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->outputOffset = bodySize;
91     func->calculateSize();
92     bodySize += func->getSize();
93   }
94 
95   createHeader(bodySize);
96 }
97 
98 void CodeSection::writeTo(uint8_t *buf) {
99   log("writing " + toString(*this));
100   log(" size=" + Twine(getSize()));
101   log(" headersize=" + Twine(header.size()));
102   log(" codeheadersize=" + Twine(codeSectionHeader.size()));
103   buf += offset;
104 
105   // Write section header
106   memcpy(buf, header.data(), header.size());
107   buf += header.size();
108 
109   // Write code section headers
110   memcpy(buf, codeSectionHeader.data(), codeSectionHeader.size());
111 
112   // Write code section bodies
113   for (const InputChunk *chunk : functions)
114     chunk->writeTo(buf);
115 }
116 
117 uint32_t CodeSection::getNumRelocations() const {
118   uint32_t count = 0;
119   for (const InputChunk *func : functions)
120     count += func->getNumRelocations();
121   return count;
122 }
123 
124 void CodeSection::writeRelocations(raw_ostream &os) const {
125   for (const InputChunk *c : functions)
126     c->writeRelocations(os);
127 }
128 
129 void DataSection::finalizeContents() {
130   raw_string_ostream os(dataSectionHeader);
131   unsigned segmentCount =
132       std::count_if(segments.begin(), segments.end(),
133                     [](OutputSegment *segment) { return !segment->isBss; });
134 
135   writeUleb128(os, segmentCount, "data segment count");
136   os.flush();
137   bodySize = dataSectionHeader.size();
138 
139   assert((!config->isPic || segments.size() <= 1) &&
140          "Currenly only a single data segment is supported in PIC mode");
141 
142   for (OutputSegment *segment : segments) {
143     if (segment->isBss)
144       continue;
145     raw_string_ostream os(segment->header);
146     writeUleb128(os, segment->initFlags, "init flags");
147     if (segment->initFlags & WASM_SEGMENT_HAS_MEMINDEX)
148       writeUleb128(os, 0, "memory index");
149     if ((segment->initFlags & WASM_SEGMENT_IS_PASSIVE) == 0) {
150       WasmInitExpr initExpr;
151       if (config->isPic) {
152         initExpr.Opcode = WASM_OPCODE_GLOBAL_GET;
153         initExpr.Value.Global = WasmSym::memoryBase->getGlobalIndex();
154       } else {
155         // FIXME(wvo): I64?
156         initExpr.Opcode = WASM_OPCODE_I32_CONST;
157         initExpr.Value.Int32 = segment->startVA;
158       }
159       writeInitExpr(os, initExpr);
160     }
161     writeUleb128(os, segment->size, "segment size");
162     os.flush();
163 
164     segment->sectionOffset = bodySize;
165     bodySize += segment->header.size() + segment->size;
166     log("Data segment: size=" + Twine(segment->size) + ", startVA=" +
167         Twine::utohexstr(segment->startVA) + ", name=" + segment->name);
168 
169     for (InputSegment *inputSeg : segment->inputSegments)
170       inputSeg->outputOffset = segment->sectionOffset + segment->header.size() +
171                                inputSeg->outputSegmentOffset;
172   }
173 
174   createHeader(bodySize);
175 }
176 
177 void DataSection::writeTo(uint8_t *buf) {
178   log("writing " + toString(*this) + " size=" + Twine(getSize()) +
179       " body=" + Twine(bodySize));
180   buf += offset;
181 
182   // Write section header
183   memcpy(buf, header.data(), header.size());
184   buf += header.size();
185 
186   // Write data section headers
187   memcpy(buf, dataSectionHeader.data(), dataSectionHeader.size());
188 
189   for (const OutputSegment *segment : segments) {
190     if (segment->isBss)
191       continue;
192     // Write data segment header
193     uint8_t *segStart = buf + segment->sectionOffset;
194     memcpy(segStart, segment->header.data(), segment->header.size());
195 
196     // Write segment data payload
197     for (const InputChunk *chunk : segment->inputSegments)
198       chunk->writeTo(buf);
199   }
200 }
201 
202 uint32_t DataSection::getNumRelocations() const {
203   uint32_t count = 0;
204   for (const OutputSegment *seg : segments)
205     for (const InputChunk *inputSeg : seg->inputSegments)
206       count += inputSeg->getNumRelocations();
207   return count;
208 }
209 
210 void DataSection::writeRelocations(raw_ostream &os) const {
211   for (const OutputSegment *seg : segments)
212     for (const InputChunk *c : seg->inputSegments)
213       c->writeRelocations(os);
214 }
215 
216 bool DataSection::isNeeded() const {
217   for (const OutputSegment *seg : segments)
218     if (!seg->isBss)
219       return true;
220   return false;
221 }
222 
223 void CustomSection::finalizeContents() {
224   raw_string_ostream os(nameData);
225   encodeULEB128(name.size(), os);
226   os << name;
227   os.flush();
228 
229   for (InputSection *section : inputSections) {
230     section->outputOffset = payloadSize;
231     section->outputSec = this;
232     payloadSize += section->getSize();
233   }
234 
235   createHeader(payloadSize + nameData.size());
236 }
237 
238 void CustomSection::writeTo(uint8_t *buf) {
239   log("writing " + toString(*this) + " size=" + Twine(getSize()) +
240       " chunks=" + Twine(inputSections.size()));
241 
242   assert(offset);
243   buf += offset;
244 
245   // Write section header
246   memcpy(buf, header.data(), header.size());
247   buf += header.size();
248   memcpy(buf, nameData.data(), nameData.size());
249   buf += nameData.size();
250 
251   // Write custom sections payload
252   for (const InputSection *section : inputSections)
253     section->writeTo(buf);
254 }
255 
256 uint32_t CustomSection::getNumRelocations() const {
257   uint32_t count = 0;
258   for (const InputSection *inputSect : inputSections)
259     count += inputSect->getNumRelocations();
260   return count;
261 }
262 
263 void CustomSection::writeRelocations(raw_ostream &os) const {
264   for (const InputSection *s : inputSections)
265     s->writeRelocations(os);
266 }
267 
268 } // namespace wasm
269 } // namespace lld
270