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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"
#define DEBUG_TYPE "lld"
using namespace llvm;
using namespace llvm::wasm;
using namespace llvm::support::endian;
using namespace lld;
using namespace lld::wasm;
StringRef lld::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");
}
std::string lld::toString(const InputChunk *c) {
return (toString(c->file) + ":(" + c->getName() + ")").str();
}
StringRef InputChunk::getComdatName() const {
uint32_t index = getComdat();
if (index == UINT32_MAX)
return StringRef();
return file->getWasmObj()->linkingData().Comdats[index];
}
void InputChunk::verifyRelocTargets() const {
for (const WasmRelocation &rel : relocations) {
uint32_t existingValue;
unsigned bytesRead = 0;
uint32_t offset = rel.Offset - getInputSectionOffset();
const uint8_t *loc = data().data() + offset;
switch (rel.Type) {
case R_WASM_TYPE_INDEX_LEB:
case R_WASM_FUNCTION_INDEX_LEB:
case R_WASM_GLOBAL_INDEX_LEB:
case R_WASM_EVENT_INDEX_LEB:
case R_WASM_MEMORY_ADDR_LEB:
existingValue = decodeULEB128(loc, &bytesRead);
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:
existingValue = static_cast<uint32_t>(decodeSLEB128(loc, &bytesRead));
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:
existingValue = static_cast<uint32_t>(read32le(loc));
break;
default:
llvm_unreachable("unknown relocation type");
}
if (bytesRead && bytesRead != 5)
warn("expected LEB at relocation site be 5-byte padded");
if (rel.Type != R_WASM_GLOBAL_INDEX_LEB) {
uint32_t expectedValue = file->calcExpectedValue(rel);
if (expectedValue != existingValue)
warn("unexpected existing value for " + relocTypeToString(rel.Type) +
": existing=" + Twine(existingValue) +
" expected=" + Twine(expectedValue));
}
}
}
// Copy this input chunk to an mmap'ed output file and apply relocations.
void InputChunk::writeTo(uint8_t *buf) const {
// Copy contents
memcpy(buf + outputOffset, data().data(), data().size());
// Apply relocations
if (relocations.empty())
return;
#ifndef NDEBUG
verifyRelocTargets();
#endif
LLVM_DEBUG(dbgs() << "applying relocations: " << toString(this)
<< " count=" << relocations.size() << "\n");
int32_t off = outputOffset - getInputSectionOffset();
for (const WasmRelocation &rel : relocations) {
uint8_t *loc = buf + rel.Offset + off;
uint32_t value = file->calcNewValue(rel);
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
<< " value=" << value << " offset=" << rel.Offset
<< "\n");
switch (rel.Type) {
case R_WASM_TYPE_INDEX_LEB:
case R_WASM_FUNCTION_INDEX_LEB:
case R_WASM_GLOBAL_INDEX_LEB:
case R_WASM_EVENT_INDEX_LEB:
case R_WASM_MEMORY_ADDR_LEB:
encodeULEB128(value, loc, 5);
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:
encodeSLEB128(static_cast<int32_t>(value), loc, 5);
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:
write32le(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 = outputOffset - 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");
}
}
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,
uint32_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_EVENT_INDEX_LEB:
case R_WASM_MEMORY_ADDR_LEB:
return encodeULEB128(value, buf);
case R_WASM_TABLE_INDEX_SLEB:
case R_WASM_MEMORY_ADDR_SLEB:
return encodeSLEB128(static_cast<int32_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_EVENT_INDEX_LEB:
case R_WASM_MEMORY_ADDR_LEB:
case R_WASM_TABLE_INDEX_SLEB:
case R_WASM_MEMORY_ADDR_SLEB:
return 5;
default:
llvm_unreachable("unexpected relocation type");
}
}
static unsigned getRelocWidth(const WasmRelocation &rel, uint32_t value) {
uint8_t buf[5];
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;
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));
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::writeTo(uint8_t *buf) const {
if (!file || !config->compressRelocations)
return InputChunk::writeTo(buf);
buf += outputOffset;
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;
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));
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");
}
// 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 InputSegment::generateRelocationCode(raw_ostream &os) const {
LLVM_DEBUG(dbgs() << "generating runtime relocations: " << getName()
<< " count=" << relocations.size() << "\n");
// TODO(sbc): Encode the relocations in the data section and write a loop
// here to apply them.
uint32_t segmentVA = outputSeg->startVA + outputSegmentOffset;
for (const WasmRelocation &rel : relocations) {
uint32_t offset = rel.Offset - getInputSectionOffset();
uint32_t outputOffset = segmentVA + offset;
LLVM_DEBUG(dbgs() << "gen reloc: type=" << relocTypeToString(rel.Type)
<< " addend=" << rel.Addend << " index=" << rel.Index
<< " output offset=" << outputOffset << "\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, WASM_OPCODE_I32_CONST, "I32_CONST");
writeSleb128(os, outputOffset, "offset");
writeU8(os, WASM_OPCODE_I32_ADD, "ADD");
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, WASM_OPCODE_I32_CONST, "CONST");
writeSleb128(os, rel.Addend, "addend");
writeU8(os, WASM_OPCODE_I32_ADD, "ADD");
}
} else {
const GlobalSymbol* baseSymbol = WasmSym::memoryBase;
if (rel.Type == R_WASM_TABLE_INDEX_I32)
baseSymbol = WasmSym::tableBase;
writeU8(os, WASM_OPCODE_GLOBAL_GET, "GLOBAL_GET");
writeUleb128(os, baseSymbol->getGlobalIndex(), "base");
writeU8(os, WASM_OPCODE_I32_CONST, "CONST");
writeSleb128(os, file->calcNewValue(rel), "offset");
writeU8(os, WASM_OPCODE_I32_ADD, "ADD");
}
// Store that value at the virtual address
writeU8(os, WASM_OPCODE_I32_STORE, "I32_STORE");
writeUleb128(os, 2, "align");
writeUleb128(os, 0, "offset");
}
}
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