1 //===- InputChunks.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 "InputChunks.h"
10 #include "Config.h"
11 #include "OutputSegment.h"
12 #include "WriterUtils.h"
13 #include "lld/Common/ErrorHandler.h"
14 #include "lld/Common/LLVM.h"
15 #include "llvm/Support/LEB128.h"
16 
17 #define DEBUG_TYPE "lld"
18 
19 using namespace llvm;
20 using namespace llvm::wasm;
21 using namespace llvm::support::endian;
22 using namespace lld;
23 using namespace lld::wasm;
24 
25 static StringRef reloctTypeToString(uint8_t RelocType) {
26   switch (RelocType) {
27 #define WASM_RELOC(NAME, REL)                                                  \
28   case REL:                                                                    \
29     return #NAME;
30 #include "llvm/BinaryFormat/WasmRelocs.def"
31 #undef WASM_RELOC
32   }
33   llvm_unreachable("unknown reloc type");
34 }
35 
36 std::string lld::toString(const InputChunk *C) {
37   return (toString(C->File) + ":(" + C->getName() + ")").str();
38 }
39 
40 StringRef InputChunk::getComdatName() const {
41   uint32_t Index = getComdat();
42   if (Index == UINT32_MAX)
43     return StringRef();
44   return File->getWasmObj()->linkingData().Comdats[Index];
45 }
46 
47 void InputChunk::verifyRelocTargets() const {
48   for (const WasmRelocation &Rel : Relocations) {
49     uint32_t ExistingValue;
50     unsigned BytesRead = 0;
51     uint32_t Offset = Rel.Offset - getInputSectionOffset();
52     const uint8_t *Loc = data().data() + Offset;
53     switch (Rel.Type) {
54     case R_WASM_TYPE_INDEX_LEB:
55     case R_WASM_FUNCTION_INDEX_LEB:
56     case R_WASM_GLOBAL_INDEX_LEB:
57     case R_WASM_EVENT_INDEX_LEB:
58     case R_WASM_MEMORY_ADDR_LEB:
59       ExistingValue = decodeULEB128(Loc, &BytesRead);
60       break;
61     case R_WASM_TABLE_INDEX_SLEB:
62     case R_WASM_MEMORY_ADDR_SLEB:
63       ExistingValue = static_cast<uint32_t>(decodeSLEB128(Loc, &BytesRead));
64       break;
65     case R_WASM_TABLE_INDEX_I32:
66     case R_WASM_MEMORY_ADDR_I32:
67     case R_WASM_FUNCTION_OFFSET_I32:
68     case R_WASM_SECTION_OFFSET_I32:
69       ExistingValue = static_cast<uint32_t>(read32le(Loc));
70       break;
71     default:
72       llvm_unreachable("unknown relocation type");
73     }
74 
75     if (BytesRead && BytesRead != 5)
76       warn("expected LEB at relocation site be 5-byte padded");
77     uint32_t ExpectedValue = File->calcExpectedValue(Rel);
78     if (ExpectedValue != ExistingValue)
79       warn("unexpected existing value for " + reloctTypeToString(Rel.Type) +
80            ": existing=" + Twine(ExistingValue) +
81            " expected=" + Twine(ExpectedValue));
82   }
83 }
84 
85 // Copy this input chunk to an mmap'ed output file and apply relocations.
86 void InputChunk::writeTo(uint8_t *Buf) const {
87   // Copy contents
88   memcpy(Buf + OutputOffset, data().data(), data().size());
89 
90   // Apply relocations
91   if (Relocations.empty())
92     return;
93 
94 #ifndef NDEBUG
95   verifyRelocTargets();
96 #endif
97 
98   LLVM_DEBUG(dbgs() << "applying relocations: " << getName()
99                     << " count=" << Relocations.size() << "\n");
100   int32_t Off = OutputOffset - getInputSectionOffset();
101 
102   for (const WasmRelocation &Rel : Relocations) {
103     uint8_t *Loc = Buf + Rel.Offset + Off;
104     uint32_t Value = File->calcNewValue(Rel);
105     LLVM_DEBUG(dbgs() << "apply reloc: type=" << reloctTypeToString(Rel.Type)
106                       << " addend=" << Rel.Addend << " index=" << Rel.Index
107                       << " value=" << Value << " offset=" << Rel.Offset
108                       << "\n");
109 
110     switch (Rel.Type) {
111     case R_WASM_TYPE_INDEX_LEB:
112     case R_WASM_FUNCTION_INDEX_LEB:
113     case R_WASM_GLOBAL_INDEX_LEB:
114     case R_WASM_EVENT_INDEX_LEB:
115     case R_WASM_MEMORY_ADDR_LEB:
116       encodeULEB128(Value, Loc, 5);
117       break;
118     case R_WASM_TABLE_INDEX_SLEB:
119     case R_WASM_MEMORY_ADDR_SLEB:
120       encodeSLEB128(static_cast<int32_t>(Value), Loc, 5);
121       break;
122     case R_WASM_TABLE_INDEX_I32:
123     case R_WASM_MEMORY_ADDR_I32:
124     case R_WASM_FUNCTION_OFFSET_I32:
125     case R_WASM_SECTION_OFFSET_I32:
126       write32le(Loc, Value);
127       break;
128     default:
129       llvm_unreachable("unknown relocation type");
130     }
131   }
132 }
133 
134 // Copy relocation entries to a given output stream.
135 // This function is used only when a user passes "-r". For a regular link,
136 // we consume relocations instead of copying them to an output file.
137 void InputChunk::writeRelocations(raw_ostream &OS) const {
138   if (Relocations.empty())
139     return;
140 
141   int32_t Off = OutputOffset - getInputSectionOffset();
142   LLVM_DEBUG(dbgs() << "writeRelocations: " << File->getName()
143                     << " offset=" << Twine(Off) << "\n");
144 
145   for (const WasmRelocation &Rel : Relocations) {
146     writeUleb128(OS, Rel.Type, "reloc type");
147     writeUleb128(OS, Rel.Offset + Off, "reloc offset");
148     writeUleb128(OS, File->calcNewIndex(Rel), "reloc index");
149 
150     switch (Rel.Type) {
151     case R_WASM_MEMORY_ADDR_LEB:
152     case R_WASM_MEMORY_ADDR_SLEB:
153     case R_WASM_MEMORY_ADDR_I32:
154     case R_WASM_FUNCTION_OFFSET_I32:
155     case R_WASM_SECTION_OFFSET_I32:
156       writeSleb128(OS, File->calcNewAddend(Rel), "reloc addend");
157       break;
158     }
159   }
160 }
161 
162 void InputFunction::setFunctionIndex(uint32_t Index) {
163   LLVM_DEBUG(dbgs() << "InputFunction::setFunctionIndex: " << getName()
164                     << " -> " << Index << "\n");
165   assert(!hasFunctionIndex());
166   FunctionIndex = Index;
167 }
168 
169 void InputFunction::setTableIndex(uint32_t Index) {
170   LLVM_DEBUG(dbgs() << "InputFunction::setTableIndex: " << getName() << " -> "
171                     << Index << "\n");
172   assert(!hasTableIndex());
173   TableIndex = Index;
174 }
175 
176 // Write a relocation value without padding and return the number of bytes
177 // witten.
178 static unsigned writeCompressedReloc(uint8_t *Buf, const WasmRelocation &Rel,
179                                      uint32_t Value) {
180   switch (Rel.Type) {
181   case R_WASM_TYPE_INDEX_LEB:
182   case R_WASM_FUNCTION_INDEX_LEB:
183   case R_WASM_GLOBAL_INDEX_LEB:
184   case R_WASM_EVENT_INDEX_LEB:
185   case R_WASM_MEMORY_ADDR_LEB:
186     return encodeULEB128(Value, Buf);
187   case R_WASM_TABLE_INDEX_SLEB:
188   case R_WASM_MEMORY_ADDR_SLEB:
189     return encodeSLEB128(static_cast<int32_t>(Value), Buf);
190   default:
191     llvm_unreachable("unexpected relocation type");
192   }
193 }
194 
195 static unsigned getRelocWidthPadded(const WasmRelocation &Rel) {
196   switch (Rel.Type) {
197   case R_WASM_TYPE_INDEX_LEB:
198   case R_WASM_FUNCTION_INDEX_LEB:
199   case R_WASM_GLOBAL_INDEX_LEB:
200   case R_WASM_EVENT_INDEX_LEB:
201   case R_WASM_MEMORY_ADDR_LEB:
202   case R_WASM_TABLE_INDEX_SLEB:
203   case R_WASM_MEMORY_ADDR_SLEB:
204     return 5;
205   default:
206     llvm_unreachable("unexpected relocation type");
207   }
208 }
209 
210 static unsigned getRelocWidth(const WasmRelocation &Rel, uint32_t Value) {
211   uint8_t Buf[5];
212   return writeCompressedReloc(Buf, Rel, Value);
213 }
214 
215 // Relocations of type LEB and SLEB in the code section are padded to 5 bytes
216 // so that a fast linker can blindly overwrite them without needing to worry
217 // about the number of bytes needed to encode the values.
218 // However, for optimal output the code section can be compressed to remove
219 // the padding then outputting non-relocatable files.
220 // In this case we need to perform a size calculation based on the value at each
221 // relocation.  At best we end up saving 4 bytes for each relocation entry.
222 //
223 // This function only computes the final output size.  It must be called
224 // before getSize() is used to calculate of layout of the code section.
225 void InputFunction::calculateSize() {
226   if (!File || !Config->CompressRelocations)
227     return;
228 
229   LLVM_DEBUG(dbgs() << "calculateSize: " << getName() << "\n");
230 
231   const uint8_t *SecStart = File->CodeSection->Content.data();
232   const uint8_t *FuncStart = SecStart + getInputSectionOffset();
233   uint32_t FunctionSizeLength;
234   decodeULEB128(FuncStart, &FunctionSizeLength);
235 
236   uint32_t Start = getInputSectionOffset();
237   uint32_t End = Start + Function->Size;
238 
239   uint32_t LastRelocEnd = Start + FunctionSizeLength;
240   for (const WasmRelocation &Rel : Relocations) {
241     LLVM_DEBUG(dbgs() << "  region: " << (Rel.Offset - LastRelocEnd) << "\n");
242     CompressedFuncSize += Rel.Offset - LastRelocEnd;
243     CompressedFuncSize += getRelocWidth(Rel, File->calcNewValue(Rel));
244     LastRelocEnd = Rel.Offset + getRelocWidthPadded(Rel);
245   }
246   LLVM_DEBUG(dbgs() << "  final region: " << (End - LastRelocEnd) << "\n");
247   CompressedFuncSize += End - LastRelocEnd;
248 
249   // Now we know how long the resulting function is we can add the encoding
250   // of its length
251   uint8_t Buf[5];
252   CompressedSize = CompressedFuncSize + encodeULEB128(CompressedFuncSize, Buf);
253 
254   LLVM_DEBUG(dbgs() << "  calculateSize orig: " << Function->Size << "\n");
255   LLVM_DEBUG(dbgs() << "  calculateSize  new: " << CompressedSize << "\n");
256 }
257 
258 // Override the default writeTo method so that we can (optionally) write the
259 // compressed version of the function.
260 void InputFunction::writeTo(uint8_t *Buf) const {
261   if (!File || !Config->CompressRelocations)
262     return InputChunk::writeTo(Buf);
263 
264   Buf += OutputOffset;
265   uint8_t *Orig = Buf;
266   (void)Orig;
267 
268   const uint8_t *SecStart = File->CodeSection->Content.data();
269   const uint8_t *FuncStart = SecStart + getInputSectionOffset();
270   const uint8_t *End = FuncStart + Function->Size;
271   uint32_t Count;
272   decodeULEB128(FuncStart, &Count);
273   FuncStart += Count;
274 
275   LLVM_DEBUG(dbgs() << "write func: " << getName() << "\n");
276   Buf += encodeULEB128(CompressedFuncSize, Buf);
277   const uint8_t *LastRelocEnd = FuncStart;
278   for (const WasmRelocation &Rel : Relocations) {
279     unsigned ChunkSize = (SecStart + Rel.Offset) - LastRelocEnd;
280     LLVM_DEBUG(dbgs() << "  write chunk: " << ChunkSize << "\n");
281     memcpy(Buf, LastRelocEnd, ChunkSize);
282     Buf += ChunkSize;
283     Buf += writeCompressedReloc(Buf, Rel, File->calcNewValue(Rel));
284     LastRelocEnd = SecStart + Rel.Offset + getRelocWidthPadded(Rel);
285   }
286 
287   unsigned ChunkSize = End - LastRelocEnd;
288   LLVM_DEBUG(dbgs() << "  write final chunk: " << ChunkSize << "\n");
289   memcpy(Buf, LastRelocEnd, ChunkSize);
290   LLVM_DEBUG(dbgs() << "  total: " << (Buf + ChunkSize - Orig) << "\n");
291 }
292