| 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. |
| 22 | void 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>(Val: c)) |
| 36 | if (sc->live && !sc->isDWARF()) |
| 37 | worklist.push_back(Elt: sc); |
| 38 | |
| 39 | auto enqueue = [&](SectionChunk *c) { |
| 40 | if (c->live) |
| 41 | return; |
| 42 | c->live = true; |
| 43 | worklist.push_back(Elt: c); |
| 44 | }; |
| 45 | |
| 46 | auto addSym = [&](Symbol *b) { |
| 47 | if (auto *sym = dyn_cast<DefinedRegular>(Val: b)) |
| 48 | enqueue(sym->getChunk()); |
| 49 | else if (auto *sym = dyn_cast<DefinedImportData>(Val: b)) |
| 50 | sym->file->live = true; |
| 51 | else if (auto *sym = dyn_cast<DefinedImportThunk>(Val: 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 |