1//===- OutputSections.cpp -------------------------------------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8
9#include "OutputSections.h"
10#include "InputChunks.h"
11#include "InputElement.h"
12#include "InputFiles.h"
13#include "OutputSegment.h"
14#include "WriterUtils.h"
15#include "lld/Common/ErrorHandler.h"
16#include "lld/Common/Memory.h"
17#include "llvm/ADT/Twine.h"
18#include "llvm/Support/LEB128.h"
19#include "llvm/Support/Parallel.h"
20
21#define DEBUG_TYPE "lld"
22
23using namespace llvm;
24using namespace llvm::wasm;
25
26namespace lld {
27
28// Returns a string, e.g. "FUNCTION(.text)".
29std::string toString(const wasm::OutputSection &sec) {
30  if (!sec.name.empty())
31    return (sec.getSectionName() + "(" + sec.name + ")").str();
32  return std::string(sec.getSectionName());
33}
34
35namespace wasm {
36StringRef OutputSection::getSectionName() const {
37  return sectionTypeToString(type);
38}
39
40void OutputSection::createHeader(size_t bodySize) {
41  raw_string_ostream os(header);
42  debugWrite(os.tell(), "section type [" + getSectionName() + "]");
43  encodeULEB128(type, os);
44  writeUleb128(os, bodySize, "section size");
45  os.flush();
46  log("createHeader: " + toString(*this) + " body=" + Twine(bodySize) +
47      " total=" + Twine(getSize()));
48}
49
50void CodeSection::finalizeContents() {
51  raw_string_ostream os(codeSectionHeader);
52  writeUleb128(os, functions.size(), "function count");
53  os.flush();
54  bodySize = codeSectionHeader.size();
55
56  for (InputFunction *func : functions) {
57    func->outputSec = this;
58    func->outSecOff = bodySize;
59    func->calculateSize();
60    // All functions should have a non-empty body at this point
61    assert(func->getSize());
62    bodySize += func->getSize();
63  }
64
65  createHeader(bodySize);
66}
67
68void CodeSection::writeTo(uint8_t *buf) {
69  log("writing " + toString(*this) + " offset=" + Twine(offset) +
70      " size=" + Twine(getSize()));
71  log(" headersize=" + Twine(header.size()));
72  log(" codeheadersize=" + Twine(codeSectionHeader.size()));
73  buf += offset;
74
75  // Write section header
76  memcpy(buf, header.data(), header.size());
77  buf += header.size();
78
79  // Write code section headers
80  memcpy(buf, codeSectionHeader.data(), codeSectionHeader.size());
81
82  // Write code section bodies
83  for (const InputChunk *chunk : functions)
84    chunk->writeTo(buf);
85}
86
87uint32_t CodeSection::getNumRelocations() const {
88  uint32_t count = 0;
89  for (const InputChunk *func : functions)
90    count += func->getNumRelocations();
91  return count;
92}
93
94void CodeSection::writeRelocations(raw_ostream &os) const {
95  for (const InputChunk *c : functions)
96    c->writeRelocations(os);
97}
98
99void DataSection::finalizeContents() {
100  raw_string_ostream os(dataSectionHeader);
101  unsigned segmentCount = llvm::count_if(segments, [](OutputSegment *segment) {
102    return segment->requiredInBinary();
103  });
104#ifndef NDEBUG
105  unsigned activeCount = llvm::count_if(segments, [](OutputSegment *segment) {
106    return (segment->initFlags & WASM_DATA_SEGMENT_IS_PASSIVE) == 0;
107  });
108#endif
109
110  assert((config->sharedMemory || !config->isPic || config->extendedConst ||
111          activeCount <= 1) &&
112         "output segments should have been combined by now");
113
114  writeUleb128(os, segmentCount, "data segment count");
115  os.flush();
116  bodySize = dataSectionHeader.size();
117  bool is64 = config->is64.value_or(false);
118
119  for (OutputSegment *segment : segments) {
120    if (!segment->requiredInBinary())
121      continue;
122    raw_string_ostream os(segment->header);
123    writeUleb128(os, segment->initFlags, "init flags");
124    if (segment->initFlags & WASM_DATA_SEGMENT_HAS_MEMINDEX)
125      writeUleb128(os, 0, "memory index");
126    if ((segment->initFlags & WASM_DATA_SEGMENT_IS_PASSIVE) == 0) {
127      if (config->isPic && config->extendedConst) {
128        writeU8(os, WASM_OPCODE_GLOBAL_GET, "global get");
129        writeUleb128(os, WasmSym::memoryBase->getGlobalIndex(),
130                     "literal (global index)");
131        if (segment->startVA) {
132          writePtrConst(os, segment->startVA, is64, "offset");
133          writeU8(os, is64 ? WASM_OPCODE_I64_ADD : WASM_OPCODE_I32_ADD, "add");
134        }
135        writeU8(os, WASM_OPCODE_END, "opcode:end");
136      } else {
137        WasmInitExpr initExpr;
138        initExpr.Extended = false;
139        if (config->isPic) {
140          assert(segment->startVA == 0);
141          initExpr.Inst.Opcode = WASM_OPCODE_GLOBAL_GET;
142          initExpr.Inst.Value.Global = WasmSym::memoryBase->getGlobalIndex();
143        } else {
144          initExpr = intConst(segment->startVA, is64);
145        }
146        writeInitExpr(os, initExpr);
147      }
148    }
149    writeUleb128(os, segment->size, "segment size");
150    os.flush();
151
152    segment->sectionOffset = bodySize;
153    bodySize += segment->header.size() + segment->size;
154    log("Data segment: size=" + Twine(segment->size) + ", startVA=" +
155        Twine::utohexstr(segment->startVA) + ", name=" + segment->name);
156
157    for (InputChunk *inputSeg : segment->inputSegments) {
158      inputSeg->outputSec = this;
159      inputSeg->outSecOff = segment->sectionOffset + segment->header.size() +
160                            inputSeg->outputSegmentOffset;
161    }
162  }
163
164  createHeader(bodySize);
165}
166
167void DataSection::writeTo(uint8_t *buf) {
168  log("writing " + toString(*this) + " offset=" + Twine(offset) +
169      " size=" + Twine(getSize()) + " body=" + Twine(bodySize));
170  buf += offset;
171
172  // Write section header
173  memcpy(buf, header.data(), header.size());
174  buf += header.size();
175
176  // Write data section headers
177  memcpy(buf, dataSectionHeader.data(), dataSectionHeader.size());
178
179  for (const OutputSegment *segment : segments) {
180    if (!segment->requiredInBinary())
181      continue;
182    // Write data segment header
183    uint8_t *segStart = buf + segment->sectionOffset;
184    memcpy(segStart, segment->header.data(), segment->header.size());
185
186    // Write segment data payload
187    for (const InputChunk *chunk : segment->inputSegments)
188      chunk->writeTo(buf);
189  }
190}
191
192uint32_t DataSection::getNumRelocations() const {
193  uint32_t count = 0;
194  for (const OutputSegment *seg : segments)
195    for (const InputChunk *inputSeg : seg->inputSegments)
196      count += inputSeg->getNumRelocations();
197  return count;
198}
199
200void DataSection::writeRelocations(raw_ostream &os) const {
201  for (const OutputSegment *seg : segments)
202    for (const InputChunk *c : seg->inputSegments)
203      c->writeRelocations(os);
204}
205
206bool DataSection::isNeeded() const {
207  for (const OutputSegment *seg : segments)
208    if (seg->requiredInBinary())
209      return true;
210  return false;
211}
212
213// Lots of duplication here with OutputSegment::finalizeInputSegments
214void CustomSection::finalizeInputSections() {
215  SyntheticMergedChunk *mergedSection = nullptr;
216  std::vector<InputChunk *> newSections;
217
218  for (InputChunk *s : inputSections) {
219    s->outputSec = this;
220    MergeInputChunk *ms = dyn_cast<MergeInputChunk>(s);
221    if (!ms) {
222      newSections.push_back(s);
223      continue;
224    }
225
226    if (!mergedSection) {
227      mergedSection =
228          make<SyntheticMergedChunk>(name, 0, WASM_SEG_FLAG_STRINGS);
229      newSections.push_back(mergedSection);
230      mergedSection->outputSec = this;
231    }
232    mergedSection->addMergeChunk(ms);
233  }
234
235  if (!mergedSection)
236    return;
237
238  mergedSection->finalizeContents();
239  inputSections = newSections;
240}
241
242void CustomSection::finalizeContents() {
243  finalizeInputSections();
244
245  raw_string_ostream os(nameData);
246  encodeULEB128(name.size(), os);
247  os << name;
248  os.flush();
249
250  for (InputChunk *section : inputSections) {
251    assert(!section->discarded);
252    section->outSecOff = payloadSize;
253    payloadSize += section->getSize();
254  }
255
256  createHeader(payloadSize + nameData.size());
257}
258
259void CustomSection::writeTo(uint8_t *buf) {
260  log("writing " + toString(*this) + " offset=" + Twine(offset) +
261      " size=" + Twine(getSize()) + " chunks=" + Twine(inputSections.size()));
262
263  assert(offset);
264  buf += offset;
265
266  // Write section header
267  memcpy(buf, header.data(), header.size());
268  buf += header.size();
269  memcpy(buf, nameData.data(), nameData.size());
270  buf += nameData.size();
271
272  // Write custom sections payload
273  for (const InputChunk *section : inputSections)
274    section->writeTo(buf);
275}
276
277uint32_t CustomSection::getNumRelocations() const {
278  uint32_t count = 0;
279  for (const InputChunk *inputSect : inputSections)
280    count += inputSect->getNumRelocations();
281  return count;
282}
283
284void CustomSection::writeRelocations(raw_ostream &os) const {
285  for (const InputChunk *s : inputSections)
286    s->writeRelocations(os);
287}
288
289} // namespace wasm
290} // namespace lld
291