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428a7c1b38
ICF previously operated only within a given OutputSection. We would merge all CFStrings first, then merge all regular code sections in a second phase. This worked fine since CFStrings would never reference regular `__text` sections. However, I would like to expand ICF to merge functions that reference unwind info. Unwind info references the LSDA section, which can in turn reference the `__text` section, so we cannot perform ICF in phases. In order to have ICF operate on InputSections spanning multiple OutputSections, we need a way to distinguish InputSections that are destined for different OutputSections, so that we don't fold across section boundaries. We achieve this by creating OutputSections early, and setting `InputSection::parent` to point to them. This is what LLD-ELF does. (This change should also make it easier to implement the `section$start$` symbols.) This diff also folds InputSections w/o checking their flags, which I think is the right behavior -- if they are destined for the same OutputSection, they will have the same flags in the output (even if their input flags differ). I.e. the `parent` pointer check subsumes the `flags` check. In practice this has nearly no effect (ICF did not become any more effective on chromium_framework). I've also updated ICF.cpp's block comment to better reflect its current status. Reviewed By: #lld-macho, smeenai Differential Revision: https://reviews.llvm.org/D105641
97 lines
3.3 KiB
C++
97 lines
3.3 KiB
C++
//===- ConcatOutputSection.h ------------------------------------*- C++ -*-===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLD_MACHO_MERGED_OUTPUT_SECTION_H
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#define LLD_MACHO_MERGED_OUTPUT_SECTION_H
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#include "InputSection.h"
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#include "OutputSection.h"
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#include "lld/Common/LLVM.h"
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#include "llvm/ADT/DenseMap.h"
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#include "llvm/ADT/MapVector.h"
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namespace lld {
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namespace macho {
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class Defined;
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// Linking multiple files will inevitably mean resolving sections in different
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// files that are labeled with the same segment and section name. This class
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// contains all such sections and writes the data from each section sequentially
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// in the final binary.
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class ConcatOutputSection final : public OutputSection {
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public:
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explicit ConcatOutputSection(StringRef name)
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: OutputSection(ConcatKind, name) {}
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const ConcatInputSection *firstSection() const { return inputs.front(); }
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const ConcatInputSection *lastSection() const { return inputs.back(); }
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bool isNeeded() const override { return !inputs.empty(); }
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// These accessors will only be valid after finalizing the section
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uint64_t getSize() const override { return size; }
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uint64_t getFileSize() const override { return fileSize; }
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void addInput(ConcatInputSection *input);
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void finalize() override;
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bool needsThunks() const;
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uint64_t estimateStubsInRangeVA(size_t callIdx) const;
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void writeTo(uint8_t *buf) const override;
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std::vector<ConcatInputSection *> inputs;
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std::vector<ConcatInputSection *> thunks;
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static bool classof(const OutputSection *sec) {
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return sec->kind() == ConcatKind;
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}
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static ConcatOutputSection *getOrCreateForInput(const InputSection *);
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private:
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void finalizeFlags(InputSection *input);
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size_t size = 0;
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uint64_t fileSize = 0;
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};
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// We maintain one ThunkInfo per real function.
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//
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// The "active thunk" is represented by the sym/isec pair that
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// turns-over during finalize(): as the call-site address advances,
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// the active thunk goes out of branch-range, and we create a new
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// thunk to take its place.
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//
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// The remaining members -- bools and counters -- apply to the
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// collection of thunks associated with the real function.
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struct ThunkInfo {
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// These denote the active thunk:
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Defined *sym = nullptr; // private-extern symbol for active thunk
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ConcatInputSection *isec = nullptr; // input section for active thunk
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// The following values are cumulative across all thunks on this function
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uint32_t callSiteCount = 0; // how many calls to the real function?
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uint32_t callSitesUsed = 0; // how many call sites processed so-far?
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uint32_t thunkCallCount = 0; // how many call sites went to thunk?
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uint8_t sequence = 0; // how many thunks created so-far?
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};
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NamePair maybeRenameSection(NamePair key);
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// Output sections are added to output segments in iteration order
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// of ConcatOutputSection, so must have deterministic iteration order.
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extern llvm::MapVector<NamePair, ConcatOutputSection *> concatOutputSections;
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extern llvm::DenseMap<Symbol *, ThunkInfo> thunkMap;
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} // namespace macho
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} // namespace lld
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#endif
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