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/Object/Wasm.h"
28 
29 namespace lld {
30 namespace wasm {
31 
32 class ObjFile;
33 class OutputSegment;
34 class OutputSection;
35 
36 class InputChunk {
37 public:
38   enum Kind { DataSegment, Function, SyntheticFunction, Section };
39 
40   Kind kind() const { return sectionKind; }
41 
42   virtual uint32_t getSize() const { return data().size(); }
43   virtual uint32_t getInputSize() const { return getSize(); };
44 
45   virtual void writeTo(uint8_t *sectionStart) const;
46 
47   ArrayRef<WasmRelocation> getRelocations() const { return relocations; }
48   void setRelocations(ArrayRef<WasmRelocation> rs) { relocations = rs; }
49 
50   virtual StringRef getName() const = 0;
51   virtual StringRef getDebugName() const = 0;
52   virtual uint32_t getComdat() const = 0;
53   StringRef getComdatName() const;
54   virtual uint32_t getInputSectionOffset() const = 0;
55 
56   size_t getNumRelocations() const { return relocations.size(); }
57   void writeRelocations(llvm::raw_ostream &os) const;
58 
59   ObjFile *file;
60   OutputSection *outputSec = nullptr;
61   // Offset withing the output section
62   int32_t outputOffset = 0;
63 
64   // Signals that the section is part of the output.  The garbage collector,
65   // and COMDAT handling can set a sections' Live bit.
66   // If GC is disabled, all sections start out as live by default.
67   unsigned live : 1;
68 
69   // Signals the chunk was discarded by COMDAT handling.
70   unsigned discarded : 1;
71 
72 protected:
73   InputChunk(ObjFile *f, Kind k)
74       : file(f), live(!config->gcSections), discarded(false), sectionKind(k) {}
75   virtual ~InputChunk() = default;
76   virtual ArrayRef<uint8_t> data() const = 0;
77   virtual uint64_t getTombstone() const { return 0; }
78 
79   // Verifies the existing data at relocation targets matches our expectations.
80   // This is performed only debug builds as an extra sanity check.
81   void verifyRelocTargets() const;
82 
83   ArrayRef<WasmRelocation> relocations;
84   Kind sectionKind;
85 };
86 
87 // Represents a WebAssembly data segment which can be included as part of
88 // an output data segments.  Note that in WebAssembly, unlike ELF and other
89 // formats, used the term "data segment" to refer to the continuous regions of
90 // memory that make on the data section. See:
91 // https://webassembly.github.io/spec/syntax/modules.html#syntax-data
92 //
93 // For example, by default, clang will produce a separate data section for
94 // each global variable.
95 class InputSegment : public InputChunk {
96 public:
97   InputSegment(const WasmSegment &seg, ObjFile *f)
98       : InputChunk(f, InputChunk::DataSegment), segment(seg) {}
99 
100   static bool classof(const InputChunk *c) { return c->kind() == DataSegment; }
101 
102   void generateRelocationCode(raw_ostream &os) const;
103 
104   uint32_t getAlignment() const { return segment.Data.Alignment; }
105   StringRef getName() const override { return segment.Data.Name; }
106   StringRef getDebugName() const override { return StringRef(); }
107   uint32_t getComdat() const override { return segment.Data.Comdat; }
108   uint32_t getInputSectionOffset() const override {
109     return segment.SectionOffset;
110   }
111   uint64_t getVA() const;
112 
113   const OutputSegment *outputSeg = nullptr;
114   int32_t outputSegmentOffset = 0;
115 
116 protected:
117   ArrayRef<uint8_t> data() const override { return segment.Data.Content; }
118 
119   const WasmSegment &segment;
120 };
121 
122 // Represents a single wasm function within and input file.  These are
123 // combined to create the final output CODE section.
124 class InputFunction : public InputChunk {
125 public:
126   InputFunction(const WasmSignature &s, const WasmFunction *func, ObjFile *f)
127       : InputChunk(f, InputChunk::Function), signature(s), function(func),
128         exportName(func && func->ExportName.hasValue()
129                        ? (*func->ExportName).str()
130                        : llvm::Optional<std::string>()) {}
131 
132   static bool classof(const InputChunk *c) {
133     return c->kind() == InputChunk::Function ||
134            c->kind() == InputChunk::SyntheticFunction;
135   }
136 
137   void writeTo(uint8_t *sectionStart) const override;
138   StringRef getName() const override { return function->SymbolName; }
139   StringRef getDebugName() const override { return function->DebugName; }
140   llvm::Optional<StringRef> getExportName() const {
141     return exportName.hasValue() ? llvm::Optional<StringRef>(*exportName)
142                                  : llvm::Optional<StringRef>();
143   }
144   void setExportName(std::string exportName) { this->exportName = exportName; }
145   uint32_t getComdat() const override { return function->Comdat; }
146   uint32_t getFunctionInputOffset() const { return getInputSectionOffset(); }
147   uint32_t getFunctionCodeOffset() const { return function->CodeOffset; }
148   uint32_t getSize() const override {
149     if (config->compressRelocations && file) {
150       assert(compressedSize);
151       return compressedSize;
152     }
153     return data().size();
154   }
155   uint32_t getInputSize() const override { return function->Size; }
156   uint32_t getFunctionIndex() const { return functionIndex.getValue(); }
157   bool hasFunctionIndex() const { return functionIndex.hasValue(); }
158   void setFunctionIndex(uint32_t index);
159   uint32_t getInputSectionOffset() const override {
160     return function->CodeSectionOffset;
161   }
162   uint32_t getTableIndex() const { return tableIndex.getValue(); }
163   bool hasTableIndex() const { return tableIndex.hasValue(); }
164   void setTableIndex(uint32_t index);
165 
166   // The size of a given input function can depend on the values of the
167   // LEB relocations within it.  This finalizeContents method is called after
168   // all the symbol values have be calculated but before getSize() is ever
169   // called.
170   void calculateSize();
171 
172   const WasmSignature &signature;
173 
174 protected:
175   ArrayRef<uint8_t> data() const override {
176     assert(!config->compressRelocations);
177     return file->codeSection->Content.slice(getInputSectionOffset(),
178                                             function->Size);
179   }
180 
181   const WasmFunction *function;
182   llvm::Optional<std::string> exportName;
183   llvm::Optional<uint32_t> functionIndex;
184   llvm::Optional<uint32_t> tableIndex;
185   uint32_t compressedFuncSize = 0;
186   uint32_t compressedSize = 0;
187 };
188 
189 class SyntheticFunction : public InputFunction {
190 public:
191   SyntheticFunction(const WasmSignature &s, StringRef name,
192                     StringRef debugName = {})
193       : InputFunction(s, nullptr, nullptr), name(name), debugName(debugName) {
194     sectionKind = InputChunk::SyntheticFunction;
195   }
196 
197   static bool classof(const InputChunk *c) {
198     return c->kind() == InputChunk::SyntheticFunction;
199   }
200 
201   StringRef getName() const override { return name; }
202   StringRef getDebugName() const override { return debugName; }
203   uint32_t getComdat() const override { return UINT32_MAX; }
204 
205   void setBody(ArrayRef<uint8_t> body_) { body = body_; }
206 
207 protected:
208   ArrayRef<uint8_t> data() const override { return body; }
209 
210   StringRef name;
211   StringRef debugName;
212   ArrayRef<uint8_t> body;
213 };
214 
215 // Represents a single Wasm Section within an input file.
216 class InputSection : public InputChunk {
217 public:
218   InputSection(const WasmSection &s, ObjFile *f)
219       : InputChunk(f, InputChunk::Section), section(s), tombstoneValue(getTombstoneForSection(s.Name)) {
220     assert(section.Type == llvm::wasm::WASM_SEC_CUSTOM);
221   }
222 
223   StringRef getName() const override { return section.Name; }
224   StringRef getDebugName() const override { return StringRef(); }
225   uint32_t getComdat() const override { return section.Comdat; }
226 
227 protected:
228   ArrayRef<uint8_t> data() const override { return section.Content; }
229 
230   // Offset within the input section.  This is only zero since this chunk
231   // type represents an entire input section, not part of one.
232   uint32_t getInputSectionOffset() const override { return 0; }
233   uint64_t getTombstone() const override { return tombstoneValue; }
234   static uint64_t getTombstoneForSection(StringRef name);
235 
236   const WasmSection &section;
237   const uint64_t tombstoneValue;
238 };
239 
240 } // namespace wasm
241 
242 std::string toString(const wasm::InputChunk *);
243 StringRef relocTypeToString(uint8_t relocType);
244 
245 } // namespace lld
246 
247 #endif // LLD_WASM_INPUT_CHUNKS_H
248