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