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llvm-project/lld/wasm/OutputSections.cpp

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//===- OutputSections.cpp -------------------------------------------------===//
//
// The LLVM Linker
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#include "OutputSections.h"
#include "Config.h"
#include "InputFiles.h"
#include "OutputSegment.h"
#include "SymbolTable.h"
#include "lld/Common/ErrorHandler.h"
#include "lld/Common/Memory.h"
#include "lld/Common/Threads.h"
#include "llvm/ADT/Twine.h"
#include "llvm/Support/LEB128.h"
#define DEBUG_TYPE "lld"
using namespace llvm;
using namespace llvm::wasm;
using namespace lld;
using namespace lld::wasm;
enum class RelocEncoding {
Uleb128,
Sleb128,
I32,
};
static StringRef sectionTypeToString(uint32_t SectionType) {
switch (SectionType) {
case WASM_SEC_CUSTOM:
return "CUSTOM";
case WASM_SEC_TYPE:
return "TYPE";
case WASM_SEC_IMPORT:
return "IMPORT";
case WASM_SEC_FUNCTION:
return "FUNCTION";
case WASM_SEC_TABLE:
return "TABLE";
case WASM_SEC_MEMORY:
return "MEMORY";
case WASM_SEC_GLOBAL:
return "GLOBAL";
case WASM_SEC_EXPORT:
return "EXPORT";
case WASM_SEC_START:
return "START";
case WASM_SEC_ELEM:
return "ELEM";
case WASM_SEC_CODE:
return "CODE";
case WASM_SEC_DATA:
return "DATA";
default:
fatal("invalid section type");
}
}
std::string lld::toString(OutputSection *Section) {
std::string rtn = sectionTypeToString(Section->Type);
if (!Section->Name.empty())
rtn += "(" + Section->Name + ")";
return rtn;
}
static void applyRelocation(uint8_t *Buf, const OutputRelocation &Reloc) {
DEBUG(dbgs() << "write reloc: type=" << Reloc.Reloc.Type
<< " index=" << Reloc.Reloc.Index << " new=" << Reloc.NewIndex
<< " value=" << Reloc.Value << " offset=" << Reloc.Reloc.Offset
<< "\n");
Buf += Reloc.Reloc.Offset;
int64_t ExistingValue;
switch (Reloc.Reloc.Type) {
case R_WEBASSEMBLY_TYPE_INDEX_LEB:
case R_WEBASSEMBLY_FUNCTION_INDEX_LEB:
ExistingValue = decodeULEB128(Buf);
if (ExistingValue != Reloc.Reloc.Index) {
DEBUG(dbgs() << "existing value: " << decodeULEB128(Buf) << "\n");
assert(decodeULEB128(Buf) == Reloc.Reloc.Index);
}
LLVM_FALLTHROUGH;
case R_WEBASSEMBLY_MEMORY_ADDR_LEB:
case R_WEBASSEMBLY_GLOBAL_INDEX_LEB:
encodeULEB128(Reloc.Value, Buf, 5);
break;
case R_WEBASSEMBLY_TABLE_INDEX_SLEB:
ExistingValue = decodeSLEB128(Buf);
if (ExistingValue != Reloc.Reloc.Index) {
DEBUG(dbgs() << "existing value: " << decodeSLEB128(Buf) << "\n");
assert(decodeSLEB128(Buf) == Reloc.Reloc.Index);
}
LLVM_FALLTHROUGH;
case R_WEBASSEMBLY_MEMORY_ADDR_SLEB:
encodeSLEB128(static_cast<int32_t>(Reloc.Value), Buf, 5);
break;
case R_WEBASSEMBLY_TABLE_INDEX_I32:
case R_WEBASSEMBLY_MEMORY_ADDR_I32:
support::endian::write32<support::little>(Buf, Reloc.Value);
break;
default:
llvm_unreachable("unknown relocation type");
}
}
static void applyRelocations(uint8_t *Buf,
const std::vector<OutputRelocation> &Relocs) {
log("applyRelocations: count=" + Twine(Relocs.size()));
for (const OutputRelocation &Reloc : Relocs) {
applyRelocation(Buf, Reloc);
}
}
// Relocations contain an index into the function, global or table index
// space of the input file. This function takes a relocation and returns the
// relocated index (i.e. translates from the input index space to the output
// index space).
static uint32_t calcNewIndex(const ObjFile &File, const WasmRelocation &Reloc) {
switch (Reloc.Type) {
case R_WEBASSEMBLY_TYPE_INDEX_LEB:
return File.relocateTypeIndex(Reloc.Index);
case R_WEBASSEMBLY_FUNCTION_INDEX_LEB:
return File.relocateFunctionIndex(Reloc.Index);
case R_WEBASSEMBLY_TABLE_INDEX_I32:
case R_WEBASSEMBLY_TABLE_INDEX_SLEB:
return File.relocateTableIndex(Reloc.Index);
case R_WEBASSEMBLY_GLOBAL_INDEX_LEB:
case R_WEBASSEMBLY_MEMORY_ADDR_LEB:
case R_WEBASSEMBLY_MEMORY_ADDR_SLEB:
case R_WEBASSEMBLY_MEMORY_ADDR_I32:
return File.relocateGlobalIndex(Reloc.Index);
default:
llvm_unreachable("unknown relocation type");
}
}
// Take a vector of relocations from an input file and create output
// relocations based on them. Calculates the updated index and offset for
// each relocation as well as the value to write out in the final binary.
static void calcRelocations(const ObjFile &File,
ArrayRef<WasmRelocation> Relocs,
std::vector<OutputRelocation> &OutputRelocs,
int32_t OutputOffset) {
log("calcRelocations: " + File.getName() + " offset=" + Twine(OutputOffset));
for (const WasmRelocation &Reloc : Relocs) {
int64_t NewIndex = calcNewIndex(File, Reloc);
OutputRelocation NewReloc;
NewReloc.Reloc = Reloc;
NewReloc.Reloc.Offset += OutputOffset;
NewReloc.NewIndex = NewIndex;
DEBUG(dbgs() << "reloc: type=" << Reloc.Type << " index=" << Reloc.Index
<< " offset=" << Reloc.Offset << " new=" << NewIndex
<< " newOffset=" << NewReloc.Reloc.Offset << "\n");
switch (Reloc.Type) {
case R_WEBASSEMBLY_MEMORY_ADDR_SLEB:
case R_WEBASSEMBLY_MEMORY_ADDR_I32:
case R_WEBASSEMBLY_MEMORY_ADDR_LEB:
NewReloc.Value = File.getRelocatedAddress(Reloc.Index);
if (NewReloc.Value != UINT32_MAX)
NewReloc.Value += Reloc.Addend;
break;
default:
NewReloc.Value = NewIndex;
}
OutputRelocs.emplace_back(NewReloc);
}
}
void OutputSection::createHeader(size_t BodySize) {
raw_string_ostream OS(Header);
debugWrite(OS.tell(),
"section type [" + Twine(sectionTypeToString(Type)) + "]");
writeUleb128(OS, Type, nullptr);
writeUleb128(OS, BodySize, "section size");
OS.flush();
log("createHeader: " + toString(this) + " body=" + Twine(BodySize) +
" total=" + Twine(getSize()));
}
CodeSection::CodeSection(uint32_t NumFunctions, std::vector<ObjFile *> &Objs)
: OutputSection(WASM_SEC_CODE), InputObjects(Objs) {
raw_string_ostream OS(CodeSectionHeader);
writeUleb128(OS, NumFunctions, "function count");
OS.flush();
BodySize = CodeSectionHeader.size();
for (ObjFile *File : InputObjects) {
if (!File->CodeSection)
continue;
File->CodeOffset = BodySize;
ArrayRef<uint8_t> Content = File->CodeSection->Content;
unsigned HeaderSize = 0;
decodeULEB128(Content.data(), &HeaderSize);
calcRelocations(*File, File->CodeSection->Relocations,
File->CodeRelocations, BodySize - HeaderSize);
size_t PayloadSize = Content.size() - HeaderSize;
BodySize += PayloadSize;
}
createHeader(BodySize);
}
void CodeSection::writeTo(uint8_t *Buf) {
log("writing " + toString(this));
log(" size=" + Twine(getSize()));
Buf += Offset;
// Write section header
memcpy(Buf, Header.data(), Header.size());
Buf += Header.size();
uint8_t *ContentsStart = Buf;
// Write code section headers
memcpy(Buf, CodeSectionHeader.data(), CodeSectionHeader.size());
Buf += CodeSectionHeader.size();
// Write code section bodies
parallelForEach(InputObjects, [ContentsStart](ObjFile *File) {
if (!File->CodeSection)
return;
ArrayRef<uint8_t> Content(File->CodeSection->Content);
// Payload doesn't include the initial header (function count)
unsigned HeaderSize = 0;
decodeULEB128(Content.data(), &HeaderSize);
size_t PayloadSize = Content.size() - HeaderSize;
memcpy(ContentsStart + File->CodeOffset, Content.data() + HeaderSize,
PayloadSize);
log("applying relocations for: " + File->getName());
if (File->CodeRelocations.size())
applyRelocations(ContentsStart, File->CodeRelocations);
});
}
uint32_t CodeSection::numRelocations() const {
uint32_t Count = 0;
for (ObjFile *File : InputObjects)
Count += File->CodeRelocations.size();
return Count;
}
void CodeSection::writeRelocations(raw_ostream &OS) const {
for (ObjFile *File : InputObjects)
for (const OutputRelocation &Reloc : File->CodeRelocations)
writeReloc(OS, Reloc);
}
DataSection::DataSection(std::vector<OutputSegment *> &Segments)
: OutputSection(WASM_SEC_DATA), Segments(Segments) {
raw_string_ostream OS(DataSectionHeader);
writeUleb128(OS, Segments.size(), "data segment count");
OS.flush();
BodySize = DataSectionHeader.size();
for (OutputSegment *Segment : Segments) {
raw_string_ostream OS(Segment->Header);
writeUleb128(OS, 0, "memory index");
writeUleb128(OS, WASM_OPCODE_I32_CONST, "opcode:i32const");
writeSleb128(OS, Segment->StartVA, "memory offset");
writeUleb128(OS, WASM_OPCODE_END, "opcode:end");
writeUleb128(OS, Segment->Size, "segment size");
OS.flush();
Segment->setSectionOffset(BodySize);
BodySize += Segment->Header.size();
log("Data segment: size=" + Twine(Segment->Size));
for (const InputSegment *InputSeg : Segment->InputSegments) {
uint32_t InputOffset = InputSeg->getInputSectionOffset();
uint32_t OutputOffset = Segment->getSectionOffset() +
Segment->Header.size() +
InputSeg->getOutputSegmentOffset();
calcRelocations(*InputSeg->File, InputSeg->Relocations, Relocations,
OutputOffset - InputOffset);
}
BodySize += Segment->Size;
}
createHeader(BodySize);
}
void DataSection::writeTo(uint8_t *Buf) {
log("writing " + toString(this) + " size=" + Twine(getSize()) +
" body=" + Twine(BodySize));
Buf += Offset;
// Write section header
memcpy(Buf, Header.data(), Header.size());
Buf += Header.size();
uint8_t *ContentsStart = Buf;
// Write data section headers
memcpy(Buf, DataSectionHeader.data(), DataSectionHeader.size());
parallelForEach(Segments, [ContentsStart](const OutputSegment *Segment) {
// Write data segment header
uint8_t *SegStart = ContentsStart + Segment->getSectionOffset();
memcpy(SegStart, Segment->Header.data(), Segment->Header.size());
// Write segment data payload
for (const InputSegment *Input : Segment->InputSegments) {
ArrayRef<uint8_t> Content(Input->Segment->Data.Content);
memcpy(SegStart + Segment->Header.size() +
Input->getOutputSegmentOffset(),
Content.data(), Content.size());
}
});
applyRelocations(ContentsStart, Relocations);
}
void DataSection::writeRelocations(raw_ostream &OS) const {
for (const OutputRelocation &Reloc : Relocations)
writeReloc(OS, Reloc);
}
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