1 //===- MarkLive.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 "COFFLinkerContext.h" 10 #include "Chunks.h" 11 #include "Symbols.h" 12 #include "lld/Common/Timer.h" 13 #include "llvm/Support/TimeProfiler.h" 14 15 namespace lld::coff { 16 17 // Set live bit on for each reachable chunk. Unmarked (unreachable) 18 // COMDAT chunks will be ignored by Writer, so they will be excluded 19 // from the final output. markLive(COFFLinkerContext & ctx)20void markLive(COFFLinkerContext &ctx) { 21 llvm::TimeTraceScope timeScope("Mark live"); 22 ScopedTimer t(ctx.gcTimer); 23 24 // We build up a worklist of sections which have been marked as live. We only 25 // push into the worklist when we discover an unmarked section, and we mark 26 // as we push, so sections never appear twice in the list. 27 SmallVector<SectionChunk *, 256> worklist; 28 29 // COMDAT section chunks are dead by default. Add non-COMDAT chunks. Do not 30 // traverse DWARF sections. They are live, but they should not keep other 31 // sections alive. 32 for (Chunk *c : ctx.driver.getChunks()) 33 if (auto *sc = dyn_cast<SectionChunk>(c)) 34 if (sc->live && !sc->isDWARF()) 35 worklist.push_back(sc); 36 37 auto enqueue = [&](SectionChunk *c) { 38 if (c->live) 39 return; 40 c->live = true; 41 worklist.push_back(c); 42 }; 43 44 std::function<void(Symbol *)> addSym; 45 46 auto addImportFile = [&](ImportFile *file) { 47 file->live = true; 48 if (file->impchkThunk && file->impchkThunk->exitThunk) 49 addSym(file->impchkThunk->exitThunk); 50 }; 51 52 addSym = [&](Symbol *b) { 53 if (auto *sym = dyn_cast<DefinedRegular>(b)) { 54 enqueue(sym->getChunk()); 55 } else if (auto *sym = dyn_cast<DefinedImportData>(b)) { 56 addImportFile(sym->file); 57 } else if (auto *sym = dyn_cast<DefinedImportThunk>(b)) { 58 addImportFile(sym->wrappedSym->file); 59 sym->getChunk()->live = true; 60 } 61 }; 62 63 // Add GC root chunks. 64 for (Symbol *b : ctx.config.gcroot) 65 addSym(b); 66 67 while (!worklist.empty()) { 68 SectionChunk *sc = worklist.pop_back_val(); 69 assert(sc->live && "We mark as live when pushing onto the worklist!"); 70 71 // Mark all symbols listed in the relocation table for this section. 72 for (Symbol *b : sc->symbols()) 73 if (b) 74 addSym(b); 75 76 // Mark associative sections if any. 77 for (SectionChunk &c : sc->children()) 78 enqueue(&c); 79 80 // Mark EC entry thunks. 81 if (Defined *entryThunk = sc->getEntryThunk()) 82 addSym(entryThunk); 83 } 84 } 85 } 86