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)".
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 {
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 
69 StringRef OutputSection::getSectionName() const {
70   return sectionTypeToString(type);
71 }
72 
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 
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     // All functions should have a non-empty body at this point
94     assert(func->getSize());
95     bodySize += func->getSize();
96   }
97 
98   createHeader(bodySize);
99 }
100 
101 void CodeSection::writeTo(uint8_t *buf) {
102   log("writing " + toString(*this));
103   log(" size=" + Twine(getSize()));
104   log(" headersize=" + Twine(header.size()));
105   log(" codeheadersize=" + Twine(codeSectionHeader.size()));
106   buf += offset;
107 
108   // Write section header
109   memcpy(buf, header.data(), header.size());
110   buf += header.size();
111 
112   // Write code section headers
113   memcpy(buf, codeSectionHeader.data(), codeSectionHeader.size());
114 
115   // Write code section bodies
116   for (const InputChunk *chunk : functions)
117     chunk->writeTo(buf);
118 }
119 
120 uint32_t CodeSection::getNumRelocations() const {
121   uint32_t count = 0;
122   for (const InputChunk *func : functions)
123     count += func->getNumRelocations();
124   return count;
125 }
126 
127 void CodeSection::writeRelocations(raw_ostream &os) const {
128   for (const InputChunk *c : functions)
129     c->writeRelocations(os);
130 }
131 
132 void DataSection::finalizeContents() {
133   raw_string_ostream os(dataSectionHeader);
134   unsigned segmentCount =
135       std::count_if(segments.begin(), segments.end(),
136                     [](OutputSegment *segment) { return !segment->isBss; });
137 
138 #ifndef NDEBUG
139   unsigned activeCount = std::count_if(
140       segments.begin(), segments.end(), [](OutputSegment *segment) {
141         return (segment->initFlags & WASM_SEGMENT_IS_PASSIVE) == 0;
142       });
143 #endif
144 
145   assert((!config->isPic || activeCount <= 1) &&
146          "Currenly only a single data segment is supported in PIC mode");
147 
148   writeUleb128(os, segmentCount, "data segment count");
149   os.flush();
150   bodySize = dataSectionHeader.size();
151 
152   for (OutputSegment *segment : segments) {
153     if (segment->isBss)
154       continue;
155     raw_string_ostream os(segment->header);
156     writeUleb128(os, segment->initFlags, "init flags");
157     if (segment->initFlags & WASM_SEGMENT_HAS_MEMINDEX)
158       writeUleb128(os, 0, "memory index");
159     if ((segment->initFlags & WASM_SEGMENT_IS_PASSIVE) == 0) {
160       WasmInitExpr initExpr;
161       if (config->isPic) {
162         initExpr.Opcode = WASM_OPCODE_GLOBAL_GET;
163         initExpr.Value.Global = WasmSym::memoryBase->getGlobalIndex();
164       } else {
165         // FIXME(wvo): I64?
166         initExpr.Opcode = WASM_OPCODE_I32_CONST;
167         initExpr.Value.Int32 = segment->startVA;
168       }
169       writeInitExpr(os, initExpr);
170     }
171     writeUleb128(os, segment->size, "segment size");
172     os.flush();
173 
174     segment->sectionOffset = bodySize;
175     bodySize += segment->header.size() + segment->size;
176     log("Data segment: size=" + Twine(segment->size) + ", startVA=" +
177         Twine::utohexstr(segment->startVA) + ", name=" + segment->name);
178 
179     for (InputSegment *inputSeg : segment->inputSegments) {
180       inputSeg->outputSec = this;
181       inputSeg->outputOffset = segment->sectionOffset + segment->header.size() +
182                                inputSeg->outputSegmentOffset;
183     }
184   }
185 
186   createHeader(bodySize);
187 }
188 
189 void DataSection::writeTo(uint8_t *buf) {
190   log("writing " + toString(*this) + " size=" + Twine(getSize()) +
191       " body=" + Twine(bodySize));
192   buf += offset;
193 
194   // Write section header
195   memcpy(buf, header.data(), header.size());
196   buf += header.size();
197 
198   // Write data section headers
199   memcpy(buf, dataSectionHeader.data(), dataSectionHeader.size());
200 
201   for (const OutputSegment *segment : segments) {
202     if (segment->isBss)
203       continue;
204     // Write data segment header
205     uint8_t *segStart = buf + segment->sectionOffset;
206     memcpy(segStart, segment->header.data(), segment->header.size());
207 
208     // Write segment data payload
209     for (const InputChunk *chunk : segment->inputSegments)
210       chunk->writeTo(buf);
211   }
212 }
213 
214 uint32_t DataSection::getNumRelocations() const {
215   uint32_t count = 0;
216   for (const OutputSegment *seg : segments)
217     for (const InputChunk *inputSeg : seg->inputSegments)
218       count += inputSeg->getNumRelocations();
219   return count;
220 }
221 
222 void DataSection::writeRelocations(raw_ostream &os) const {
223   for (const OutputSegment *seg : segments)
224     for (const InputChunk *c : seg->inputSegments)
225       c->writeRelocations(os);
226 }
227 
228 bool DataSection::isNeeded() const {
229   for (const OutputSegment *seg : segments)
230     if (!seg->isBss)
231       return true;
232   return false;
233 }
234 
235 void CustomSection::finalizeContents() {
236   raw_string_ostream os(nameData);
237   encodeULEB128(name.size(), os);
238   os << name;
239   os.flush();
240 
241   for (InputSection *section : inputSections) {
242     assert(!section->discarded);
243     section->outputSec = this;
244     section->outputOffset = payloadSize;
245     payloadSize += section->getSize();
246   }
247 
248   createHeader(payloadSize + nameData.size());
249 }
250 
251 void CustomSection::writeTo(uint8_t *buf) {
252   log("writing " + toString(*this) + " size=" + Twine(getSize()) +
253       " chunks=" + Twine(inputSections.size()));
254 
255   assert(offset);
256   buf += offset;
257 
258   // Write section header
259   memcpy(buf, header.data(), header.size());
260   buf += header.size();
261   memcpy(buf, nameData.data(), nameData.size());
262   buf += nameData.size();
263 
264   // Write custom sections payload
265   for (const InputSection *section : inputSections)
266     section->writeTo(buf);
267 }
268 
269 uint32_t CustomSection::getNumRelocations() const {
270   uint32_t count = 0;
271   for (const InputSection *inputSect : inputSections)
272     count += inputSect->getNumRelocations();
273   return count;
274 }
275 
276 void CustomSection::writeRelocations(raw_ostream &os) const {
277   for (const InputSection *s : inputSections)
278     s->writeRelocations(os);
279 }
280 
281 } // namespace wasm
282 } // namespace lld
283