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llvm-project/lld/COFF/Writer.cpp

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//===- Writer.cpp ---------------------------------------------------------===//
//
// The LLVM Linker
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#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/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 SectorSize = 512;
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;
namespace {
class DebugDirectoryChunk : public Chunk {
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 + OutputSectionOff);
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 Chunk {
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 + OutputSectionOff);
// variable sized field (PDB Path)
char *P = reinterpret_cast<char *>(B + OutputSectionOff + sizeof(*BuildId));
if (!Config->PDBAltPath.empty())
memcpy(P, Config->PDBAltPath.data(), Config->PDBAltPath.size());
P[Config->PDBAltPath.size()] = '\0';
}
mutable codeview::DebugInfo *BuildId = nullptr;
};
// 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(
std::map<std::pair<StringRef, uint32_t>, std::vector<Chunk *>> &Map);
void createExportTable();
void mergeSections();
void readRelocTargets();
void assignAddresses();
void finalizeAddresses();
void removeEmptySections();
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);
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::map<StringRef, std::vector<DefinedImportData *>> binImports();
std::unique_ptr<FileOutputBuffer> &Buffer;
std::vector<OutputSection *> OutputSections;
std::vector<char> Strtab;
std::vector<llvm::object::coff_symbol16> OutputSymtab;
IdataContents Idata;
Chunk *ImportTableStart = nullptr;
uint64_t ImportTableSize = 0;
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);
C->setOutputSection(this);
}
void OutputSection::insertChunkAtStart(Chunk *C) {
Chunks.insert(Chunks.begin(), C);
C->setOutputSection(this);
}
void OutputSection::setPermissions(uint32_t C) {
Header.Characteristics &= ~PermMask;
Header.Characteristics |= C;
}
void OutputSection::merge(OutputSection *Other) {
for (Chunk *C : Other->Chunks)
C->setOutputSection(this);
Chunks.insert(Chunks.end(), Other->Chunks.begin(), Other->Chunks.end());
Other->Chunks.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));
}
}
} // 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) {
assert(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;
}
}
// 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};
RangeExtensionThunk *C = make<RangeExtensionThunk>(Target);
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(std::vector<Chunk *> &Chunks, int Margin) {
bool AddressesChanged = false;
DenseMap<uint64_t, Defined *> LastThunks;
size_t ThunksSize = 0;
// Recheck Chunks.size() each iteration, since we can insert more
// elements into it.
for (size_t I = 0; I != Chunks.size(); ++I) {
SectionChunk *SC = dyn_cast_or_null<SectionChunk>(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;
for (size_t J = 0, E = SC->Relocs.size(); J < E; ++J) {
const coff_relocation &Rel = SC->Relocs[J];
Symbol *&RelocTarget = SC->RelocTargets[J];
// 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 ThunkSize 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.
Chunks.insert(Chunks.begin() + ThunkInsertionSpot, ThunkChunk);
ThunkInsertionSpot++;
ThunksSize += ThunkChunk->getSize();
ThunkInsertionRVA += ThunkChunk->getSize();
AddressesChanged = true;
}
RelocTarget = Thunk;
}
}
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;
for (size_t J = 0, E = SC->Relocs.size(); J < E; ++J) {
const coff_relocation &Rel = SC->Relocs[J];
Symbol *RelocTarget = SC->RelocTargets[J];
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)
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;
for (Chunk *C : Sec->Chunks)
C->resetRelocTargets();
}
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->Chunks, 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();
readRelocTargets();
finalizeAddresses();
removeEmptySections();
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);
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('$').first;
// Treat a later period as a separator for MinGW, for sections like
// ".ctors.01234".
return S.substr(0, S.find('.', 1));
}
// For /order.
static void sortBySectionOrder(std::vector<Chunk *> &Chunks) {
auto GetPriority = [](const Chunk *C) {
if (auto *Sec = dyn_cast<SectionChunk>(C))
if (Sec->Sym)
return Config->Order.lookup(Sec->Sym->getName());
return 0;
};
std::stable_sort(Chunks.begin(), Chunks.end(),
[=](const Chunk *A, const Chunk *B) {
return GetPriority(A) < GetPriority(B);
});
}
// Sort concrete section chunks from GNU import libraries.
//
// GNU binutils doesn't use short import files, but instead produces import
// libraries that consist of object files, with section chunks for the .idata$*
// 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$* section need
// to be grouped by library, and sorted alphabetically within each library
// (which makes sure the header comes first and the trailer last).
static bool fixGnuImportChunks(
std::map<std::pair<StringRef, uint32_t>, std::vector<Chunk *>> &Map) {
uint32_t RDATA = IMAGE_SCN_CNT_INITIALIZED_DATA | IMAGE_SCN_MEM_READ;
// Make sure all .idata$* section chunks are mapped as RDATA in order to
// be sorted into the same sections as our own synthesized .idata chunks.
for (auto &Pair : Map) {
StringRef SectionName = Pair.first.first;
uint32_t OutChars = Pair.first.second;
if (!SectionName.startswith(".idata"))
continue;
if (OutChars == RDATA)
continue;
std::vector<Chunk *> &SrcVect = Pair.second;
std::vector<Chunk *> &DestVect = Map[{SectionName, RDATA}];
DestVect.insert(DestVect.end(), SrcVect.begin(), SrcVect.end());
SrcVect.clear();
}
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 &Pair : Map) {
StringRef SectionName = Pair.first.first;
if (!SectionName.startswith(".idata"))
continue;
std::vector<Chunk *> &Chunks = Pair.second;
if (!Chunks.empty())
HasIdata = true;
std::stable_sort(Chunks.begin(), Chunks.end(), [&](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.
static void addSyntheticIdata(
IdataContents &Idata,
std::map<std::pair<StringRef, uint32_t>, std::vector<Chunk *>> &Map) {
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) {
std::vector<Chunk *> &DestVect = Map[{N, RDATA}];
DestVect.insert(DestVect.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(
std::map<std::pair<StringRef, uint32_t>, std::vector<Chunk *>> &Map) {
uint32_t RDATA = IMAGE_SCN_CNT_INITIALIZED_DATA | IMAGE_SCN_MEM_READ;
std::vector<Chunk *> &ImportTables = Map[{".idata$2", RDATA}];
if (!ImportTables.empty())
ImportTableStart = ImportTables.front();
for (Chunk *C : ImportTables)
ImportTableSize += C->getSize();
std::vector<Chunk *> &IAT = Map[{".idata$5", RDATA}];
if (!IAT.empty())
IATStart = IAT.front();
for (Chunk *C : IAT)
IATSize += C->getSize();
}
// 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.
std::map<std::pair<StringRef, uint32_t>, std::vector<Chunk *>> Map;
for (Chunk *C : Symtab->getChunks()) {
auto *SC = dyn_cast<SectionChunk>(C);
if (SC && !SC->Live) {
if (Config->Verbose)
SC->printDiscardedMessage();
continue;
}
Map[{C->getSectionName(), C->getOutputCharacteristics()}].push_back(C);
}
// Even in non MinGW cases, we might need to link against GNU import
// libraries.
bool HasIdata = fixGnuImportChunks(Map);
if (!Idata.empty())
HasIdata = true;
if (HasIdata)
addSyntheticIdata(Idata, Map);
// Process an /order option.
if (!Config->Order.empty())
for (auto &Pair : Map)
sortBySectionOrder(Pair.second);
if (HasIdata)
locateImportTables(Map);
// 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 &Pair : Map) {
StringRef Name = getOutputSectionName(Pair.first.first);
uint32_t OutChars = Pair.first.second;
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 " + Pair.first.first + " -> " + Name);
sortCRTSectionChunks(Pair.second);
}
OutputSection *Sec = CreateSection(Name, OutChars);
std::vector<Chunk *> &Chunks = Pair.second;
for (Chunk *C : Chunks)
Sec->addChunk(C);
}
// Finally, move some output sections to the end.
auto SectionOrder = [&](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;
};
std::stable_sort(OutputSections.begin(), OutputSections.end(),
[&](OutputSection *S, OutputSection *T) {
return SectionOrder(S) < SectionOrder(T);
});
}
void Writer::createMiscChunks() {
for (auto &P : MergeChunk::Instances)
RdataSec->addChunk(P.second);
// 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->Machine == I386)
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 (Config->Exports.empty())
return;
for (Chunk *C : Edata.Chunks)
EdataSec->addChunk(C);
}
// 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());
uint32_t Idx = 1;
for (OutputSection *Sec : OutputSections)
Sec->SectionIndex = Idx++;
}
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;
}
}
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, SectorSize);
}
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 initialize their relocation targets.
void Writer::readRelocTargets() {
for (OutputSection *Sec : OutputSections)
for_each(parallel::par, Sec->Chunks.begin(), Sec->Chunks.end(),
[&](Chunk *C) { C->readRelocTargets(); });
}
// 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, SectorSize);
uint64_t RVA = PageSize; // The first page is kept unmapped.
FileSize = SizeOfHeaders;
for (OutputSection *Sec : OutputSections) {
if (Sec == RelocSec)
addBaserels();
uint64_t RawSize = 0, VirtualSize = 0;
Sec->Header.VirtualAddress = RVA;
for (Chunk *C : Sec->Chunks) {
VirtualSize = alignTo(VirtualSize, C->Alignment);
C->setRVA(RVA + VirtualSize);
C->OutputSectionOff = VirtualSize;
C->finalizeContents();
VirtualSize += C->getSize();
if (C->hasData())
RawSize = alignTo(VirtualSize, SectorSize);
}
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, PageSize);
FileSize += alignTo(RawSize, SectorSize);
}
SizeOfImage = alignTo(RVA, PageSize);
}
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;
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 = PageSize;
PE->FileAlignment = SectorSize;
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 (!Config->Exports.empty()) {
Dir[EXPORT_TABLE].RelativeVirtualAddress = Edata.getRVA();
Dir[EXPORT_TABLE].Size = Edata.getSize();
}
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() {
// Set the no SEH characteristic on x86 binaries unless we find exception
// handlers.
SetNoSEHCharacteristic = true;
SymbolRVASet Handlers;
for (ObjFile *File : ObjFile::Instances) {
// FIXME: We should error here instead of earlier unless /safeseh:no was
// passed.
if (!File->hasSafeSEH())
return;
markSymbolsForRVATable(File, File->getSXDataChunks(), Handlers);
}
// Remove the "no SEH" characteristic if all object files were built with
// safeseh, we found some exception handlers, and there is a load config in
// the object.
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});
}
// 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->Relocs) {
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);
if (auto *D = dyn_cast_or_null<DefinedCOFF>(Ref)) {
if (D->getCOFFSymbol().getComplexType() != COFF::IMAGE_SYM_DTYPE_FUNCTION)
// Ignore relocations against non-functions (e.g. labels).
continue;
// Mark the symbol if it's in an executable section.
Chunk *RefChunk = D->getChunk();
OutputSection *OS = RefChunk ? RefChunk->getOutputSection() : nullptr;
if (OS && OS->Header.Characteristics & IMAGE_SCN_MEM_EXECUTE)
addSymbolToRVASet(UsedSymbols, D);
}
}
}
}
// 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)
addSymbolToRVASet(AddressTakenSyms, cast<Defined>(Config->Entry));
// Ensure sections referenced in the gfid table are 16-byte aligned.
for (const ChunkAndOffset &C : AddressTakenSyms)
if (C.InputChunk->Alignment < 16)
C.InputChunk->Alignment = 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());
for_each(parallel::par, Sec->Chunks.begin(), Sec->Chunks.end(),
[&](Chunk *C) { C->writeTo(SecBuf); });
}
}
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;
if (Config->Repro)
Timestamp = static_cast<uint32_t>(xxHash64(OutputFileData));
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) {
return Buffer->getBufferStart() + C->getOutputSection()->getFileOff() +
C->getRVA() - C->getOutputSection()->getRVA();
};
uint8_t *Begin = BufAddr(FirstPdata);
uint8_t *End = BufAddr(LastPdata) + LastPdata->getSize();
if (Config->Machine == AMD64) {
struct Entry { ulittle32_t Begin, End, Unwind; };
sort(parallel::par, (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; };
sort(parallel::par, (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();
};
std::stable_sort(Chunks.begin(), Chunks.end(), 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));
}
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