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   os.flush();
  46   log("createHeader: " + toString(*this) + " body=" + Twine(bodySize) +
  47       " total=" + Twine(getSize()));
  48 }
  49
  50 void 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
  68 void 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
  87 uint32_t CodeSection::getNumRelocations() const {
  88   uint32_t count = 0;
  89   for (const InputChunk *func : functions)
  90     count += func->getNumRelocations();
  91   return count;
  92 }
  93
  94 void CodeSection::writeRelocations(raw_ostream &os) const {
  95   for (const InputChunk *c : functions)
  96     c->writeRelocations(os);
  97 }
  98
  99 void 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
 167 void 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
 192 uint32_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
 200 void 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
 206 bool 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
 214 void 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
 242 void 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
 259 void 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
 277 uint32_t CustomSection::getNumRelocations() const {
 278   uint32_t count = 0;
 279   for (const InputChunk *inputSect : inputSections)
 280     count += inputSect->getNumRelocations();
 281   return count;
 282 }
 283
 284 void CustomSection::writeRelocations(raw_ostream &os) const {
 285   for (const InputChunk *s : inputSections)
 286     s->writeRelocations(os);
 287 }
 288
 289 } // namespace wasm
 290 } // namespace lld