non-memory-mapped) sections to the end of file
// because the loader cannot handle holes. Stripping can remove other
// discardable ones than .reloc, which is first of them (created early).
if (s->header.Characteristics & IMAGE_SCN_MEM_DISCARDABLE)
return 2;
// .rsrc should come at the end of the non-discardable sections because its
// size may change by the Win32 UpdateResources() function, causing
// subsequent sections to move (see https://crbug.com/827082).
if (s == rsrcSec)
return 1;
return 0;
};
llvm::stable_sort(outputSections,
[&](const OutputSection *s, const OutputSection *t) {
return sectionOrder(s) < sectionOrder(t);
});
}
void Writer::createMiscChunks() {
for (MergeChunk *p : MergeChunk::instances) {
if (p) {
p->finalizeContents();
rdataSec->addChunk(p);
}
}
// Create thunks for locally-dllimported symbols.
if (!symtab->localImportChunks.empty()) {
for (Chunk *c : symtab->localImportChunks)
rdataSec->addChunk(c);
}
// Create Debug Information Chunks
OutputSection *debugInfoSec = config->mingw ? buildidSec : rdataSec;
if (config->debug || config->repro) {
debugDirectory = make<DebugDirectoryChunk>(debugRecords, config->repro);
debugInfoSec->addChunk(debugDirectory);
}
if (config->debug) {
// Make a CVDebugRecordChunk even when /DEBUG:CV is not specified. We
// output a PDB no matter what, and this chunk provides the only means of
// allowing a debugger to match a PDB and an executable. So we need it even
// if we're ultimately not going to write CodeView data to the PDB.
buildId = make<CVDebugRecordChunk>();
debugRecords.push_back(buildId);
for (Chunk *c : debugRecords)
debugInfoSec->addChunk(c);
}
// Create SEH table. x86-only.
if (config->safeSEH)
createSEHTable();
// Create /guard:cf tables if requested.
if (config->guardCF != GuardCFLevel::Off)
createGuardCFTables();
if (config->mingw) {
createRuntimePseudoRelocs();
insertCtorDtorSymbols();
}
}
// Create .idata section for the DLL-imported symbol table.
// The format of this section is inherently Windows-specific.
// IdataContents class abstracted away the details for us,
// so we just let it create chunks and add them to the section.
void Writer::createImportTables() {
// Initialize DLLOrder so that import entries are ordered in
// the same order as in the command line. (That affects DLL
// initialization order, and this ordering is MSVC-compatible.)
for (ImportFile *file : ImportFile::instances) {
if (!file->live)
continue;
std::string dll = StringRef(file->dllName).lower();
if (config->dllOrder.count(dll) == 0)
config->dllOrder[dll] = config->dllOrder.size();
if (file->impSym && !isa<DefinedImportData>(file->impSym))
fatal(toString(*file->impSym) + " was replaced");
DefinedImportData *impSym = cast_or_null<DefinedImportData>(file->impSym);
if (config->delayLoads.count(StringRef(file->dllName).lower())) {
if (!file->thunkSym)
fatal("cannot delay-load " + toString(file) +
" due to import of data: " + toString(*impSym));
delayIdata.add(impSym);
} else {
idata.add(impSym);
}
}
}
void Writer::appendImportThunks() {
if (ImportFile::instances.empty())
return;
for (ImportFile *file : ImportFile::instances) {
if (!file->live)
continue;
if (!file->thunkSym)
continue;
if (!isa<DefinedImportThunk>(file->thunkSym))
fatal(toString(*file->thunkSym) + " was replaced");
DefinedImportThunk *thunk = cast<DefinedImportThunk>(file->thunkSym);
if (file->thunkLive)
textSec->addChunk(thunk->getChunk());
}
if (!delayIdata.empty()) {
Defined *helper = cast<Defined>(config->delayLoadHelper);
delayIdata.create(helper);
for (Chunk *c : delayIdata.getChunks())
didatSec->addChunk(c);
for (Chunk *c : delayIdata.getDataChunks())
dataSec->addChunk(c);
for (Chunk *c : delayIdata.getCodeChunks())
textSec->addChunk(c);
}
}
void Writer::createExportTable() {
if (!edataSec->chunks.empty()) {
// Allow using a custom built export table from input object files, instead
// of having the linker synthesize the tables.
if (config->hadExplicitExports)
warn("literal .edata sections override exports");
} else if (!config->exports.empty()) {
for (Chunk *c : edata.chunks)
edataSec->addChunk(c);
}
if (!edataSec->chunks.empty()) {
edataStart = edataSec->chunks.front();
edataEnd = edataSec->chunks.back();
}
}
void Writer::removeUnusedSections() {
// Remove sections that we can be sure won't get content, to avoid
// allocating space for their section headers.
auto isUnused = [this](OutputSection *s) {
if (s == relocSec)
return false; // This section is populated later.
// MergeChunks have zero size at this point, as their size is finalized
// later. Only remove sections that have no Chunks at all.
return s->chunks.empty();
};
outputSections.erase(
std::remove_if(outputSections.begin(), outputSections.end(), isUnused),
outputSections.end());
}
// The Windows loader doesn't seem to like empty sections,
// so we remove them if any.
void Writer::removeEmptySections() {
auto isEmpty = [](OutputSection *s) { return s->getVirtualSize() == 0; };
outputSections.erase(
std::remove_if(outputSections.begin(), outputSections.end(), isEmpty),
outputSections.end());
}
void Writer::assignOutputSectionIndices() {
// Assign final output section indices, and assign each chunk to its output
// section.
uint32_t idx = 1;
for (OutputSection *os : outputSections) {
os->sectionIndex = idx;
for (Chunk *c : os->chunks)
c->setOutputSectionIdx(idx);
++idx;
}
// Merge chunks are containers of chunks, so assign those an output section
// too.
for (MergeChunk *mc : MergeChunk::instances)
if (mc)
for (SectionChunk *sc : mc->sections)
if (sc && sc->live)
sc->setOutputSectionIdx(mc->getOutputSectionIdx());
}
size_t Writer::addEntryToStringTable(StringRef str) {
assert(str.size() > COFF::NameSize);
size_t offsetOfEntry = strtab.size() + 4; // +4 for the size field
strtab.insert(strtab.end(), str.begin(), str.end());
strtab.push_back('\0');
return offsetOfEntry;
}
Optional<coff_symbol16> Writer::createSymbol(Defined *def) {
coff_symbol16 sym;
switch (def->kind()) {
case Symbol::DefinedAbsoluteKind:
sym.Value = def->getRVA();
sym.SectionNumber = IMAGE_SYM_ABSOLUTE;
break;
case Symbol::DefinedSyntheticKind:
// Relative symbols are unrepresentable in a COFF symbol table.
return None;
default: {
// Don't write symbols that won't be written to the output to the symbol
// table.
Chunk *c = def->getChunk();
if (!c)
return None;
OutputSection *os = c->getOutputSection();
if (!os)
return None;
sym.Value = def->getRVA() - os->getRVA();
sym.SectionNumber = os->sectionIndex;
break;
}
}
// Symbols that are runtime pseudo relocations don't point to the actual
// symbol data itself (as they are imported), but points to the IAT entry
// instead. Avoid emitting them to the symbol table, as they can confuse
// debuggers.
if (def->isRuntimePseudoReloc)
return None;
StringRef name = def->getName();
if (name.size() > COFF::NameSize) {
sym.Name.Offset.Zeroes = 0;
sym.Name.Offset.Offset = addEntryToStringTable(name);
} else {
memset(sym.Name.ShortName, 0, COFF::NameSize);
memcpy(sym.Name.ShortName, name.data(), name.size());
}
if (auto *d = dyn_cast<DefinedCOFF>(def)) {
COFFSymbolRef ref = d->getCOFFSymbol();
sym.Type = ref.getType();
sym.StorageClass = ref.getStorageClass();
} else {
sym.Type = IMAGE_SYM_TYPE_NULL;
sym.StorageClass = IMAGE_SYM_CLASS_EXTERNAL;
}
sym.NumberOfAuxSymbols = 0;
return sym;
}
void Writer::createSymbolAndStringTable() {
// PE/COFF images are limited to 8 byte section names. Longer names can be
// supported by writing a non-standard string table, but this string table is
// not mapped at runtime and the long names will therefore be inaccessible.
// link.exe always truncates section names to 8 bytes, whereas binutils always
// preserves long section names via the string table. LLD adopts a hybrid
// solution where discardable sections have long names preserved and
// non-discardable sections have their names truncated, to ensure that any
// section which is mapped at runtime also has its name mapped at runtime.
for (OutputSection *sec : outputSections) {
if (sec->name.size() <= COFF::NameSize)
continue;
if ((sec->header.Characteristics & IMAGE_SCN_MEM_DISCARDABLE) == 0)
continue;
sec->setStringTableOff(addEntryToStringTable(sec->name));
}
if (config->debugDwarf || config->debugSymtab) {
for (ObjFile *file : ObjFile::instances) {
for (Symbol *b : file->getSymbols()) {
auto *d = dyn_cast_or_null<Defined>(b);
if (!d || d->writtenToSymtab)
continue;
d->writtenToSymtab = true;
if (Optional<coff_symbol16> sym = createSymbol(d))
outputSymtab.push_back(*sym);
}
}
}
if (outputSymtab.empty() && strtab.empty())
return;
// We position the symbol table to be adjacent to the end of the last section.
uint64_t fileOff = fileSize;
pointerToSymbolTable = fileOff;
fileOff += outputSymtab.size() * sizeof(coff_symbol16);
fileOff += 4 + strtab.size();
fileSize = alignTo(fileOff, config->fileAlign);
}
void Writer::mergeSections() {
if (!pdataSec->chunks.empty()) {
firstPdata = pdataSec->chunks.front();
lastPdata = pdataSec->chunks.back();
}
for (auto &p : config->merge) {
StringRef toName = p.second;
if (p.first == toName)
continue;
StringSet<> names;
while (1) {
if (!names.insert(toName).second)
fatal("/merge: cycle found for section '" + p.first + "'");
auto i = config->merge.find(toName);
if (i == config->merge.end())
break;
toName = i->second;
}
OutputSection *from = findSection(p.first);
OutputSection *to = findSection(toName);
if (!from)
continue;
if (!to) {
from->name = toName;
continue;
}
to->merge(from);
}
}
// Visits all sections to assign incremental, non-overlapping RVAs and
// file offsets.
void Writer::assignAddresses() {
sizeOfHeaders = dosStubSize + sizeof(PEMagic) + sizeof(coff_file_header) +
sizeof(data_directory) * numberOfDataDirectory +
sizeof(coff_section) * outputSections.size();
sizeOfHeaders +=
config->is64() ? sizeof(pe32plus_header) : sizeof(pe32_header);
sizeOfHeaders = alignTo(sizeOfHeaders, config->fileAlign);
fileSize = sizeOfHeaders;
// The first page is kept unmapped.
uint64_t rva = alignTo(sizeOfHeaders, config->align);
for (OutputSection *sec : outputSections) {
if (sec == relocSec)
addBaserels();
uint64_t rawSize = 0, virtualSize = 0;
sec->header.VirtualAddress = rva;
// If /FUNCTIONPADMIN is used, functions are padded in order to create a
// hotpatchable image.
const bool isCodeSection =
(sec->header.Characteristics & IMAGE_SCN_CNT_CODE) &&
(sec->header.Characteristics & IMAGE_SCN_MEM_READ) &&
(sec->header.Characteristics & IMAGE_SCN_MEM_EXECUTE);
uint32_t padding = isCodeSection ? config->functionPadMin : 0;
for (Chunk *c : sec->chunks) {
if (padding && c->isHotPatchable())
virtualSize += padding;
virtualSize = alignTo(virtualSize, c->getAlignment());
c->setRVA(rva + virtualSize);
virtualSize += c->getSize();
if (c->hasData)
rawSize = alignTo(virtualSize, config->fileAlign);
}
if (virtualSize > UINT32_MAX)
error("section larger than 4 GiB: " + sec->name);
sec->header.VirtualSize = virtualSize;
sec->header.SizeOfRawData = rawSize;
if (rawSize != 0)
sec->header.PointerToRawData = fileSize;
rva += alignTo(virtualSize, config->align);
fileSize += alignTo(rawSize, config->fileAlign);
}
sizeOfImage = alignTo(rva, config->align);
// Assign addresses to sections in MergeChunks.
for (MergeChunk *mc : MergeChunk::instances)
if (mc)
mc->assignSubsectionRVAs();
}
template <typename PEHeaderTy> void Writer::writeHeader() {
// Write DOS header. For backwards compatibility, the first part of a PE/COFF
// executable consists of an MS-DOS MZ executable. If the executable is run
// under DOS, that program gets run (usually to just print an error message).
// When run under Windows, the loader looks at AddressOfNewExeHeader and uses
// the PE header instead.
uint8_t *buf = buffer->getBufferStart();
auto *dos = reinterpret_cast<dos_header *>(buf);
buf += sizeof(dos_header);
dos->Magic[0] = 'M';
dos->Magic[1] = 'Z';
dos->UsedBytesInTheLastPage = dosStubSize % 512;
dos->FileSizeInPages = divideCeil(dosStubSize, 512);
dos->HeaderSizeInParagraphs = sizeof(dos_header) / 16;
dos->AddressOfRelocationTable = sizeof(dos_header);
dos->AddressOfNewExeHeader = dosStubSize;
// Write DOS program.
memcpy(buf, dosProgram, sizeof(dosProgram));
buf += sizeof(dosProgram);
// Write PE magic
memcpy(buf, PEMagic, sizeof(PEMagic));
buf += sizeof(PEMagic);
// Write COFF header
auto *coff = reinterpret_cast<coff_file_header *>(buf);
buf += sizeof(*coff);
coff->Machine = config->machine;
coff->NumberOfSections = outputSections.size();
coff->Characteristics = IMAGE_FILE_EXECUTABLE_IMAGE;
if (config->largeAddressAware)
coff->Characteristics |= IMAGE_FILE_LARGE_ADDRESS_AWARE;
if (!config->is64())
coff->Characteristics |= IMAGE_FILE_32BIT_MACHINE;
if (config->dll)
coff->Characteristics |= IMAGE_FILE_DLL;
if (!config->relocatable)
coff->Characteristics |= IMAGE_FILE_RELOCS_STRIPPED;
if (config->swaprunCD)
coff->Characteristics |= IMAGE_FILE_REMOVABLE_RUN_FROM_SWAP;
if (config->swaprunNet)
coff->Characteristics |= IMAGE_FILE_NET_RUN_FROM_SWAP;
coff->SizeOfOptionalHeader =
sizeof(PEHeaderTy) + sizeof(data_directory) * numberOfDataDirectory;
// Write PE header
auto *pe = reinterpret_cast<PEHeaderTy *>(buf);
buf += sizeof(*pe);
pe->Magic = config->is64() ? PE32Header::PE32_PLUS : PE32Header::PE32;
// If {Major,Minor}LinkerVersion is left at 0.0, then for some
// reason signing the resulting PE file with Authenticode produces a
// signature that fails to validate on Windows 7 (but is OK on 10).
// Set it to 14.0, which is what VS2015 outputs, and which avoids
// that problem.
pe->MajorLinkerVersion = 14;
pe->MinorLinkerVersion = 0;
pe->ImageBase = config->imageBase;
pe->SectionAlignment = config->align;
pe->FileAlignment = config->fileAlign;
pe->MajorImageVersion = config->majorImageVersion;
pe->MinorImageVersion = config->minorImageVersion;
pe->MajorOperatingSystemVersion = config->majorOSVersion;
pe->MinorOperatingSystemVersion = config->minorOSVersion;
pe->MajorSubsystemVersion = config->majorOSVersion;
pe->MinorSubsystemVersion = config->minorOSVersion;
pe->Subsystem = config->subsystem;
pe->SizeOfImage = sizeOfImage;
pe->SizeOfHeaders = sizeOfHeaders;
if (!config->noEntry) {
Defined *entry = cast<Defined>(config->entry);
pe->AddressOfEntryPoint = entry->getRVA();
// Pointer to thumb code must have the LSB set, so adjust it.
if (config->machine == ARMNT)
pe->AddressOfEntryPoint |= 1;
}
pe->SizeOfStackReserve = config->stackReserve;
pe->SizeOfStackCommit = config->stackCommit;
pe->SizeOfHeapReserve = config->heapReserve;
pe->SizeOfHeapCommit = config->heapCommit;
if (config->appContainer)
pe->DLLCharacteristics |= IMAGE_DLL_CHARACTERISTICS_APPCONTAINER;
if (config->dynamicBase)
pe->DLLCharacteristics |= IMAGE_DLL_CHARACTERISTICS_DYNAMIC_BASE;
if (config->highEntropyVA)
pe->DLLCharacteristics |= IMAGE_DLL_CHARACTERISTICS_HIGH_ENTROPY_VA;
if (!config->allowBind)
pe->DLLCharacteristics |= IMAGE_DLL_CHARACTERISTICS_NO_BIND;
if (config->nxCompat)
pe->DLLCharacteristics |= IMAGE_DLL_CHARACTERISTICS_NX_COMPAT;
if (!config->allowIsolation)
pe->DLLCharacteristics |= IMAGE_DLL_CHARACTERISTICS_NO_ISOLATION;
if (config->guardCF != GuardCFLevel::Off)
pe->DLLCharacteristics |= IMAGE_DLL_CHARACTERISTICS_GUARD_CF;
if (config->integrityCheck)
pe->DLLCharacteristics |= IMAGE_DLL_CHARACTERISTICS_FORCE_INTEGRITY;
if (setNoSEHCharacteristic)
pe->DLLCharacteristics |= IMAGE_DLL_CHARACTERISTICS_NO_SEH;
if (config->terminalServerAware)
pe->DLLCharacteristics |= IMAGE_DLL_CHARACTERISTICS_TERMINAL_SERVER_AWARE;
pe->NumberOfRvaAndSize = numberOfDataDirectory;
if (textSec->getVirtualSize()) {
pe->BaseOfCode = textSec->getRVA();
pe->SizeOfCode = textSec->getRawSize();
}
pe->SizeOfInitializedData = getSizeOfInitializedData();
// Write data directory
auto *dir = reinterpret_cast<data_directory *>(buf);
buf += sizeof(*dir) * numberOfDataDirectory;
if (edataStart) {
dir[EXPORT_TABLE].RelativeVirtualAddress = edataStart->getRVA();
dir[EXPORT_TABLE].Size =
edataEnd->getRVA() + edataEnd->getSize() - edataStart->getRVA();
}
if (importTableStart) {
dir[IMPORT_TABLE].RelativeVirtualAddress = importTableStart->getRVA();
dir[IMPORT_TABLE].Size = importTableSize;
}
if (iatStart) {
dir[IAT].RelativeVirtualAddress = iatStart->getRVA();
dir[IAT].Size = iatSize;
}
if (rsrcSec->getVirtualSize()) {
dir[RESOURCE_TABLE].RelativeVirtualAddress = rsrcSec->getRVA();
dir[RESOURCE_TABLE].Size = rsrcSec->getVirtualSize();
}
if (firstPdata) {
dir[EXCEPTION_TABLE].RelativeVirtualAddress = firstPdata->getRVA();
dir[EXCEPTION_TABLE].Size =
lastPdata->getRVA() + lastPdata->getSize() - firstPdata->getRVA();
}
if (relocSec->getVirtualSize()) {
dir[BASE_RELOCATION_TABLE].RelativeVirtualAddress = relocSec->getRVA();
dir[BASE_RELOCATION_TABLE].Size = relocSec->getVirtualSize();
}
if (Symbol *sym = symtab->findUnderscore("_tls_used")) {
if (Defined *b = dyn_cast<Defined>(sym)) {
dir[TLS_TABLE].RelativeVirtualAddress = b->getRVA();
dir[TLS_TABLE].Size = config->is64()
? sizeof(object::coff_tls_directory64)
: sizeof(object::coff_tls_directory32);
}
}
if (debugDirectory) {
dir[DEBUG_DIRECTORY].RelativeVirtualAddress = debugDirectory->getRVA();
dir[DEBUG_DIRECTORY].Size = debugDirectory->getSize();
}
if (Symbol *sym = symtab->findUnderscore("_load_config_used")) {
if (auto *b = dyn_cast<DefinedRegular>(sym)) {
SectionChunk *sc = b->getChunk();
assert(b->getRVA() >= sc->getRVA());
uint64_t offsetInChunk = b->getRVA() - sc->getRVA();
if (!sc->hasData || offsetInChunk + 4 > sc->getSize())
fatal("_load_config_used is malformed");
ArrayRef<uint8_t> secContents = sc->getContents();
uint32_t loadConfigSize =
*reinterpret_cast<const ulittle32_t *>(&secContents[offsetInChunk]);
if (offsetInChunk + loadConfigSize > sc->getSize())
fatal("_load_config_used is too large");
dir[LOAD_CONFIG_TABLE].RelativeVirtualAddress = b->getRVA();
dir[LOAD_CONFIG_TABLE].Size = loadConfigSize;
}
}
if (!delayIdata.empty()) {
dir[DELAY_IMPORT_DESCRIPTOR].RelativeVirtualAddress =
delayIdata.getDirRVA();
dir[DELAY_IMPORT_DESCRIPTOR].Size = delayIdata.getDirSize();
}
// Write section table
for (OutputSection *sec : outputSections) {
sec->writeHeaderTo(buf);
buf += sizeof(coff_section);
}
sectionTable = ArrayRef<uint8_t>(
buf - outputSections.size() * sizeof(coff_section), buf);
if (outputSymtab.empty() && strtab.empty())
return;
coff->PointerToSymbolTable = pointerToSymbolTable;
uint32_t numberOfSymbols = outputSymtab.size();
coff->NumberOfSymbols = numberOfSymbols;
auto *symbolTable = reinterpret_cast<coff_symbol16 *>(
buffer->getBufferStart() + coff->PointerToSymbolTable);
for (size_t i = 0; i != numberOfSymbols; ++i)
symbolTable[i] = outputSymtab[i];
// Create the string table, it follows immediately after the symbol table.
// The first 4 bytes is length including itself.
buf = reinterpret_cast<uint8_t *>(&symbolTable[numberOfSymbols]);
write32le(buf, strtab.size() + 4);
if (!strtab.empty())
memcpy(buf + 4, strtab.data(), strtab.size());
}
void Writer::openFile(StringRef path) {
buffer = CHECK(
FileOutputBuffer::create(path, fileSize, FileOutputBuffer::F_executable),
"failed to open " + path);
}
void Writer::createSEHTable() {
SymbolRVASet handlers;
for (ObjFile *file : ObjFile::instances) {
if (!file->hasSafeSEH())
error("/safeseh: " + file->getName() + " is not compatible with SEH");
markSymbolsForRVATable(file, file->getSXDataChunks(), handlers);
}
// Set the "no SEH" characteristic if there really were no handlers, or if
// there is no load config object to point to the table of handlers.
setNoSEHCharacteristic =
handlers.empty() || !symtab->findUnderscore("_load_config_used");
maybeAddRVATable(std::move(handlers), "__safe_se_handler_table",
"__safe_se_handler_count");
}
// Add a symbol to an RVA set. Two symbols may have the same RVA, but an RVA set
// cannot contain duplicates. Therefore, the set is uniqued by Chunk and the
// symbol's offset into that Chunk.
static void addSymbolToRVASet(SymbolRVASet &rvaSet, Defined *s) {
Chunk *c = s->getChunk();
if (auto *sc = dyn_cast<SectionChunk>(c))
c = sc->repl; // Look through ICF replacement.
uint32_t off = s->getRVA() - (c ? c->getRVA() : 0);
rvaSet.insert({c, off});
}
// Given a symbol, add it to the GFIDs table if it is a live, defined, function
// symbol in an executable section.
static void maybeAddAddressTakenFunction(SymbolRVASet &addressTakenSyms,
Symbol *s) {
if (!s)
return;
switch (s->kind()) {
case Symbol::DefinedLocalImportKind:
case Symbol::DefinedImportDataKind:
// Defines an __imp_ pointer, so it is data, so it is ignored.
break;
case Symbol::DefinedCommonKind:
// Common is always data, so it is ignored.
break;
case Symbol::DefinedAbsoluteKind:
case Symbol::DefinedSyntheticKind:
// Absolute is never code, synthetic generally isn't and usually isn't
// determinable.
break;
case Symbol::LazyArchiveKind:
case Symbol::LazyObjectKind:
case Symbol::UndefinedKind:
// Undefined symbols resolve to zero, so they don't have an RVA. Lazy
// symbols shouldn't have relocations.
break;
case Symbol::DefinedImportThunkKind:
// Thunks are always code, include them.
addSymbolToRVASet(addressTakenSyms, cast<Defined>(s));
break;
case Symbol::DefinedRegularKind: {
// This is a regular, defined, symbol from a COFF file. Mark the symbol as
// address taken if the symbol type is function and it's in an executable
// section.
auto *d = cast<DefinedRegular>(s);
if (d->getCOFFSymbol().getComplexType() == COFF::IMAGE_SYM_DTYPE_FUNCTION) {
SectionChunk *sc = dyn_cast<SectionChunk>(d->getChunk());
if (sc && sc->live &&
sc->getOutputCharacteristics() & IMAGE_SCN_MEM_EXECUTE)
addSymbolToRVASet(addressTakenSyms, d);
}
break;
}
}
}
// Visit all relocations from all section contributions of this object file and
// mark the relocation target as address-taken.
static void markSymbolsWithRelocations(ObjFile *file,
SymbolRVASet &usedSymbols) {
for (Chunk *c : file->getChunks()) {
// We only care about live section chunks. Common chunks and other chunks
// don't generally contain relocations.
SectionChunk *sc = dyn_cast<SectionChunk>(c);
if (!sc || !sc->live)
continue;
for (const coff_relocation &reloc : sc->getRelocs()) {
if (config->machine == I386 && reloc.Type == COFF::IMAGE_REL_I386_REL32)
// Ignore relative relocations on x86. On x86_64 they can't be ignored
// since they're also used to compute absolute addresses.
continue;
Symbol *ref = sc->file->getSymbol(reloc.SymbolTableIndex);
maybeAddAddressTakenFunction(usedSymbols, ref);
}
}
}
// Create the guard function id table. This is a table of RVAs of all
// address-taken functions. It is sorted and uniqued, just like the safe SEH
// table.
void Writer::createGuardCFTables() {
SymbolRVASet addressTakenSyms;
SymbolRVASet longJmpTargets;
for (ObjFile *file : ObjFile::instances) {
// If the object was compiled with /guard:cf, the address taken symbols
// are in .gfids$y sections, and the longjmp targets are in .gljmp$y
// sections. If the object was not compiled with /guard:cf, we assume there
// were no setjmp targets, and that all code symbols with relocations are
// possibly address-taken.
if (file->hasGuardCF()) {
markSymbolsForRVATable(file, file->getGuardFidChunks(), addressTakenSyms);
markSymbolsForRVATable(file, file->getGuardLJmpChunks(), longJmpTargets);
} else {
markSymbolsWithRelocations(file, addressTakenSyms);
}
}
// Mark the image entry as address-taken.
if (config->entry)
maybeAddAddressTakenFunction(addressTakenSyms, config->entry);
// Mark exported symbols in executable sections as address-taken.
for (Export &e : config->exports)
maybeAddAddressTakenFunction(addressTakenSyms, e.sym);
// Ensure sections referenced in the gfid table are 16-byte aligned.
for (const ChunkAndOffset &c : addressTakenSyms)
if (c.inputChunk->getAlignment() < 16)
c.inputChunk->setAlignment(16);
maybeAddRVATable(std::move(addressTakenSyms), "__guard_fids_table",
"__guard_fids_count");
// Add the longjmp target table unless the user told us not to.
if (config->guardCF == GuardCFLevel::Full)
maybeAddRVATable(std::move(longJmpTargets), "__guard_longjmp_table",
"__guard_longjmp_count");
// Set __guard_flags, which will be used in the load config to indicate that
// /guard:cf was enabled.
uint32_t guardFlags = uint32_t(coff_guard_flags::CFInstrumented) |
uint32_t(coff_guard_flags::HasFidTable);
if (config->guardCF == GuardCFLevel::Full)
guardFlags |= uint32_t(coff_guard_flags::HasLongJmpTable);
Symbol *flagSym = symtab->findUnderscore("__guard_flags");
cast<DefinedAbsolute>(flagSym)->setVA(guardFlags);
}
// Take a list of input sections containing symbol table indices and add those
// symbols to an RVA table. The challenge is that symbol RVAs are not known and
// depend on the table size, so we can't directly build a set of integers.
void Writer::markSymbolsForRVATable(ObjFile *file,
ArrayRef<SectionChunk *> symIdxChunks,
SymbolRVASet &tableSymbols) {
for (SectionChunk *c : symIdxChunks) {
// Skip sections discarded by linker GC. This comes up when a .gfids section
// is associated with something like a vtable and the vtable is discarded.
// In this case, the associated gfids section is discarded, and we don't
// mark the virtual member functions as address-taken by the vtable.
if (!c->live)
continue;
// Validate that the contents look like symbol table indices.
ArrayRef<uint8_t> data = c->getContents();
if (data.size() % 4 != 0) {
warn("ignoring " + c->getSectionName() +
" symbol table index section in object " + toString(file));
continue;
}
// Read each symbol table index and check if that symbol was included in the
// final link. If so, add it to the table symbol set.
ArrayRef<ulittle32_t> symIndices(
reinterpret_cast<const ulittle32_t *>(data.data()), data.size() / 4);
ArrayRef<Symbol *> objSymbols = file->getSymbols();
for (uint32_t symIndex : symIndices) {
if (symIndex >= objSymbols.size()) {
warn("ignoring invalid symbol table index in section " +
c->getSectionName() + " in object " + toString(file));
continue;
}
if (Symbol *s = objSymbols[symIndex]) {
if (s->isLive())
addSymbolToRVASet(tableSymbols, cast<Defined>(s));
}
}
}
}
// Replace the absolute table symbol with a synthetic symbol pointing to
// tableChunk so that we can emit base relocations for it and resolve section
// relative relocations.
void Writer::maybeAddRVATable(SymbolRVASet tableSymbols, StringRef tableSym,
StringRef countSym) {
if (tableSymbols.empty())
return;
RVATableChunk *tableChunk = make<RVATableChunk>(std::move(tableSymbols));
rdataSec->addChunk(tableChunk);
Symbol *t = symtab->findUnderscore(tableSym);
Symbol *c = symtab->findUnderscore(countSym);
replaceSymbol<DefinedSynthetic>(t, t->getName(), tableChunk);
cast<DefinedAbsolute>(c)->setVA(tableChunk->getSize() / 4);
}
// MinGW specific. Gather all relocations that are imported from a DLL even
// though the code didn't expect it to, produce the table that the runtime
// uses for fixing them up, and provide the synthetic symbols that the
// runtime uses for finding the table.
void Writer::createRuntimePseudoRelocs() {
std::vector<RuntimePseudoReloc> rels;
for (Chunk *c : symtab->getChunks()) {
auto *sc = dyn_cast<SectionChunk>(c);
if (!sc || !sc->live)
continue;
sc->getRuntimePseudoRelocs(rels);
}
if (!rels.empty())
log("Writing " + Twine(rels.size()) + " runtime pseudo relocations");
PseudoRelocTableChunk *table = make<PseudoRelocTableChunk>(rels);
rdataSec->addChunk(table);
EmptyChunk *endOfList = make<EmptyChunk>();
rdataSec->addChunk(endOfList);
Symbol *headSym = symtab->findUnderscore("__RUNTIME_PSEUDO_RELOC_LIST__");
Symbol *endSym = symtab->findUnderscore("__RUNTIME_PSEUDO_RELOC_LIST_END__");
replaceSymbol<DefinedSynthetic>(headSym, headSym->getName(), table);
replaceSymbol<DefinedSynthetic>(endSym, endSym->getName(), endOfList);
}
// MinGW specific.
// The MinGW .ctors and .dtors lists have sentinels at each end;
// a (uintptr_t)-1 at the start and a (uintptr_t)0 at the end.
// There's a symbol pointing to the start sentinel pointer, __CTOR_LIST__
// and __DTOR_LIST__ respectively.
void Writer::insertCtorDtorSymbols() {
AbsolutePointerChunk *ctorListHead = make<AbsolutePointerChunk>(-1);
AbsolutePointerChunk *ctorListEnd = make<AbsolutePointerChunk>(0);
AbsolutePointerChunk *dtorListHead = make<AbsolutePointerChunk>(-1);
AbsolutePointerChunk *dtorListEnd = make<AbsolutePointerChunk>(0);
ctorsSec->insertChunkAtStart(ctorListHead);
ctorsSec->addChunk(ctorListEnd);
dtorsSec->insertChunkAtStart(dtorListHead);
dtorsSec->addChunk(dtorListEnd);
Symbol *ctorListSym = symtab->findUnderscore("__CTOR_LIST__");
Symbol *dtorListSym = symtab->findUnderscore("__DTOR_LIST__");
replaceSymbol<DefinedSynthetic>(ctorListSym, ctorListSym->getName(),
ctorListHead);
replaceSymbol<DefinedSynthetic>(dtorListSym, dtorListSym->getName(),
dtorListHead);
}
// Handles /section options to allow users to overwrite
// section attributes.
void Writer::setSectionPermissions() {
for (auto &p : config->section) {
StringRef name = p.first;
uint32_t perm = p.second;
for (OutputSection *sec : outputSections)
if (sec->name == name)
sec->setPermissions(perm);
}
}
// Write section contents to a mmap'ed file.
void Writer::writeSections() {
// Record the number of sections to apply section index relocations
// against absolute symbols. See applySecIdx in Chunks.cpp..
DefinedAbsolute::numOutputSections = outputSections.size();
uint8_t *buf = buffer->getBufferStart();
for (OutputSection *sec : outputSections) {
uint8_t *secBuf = buf + sec->getFileOff();
// Fill gaps between functions in .text with INT3 instructions
// instead of leaving as NUL bytes (which can be interpreted as
// ADD instructions).
if (sec->header.Characteristics & IMAGE_SCN_CNT_CODE)
memset(secBuf, 0xCC, sec->getRawSize());
parallelForEach(sec->chunks, [&](Chunk *c) {
c->writeTo(secBuf + c->getRVA() - sec->getRVA());
});
}
}
void Writer::writeBuildId() {
// There are two important parts to the build ID.
// 1) If building with debug info, the COFF debug directory contains a
// timestamp as well as a Guid and Age of the PDB.
// 2) In all cases, the PE COFF file header also contains a timestamp.
// For reproducibility, instead of a timestamp we want to use a hash of the
// PE contents.
if (config->debug) {
assert(buildId && "BuildId is not set!");
// BuildId->BuildId was filled in when the PDB was written.
}
// At this point the only fields in the COFF file which remain unset are the
// "timestamp" in the COFF file header, and the ones in the coff debug
// directory. Now we can hash the file and write that hash to the various
// timestamp fields in the file.
StringRef outputFileData(
reinterpret_cast<const char *>(buffer->getBufferStart()),
buffer->getBufferSize());
uint32_t timestamp = config->timestamp;
uint64_t hash = 0;
bool generateSyntheticBuildId =
config->mingw && config->debug && config->pdbPath.empty();
if (config->repro || generateSyntheticBuildId)
hash = xxHash64(outputFileData);
if (config->repro)
timestamp = static_cast<uint32_t>(hash);
if (generateSyntheticBuildId) {
// For MinGW builds without a PDB file, we still generate a build id
// to allow associating a crash dump to the executable.
buildId->buildId->PDB70.CVSignature = OMF::Signature::PDB70;
buildId->buildId->PDB70.Age = 1;
memcpy(buildId->buildId->PDB70.Signature, &hash, 8);
// xxhash only gives us 8 bytes, so put some fixed data in the other half.
memcpy(&buildId->buildId->PDB70.Signature[8], "LLD PDB.", 8);
}
if (debugDirectory)
debugDirectory->setTimeDateStamp(timestamp);
uint8_t *buf = buffer->getBufferStart();
buf += dosStubSize + sizeof(PEMagic);
object::coff_file_header *coffHeader =
reinterpret_cast<coff_file_header *>(buf);
coffHeader->TimeDateStamp = timestamp;
}
// Sort .pdata section contents according to PE/COFF spec 5.5.
void Writer::sortExceptionTable() {
if (!firstPdata)
return;
// We assume .pdata contains function table entries only.
auto bufAddr = [&](Chunk *c) {
OutputSection *os = c->getOutputSection();
return buffer->getBufferStart() + os->getFileOff() + c->getRVA() -
os->getRVA();
};
uint8_t *begin = bufAddr(firstPdata);
uint8_t *end = bufAddr(lastPdata) + lastPdata->getSize();
if (config->machine == AMD64) {
struct Entry { ulittle32_t begin, end, unwind; };
parallelSort(
MutableArrayRef<Entry>((Entry *)begin, (Entry *)end),
[](const Entry &a, const Entry &b) { return a.begin < b.begin; });
return;
}
if (config->machine == ARMNT || config->machine == ARM64) {
struct Entry { ulittle32_t begin, unwind; };
parallelSort(
MutableArrayRef<Entry>((Entry *)begin, (Entry *)end),
[](const Entry &a, const Entry &b) { return a.begin < b.begin; });
return;
}
errs() << "warning: don't know how to handle .pdata.\n";
}
// The CRT section contains, among other things, the array of function
// pointers that initialize every global variable that is not trivially
// constructed. The CRT calls them one after the other prior to invoking
// main().
//
// As per C++ spec, 3.6.2/2.3,
// "Variables with ordered initialization defined within a single
// translation unit shall be initialized in the order of their definitions
// in the translation unit"
//
// It is therefore critical to sort the chunks containing the function
// pointers in the order that they are listed in the object file (top to
// bottom), otherwise global objects might not be initialized in the
// correct order.
void Writer::sortCRTSectionChunks(std::vector<Chunk *> &chunks) {
auto sectionChunkOrder = [](const Chunk *a, const Chunk *b) {
auto sa = dyn_cast<SectionChunk>(a);
auto sb = dyn_cast<SectionChunk>(b);
assert(sa && sb && "Non-section chunks in CRT section!");
StringRef sAObj = sa->file->mb.getBufferIdentifier();
StringRef sBObj = sb->file->mb.getBufferIdentifier();
return sAObj == sBObj && sa->getSectionNumber() < sb->getSectionNumber();
};
llvm::stable_sort(chunks, sectionChunkOrder);
if (config->verbose) {
for (auto &c : chunks) {
auto sc = dyn_cast<SectionChunk>(c);
log(" " + sc->file->mb.getBufferIdentifier().str() +
", SectionID: " + Twine(sc->getSectionNumber()));
}
}
}
OutputSection *Writer::findSection(StringRef name) {
for (OutputSection *sec : outputSections)
if (sec->name == name)
return sec;
return nullptr;
}
uint32_t Writer::getSizeOfInitializedData() {
uint32_t res = 0;
for (OutputSection *s : outputSections)
if (s->header.Characteristics & IMAGE_SCN_CNT_INITIALIZED_DATA)
res += s->getRawSize();
return res;
}
// Add base relocations to .reloc section.
void Writer::addBaserels() {
if (!config->relocatable)
return;
relocSec->chunks.clear();
std::vector<Baserel> v;
for (OutputSection *sec : outputSections) {
if (sec->header.Characteristics & IMAGE_SCN_MEM_DISCARDABLE)
continue;
// Collect all locations for base relocations.
for (Chunk *c : sec->chunks)
c->getBaserels(&v);
// Add the addresses to .reloc section.
if (!v.empty())
addBaserelBlocks(v);
v.clear();
}
}
// Add addresses to .reloc section. Note that addresses are grouped by page.
void Writer::addBaserelBlocks(std::vector<Baserel> &v) {
const uint32_t mask = ~uint32_t(pageSize - 1);
uint32_t page = v[0].rva & mask;
size_t i = 0, j = 1;
for (size_t e = v.size(); j < e; ++j) {
uint32_t p = v[j].rva & mask;
if (p == page)
continue;
relocSec->addChunk(make<BaserelChunk>(page, &v[i], &v[0] + j));
i = j;
page = p;
}
if (i == j)
return;
relocSec->addChunk(make<BaserelChunk>(page, &v[i], &v[0] + j));
}
PartialSection *Writer::createPartialSection(StringRef name,
uint32_t outChars) {
PartialSection *&pSec = partialSections[{name, outChars}];
if (pSec)
return pSec;
pSec = make<PartialSection>(name, outChars);
return pSec;
}
PartialSection *Writer::findPartialSection(StringRef name, uint32_t outChars) {
auto it = partialSections.find({name, outChars});
if (it != partialSections.end())
return it->second;
return nullptr;
}
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