9aa82f76ac
This is a different implementation than r303225 (which was reverted in r303270, re-submitted in r303304 and then re-reverted in r303527). In the previous patch, I tried to add Live bit to each dllimported symbol. It turned out that it didn't work with "oldnames.lib" which contains a lot of weak aliases to dllimported symbols. The way we handle weak aliases is to check if undefined symbols can be resolved using weak aliases, and if so, memcpy the Defined symbols to weak Undefined symbols, so that any references to weak aliases automatically see defined symbols instead of undefined ones. This memcpy happens before MarkLive kicks in. That means we may have multiple copies of dllimported symbols. So turning on one instance's Live bit is not enough. This patch moves the Live bit to dllimport file. Since multiple copies of dllsymbols still point to the same file, we can use it as the central repository to keep track of liveness. Differential Revision: https://reviews.llvm.org/D33520 llvm-svn: 303814
69 lines
2.0 KiB
C++
69 lines
2.0 KiB
C++
//===- MarkLive.cpp -------------------------------------------------------===//
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//
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// The LLVM Linker
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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#include "Chunks.h"
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#include "Symbols.h"
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#include "llvm/ADT/STLExtras.h"
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#include <vector>
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namespace lld {
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namespace coff {
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// Set live bit on for each reachable chunk. Unmarked (unreachable)
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// COMDAT chunks will be ignored by Writer, so they will be excluded
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// from the final output.
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void markLive(const std::vector<Chunk *> &Chunks) {
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// We build up a worklist of sections which have been marked as live. We only
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// push into the worklist when we discover an unmarked section, and we mark
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// as we push, so sections never appear twice in the list.
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SmallVector<SectionChunk *, 256> Worklist;
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// COMDAT section chunks are dead by default. Add non-COMDAT chunks.
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for (Chunk *C : Chunks)
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if (auto *SC = dyn_cast<SectionChunk>(C))
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if (SC->isLive())
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Worklist.push_back(SC);
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auto Enqueue = [&](SectionChunk *C) {
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if (C->isLive())
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return;
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C->markLive();
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Worklist.push_back(C);
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};
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auto AddSym = [&](SymbolBody *B) {
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if (auto *Sym = dyn_cast<DefinedRegular>(B))
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Enqueue(Sym->getChunk());
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else if (auto *Sym = dyn_cast<DefinedImportData>(B))
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Sym->File->Live = true;
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else if (auto *Sym = dyn_cast<DefinedImportThunk>(B))
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Sym->WrappedSym->File->Live = true;
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};
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// Add GC root chunks.
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for (SymbolBody *B : Config->GCRoot)
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AddSym(B);
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while (!Worklist.empty()) {
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SectionChunk *SC = Worklist.pop_back_val();
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assert(SC->isLive() && "We mark as live when pushing onto the worklist!");
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// Mark all symbols listed in the relocation table for this section.
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for (SymbolBody *B : SC->symbols())
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AddSym(B);
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// Mark associative sections if any.
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for (SectionChunk *C : SC->children())
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Enqueue(C);
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}
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}
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}
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}
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