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)".
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 {
36 StringRef OutputSection::getSectionName() const {
37   return sectionTypeToString(type);
38 }
39 
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 
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 
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 
87 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 
94 void CodeSection::writeRelocations(raw_ostream &os) const {
95   for (const InputChunk *c : functions)
96     c->writeRelocations(os);
97 }
98 
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.getValueOr(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 
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 
193 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 
201 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 
207 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
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 
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 
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 
278 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 
285 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