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)".
toString(const wasm::OutputSection & sec)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 {
getSectionName() const36 StringRef OutputSection::getSectionName() const {
37 return sectionTypeToString(type);
38 }
39
createHeader(size_t bodySize)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
finalizeContents()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
writeTo(uint8_t * buf)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
getNumRelocations() const87 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
writeRelocations(raw_ostream & os) const94 void CodeSection::writeRelocations(raw_ostream &os) const {
95 for (const InputChunk *c : functions)
96 c->writeRelocations(os);
97 }
98
finalizeContents()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
writeTo(uint8_t * buf)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
getNumRelocations() const192 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
writeRelocations(raw_ostream & os) const200 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
isNeeded() const206 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
finalizeInputSections()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
finalizeContents()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
writeTo(uint8_t * buf)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
getNumRelocations() const277 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
writeRelocations(raw_ostream & os) const284 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
291