1//===- InputChunks.h --------------------------------------------*- C++ -*-===// 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// An InputChunks represents an indivisible opaque region of a input wasm file. 10// i.e. a single wasm data segment or a single wasm function. 11// 12// They are written directly to the mmap'd output file after which relocations 13// are applied. Because each Chunk is independent they can be written in 14// parallel. 15// 16// Chunks are also unit on which garbage collection (--gc-sections) operates. 17// 18//===----------------------------------------------------------------------===// 19 20#ifndef LLD_WASM_INPUT_CHUNKS_H 21#define LLD_WASM_INPUT_CHUNKS_H 22 23#include "Config.h" 24#include "InputFiles.h" 25#include "lld/Common/ErrorHandler.h" 26#include "lld/Common/LLVM.h" 27#include "llvm/ADT/CachedHashString.h" 28#include "llvm/MC/StringTableBuilder.h" 29#include "llvm/Object/Wasm.h" 30#include <optional> 31 32namespace lld { 33namespace wasm { 34 35class ObjFile; 36class OutputSegment; 37class OutputSection; 38 39class InputChunk { 40public: 41 enum Kind { 42 DataSegment, 43 Merge, 44 MergedChunk, 45 Function, 46 SyntheticFunction, 47 Section, 48 }; 49 50 StringRef name; 51 StringRef debugName; 52 53 Kind kind() const { return (Kind)sectionKind; } 54 55 uint32_t getSize() const; 56 uint32_t getInputSize() const; 57 58 void writeTo(uint8_t *buf) const; 59 void relocate(uint8_t *buf) const; 60 61 ArrayRef<WasmRelocation> getRelocations() const { return relocations; } 62 void setRelocations(ArrayRef<WasmRelocation> rs) { relocations = rs; } 63 64 // Translate an offset into the input chunk to an offset in the output 65 // section. 66 uint64_t getOffset(uint64_t offset) const; 67 // Translate an offset into the input chunk into an offset into the output 68 // chunk. For data segments (InputSegment) this will return and offset into 69 // the output segment. For MergeInputChunk, this will return an offset into 70 // the parent merged chunk. For other chunk types this is no-op and we just 71 // return unmodified offset. 72 uint64_t getChunkOffset(uint64_t offset) const; 73 uint64_t getVA(uint64_t offset = 0) const; 74 75 uint32_t getComdat() const { return comdat; } 76 StringRef getComdatName() const; 77 uint32_t getInputSectionOffset() const { return inputSectionOffset; } 78 79 size_t getNumRelocations() const { return relocations.size(); } 80 void writeRelocations(llvm::raw_ostream &os) const; 81 void generateRelocationCode(raw_ostream &os) const; 82 83 bool isTLS() const { return flags & llvm::wasm::WASM_SEG_FLAG_TLS; } 84 85 ObjFile *file; 86 OutputSection *outputSec = nullptr; 87 uint32_t comdat = UINT32_MAX; 88 uint32_t inputSectionOffset = 0; 89 uint32_t alignment; 90 uint32_t flags; 91 92 // Only applies to data segments. 93 uint32_t outputSegmentOffset = 0; 94 const OutputSegment *outputSeg = nullptr; 95 96 // After assignAddresses is called, this represents the offset from 97 // the beginning of the output section this chunk was assigned to. 98 int32_t outSecOff = 0; 99 100 uint8_t sectionKind : 3; 101 102 // Signals that the section is part of the output. The garbage collector, 103 // and COMDAT handling can set a sections' Live bit. 104 // If GC is disabled, all sections start out as live by default. 105 unsigned live : 1; 106 107 // Signals the chunk was discarded by COMDAT handling. 108 unsigned discarded : 1; 109 110protected: 111 InputChunk(ObjFile *f, Kind k, StringRef name, uint32_t alignment = 0, 112 uint32_t flags = 0) 113 : name(name), file(f), alignment(alignment), flags(flags), sectionKind(k), 114 live(!config->gcSections), discarded(false) {} 115 ArrayRef<uint8_t> data() const { return rawData; } 116 uint64_t getTombstone() const; 117 118 ArrayRef<WasmRelocation> relocations; 119 ArrayRef<uint8_t> rawData; 120}; 121 122// Represents a WebAssembly data segment which can be included as part of 123// an output data segments. Note that in WebAssembly, unlike ELF and other 124// formats, used the term "data segment" to refer to the continuous regions of 125// memory that make on the data section. See: 126// https://webassembly.github.io/spec/syntax/modules.html#syntax-data 127// 128// For example, by default, clang will produce a separate data section for 129// each global variable. 130class InputSegment : public InputChunk { 131public: 132 InputSegment(const WasmSegment &seg, ObjFile *f) 133 : InputChunk(f, InputChunk::DataSegment, seg.Data.Name, 134 seg.Data.Alignment, seg.Data.LinkingFlags), 135 segment(seg) { 136 rawData = segment.Data.Content; 137 comdat = segment.Data.Comdat; 138 inputSectionOffset = segment.SectionOffset; 139 } 140 141 static bool classof(const InputChunk *c) { return c->kind() == DataSegment; } 142 143protected: 144 const WasmSegment &segment; 145}; 146 147class SyntheticMergedChunk; 148 149// Merge segment handling copied from lld/ELF/InputSection.h. Keep in sync 150// where possible. 151 152// SectionPiece represents a piece of splittable segment contents. 153// We allocate a lot of these and binary search on them. This means that they 154// have to be as compact as possible, which is why we don't store the size (can 155// be found by looking at the next one). 156struct SectionPiece { 157 SectionPiece(size_t off, uint32_t hash, bool live) 158 : inputOff(off), live(live || !config->gcSections), hash(hash >> 1) {} 159 160 uint32_t inputOff; 161 uint32_t live : 1; 162 uint32_t hash : 31; 163 uint64_t outputOff = 0; 164}; 165 166static_assert(sizeof(SectionPiece) == 16, "SectionPiece is too big"); 167 168// This corresponds segments marked as WASM_SEG_FLAG_STRINGS. 169class MergeInputChunk : public InputChunk { 170public: 171 MergeInputChunk(const WasmSegment &seg, ObjFile *f) 172 : InputChunk(f, Merge, seg.Data.Name, seg.Data.Alignment, 173 seg.Data.LinkingFlags) { 174 rawData = seg.Data.Content; 175 comdat = seg.Data.Comdat; 176 inputSectionOffset = seg.SectionOffset; 177 } 178 179 MergeInputChunk(const WasmSection &s, ObjFile *f) 180 : InputChunk(f, Merge, s.Name, 0, llvm::wasm::WASM_SEG_FLAG_STRINGS) { 181 assert(s.Type == llvm::wasm::WASM_SEC_CUSTOM); 182 comdat = s.Comdat; 183 rawData = s.Content; 184 } 185 186 static bool classof(const InputChunk *s) { return s->kind() == Merge; } 187 void splitIntoPieces(); 188 189 // Translate an offset in the input section to an offset in the parent 190 // MergeSyntheticSection. 191 uint64_t getParentOffset(uint64_t offset) const; 192 193 // Splittable sections are handled as a sequence of data 194 // rather than a single large blob of data. 195 std::vector<SectionPiece> pieces; 196 197 // Returns I'th piece's data. This function is very hot when 198 // string merging is enabled, so we want to inline. 199 LLVM_ATTRIBUTE_ALWAYS_INLINE 200 llvm::CachedHashStringRef getData(size_t i) const { 201 size_t begin = pieces[i].inputOff; 202 size_t end = 203 (pieces.size() - 1 == i) ? data().size() : pieces[i + 1].inputOff; 204 return {toStringRef(data().slice(begin, end - begin)), pieces[i].hash}; 205 } 206 207 // Returns the SectionPiece at a given input section offset. 208 SectionPiece *getSectionPiece(uint64_t offset); 209 const SectionPiece *getSectionPiece(uint64_t offset) const { 210 return const_cast<MergeInputChunk *>(this)->getSectionPiece(offset); 211 } 212 213 SyntheticMergedChunk *parent = nullptr; 214 215private: 216 void splitStrings(ArrayRef<uint8_t> a); 217}; 218 219// SyntheticMergedChunk is a class that allows us to put mergeable 220// sections with different attributes in a single output sections. To do that we 221// put them into SyntheticMergedChunk synthetic input sections which are 222// attached to regular output sections. 223class SyntheticMergedChunk : public InputChunk { 224public: 225 SyntheticMergedChunk(StringRef name, uint32_t alignment, uint32_t flags) 226 : InputChunk(nullptr, InputChunk::MergedChunk, name, alignment, flags), 227 builder(llvm::StringTableBuilder::RAW, llvm::Align(1ULL << alignment)) { 228 } 229 230 static bool classof(const InputChunk *c) { 231 return c->kind() == InputChunk::MergedChunk; 232 } 233 234 void addMergeChunk(MergeInputChunk *ms) { 235 comdat = ms->getComdat(); 236 ms->parent = this; 237 chunks.push_back(ms); 238 } 239 240 void finalizeContents(); 241 242 llvm::StringTableBuilder builder; 243 244protected: 245 std::vector<MergeInputChunk *> chunks; 246}; 247 248// Represents a single wasm function within and input file. These are 249// combined to create the final output CODE section. 250class InputFunction : public InputChunk { 251public: 252 InputFunction(const WasmSignature &s, const WasmFunction *func, ObjFile *f) 253 : InputChunk(f, InputChunk::Function, func->SymbolName), signature(s), 254 function(func), 255 exportName(func && func->ExportName ? (*func->ExportName).str() 256 : std::optional<std::string>()) { 257 inputSectionOffset = function->CodeSectionOffset; 258 rawData = 259 file->codeSection->Content.slice(inputSectionOffset, function->Size); 260 debugName = function->DebugName; 261 comdat = function->Comdat; 262 } 263 264 InputFunction(StringRef name, const WasmSignature &s) 265 : InputChunk(nullptr, InputChunk::Function, name), signature(s) {} 266 267 static bool classof(const InputChunk *c) { 268 return c->kind() == InputChunk::Function || 269 c->kind() == InputChunk::SyntheticFunction; 270 } 271 272 std::optional<StringRef> getExportName() const { 273 return exportName ? std::optional<StringRef>(*exportName) 274 : std::optional<StringRef>(); 275 } 276 void setExportName(std::string exportName) { this->exportName = exportName; } 277 uint32_t getFunctionInputOffset() const { return getInputSectionOffset(); } 278 uint32_t getFunctionCodeOffset() const { return function->CodeOffset; } 279 uint32_t getFunctionIndex() const { return *functionIndex; } 280 bool hasFunctionIndex() const { return functionIndex.has_value(); } 281 void setFunctionIndex(uint32_t index); 282 uint32_t getTableIndex() const { return *tableIndex; } 283 bool hasTableIndex() const { return tableIndex.has_value(); } 284 void setTableIndex(uint32_t index); 285 void writeCompressed(uint8_t *buf) const; 286 287 // The size of a given input function can depend on the values of the 288 // LEB relocations within it. This finalizeContents method is called after 289 // all the symbol values have be calculated but before getSize() is ever 290 // called. 291 void calculateSize(); 292 293 const WasmSignature &signature; 294 295 uint32_t getCompressedSize() const { 296 assert(compressedSize); 297 return compressedSize; 298 } 299 300 const WasmFunction *function; 301 302protected: 303 std::optional<std::string> exportName; 304 std::optional<uint32_t> functionIndex; 305 std::optional<uint32_t> tableIndex; 306 uint32_t compressedFuncSize = 0; 307 uint32_t compressedSize = 0; 308}; 309 310class SyntheticFunction : public InputFunction { 311public: 312 SyntheticFunction(const WasmSignature &s, StringRef name, 313 StringRef debugName = {}) 314 : InputFunction(name, s) { 315 sectionKind = InputChunk::SyntheticFunction; 316 this->debugName = debugName; 317 } 318 319 static bool classof(const InputChunk *c) { 320 return c->kind() == InputChunk::SyntheticFunction; 321 } 322 323 void setBody(ArrayRef<uint8_t> body) { rawData = body; } 324}; 325 326// Represents a single Wasm Section within an input file. 327class InputSection : public InputChunk { 328public: 329 InputSection(const WasmSection &s, ObjFile *f) 330 : InputChunk(f, InputChunk::Section, s.Name), 331 tombstoneValue(getTombstoneForSection(s.Name)), section(s) { 332 assert(section.Type == llvm::wasm::WASM_SEC_CUSTOM); 333 comdat = section.Comdat; 334 rawData = section.Content; 335 } 336 337 static bool classof(const InputChunk *c) { 338 return c->kind() == InputChunk::Section; 339 } 340 341 const uint64_t tombstoneValue; 342 343protected: 344 static uint64_t getTombstoneForSection(StringRef name); 345 const WasmSection §ion; 346}; 347 348} // namespace wasm 349 350std::string toString(const wasm::InputChunk *); 351StringRef relocTypeToString(uint8_t relocType); 352 353} // namespace lld 354 355#endif // LLD_WASM_INPUT_CHUNKS_H 356