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llvm-project/lld/wasm/InputChunks.cpp

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//===- InputChunks.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 "InputChunks.h"
#include "Config.h"
#include "OutputSegment.h"
#include "WriterUtils.h"
#include "lld/Common/ErrorHandler.h"
#include "lld/Common/LLVM.h"
#include "llvm/Support/LEB128.h"
#include "llvm/Support/xxhash.h"
#define DEBUG_TYPE "lld"
using namespace llvm;
using namespace llvm::wasm;
using namespace llvm::support::endian;
namespace lld {
StringRef relocTypeToString(uint8_t relocType) {
switch (relocType) {
#define WASM_RELOC(NAME, REL) \
case REL: \
return #NAME;
#include "llvm/BinaryFormat/WasmRelocs.def"
#undef WASM_RELOC
}
llvm_unreachable("unknown reloc type");
}
bool relocIs64(uint8_t relocType) {
switch (relocType) {
case R_WASM_MEMORY_ADDR_LEB64:
case R_WASM_MEMORY_ADDR_SLEB64:
case R_WASM_MEMORY_ADDR_REL_SLEB64:
case R_WASM_MEMORY_ADDR_I64:
return true;
default:
return false;
}
}
std::string toString(const wasm::InputChunk *c) {
return (toString(c->file) + ":(" + c->getName() + ")").str();
}
namespace wasm {
StringRef InputChunk::getComdatName() const {
uint32_t index = getComdat();
if (index == UINT32_MAX)
return StringRef();
return file->getWasmObj()->linkingData().Comdats[index];
}
uint32_t InputChunk::getSize() const {
if (const auto *ms = dyn_cast<SyntheticMergedChunk>(this))
return ms->builder.getSize();
if (const auto *f = dyn_cast<InputFunction>(this)) {
if (config->compressRelocations && f->file) {
return f->getCompressedSize();
}
}
return data().size();
}
uint32_t InputChunk::getInputSize() const {
if (const auto *f = dyn_cast<InputFunction>(this))
return f->function->Size;
return getSize();
}
// Copy this input chunk to an mmap'ed output file and apply relocations.
void InputChunk::writeTo(uint8_t *buf) const {
if (const auto *f = dyn_cast<InputFunction>(this)) {
if (file && config->compressRelocations)
return f->writeCompressed(buf);
} else if (const auto *ms = dyn_cast<SyntheticMergedChunk>(this)) {
ms->builder.write(buf + outSecOff);
// Apply relocations
ms->relocate(buf + outSecOff);
return;
}
// Copy contents
memcpy(buf + outSecOff, data().data(), data().size());
// Apply relocations
relocate(buf + outSecOff);
}
void InputChunk::relocate(uint8_t *buf) const {
if (relocations.empty())
return;
LLVM_DEBUG(dbgs() << "applying relocations: " << toString(this)
<< " count=" << relocations.size() << "\n");
int32_t inputSectionOffset = getInputSectionOffset();
uint64_t tombstone = getTombstone();
for (const WasmRelocation &rel : relocations) {
uint8_t *loc = buf + rel.Offset - inputSectionOffset;
LLVM_DEBUG(dbgs() << "apply reloc: type=" << relocTypeToString(rel.Type));
if (rel.Type != R_WASM_TYPE_INDEX_LEB)
LLVM_DEBUG(dbgs() << " sym=" << file->getSymbols()[rel.Index]->getName());
LLVM_DEBUG(dbgs() << " addend=" << rel.Addend << " index=" << rel.Index
<< " offset=" << rel.Offset << "\n");
auto value = file->calcNewValue(rel, tombstone, this);
switch (rel.Type) {
case R_WASM_TYPE_INDEX_LEB:
case R_WASM_FUNCTION_INDEX_LEB:
case R_WASM_GLOBAL_INDEX_LEB:
case R_WASM_TAG_INDEX_LEB:
case R_WASM_MEMORY_ADDR_LEB:
case R_WASM_TABLE_NUMBER_LEB:
encodeULEB128(value, loc, 5);
break;
case R_WASM_MEMORY_ADDR_LEB64:
encodeULEB128(value, loc, 10);
break;
case R_WASM_TABLE_INDEX_SLEB:
case R_WASM_TABLE_INDEX_REL_SLEB:
case R_WASM_MEMORY_ADDR_SLEB:
case R_WASM_MEMORY_ADDR_REL_SLEB:
case R_WASM_MEMORY_ADDR_TLS_SLEB:
encodeSLEB128(static_cast<int32_t>(value), loc, 5);
break;
case R_WASM_TABLE_INDEX_SLEB64:
case R_WASM_TABLE_INDEX_REL_SLEB64:
case R_WASM_MEMORY_ADDR_SLEB64:
case R_WASM_MEMORY_ADDR_REL_SLEB64:
encodeSLEB128(static_cast<int64_t>(value), loc, 10);
break;
case R_WASM_TABLE_INDEX_I32:
case R_WASM_MEMORY_ADDR_I32:
case R_WASM_FUNCTION_OFFSET_I32:
case R_WASM_SECTION_OFFSET_I32:
case R_WASM_GLOBAL_INDEX_I32:
case R_WASM_MEMORY_ADDR_LOCREL_I32:
write32le(loc, value);
break;
case R_WASM_TABLE_INDEX_I64:
case R_WASM_MEMORY_ADDR_I64:
case R_WASM_FUNCTION_OFFSET_I64:
write64le(loc, value);
break;
default:
llvm_unreachable("unknown relocation type");
}
}
}
// Copy relocation entries to a given output stream.
// This function is used only when a user passes "-r". For a regular link,
// we consume relocations instead of copying them to an output file.
void InputChunk::writeRelocations(raw_ostream &os) const {
if (relocations.empty())
return;
int32_t off = outSecOff - getInputSectionOffset();
LLVM_DEBUG(dbgs() << "writeRelocations: " << file->getName()
<< " offset=" << Twine(off) << "\n");
for (const WasmRelocation &rel : relocations) {
writeUleb128(os, rel.Type, "reloc type");
writeUleb128(os, rel.Offset + off, "reloc offset");
writeUleb128(os, file->calcNewIndex(rel), "reloc index");
if (relocTypeHasAddend(rel.Type))
writeSleb128(os, file->calcNewAddend(rel), "reloc addend");
}
}
uint64_t InputChunk::getTombstone() const {
if (const auto *s = dyn_cast<InputSection>(this)) {
return s->tombstoneValue;
}
return 0;
}
void InputFunction::setFunctionIndex(uint32_t index) {
LLVM_DEBUG(dbgs() << "InputFunction::setFunctionIndex: " << getName()
<< " -> " << index << "\n");
assert(!hasFunctionIndex());
functionIndex = index;
}
void InputFunction::setTableIndex(uint32_t index) {
LLVM_DEBUG(dbgs() << "InputFunction::setTableIndex: " << getName() << " -> "
<< index << "\n");
assert(!hasTableIndex());
tableIndex = index;
}
// Write a relocation value without padding and return the number of bytes
// witten.
static unsigned writeCompressedReloc(uint8_t *buf, const WasmRelocation &rel,
uint64_t value) {
switch (rel.Type) {
case R_WASM_TYPE_INDEX_LEB:
case R_WASM_FUNCTION_INDEX_LEB:
case R_WASM_GLOBAL_INDEX_LEB:
case R_WASM_TAG_INDEX_LEB:
case R_WASM_MEMORY_ADDR_LEB:
case R_WASM_MEMORY_ADDR_LEB64:
case R_WASM_TABLE_NUMBER_LEB:
return encodeULEB128(value, buf);
case R_WASM_TABLE_INDEX_SLEB:
case R_WASM_TABLE_INDEX_SLEB64:
case R_WASM_MEMORY_ADDR_SLEB:
case R_WASM_MEMORY_ADDR_SLEB64:
return encodeSLEB128(static_cast<int64_t>(value), buf);
default:
llvm_unreachable("unexpected relocation type");
}
}
static unsigned getRelocWidthPadded(const WasmRelocation &rel) {
switch (rel.Type) {
case R_WASM_TYPE_INDEX_LEB:
case R_WASM_FUNCTION_INDEX_LEB:
case R_WASM_GLOBAL_INDEX_LEB:
case R_WASM_TAG_INDEX_LEB:
case R_WASM_MEMORY_ADDR_LEB:
case R_WASM_TABLE_NUMBER_LEB:
case R_WASM_TABLE_INDEX_SLEB:
case R_WASM_MEMORY_ADDR_SLEB:
return 5;
case R_WASM_TABLE_INDEX_SLEB64:
case R_WASM_MEMORY_ADDR_LEB64:
case R_WASM_MEMORY_ADDR_SLEB64:
return 10;
default:
llvm_unreachable("unexpected relocation type");
}
}
static unsigned getRelocWidth(const WasmRelocation &rel, uint64_t value) {
uint8_t buf[10];
return writeCompressedReloc(buf, rel, value);
}
// Relocations of type LEB and SLEB in the code section are padded to 5 bytes
// so that a fast linker can blindly overwrite them without needing to worry
// about the number of bytes needed to encode the values.
// However, for optimal output the code section can be compressed to remove
// the padding then outputting non-relocatable files.
// In this case we need to perform a size calculation based on the value at each
// relocation. At best we end up saving 4 bytes for each relocation entry.
//
// This function only computes the final output size. It must be called
// before getSize() is used to calculate of layout of the code section.
void InputFunction::calculateSize() {
if (!file || !config->compressRelocations)
return;
LLVM_DEBUG(dbgs() << "calculateSize: " << getName() << "\n");
const uint8_t *secStart = file->codeSection->Content.data();
const uint8_t *funcStart = secStart + getInputSectionOffset();
uint32_t functionSizeLength;
decodeULEB128(funcStart, &functionSizeLength);
uint32_t start = getInputSectionOffset();
uint32_t end = start + function->Size;
uint64_t tombstone = getTombstone();
uint32_t lastRelocEnd = start + functionSizeLength;
for (const WasmRelocation &rel : relocations) {
LLVM_DEBUG(dbgs() << " region: " << (rel.Offset - lastRelocEnd) << "\n");
compressedFuncSize += rel.Offset - lastRelocEnd;
compressedFuncSize +=
getRelocWidth(rel, file->calcNewValue(rel, tombstone, this));
lastRelocEnd = rel.Offset + getRelocWidthPadded(rel);
}
LLVM_DEBUG(dbgs() << " final region: " << (end - lastRelocEnd) << "\n");
compressedFuncSize += end - lastRelocEnd;
// Now we know how long the resulting function is we can add the encoding
// of its length
uint8_t buf[5];
compressedSize = compressedFuncSize + encodeULEB128(compressedFuncSize, buf);
LLVM_DEBUG(dbgs() << " calculateSize orig: " << function->Size << "\n");
LLVM_DEBUG(dbgs() << " calculateSize new: " << compressedSize << "\n");
}
// Override the default writeTo method so that we can (optionally) write the
// compressed version of the function.
void InputFunction::writeCompressed(uint8_t *buf) const {
buf += outSecOff;
uint8_t *orig = buf;
(void)orig;
const uint8_t *secStart = file->codeSection->Content.data();
const uint8_t *funcStart = secStart + getInputSectionOffset();
const uint8_t *end = funcStart + function->Size;
uint64_t tombstone = getTombstone();
uint32_t count;
decodeULEB128(funcStart, &count);
funcStart += count;
LLVM_DEBUG(dbgs() << "write func: " << getName() << "\n");
buf += encodeULEB128(compressedFuncSize, buf);
const uint8_t *lastRelocEnd = funcStart;
for (const WasmRelocation &rel : relocations) {
unsigned chunkSize = (secStart + rel.Offset) - lastRelocEnd;
LLVM_DEBUG(dbgs() << " write chunk: " << chunkSize << "\n");
memcpy(buf, lastRelocEnd, chunkSize);
buf += chunkSize;
buf += writeCompressedReloc(buf, rel,
file->calcNewValue(rel, tombstone, this));
lastRelocEnd = secStart + rel.Offset + getRelocWidthPadded(rel);
}
unsigned chunkSize = end - lastRelocEnd;
LLVM_DEBUG(dbgs() << " write final chunk: " << chunkSize << "\n");
memcpy(buf, lastRelocEnd, chunkSize);
LLVM_DEBUG(dbgs() << " total: " << (buf + chunkSize - orig) << "\n");
}
uint64_t InputChunk::getChunkOffset(uint64_t offset) const {
if (const auto *ms = dyn_cast<MergeInputChunk>(this)) {
LLVM_DEBUG(dbgs() << "getChunkOffset(merged): " << getName() << "\n");
LLVM_DEBUG(dbgs() << "offset: " << offset << "\n");
LLVM_DEBUG(dbgs() << "parentOffset: " << ms->getParentOffset(offset)
<< "\n");
assert(ms->parent);
return ms->parent->getChunkOffset(ms->getParentOffset(offset));
}
return outputSegmentOffset + offset;
}
uint64_t InputChunk::getOffset(uint64_t offset) const {
return outSecOff + getChunkOffset(offset);
}
uint64_t InputChunk::getVA(uint64_t offset) const {
return (outputSeg ? outputSeg->startVA : 0) + getChunkOffset(offset);
}
// Generate code to apply relocations to the data section at runtime.
// This is only called when generating shared libaries (PIC) where address are
// not known at static link time.
void InputChunk::generateRelocationCode(raw_ostream &os) const {
LLVM_DEBUG(dbgs() << "generating runtime relocations: " << getName()
<< " count=" << relocations.size() << "\n");
unsigned opcode_ptr_const = config->is64.getValueOr(false)
? WASM_OPCODE_I64_CONST
: WASM_OPCODE_I32_CONST;
unsigned opcode_ptr_add = config->is64.getValueOr(false)
? WASM_OPCODE_I64_ADD
: WASM_OPCODE_I32_ADD;
uint64_t tombstone = getTombstone();
// TODO(sbc): Encode the relocations in the data section and write a loop
// here to apply them.
for (const WasmRelocation &rel : relocations) {
uint64_t offset = getVA(rel.Offset) - getInputSectionOffset();
LLVM_DEBUG(dbgs() << "gen reloc: type=" << relocTypeToString(rel.Type)
<< " addend=" << rel.Addend << " index=" << rel.Index
<< " output offset=" << offset << "\n");
// Get __memory_base
writeU8(os, WASM_OPCODE_GLOBAL_GET, "GLOBAL_GET");
writeUleb128(os, WasmSym::memoryBase->getGlobalIndex(), "memory_base");
// Add the offset of the relocation
writeU8(os, opcode_ptr_const, "CONST");
writeSleb128(os, offset, "offset");
writeU8(os, opcode_ptr_add, "ADD");
bool is64 = relocIs64(rel.Type);
unsigned opcode_reloc_const =
is64 ? WASM_OPCODE_I64_CONST : WASM_OPCODE_I32_CONST;
unsigned opcode_reloc_add =
is64 ? WASM_OPCODE_I64_ADD : WASM_OPCODE_I32_ADD;
unsigned opcode_reloc_store =
is64 ? WASM_OPCODE_I64_STORE : WASM_OPCODE_I32_STORE;
Symbol *sym = file->getSymbol(rel);
// Now figure out what we want to store
if (sym->hasGOTIndex()) {
writeU8(os, WASM_OPCODE_GLOBAL_GET, "GLOBAL_GET");
writeUleb128(os, sym->getGOTIndex(), "global index");
if (rel.Addend) {
writeU8(os, opcode_reloc_const, "CONST");
writeSleb128(os, rel.Addend, "addend");
writeU8(os, opcode_reloc_add, "ADD");
}
} else {
const GlobalSymbol* baseSymbol = WasmSym::memoryBase;
if (rel.Type == R_WASM_TABLE_INDEX_I32 ||
rel.Type == R_WASM_TABLE_INDEX_I64)
baseSymbol = WasmSym::tableBase;
writeU8(os, WASM_OPCODE_GLOBAL_GET, "GLOBAL_GET");
writeUleb128(os, baseSymbol->getGlobalIndex(), "base");
writeU8(os, opcode_reloc_const, "CONST");
writeSleb128(os, file->calcNewValue(rel, tombstone, this), "offset");
writeU8(os, opcode_reloc_add, "ADD");
}
// Store that value at the virtual address
writeU8(os, opcode_reloc_store, "I32_STORE");
writeUleb128(os, 2, "align");
writeUleb128(os, 0, "offset");
}
}
// Split WASM_SEG_FLAG_STRINGS section. Such a section is a sequence of
// null-terminated strings.
void MergeInputChunk::splitStrings(ArrayRef<uint8_t> data) {
LLVM_DEBUG(llvm::dbgs() << "splitStrings\n");
size_t off = 0;
StringRef s = toStringRef(data);
while (!s.empty()) {
size_t end = s.find(0);
if (end == StringRef::npos)
fatal(toString(this) + ": string is not null terminated");
size_t size = end + 1;
pieces.emplace_back(off, xxHash64(s.substr(0, size)), true);
s = s.substr(size);
off += size;
}
}
// This function is called after we obtain a complete list of input sections
// that need to be linked. This is responsible to split section contents
// into small chunks for further processing.
//
// Note that this function is called from parallelForEach. This must be
// thread-safe (i.e. no memory allocation from the pools).
void MergeInputChunk::splitIntoPieces() {
assert(pieces.empty());
// As of now we only support WASM_SEG_FLAG_STRINGS but in the future we
// could add other types of splitting (see ELF's splitIntoPieces).
assert(flags & WASM_SEG_FLAG_STRINGS);
splitStrings(data());
}
SectionPiece *MergeInputChunk::getSectionPiece(uint64_t offset) {
if (this->data().size() <= offset)
fatal(toString(this) + ": offset is outside the section");
// If Offset is not at beginning of a section piece, it is not in the map.
// In that case we need to do a binary search of the original section piece
// vector.
auto it = partition_point(
pieces, [=](SectionPiece p) { return p.inputOff <= offset; });
return &it[-1];
}
// Returns the offset in an output section for a given input offset.
// Because contents of a mergeable section is not contiguous in output,
// it is not just an addition to a base output offset.
uint64_t MergeInputChunk::getParentOffset(uint64_t offset) const {
// If Offset is not at beginning of a section piece, it is not in the map.
// In that case we need to search from the original section piece vector.
const SectionPiece *piece = getSectionPiece(offset);
uint64_t addend = offset - piece->inputOff;
return piece->outputOff + addend;
}
void SyntheticMergedChunk::finalizeContents() {
// Add all string pieces to the string table builder to create section
// contents.
for (MergeInputChunk *sec : chunks)
for (size_t i = 0, e = sec->pieces.size(); i != e; ++i)
if (sec->pieces[i].live)
builder.add(sec->getData(i));
// Fix the string table content. After this, the contents will never change.
builder.finalize();
// finalize() fixed tail-optimized strings, so we can now get
// offsets of strings. Get an offset for each string and save it
// to a corresponding SectionPiece for easy access.
for (MergeInputChunk *sec : chunks)
for (size_t i = 0, e = sec->pieces.size(); i != e; ++i)
if (sec->pieces[i].live)
sec->pieces[i].outputOff = builder.getOffset(sec->getData(i));
}
uint64_t InputSection::getTombstoneForSection(StringRef name) {
// When a function is not live we need to update relocations referring to it.
// If they occur in DWARF debug symbols, we want to change the pc of the
// function to -1 to avoid overlapping with a valid range. However for the
// debug_ranges and debug_loc sections that would conflict with the existing
// meaning of -1 so we use -2.
// Returning 0 means there is no tombstone value for this section, and relocation
// will just use the addend.
if (!name.startswith(".debug_"))
return 0;
if (name.equals(".debug_ranges") || name.equals(".debug_loc"))
return UINT64_C(-2);
return UINT64_C(-1);
}
} // namespace wasm
} // namespace lld
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