a2404f11c7
Previously, our unwind info finalization logic assumed that the LSDA
section referenced by `__compact_unwind` was already finalized before
`__TEXT,__unwind_info` itself. However, that assumption could be broken
by the use of `-rename_section` -- it could be (and is) used to move
`__gcc_except_tab` it into a different segment later in the file.
(__TEXT is always the first non-zerofill segment, so any rename
basically guarantees that the section will be ordered after
`__unwind_info`.)
To handle this case, we compare LSDA relocations instead of their final
values in `UnwindInfoSection::finalize()`, and we actually relocate
those LSDAs in `UnwindInfoSection::writeTo()`. In order to do this, we
need an easy way to track which Symbol a given CUE corresponds to. My
solution was to change our `cuPtrVector` into a vector of indices, with
each index used for both the symbols vector (`symbolsVec`) as well as
the CUE vector (`cuVector`).
This change seems perf neutral. Numbers for linking chromium_framework
on my 16 core Mac Pro:
base diff difference (95% CI)
sys_time 1.248 ± 0.025 1.245 ± 0.026 [ -1.3% .. +0.8%]
user_time 3.588 ± 0.045 3.587 ± 0.037 [ -0.6% .. +0.5%]
wall_time 4.605 ± 0.069 4.595 ± 0.069 [ -1.0% .. +0.5%]
samples 42 26
Reviewed By: #lld-macho, oontvoo
Differential Revision: https://reviews.llvm.org/D113582
48 lines
1.4 KiB
C++
48 lines
1.4 KiB
C++
//===- UnwindInfoSection.h ------------------------------------------------===//
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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_UNWIND_INFO_H
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#define LLD_MACHO_UNWIND_INFO_H
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#include "ConcatOutputSection.h"
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#include "SyntheticSections.h"
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#include "llvm/ADT/MapVector.h"
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#include "mach-o/compact_unwind_encoding.h"
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namespace lld {
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namespace macho {
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class UnwindInfoSection : public SyntheticSection {
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public:
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// If all functions are free of unwind info, we can omit the unwind info
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// section entirely.
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bool isNeeded() const override { return !allEntriesAreOmitted; }
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uint64_t getSize() const override { return unwindInfoSize; }
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void addSymbol(const Defined *);
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void prepareRelocations();
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protected:
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UnwindInfoSection();
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virtual void prepareRelocations(ConcatInputSection *) = 0;
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llvm::MapVector<std::pair<const InputSection *, uint64_t /*Defined::value*/>,
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const Defined *>
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symbols;
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std::vector<decltype(symbols)::value_type> symbolsVec;
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uint64_t unwindInfoSize = 0;
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bool allEntriesAreOmitted = true;
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};
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UnwindInfoSection *makeUnwindInfoSection();
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} // namespace macho
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} // namespace lld
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#endif
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