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 = std::count_if(
102 segments.begin(), segments.end(),
103 [](OutputSegment *segment) { return segment->requiredInBinary(); });
104 #ifndef NDEBUG
105 unsigned activeCount = std::count_if(
106 segments.begin(), segments.end(), [](OutputSegment *segment) {
107 return (segment->initFlags & WASM_DATA_SEGMENT_IS_PASSIVE) == 0;
108 });
109 #endif
110
111 assert((config->sharedMemory || !config->isPic || config->extendedConst ||
112 activeCount <= 1) &&
113 "output segments should have been combined by now");
114
115 writeUleb128(os, segmentCount, "data segment count");
116 os.flush();
117 bodySize = dataSectionHeader.size();
118 bool is64 = config->is64.value_or(false);
119
120 for (OutputSegment *segment : segments) {
121 if (!segment->requiredInBinary())
122 continue;
123 raw_string_ostream os(segment->header);
124 writeUleb128(os, segment->initFlags, "init flags");
125 if (segment->initFlags & WASM_DATA_SEGMENT_HAS_MEMINDEX)
126 writeUleb128(os, 0, "memory index");
127 if ((segment->initFlags & WASM_DATA_SEGMENT_IS_PASSIVE) == 0) {
128 if (config->isPic && config->extendedConst) {
129 writeU8(os, WASM_OPCODE_GLOBAL_GET, "global get");
130 writeUleb128(os, WasmSym::memoryBase->getGlobalIndex(),
131 "literal (global index)");
132 if (segment->startVA) {
133 writePtrConst(os, segment->startVA, is64, "offset");
134 writeU8(os, is64 ? WASM_OPCODE_I64_ADD : WASM_OPCODE_I32_ADD, "add");
135 }
136 writeU8(os, WASM_OPCODE_END, "opcode:end");
137 } else {
138 WasmInitExpr initExpr;
139 initExpr.Extended = false;
140 if (config->isPic) {
141 assert(segment->startVA == 0);
142 initExpr.Inst.Opcode = WASM_OPCODE_GLOBAL_GET;
143 initExpr.Inst.Value.Global = WasmSym::memoryBase->getGlobalIndex();
144 } else {
145 initExpr = intConst(segment->startVA, is64);
146 }
147 writeInitExpr(os, initExpr);
148 }
149 }
150 writeUleb128(os, segment->size, "segment size");
151 os.flush();
152
153 segment->sectionOffset = bodySize;
154 bodySize += segment->header.size() + segment->size;
155 log("Data segment: size=" + Twine(segment->size) + ", startVA=" +
156 Twine::utohexstr(segment->startVA) + ", name=" + segment->name);
157
158 for (InputChunk *inputSeg : segment->inputSegments) {
159 inputSeg->outputSec = this;
160 inputSeg->outSecOff = segment->sectionOffset + segment->header.size() +
161 inputSeg->outputSegmentOffset;
162 }
163 }
164
165 createHeader(bodySize);
166 }
167
writeTo(uint8_t * buf)168 void DataSection::writeTo(uint8_t *buf) {
169 log("writing " + toString(*this) + " offset=" + Twine(offset) +
170 " size=" + Twine(getSize()) + " body=" + Twine(bodySize));
171 buf += offset;
172
173 // Write section header
174 memcpy(buf, header.data(), header.size());
175 buf += header.size();
176
177 // Write data section headers
178 memcpy(buf, dataSectionHeader.data(), dataSectionHeader.size());
179
180 for (const OutputSegment *segment : segments) {
181 if (!segment->requiredInBinary())
182 continue;
183 // Write data segment header
184 uint8_t *segStart = buf + segment->sectionOffset;
185 memcpy(segStart, segment->header.data(), segment->header.size());
186
187 // Write segment data payload
188 for (const InputChunk *chunk : segment->inputSegments)
189 chunk->writeTo(buf);
190 }
191 }
192
getNumRelocations() const193 uint32_t DataSection::getNumRelocations() const {
194 uint32_t count = 0;
195 for (const OutputSegment *seg : segments)
196 for (const InputChunk *inputSeg : seg->inputSegments)
197 count += inputSeg->getNumRelocations();
198 return count;
199 }
200
writeRelocations(raw_ostream & os) const201 void DataSection::writeRelocations(raw_ostream &os) const {
202 for (const OutputSegment *seg : segments)
203 for (const InputChunk *c : seg->inputSegments)
204 c->writeRelocations(os);
205 }
206
isNeeded() const207 bool DataSection::isNeeded() const {
208 for (const OutputSegment *seg : segments)
209 if (seg->requiredInBinary())
210 return true;
211 return false;
212 }
213
214 // Lots of duplication here with OutputSegment::finalizeInputSegments
finalizeInputSections()215 void CustomSection::finalizeInputSections() {
216 SyntheticMergedChunk *mergedSection = nullptr;
217 std::vector<InputChunk *> newSections;
218
219 for (InputChunk *s : inputSections) {
220 s->outputSec = this;
221 MergeInputChunk *ms = dyn_cast<MergeInputChunk>(s);
222 if (!ms) {
223 newSections.push_back(s);
224 continue;
225 }
226
227 if (!mergedSection) {
228 mergedSection =
229 make<SyntheticMergedChunk>(name, 0, WASM_SEG_FLAG_STRINGS);
230 newSections.push_back(mergedSection);
231 mergedSection->outputSec = this;
232 }
233 mergedSection->addMergeChunk(ms);
234 }
235
236 if (!mergedSection)
237 return;
238
239 mergedSection->finalizeContents();
240 inputSections = newSections;
241 }
242
finalizeContents()243 void CustomSection::finalizeContents() {
244 finalizeInputSections();
245
246 raw_string_ostream os(nameData);
247 encodeULEB128(name.size(), os);
248 os << name;
249 os.flush();
250
251 for (InputChunk *section : inputSections) {
252 assert(!section->discarded);
253 section->outSecOff = payloadSize;
254 payloadSize += section->getSize();
255 }
256
257 createHeader(payloadSize + nameData.size());
258 }
259
writeTo(uint8_t * buf)260 void CustomSection::writeTo(uint8_t *buf) {
261 log("writing " + toString(*this) + " offset=" + Twine(offset) +
262 " size=" + Twine(getSize()) + " chunks=" + Twine(inputSections.size()));
263
264 assert(offset);
265 buf += offset;
266
267 // Write section header
268 memcpy(buf, header.data(), header.size());
269 buf += header.size();
270 memcpy(buf, nameData.data(), nameData.size());
271 buf += nameData.size();
272
273 // Write custom sections payload
274 for (const InputChunk *section : inputSections)
275 section->writeTo(buf);
276 }
277
getNumRelocations() const278 uint32_t CustomSection::getNumRelocations() const {
279 uint32_t count = 0;
280 for (const InputChunk *inputSect : inputSections)
281 count += inputSect->getNumRelocations();
282 return count;
283 }
284
writeRelocations(raw_ostream & os) const285 void CustomSection::writeRelocations(raw_ostream &os) const {
286 for (const InputChunk *s : inputSections)
287 s->writeRelocations(os);
288 }
289
290 } // namespace wasm
291 } // namespace lld
292