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 "InputFiles.h"
12 #include "OutputSegment.h"
13 #include "WriterUtils.h"
14 #include "lld/Common/ErrorHandler.h"
15 #include "llvm/ADT/Twine.h"
16 #include "llvm/Support/LEB128.h"
17 #include "llvm/Support/Parallel.h"
18
19 #define DEBUG_TYPE "lld"
20
21 using namespace llvm;
22 using namespace llvm::wasm;
23
24 namespace lld {
25
26 // Returns a string, e.g. "FUNCTION(.text)".
toString(const wasm::OutputSection & sec)27 std::string toString(const wasm::OutputSection &sec) {
28 if (!sec.name.empty())
29 return (sec.getSectionName() + "(" + sec.name + ")").str();
30 return std::string(sec.getSectionName());
31 }
32
33 namespace wasm {
sectionTypeToString(uint32_t sectionType)34 static StringRef sectionTypeToString(uint32_t sectionType) {
35 switch (sectionType) {
36 case WASM_SEC_CUSTOM:
37 return "CUSTOM";
38 case WASM_SEC_TYPE:
39 return "TYPE";
40 case WASM_SEC_IMPORT:
41 return "IMPORT";
42 case WASM_SEC_FUNCTION:
43 return "FUNCTION";
44 case WASM_SEC_TABLE:
45 return "TABLE";
46 case WASM_SEC_MEMORY:
47 return "MEMORY";
48 case WASM_SEC_GLOBAL:
49 return "GLOBAL";
50 case WASM_SEC_EVENT:
51 return "EVENT";
52 case WASM_SEC_EXPORT:
53 return "EXPORT";
54 case WASM_SEC_START:
55 return "START";
56 case WASM_SEC_ELEM:
57 return "ELEM";
58 case WASM_SEC_CODE:
59 return "CODE";
60 case WASM_SEC_DATA:
61 return "DATA";
62 case WASM_SEC_DATACOUNT:
63 return "DATACOUNT";
64 default:
65 fatal("invalid section type");
66 }
67 }
68
getSectionName() const69 StringRef OutputSection::getSectionName() const {
70 return sectionTypeToString(type);
71 }
72
createHeader(size_t bodySize)73 void OutputSection::createHeader(size_t bodySize) {
74 raw_string_ostream os(header);
75 debugWrite(os.tell(), "section type [" + getSectionName() + "]");
76 encodeULEB128(type, os);
77 writeUleb128(os, bodySize, "section size");
78 os.flush();
79 log("createHeader: " + toString(*this) + " body=" + Twine(bodySize) +
80 " total=" + Twine(getSize()));
81 }
82
finalizeContents()83 void CodeSection::finalizeContents() {
84 raw_string_ostream os(codeSectionHeader);
85 writeUleb128(os, functions.size(), "function count");
86 os.flush();
87 bodySize = codeSectionHeader.size();
88
89 for (InputFunction *func : functions) {
90 func->outputSec = this;
91 func->outputOffset = bodySize;
92 func->calculateSize();
93 bodySize += func->getSize();
94 }
95
96 createHeader(bodySize);
97 }
98
writeTo(uint8_t * buf)99 void CodeSection::writeTo(uint8_t *buf) {
100 log("writing " + toString(*this));
101 log(" size=" + Twine(getSize()));
102 log(" headersize=" + Twine(header.size()));
103 log(" codeheadersize=" + Twine(codeSectionHeader.size()));
104 buf += offset;
105
106 // Write section header
107 memcpy(buf, header.data(), header.size());
108 buf += header.size();
109
110 // Write code section headers
111 memcpy(buf, codeSectionHeader.data(), codeSectionHeader.size());
112
113 // Write code section bodies
114 for (const InputChunk *chunk : functions)
115 chunk->writeTo(buf);
116 }
117
getNumRelocations() const118 uint32_t CodeSection::getNumRelocations() const {
119 uint32_t count = 0;
120 for (const InputChunk *func : functions)
121 count += func->getNumRelocations();
122 return count;
123 }
124
writeRelocations(raw_ostream & os) const125 void CodeSection::writeRelocations(raw_ostream &os) const {
126 for (const InputChunk *c : functions)
127 c->writeRelocations(os);
128 }
129
finalizeContents()130 void DataSection::finalizeContents() {
131 raw_string_ostream os(dataSectionHeader);
132 unsigned segmentCount =
133 std::count_if(segments.begin(), segments.end(),
134 [](OutputSegment *segment) { return !segment->isBss; });
135
136 writeUleb128(os, segmentCount, "data segment count");
137 os.flush();
138 bodySize = dataSectionHeader.size();
139
140 assert((!config->isPic || segments.size() <= 1) &&
141 "Currenly only a single data segment is supported in PIC mode");
142
143 for (OutputSegment *segment : segments) {
144 if (segment->isBss)
145 continue;
146 raw_string_ostream os(segment->header);
147 writeUleb128(os, segment->initFlags, "init flags");
148 if (segment->initFlags & WASM_SEGMENT_HAS_MEMINDEX)
149 writeUleb128(os, 0, "memory index");
150 if ((segment->initFlags & WASM_SEGMENT_IS_PASSIVE) == 0) {
151 WasmInitExpr initExpr;
152 if (config->isPic) {
153 initExpr.Opcode = WASM_OPCODE_GLOBAL_GET;
154 initExpr.Value.Global = WasmSym::memoryBase->getGlobalIndex();
155 } else {
156 // FIXME(wvo): I64?
157 initExpr.Opcode = WASM_OPCODE_I32_CONST;
158 initExpr.Value.Int32 = segment->startVA;
159 }
160 writeInitExpr(os, initExpr);
161 }
162 writeUleb128(os, segment->size, "segment size");
163 os.flush();
164
165 segment->sectionOffset = bodySize;
166 bodySize += segment->header.size() + segment->size;
167 log("Data segment: size=" + Twine(segment->size) + ", startVA=" +
168 Twine::utohexstr(segment->startVA) + ", name=" + segment->name);
169
170 for (InputSegment *inputSeg : segment->inputSegments) {
171 inputSeg->outputSec = this;
172 inputSeg->outputOffset = segment->sectionOffset + segment->header.size() +
173 inputSeg->outputSegmentOffset;
174 }
175 }
176
177 createHeader(bodySize);
178 }
179
writeTo(uint8_t * buf)180 void DataSection::writeTo(uint8_t *buf) {
181 log("writing " + toString(*this) + " size=" + Twine(getSize()) +
182 " body=" + Twine(bodySize));
183 buf += offset;
184
185 // Write section header
186 memcpy(buf, header.data(), header.size());
187 buf += header.size();
188
189 // Write data section headers
190 memcpy(buf, dataSectionHeader.data(), dataSectionHeader.size());
191
192 for (const OutputSegment *segment : segments) {
193 if (segment->isBss)
194 continue;
195 // Write data segment header
196 uint8_t *segStart = buf + segment->sectionOffset;
197 memcpy(segStart, segment->header.data(), segment->header.size());
198
199 // Write segment data payload
200 for (const InputChunk *chunk : segment->inputSegments)
201 chunk->writeTo(buf);
202 }
203 }
204
getNumRelocations() const205 uint32_t DataSection::getNumRelocations() const {
206 uint32_t count = 0;
207 for (const OutputSegment *seg : segments)
208 for (const InputChunk *inputSeg : seg->inputSegments)
209 count += inputSeg->getNumRelocations();
210 return count;
211 }
212
writeRelocations(raw_ostream & os) const213 void DataSection::writeRelocations(raw_ostream &os) const {
214 for (const OutputSegment *seg : segments)
215 for (const InputChunk *c : seg->inputSegments)
216 c->writeRelocations(os);
217 }
218
isNeeded() const219 bool DataSection::isNeeded() const {
220 for (const OutputSegment *seg : segments)
221 if (!seg->isBss)
222 return true;
223 return false;
224 }
225
finalizeContents()226 void CustomSection::finalizeContents() {
227 raw_string_ostream os(nameData);
228 encodeULEB128(name.size(), os);
229 os << name;
230 os.flush();
231
232 for (InputSection *section : inputSections) {
233 section->outputSec = this;
234 section->outputOffset = payloadSize;
235 payloadSize += section->getSize();
236 }
237
238 createHeader(payloadSize + nameData.size());
239 }
240
writeTo(uint8_t * buf)241 void CustomSection::writeTo(uint8_t *buf) {
242 log("writing " + toString(*this) + " size=" + Twine(getSize()) +
243 " chunks=" + Twine(inputSections.size()));
244
245 assert(offset);
246 buf += offset;
247
248 // Write section header
249 memcpy(buf, header.data(), header.size());
250 buf += header.size();
251 memcpy(buf, nameData.data(), nameData.size());
252 buf += nameData.size();
253
254 // Write custom sections payload
255 for (const InputSection *section : inputSections)
256 section->writeTo(buf);
257 }
258
getNumRelocations() const259 uint32_t CustomSection::getNumRelocations() const {
260 uint32_t count = 0;
261 for (const InputSection *inputSect : inputSections)
262 count += inputSect->getNumRelocations();
263 return count;
264 }
265
writeRelocations(raw_ostream & os) const266 void CustomSection::writeRelocations(raw_ostream &os) const {
267 for (const InputSection *s : inputSections)
268 s->writeRelocations(os);
269 }
270
271 } // namespace wasm
272 } // namespace lld
273