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 static StringRef sectionTypeToString(uint32_t sectionType) {
  37   switch (sectionType) {
  38   case WASM_SEC_CUSTOM:
  39     return "CUSTOM";
  40   case WASM_SEC_TYPE:
  41     return "TYPE";
  42   case WASM_SEC_IMPORT:
  43     return "IMPORT";
  44   case WASM_SEC_FUNCTION:
  45     return "FUNCTION";
  46   case WASM_SEC_TABLE:
  47     return "TABLE";
  48   case WASM_SEC_MEMORY:
  49     return "MEMORY";
  50   case WASM_SEC_GLOBAL:
  51     return "GLOBAL";
  52   case WASM_SEC_TAG:
  53     return "TAG";
  54   case WASM_SEC_EXPORT:
  55     return "EXPORT";
  56   case WASM_SEC_START:
  57     return "START";
  58   case WASM_SEC_ELEM:
  59     return "ELEM";
  60   case WASM_SEC_CODE:
  61     return "CODE";
  62   case WASM_SEC_DATA:
  63     return "DATA";
  64   case WASM_SEC_DATACOUNT:
  65     return "DATACOUNT";
  66   default:
  67     fatal("invalid section type");
  68   }
  69 }
  70
  71 StringRef OutputSection::getSectionName() const {
  72   return sectionTypeToString(type);
  73 }
  74
  75 void OutputSection::createHeader(size_t bodySize) {
  76   raw_string_ostream os(header);
  77   debugWrite(os.tell(), "section type [" + getSectionName() + "]");
  78   encodeULEB128(type, os);
  79   writeUleb128(os, bodySize, "section size");
  80   os.flush();
  81   log("createHeader: " + toString(*this) + " body=" + Twine(bodySize) +
  82       " total=" + Twine(getSize()));
  83 }
  84
  85 void CodeSection::finalizeContents() {
  86   raw_string_ostream os(codeSectionHeader);
  87   writeUleb128(os, functions.size(), "function count");
  88   os.flush();
  89   bodySize = codeSectionHeader.size();
  90
  91   for (InputFunction *func : functions) {
  92     func->outputSec = this;
  93     func->outSecOff = bodySize;
  94     func->calculateSize();
  95     // All functions should have a non-empty body at this point
  96     assert(func->getSize());
  97     bodySize += func->getSize();
  98   }
  99
 100   createHeader(bodySize);
 101 }
 102
 103 void CodeSection::writeTo(uint8_t *buf) {
 104   log("writing " + toString(*this) + " offset=" + Twine(offset) +
 105       " size=" + Twine(getSize()));
 106   log(" headersize=" + Twine(header.size()));
 107   log(" codeheadersize=" + Twine(codeSectionHeader.size()));
 108   buf += offset;
 109
 110   // Write section header
 111   memcpy(buf, header.data(), header.size());
 112   buf += header.size();
 113
 114   // Write code section headers
 115   memcpy(buf, codeSectionHeader.data(), codeSectionHeader.size());
 116
 117   // Write code section bodies
 118   for (const InputChunk *chunk : functions)
 119     chunk->writeTo(buf);
 120 }
 121
 122 uint32_t CodeSection::getNumRelocations() const {
 123   uint32_t count = 0;
 124   for (const InputChunk *func : functions)
 125     count += func->getNumRelocations();
 126   return count;
 127 }
 128
 129 void CodeSection::writeRelocations(raw_ostream &os) const {
 130   for (const InputChunk *c : functions)
 131     c->writeRelocations(os);
 132 }
 133
 134 void DataSection::finalizeContents() {
 135   raw_string_ostream os(dataSectionHeader);
 136   unsigned segmentCount = std::count_if(
 137       segments.begin(), segments.end(),
 138       [](OutputSegment *segment) { return segment->requiredInBinary(); });
 139 #ifndef NDEBUG
 140   unsigned activeCount = std::count_if(
 141       segments.begin(), segments.end(), [](OutputSegment *segment) {
 142         return (segment->initFlags & WASM_DATA_SEGMENT_IS_PASSIVE) == 0;
 143       });
 144 #endif
 145
 146   assert((config->sharedMemory || !config->isPic || config->extendedConst ||
 147           activeCount <= 1) &&
 148          "output segments should have been combined by now");
 149
 150   writeUleb128(os, segmentCount, "data segment count");
 151   os.flush();
 152   bodySize = dataSectionHeader.size();
 153   bool is64 = config->is64.getValueOr(false);
 154
 155   for (OutputSegment *segment : segments) {
 156     if (!segment->requiredInBinary())
 157       continue;
 158     raw_string_ostream os(segment->header);
 159     writeUleb128(os, segment->initFlags, "init flags");
 160     if (segment->initFlags & WASM_DATA_SEGMENT_HAS_MEMINDEX)
 161       writeUleb128(os, 0, "memory index");
 162     if ((segment->initFlags & WASM_DATA_SEGMENT_IS_PASSIVE) == 0) {
 163       if (config->isPic && config->extendedConst) {
 164         writeU8(os, WASM_OPCODE_GLOBAL_GET, "global get");
 165         writeUleb128(os, WasmSym::memoryBase->getGlobalIndex(),
 166                      "literal (global index)");
 167         if (segment->startVA) {
 168           writePtrConst(os, segment->startVA, is64, "offset");
 169           writeU8(os, is64 ? WASM_OPCODE_I64_ADD : WASM_OPCODE_I32_ADD, "add");
 170         }
 171         writeU8(os, WASM_OPCODE_END, "opcode:end");
 172       } else {
 173         WasmInitExpr initExpr;
 174         initExpr.Extended = false;
 175         if (config->isPic) {
 176           assert(segment->startVA == 0);
 177           initExpr.Inst.Opcode = WASM_OPCODE_GLOBAL_GET;
 178           initExpr.Inst.Value.Global = WasmSym::memoryBase->getGlobalIndex();
 179         } else {
 180           initExpr = intConst(segment->startVA, is64);
 181         }
 182         writeInitExpr(os, initExpr);
 183       }
 184     }
 185     writeUleb128(os, segment->size, "segment size");
 186     os.flush();
 187
 188     segment->sectionOffset = bodySize;
 189     bodySize += segment->header.size() + segment->size;
 190     log("Data segment: size=" + Twine(segment->size) + ", startVA=" +
 191         Twine::utohexstr(segment->startVA) + ", name=" + segment->name);
 192
 193     for (InputChunk *inputSeg : segment->inputSegments) {
 194       inputSeg->outputSec = this;
 195       inputSeg->outSecOff = segment->sectionOffset + segment->header.size() +
 196                             inputSeg->outputSegmentOffset;
 197     }
 198   }
 199
 200   createHeader(bodySize);
 201 }
 202
 203 void DataSection::writeTo(uint8_t *buf) {
 204   log("writing " + toString(*this) + " offset=" + Twine(offset) +
 205       " size=" + Twine(getSize()) + " body=" + Twine(bodySize));
 206   buf += offset;
 207
 208   // Write section header
 209   memcpy(buf, header.data(), header.size());
 210   buf += header.size();
 211
 212   // Write data section headers
 213   memcpy(buf, dataSectionHeader.data(), dataSectionHeader.size());
 214
 215   for (const OutputSegment *segment : segments) {
 216     if (!segment->requiredInBinary())
 217       continue;
 218     // Write data segment header
 219     uint8_t *segStart = buf + segment->sectionOffset;
 220     memcpy(segStart, segment->header.data(), segment->header.size());
 221
 222     // Write segment data payload
 223     for (const InputChunk *chunk : segment->inputSegments)
 224       chunk->writeTo(buf);
 225   }
 226 }
 227
 228 uint32_t DataSection::getNumRelocations() const {
 229   uint32_t count = 0;
 230   for (const OutputSegment *seg : segments)
 231     for (const InputChunk *inputSeg : seg->inputSegments)
 232       count += inputSeg->getNumRelocations();
 233   return count;
 234 }
 235
 236 void DataSection::writeRelocations(raw_ostream &os) const {
 237   for (const OutputSegment *seg : segments)
 238     for (const InputChunk *c : seg->inputSegments)
 239       c->writeRelocations(os);
 240 }
 241
 242 bool DataSection::isNeeded() const {
 243   for (const OutputSegment *seg : segments)
 244     if (seg->requiredInBinary())
 245       return true;
 246   return false;
 247 }
 248
 249 // Lots of duplication here with OutputSegment::finalizeInputSegments
 250 void CustomSection::finalizeInputSections() {
 251   SyntheticMergedChunk *mergedSection = nullptr;
 252   std::vector<InputChunk *> newSections;
 253
 254   for (InputChunk *s : inputSections) {
 255     s->outputSec = this;
 256     MergeInputChunk *ms = dyn_cast<MergeInputChunk>(s);
 257     if (!ms) {
 258       newSections.push_back(s);
 259       continue;
 260     }
 261
 262     if (!mergedSection) {
 263       mergedSection =
 264           make<SyntheticMergedChunk>(name, 0, WASM_SEG_FLAG_STRINGS);
 265       newSections.push_back(mergedSection);
 266       mergedSection->outputSec = this;
 267     }
 268     mergedSection->addMergeChunk(ms);
 269   }
 270
 271   if (!mergedSection)
 272     return;
 273
 274   mergedSection->finalizeContents();
 275   inputSections = newSections;
 276 }
 277
 278 void CustomSection::finalizeContents() {
 279   finalizeInputSections();
 280
 281   raw_string_ostream os(nameData);
 282   encodeULEB128(name.size(), os);
 283   os << name;
 284   os.flush();
 285
 286   for (InputChunk *section : inputSections) {
 287     assert(!section->discarded);
 288     section->outSecOff = payloadSize;
 289     payloadSize += section->getSize();
 290   }
 291
 292   createHeader(payloadSize + nameData.size());
 293 }
 294
 295 void CustomSection::writeTo(uint8_t *buf) {
 296   log("writing " + toString(*this) + " offset=" + Twine(offset) +
 297       " size=" + Twine(getSize()) + " chunks=" + Twine(inputSections.size()));
 298
 299   assert(offset);
 300   buf += offset;
 301
 302   // Write section header
 303   memcpy(buf, header.data(), header.size());
 304   buf += header.size();
 305   memcpy(buf, nameData.data(), nameData.size());
 306   buf += nameData.size();
 307
 308   // Write custom sections payload
 309   for (const InputChunk *section : inputSections)
 310     section->writeTo(buf);
 311 }
 312
 313 uint32_t CustomSection::getNumRelocations() const {
 314   uint32_t count = 0;
 315   for (const InputChunk *inputSect : inputSections)
 316     count += inputSect->getNumRelocations();
 317   return count;
 318 }
 319
 320 void CustomSection::writeRelocations(raw_ostream &os) const {
 321   for (const InputChunk *s : inputSections)
 322     s->writeRelocations(os);
 323 }
 324
 325 } // namespace wasm
 326 } // namespace lld