lld/wasm/OutputSections.cpp

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