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
20#define DEBUG_TYPE "lld"
21
22using namespace llvm;
23using namespace llvm::wasm;
24
25namespace lld {
26
27// Returns a string, e.g. "FUNCTION(.text)".
28std::string toString(const wasm::OutputSection &sec) {
29 if (!sec.name.empty())
30 return (sec.getSectionName() + "(" + sec.name + ")").str();
31 return std::string(sec.getSectionName());
32}
33
34namespace wasm {
35StringRef OutputSection::getSectionName() const {
36 return sectionTypeToString(type);
37}
38
39void OutputSection::createHeader(size_t bodySize) {
40 raw_string_ostream os(header);
41 debugWrite(offset: os.tell(), msg: "section type [" + getSectionName() + "]");
42 encodeULEB128(Value: type, OS&: os);
43 writeUleb128(os, number: bodySize, msg: "section size");
44 log(msg: "createHeader: " + toString(sec: *this) + " body=" + Twine(bodySize) +
45 " total=" + Twine(getSize()));
46}
47
48void CodeSection::finalizeContents() {
49 raw_string_ostream os(codeSectionHeader);
50 writeUleb128(os, number: functions.size(), msg: "function count");
51 bodySize = codeSectionHeader.size();
52
53 for (InputFunction *func : functions) {
54 func->outputSec = this;
55 func->outSecOff = bodySize;
56 func->calculateSize();
57 // All functions should have a non-empty body at this point
58 assert(func->getSize());
59 bodySize += func->getSize();
60 }
61
62 createHeader(bodySize);
63}
64
65void CodeSection::writeTo(uint8_t *buf) {
66 log(msg: "writing " + toString(sec: *this) + " offset=" + Twine(offset) +
67 " size=" + Twine(getSize()));
68 log(msg: " headersize=" + Twine(header.size()));
69 log(msg: " codeheadersize=" + Twine(codeSectionHeader.size()));
70 buf += offset;
71
72 // Write section header
73 memcpy(dest: buf, src: header.data(), n: header.size());
74 buf += header.size();
75
76 // Write code section headers
77 memcpy(dest: buf, src: codeSectionHeader.data(), n: codeSectionHeader.size());
78
79 // Write code section bodies
80 for (const InputChunk *chunk : functions)
81 chunk->writeTo(buf);
82}
83
84uint32_t CodeSection::getNumRelocations() const {
85 uint32_t count = 0;
86 for (const InputChunk *func : functions)
87 count += func->getNumRelocations();
88 return count;
89}
90
91void CodeSection::writeRelocations(raw_ostream &os) const {
92 for (const InputChunk *c : functions)
93 c->writeRelocations(os);
94}
95
96void DataSection::finalizeContents() {
97 raw_string_ostream os(dataSectionHeader);
98 unsigned segmentCount = llvm::count_if(Range&: segments, P: [](OutputSegment *segment) {
99 return segment->requiredInBinary();
100 });
101#ifndef NDEBUG
102 unsigned activeCount = llvm::count_if(segments, [](OutputSegment *segment) {
103 return segment->requiredInBinary() &&
104 (segment->initFlags & WASM_DATA_SEGMENT_IS_PASSIVE) == 0;
105 });
106#endif
107
108 assert((ctx.arg.sharedMemory || !ctx.isPic || ctx.arg.extendedConst ||
109 activeCount <= 1) &&
110 "output segments should have been combined by now");
111
112 writeUleb128(os, number: segmentCount, msg: "data segment count");
113 bodySize = dataSectionHeader.size();
114 bool is64 = ctx.arg.is64.value_or(u: false);
115
116 for (OutputSegment *segment : segments) {
117 if (!segment->requiredInBinary())
118 continue;
119 raw_string_ostream os(segment->header);
120 writeUleb128(os, number: segment->initFlags, msg: "init flags");
121 if (segment->initFlags & WASM_DATA_SEGMENT_HAS_MEMINDEX)
122 writeUleb128(os, number: 0, msg: "memory index");
123 if ((segment->initFlags & WASM_DATA_SEGMENT_IS_PASSIVE) == 0) {
124 if (ctx.isPic && ctx.arg.extendedConst) {
125 writeU8(os, byte: WASM_OPCODE_GLOBAL_GET, msg: "global get");
126 writeUleb128(os, number: ctx.sym.memoryBase->getGlobalIndex(),
127 msg: "literal (global index)");
128 if (segment->startVA) {
129 writePtrConst(os, number: segment->startVA, is64, msg: "offset");
130 writeU8(os, byte: is64 ? WASM_OPCODE_I64_ADD : WASM_OPCODE_I32_ADD, msg: "add");
131 }
132 writeU8(os, byte: WASM_OPCODE_END, msg: "opcode:end");
133 } else {
134 WasmInitExpr initExpr;
135 initExpr.Extended = false;
136 if (ctx.isPic) {
137 assert(segment->startVA == 0);
138 initExpr.Inst.Opcode = WASM_OPCODE_GLOBAL_GET;
139 initExpr.Inst.Value.Global = ctx.sym.memoryBase->getGlobalIndex();
140 } else {
141 initExpr = intConst(value: segment->startVA, is64);
142 }
143 writeInitExpr(os, initExpr);
144 }
145 }
146 writeUleb128(os, number: segment->size, msg: "segment size");
147
148 segment->sectionOffset = bodySize;
149 bodySize += segment->header.size() + segment->size;
150 log(msg: "Data segment: size=" + Twine(segment->size) + ", startVA=" +
151 Twine::utohexstr(Val: segment->startVA) + ", name=" + segment->name);
152
153 for (InputChunk *inputSeg : segment->inputSegments) {
154 inputSeg->outputSec = this;
155 inputSeg->outSecOff = segment->sectionOffset + segment->header.size() +
156 inputSeg->outputSegmentOffset;
157 }
158 }
159
160 createHeader(bodySize);
161}
162
163void DataSection::writeTo(uint8_t *buf) {
164 log(msg: "writing " + toString(sec: *this) + " offset=" + Twine(offset) +
165 " size=" + Twine(getSize()) + " body=" + Twine(bodySize));
166 buf += offset;
167
168 // Write section header
169 memcpy(dest: buf, src: header.data(), n: header.size());
170 buf += header.size();
171
172 // Write data section headers
173 memcpy(dest: buf, src: dataSectionHeader.data(), n: dataSectionHeader.size());
174
175 for (const OutputSegment *segment : segments) {
176 if (!segment->requiredInBinary())
177 continue;
178 // Write data segment header
179 uint8_t *segStart = buf + segment->sectionOffset;
180 memcpy(dest: segStart, src: segment->header.data(), n: segment->header.size());
181
182 // Write segment data payload
183 for (const InputChunk *chunk : segment->inputSegments)
184 chunk->writeTo(buf);
185 }
186}
187
188uint32_t DataSection::getNumRelocations() const {
189 uint32_t count = 0;
190 for (const OutputSegment *seg : segments)
191 for (const InputChunk *inputSeg : seg->inputSegments)
192 count += inputSeg->getNumRelocations();
193 return count;
194}
195
196void DataSection::writeRelocations(raw_ostream &os) const {
197 for (const OutputSegment *seg : segments)
198 for (const InputChunk *c : seg->inputSegments)
199 c->writeRelocations(os);
200}
201
202bool DataSection::isNeeded() const {
203 for (const OutputSegment *seg : segments)
204 if (seg->requiredInBinary())
205 return true;
206 return false;
207}
208
209// Lots of duplication here with OutputSegment::finalizeInputSegments
210void CustomSection::finalizeInputSections() {
211 SyntheticMergedChunk *mergedSection = nullptr;
212 std::vector<InputChunk *> newSections;
213
214 for (InputChunk *s : inputSections) {
215 s->outputSec = this;
216 MergeInputChunk *ms = dyn_cast<MergeInputChunk>(Val: s);
217 if (!ms) {
218 newSections.push_back(x: s);
219 continue;
220 }
221
222 if (!mergedSection) {
223 mergedSection =
224 make<SyntheticMergedChunk>(args&: name, args: 0, args: WASM_SEG_FLAG_STRINGS);
225 newSections.push_back(x: mergedSection);
226 mergedSection->outputSec = this;
227 }
228 mergedSection->addMergeChunk(ms);
229 }
230
231 if (!mergedSection)
232 return;
233
234 mergedSection->finalizeContents();
235 inputSections = newSections;
236}
237
238void CustomSection::finalizeContents() {
239 finalizeInputSections();
240
241 raw_string_ostream os(nameData);
242 encodeULEB128(Value: name.size(), OS&: os);
243 os << name;
244
245 for (InputChunk *section : inputSections) {
246 assert(!section->discarded);
247 payloadSize = alignTo(Value: payloadSize, Align: section->alignment);
248 section->outSecOff = payloadSize;
249 payloadSize += section->getSize();
250 }
251
252 createHeader(bodySize: payloadSize + nameData.size());
253}
254
255void CustomSection::writeTo(uint8_t *buf) {
256 log(msg: "writing " + toString(sec: *this) + " offset=" + Twine(offset) +
257 " size=" + Twine(getSize()) + " chunks=" + Twine(inputSections.size()));
258
259 assert(offset);
260 buf += offset;
261
262 // Write section header
263 memcpy(dest: buf, src: header.data(), n: header.size());
264 buf += header.size();
265 memcpy(dest: buf, src: nameData.data(), n: nameData.size());
266 buf += nameData.size();
267
268 // Write custom sections payload
269 for (const InputChunk *section : inputSections)
270 section->writeTo(buf);
271}
272
273uint32_t CustomSection::getNumRelocations() const {
274 uint32_t count = 0;
275 for (const InputChunk *inputSect : inputSections)
276 count += inputSect->getNumLiveRelocations();
277 return count;
278}
279
280void CustomSection::writeRelocations(raw_ostream &os) const {
281 for (const InputChunk *s : inputSections)
282 s->writeRelocations(os);
283}
284
285} // namespace wasm
286} // namespace lld
287