llvm-project

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//===- OutputSections.cpp -------------------------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#include "OutputSections.h"
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#include "InputChunks.h"
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#include "InputElement.h"
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#include "InputFiles.h"
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#include "OutputSegment.h"
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#include "WriterUtils.h"
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#include "lld/Common/ErrorHandler.h"
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#include "lld/Common/Memory.h"
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#include "llvm/ADT/Twine.h"
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#include "llvm/Support/LEB128.h"
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#include "llvm/Support/Parallel.h"
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#define DEBUG_TYPE "lld"
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using namespace llvm;
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using namespace llvm::wasm;
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namespace lld {
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// Returns a string, e.g. "FUNCTION(.text)".
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std::string toString(const wasm::OutputSection &sec) {
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  if (!sec.name.empty())
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    return (sec.getSectionName() + "(" + sec.name + ")").str();
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  return std::string(sec.getSectionName());
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}
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namespace wasm {
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StringRef OutputSection::getSectionName() const {
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  return sectionTypeToString(type);
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}
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void OutputSection::createHeader(size_t bodySize) {
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  raw_string_ostream os(header);
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  debugWrite(os.tell(), "section type [" + getSectionName() + "]");
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  encodeULEB128(type, os);
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  writeUleb128(os, bodySize, "section size");
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  os.flush();
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  log("createHeader: " + toString(*this) + " body=" + Twine(bodySize) +
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      " total=" + Twine(getSize()));
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}
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void CodeSection::finalizeContents() {
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  raw_string_ostream os(codeSectionHeader);
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  writeUleb128(os, functions.size(), "function count");
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  os.flush();
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  bodySize = codeSectionHeader.size();
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  for (InputFunction *func : functions) {
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    func->outputSec = this;
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    func->outSecOff = bodySize;
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    func->calculateSize();
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    // All functions should have a non-empty body at this point
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    assert(func->getSize());
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    bodySize += func->getSize();
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  }
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  createHeader(bodySize);
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}
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void CodeSection::writeTo(uint8_t *buf) {
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  log("writing " + toString(*this) + " offset=" + Twine(offset) +
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      " size=" + Twine(getSize()));
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  log(" headersize=" + Twine(header.size()));
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  log(" codeheadersize=" + Twine(codeSectionHeader.size()));
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  buf += offset;
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  // Write section header
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  memcpy(buf, header.data(), header.size());
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  buf += header.size();
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  // Write code section headers
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  memcpy(buf, codeSectionHeader.data(), codeSectionHeader.size());
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  // Write code section bodies
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  for (const InputChunk *chunk : functions)
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    chunk->writeTo(buf);
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}
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uint32_t CodeSection::getNumRelocations() const {
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  uint32_t count = 0;
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  for (const InputChunk *func : functions)
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    count += func->getNumRelocations();
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  return count;
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}
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void CodeSection::writeRelocations(raw_ostream &os) const {
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  for (const InputChunk *c : functions)
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    c->writeRelocations(os);
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}
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void DataSection::finalizeContents() {
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  raw_string_ostream os(dataSectionHeader);
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  unsigned segmentCount = llvm::count_if(segments, [](OutputSegment *segment) {
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    return segment->requiredInBinary();
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  });
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#ifndef NDEBUG
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  unsigned activeCount = llvm::count_if(segments, [](OutputSegment *segment) {
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    return (segment->initFlags & WASM_DATA_SEGMENT_IS_PASSIVE) == 0;
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  });
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#endif
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  assert((config->sharedMemory || !ctx.isPic || config->extendedConst ||
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          activeCount <= 1) &&
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         "output segments should have been combined by now");
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  writeUleb128(os, segmentCount, "data segment count");
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  os.flush();
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  bodySize = dataSectionHeader.size();
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  bool is64 = config->is64.value_or(false);
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  for (OutputSegment *segment : segments) {
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    if (!segment->requiredInBinary())
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      continue;
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    raw_string_ostream os(segment->header);
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    writeUleb128(os, segment->initFlags, "init flags");
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    if (segment->initFlags & WASM_DATA_SEGMENT_HAS_MEMINDEX)
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      writeUleb128(os, 0, "memory index");
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    if ((segment->initFlags & WASM_DATA_SEGMENT_IS_PASSIVE) == 0) {
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      if (ctx.isPic && config->extendedConst) {
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        writeU8(os, WASM_OPCODE_GLOBAL_GET, "global get");
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        writeUleb128(os, WasmSym::memoryBase->getGlobalIndex(),
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                     "literal (global index)");
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        if (segment->startVA) {
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          writePtrConst(os, segment->startVA, is64, "offset");
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          writeU8(os, is64 ? WASM_OPCODE_I64_ADD : WASM_OPCODE_I32_ADD, "add");
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        }
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        writeU8(os, WASM_OPCODE_END, "opcode:end");
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      } else {
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        WasmInitExpr initExpr;
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        initExpr.Extended = false;
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        if (ctx.isPic) {
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          assert(segment->startVA == 0);
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          initExpr.Inst.Opcode = WASM_OPCODE_GLOBAL_GET;
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          initExpr.Inst.Value.Global = WasmSym::memoryBase->getGlobalIndex();
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        } else {
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          initExpr = intConst(segment->startVA, is64);
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        }
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        writeInitExpr(os, initExpr);
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      }
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    }
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    writeUleb128(os, segment->size, "segment size");
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    os.flush();
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    segment->sectionOffset = bodySize;
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    bodySize += segment->header.size() + segment->size;
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    log("Data segment: size=" + Twine(segment->size) + ", startVA=" +
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        Twine::utohexstr(segment->startVA) + ", name=" + segment->name);
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    for (InputChunk *inputSeg : segment->inputSegments) {
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      inputSeg->outputSec = this;
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      inputSeg->outSecOff = segment->sectionOffset + segment->header.size() +
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                            inputSeg->outputSegmentOffset;
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    }
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  }
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  createHeader(bodySize);
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}
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void DataSection::writeTo(uint8_t *buf) {
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  log("writing " + toString(*this) + " offset=" + Twine(offset) +
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      " size=" + Twine(getSize()) + " body=" + Twine(bodySize));
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  buf += offset;
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  // Write section header
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  memcpy(buf, header.data(), header.size());
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  buf += header.size();
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  // Write data section headers
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  memcpy(buf, dataSectionHeader.data(), dataSectionHeader.size());
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  for (const OutputSegment *segment : segments) {
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    if (!segment->requiredInBinary())
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      continue;
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    // Write data segment header
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    uint8_t *segStart = buf + segment->sectionOffset;
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    memcpy(segStart, segment->header.data(), segment->header.size());
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    // Write segment data payload
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    for (const InputChunk *chunk : segment->inputSegments)
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      chunk->writeTo(buf);
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  }
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}
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uint32_t DataSection::getNumRelocations() const {
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  uint32_t count = 0;
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  for (const OutputSegment *seg : segments)
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    for (const InputChunk *inputSeg : seg->inputSegments)
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      count += inputSeg->getNumRelocations();
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  return count;
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}
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void DataSection::writeRelocations(raw_ostream &os) const {
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  for (const OutputSegment *seg : segments)
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    for (const InputChunk *c : seg->inputSegments)
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      c->writeRelocations(os);
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}
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bool DataSection::isNeeded() const {
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  for (const OutputSegment *seg : segments)
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    if (seg->requiredInBinary())
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      return true;
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  return false;
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}
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// Lots of duplication here with OutputSegment::finalizeInputSegments
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void CustomSection::finalizeInputSections() {
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  SyntheticMergedChunk *mergedSection = nullptr;
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  std::vector<InputChunk *> newSections;
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  for (InputChunk *s : inputSections) {
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    s->outputSec = this;
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    MergeInputChunk *ms = dyn_cast<MergeInputChunk>(s);
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    if (!ms) {
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      newSections.push_back(s);
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      continue;
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    }
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    if (!mergedSection) {
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      mergedSection =
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          make<SyntheticMergedChunk>(name, 0, WASM_SEG_FLAG_STRINGS);
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      newSections.push_back(mergedSection);
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      mergedSection->outputSec = this;
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    }
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    mergedSection->addMergeChunk(ms);
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  }
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  if (!mergedSection)
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    return;
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  mergedSection->finalizeContents();
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  inputSections = newSections;
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}
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void CustomSection::finalizeContents() {
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  finalizeInputSections();
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  raw_string_ostream os(nameData);
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  encodeULEB128(name.size(), os);
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  os << name;
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  os.flush();
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  for (InputChunk *section : inputSections) {
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    assert(!section->discarded);
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    section->outSecOff = payloadSize;
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    payloadSize += section->getSize();
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  }
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  createHeader(payloadSize + nameData.size());
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}
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void CustomSection::writeTo(uint8_t *buf) {
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  log("writing " + toString(*this) + " offset=" + Twine(offset) +
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      " size=" + Twine(getSize()) + " chunks=" + Twine(inputSections.size()));
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  assert(offset);
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  buf += offset;
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  // Write section header
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  memcpy(buf, header.data(), header.size());
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  buf += header.size();
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  memcpy(buf, nameData.data(), nameData.size());
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  buf += nameData.size();
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  // Write custom sections payload
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  for (const InputChunk *section : inputSections)
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    section->writeTo(buf);
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}
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uint32_t CustomSection::getNumRelocations() const {
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  uint32_t count = 0;
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  for (const InputChunk *inputSect : inputSections)
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    count += inputSect->getNumRelocations();
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  return count;
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}
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void CustomSection::writeRelocations(raw_ostream &os) const {
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  for (const InputChunk *s : inputSections)
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    s->writeRelocations(os);
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}
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} // namespace wasm
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} // namespace lld
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