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OutputSections.cpp
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OutputSections.cpp
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//===- OutputSections.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 "OutputSections.h"
#include "InputChunks.h"
#include "InputFiles.h"
#include "OutputSegment.h"
#include "WriterUtils.h"
#include "lld/Common/ErrorHandler.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;
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_EVENT:
return "EVENT";
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");
}
}
// Returns a string, e.g. "FUNCTION(.text)".
std::string lld::toString(const OutputSection &Sec) {
if (!Sec.Name.empty())
return (Sec.getSectionName() + "(" + Sec.Name + ")").str();
return Sec.getSectionName();
}
StringRef OutputSection::getSectionName() const {
return sectionTypeToString(Type);
}
void OutputSection::createHeader(size_t BodySize) {
raw_string_ostream OS(Header);
debugWrite(OS.tell(), "section type [" + getSectionName() + "]");
encodeULEB128(Type, OS);
writeUleb128(OS, BodySize, "section size");
OS.flush();
log("createHeader: " + toString(*this) + " body=" + Twine(BodySize) +
" total=" + Twine(getSize()));
}
CodeSection::CodeSection(ArrayRef<InputFunction *> Functions)
: OutputSection(WASM_SEC_CODE), Functions(Functions) {
assert(Functions.size() > 0);
raw_string_ostream OS(CodeSectionHeader);
writeUleb128(OS, Functions.size(), "function count");
OS.flush();
BodySize = CodeSectionHeader.size();
for (InputFunction *Func : Functions) {
Func->OutputOffset = BodySize;
Func->calculateSize();
BodySize += Func->getSize();
}
createHeader(BodySize);
}
void CodeSection::writeTo(uint8_t *Buf) {
log("writing " + toString(*this));
log(" size=" + Twine(getSize()));
log(" headersize=" + Twine(Header.size()));
log(" codeheadersize=" + Twine(CodeSectionHeader.size()));
Buf += Offset;
// Write section header
memcpy(Buf, Header.data(), Header.size());
Buf += Header.size();
// Write code section headers
memcpy(Buf, CodeSectionHeader.data(), CodeSectionHeader.size());
// Write code section bodies
parallelForEach(Functions,
[&](const InputChunk *Chunk) { Chunk->writeTo(Buf); });
}
uint32_t CodeSection::numRelocations() const {
uint32_t Count = 0;
for (const InputChunk *Func : Functions)
Count += Func->NumRelocations();
return Count;
}
void CodeSection::writeRelocations(raw_ostream &OS) const {
for (const InputChunk *C : Functions)
C->writeRelocations(OS);
}
DataSection::DataSection(ArrayRef<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");
WasmInitExpr InitExpr;
if (Config->Pic) {
assert(Segments.size() <= 1 &&
"Currenly only a single data segment is supported in PIC mode");
InitExpr.Opcode = WASM_OPCODE_GLOBAL_GET;
InitExpr.Value.Global = WasmSym::MemoryBase->getGlobalIndex();
} else {
InitExpr.Opcode = WASM_OPCODE_I32_CONST;
InitExpr.Value.Int32 = Segment->StartVA;
}
writeInitExpr(OS, InitExpr);
writeUleb128(OS, Segment->Size, "segment size");
OS.flush();
Segment->SectionOffset = BodySize;
BodySize += Segment->Header.size() + Segment->Size;
log("Data segment: size=" + Twine(Segment->Size));
for (InputSegment *InputSeg : Segment->InputSegments)
InputSeg->OutputOffset = Segment->SectionOffset + Segment->Header.size() +
InputSeg->OutputSegmentOffset;
}
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();
// Write data section headers
memcpy(Buf, DataSectionHeader.data(), DataSectionHeader.size());
parallelForEach(Segments, [&](const OutputSegment *Segment) {
// Write data segment header
uint8_t *SegStart = Buf + Segment->SectionOffset;
memcpy(SegStart, Segment->Header.data(), Segment->Header.size());
// Write segment data payload
for (const InputChunk *Chunk : Segment->InputSegments)
Chunk->writeTo(Buf);
});
}
uint32_t DataSection::numRelocations() const {
uint32_t Count = 0;
for (const OutputSegment *Seg : Segments)
for (const InputChunk *InputSeg : Seg->InputSegments)
Count += InputSeg->NumRelocations();
return Count;
}
void DataSection::writeRelocations(raw_ostream &OS) const {
for (const OutputSegment *Seg : Segments)
for (const InputChunk *C : Seg->InputSegments)
C->writeRelocations(OS);
}
CustomSection::CustomSection(std::string Name,
ArrayRef<InputSection *> InputSections)
: OutputSection(WASM_SEC_CUSTOM, Name), PayloadSize(0),
InputSections(InputSections) {
raw_string_ostream OS(NameData);
encodeULEB128(Name.size(), OS);
OS << Name;
OS.flush();
for (InputSection *Section : InputSections) {
Section->OutputOffset = PayloadSize;
PayloadSize += Section->getSize();
}
createHeader(PayloadSize + NameData.size());
}
void CustomSection::writeTo(uint8_t *Buf) {
log("writing " + toString(*this) + " size=" + Twine(getSize()) +
" chunks=" + Twine(InputSections.size()));
assert(Offset);
Buf += Offset;
// Write section header
memcpy(Buf, Header.data(), Header.size());
Buf += Header.size();
memcpy(Buf, NameData.data(), NameData.size());
Buf += NameData.size();
// Write custom sections payload
parallelForEach(InputSections,
[&](const InputSection *Section) { Section->writeTo(Buf); });
}
uint32_t CustomSection::numRelocations() const {
uint32_t Count = 0;
for (const InputSection *InputSect : InputSections)
Count += InputSect->NumRelocations();
return Count;
}
void CustomSection::writeRelocations(raw_ostream &OS) const {
for (const InputSection *S : InputSections)
S->writeRelocations(OS);
}