2020-08-21 04:05:13 +08:00
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//===- 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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2021-05-26 02:57:16 +08:00
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#include "ConcatOutputSection.h"
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2020-08-21 04:05:13 +08:00
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#include "SyntheticSections.h"
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#include "mach-o/compact_unwind_encoding.h"
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#include "llvm/ADT/DenseMap.h"
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#include <vector>
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namespace lld {
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namespace macho {
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[lld/mac] Implement -dead_strip
Also adds support for live_support sections, no_dead_strip sections,
.no_dead_strip symbols.
Chromium Framework 345MB unstripped -> 250MB stripped
(vs 290MB unstripped -> 236M stripped with ld64).
Doing dead stripping is a bit faster than not, because so much less
data needs to be processed:
% ministat lld_*
x lld_nostrip.txt
+ lld_strip.txt
N Min Max Median Avg Stddev
x 10 3.929414 4.07692 4.0269079 4.0089678 0.044214794
+ 10 3.8129408 3.9025559 3.8670411 3.8642573 0.024779651
Difference at 95.0% confidence
-0.144711 +/- 0.0336749
-3.60967% +/- 0.839989%
(Student's t, pooled s = 0.0358398)
This interacts with many parts of the linker. I tried to add test coverage
for all added `isLive()` checks, so that some test will fail if any of them
is removed. I checked that the test expectations for the most part match
ld64's behavior (except for live-support-iterations.s, see the comment
in the test). Interacts with:
- debug info
- export tries
- import opcodes
- flags like -exported_symbol(s_list)
- -U / dynamic_lookup
- mod_init_funcs, mod_term_funcs
- weak symbol handling
- unwind info
- stubs
- map files
- -sectcreate
- undefined, dylib, common, defined (both absolute and normal) symbols
It's possible it interacts with more features I didn't think of,
of course.
I also did some manual testing:
- check-llvm check-clang check-lld work with lld with this patch
as host linker and -dead_strip enabled
- Chromium still starts
- Chromium's base_unittests still pass, including unwind tests
Implemenation-wise, this is InputSection-based, so it'll work for
object files with .subsections_via_symbols (which includes all
object files generated by clang). I first based this on the COFF
implementation, but later realized that things are more similar to ELF.
I think it'd be good to refactor MarkLive.cpp to look more like the ELF
part at some point, but I'd like to get a working state checked in first.
Mechanical parts:
- Rename canOmitFromOutput to wasCoalesced (no behavior change)
since it really is for weak coalesced symbols
- Add noDeadStrip to Defined, corresponding to N_NO_DEAD_STRIP
(`.no_dead_strip` in asm)
Fixes PR49276.
Differential Revision: https://reviews.llvm.org/D103324
2021-05-08 05:10:05 +08:00
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template <class Ptr> struct CompactUnwindEntry {
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Ptr functionAddress;
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uint32_t functionLength;
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compact_unwind_encoding_t encoding;
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Ptr personality;
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Ptr lsda;
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};
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2020-08-21 04:05:13 +08:00
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class UnwindInfoSection : public SyntheticSection {
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public:
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bool isNeeded() const override { return compactUnwindSection != nullptr; }
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uint64_t getSize() const override { return unwindInfoSize; }
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virtual void prepareRelocations(InputSection *) = 0;
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2021-05-26 02:57:16 +08:00
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void setCompactUnwindSection(ConcatOutputSection *cuSection) {
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compactUnwindSection = cuSection;
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}
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2021-04-16 09:14:33 +08:00
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protected:
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UnwindInfoSection()
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: SyntheticSection(segment_names::text, section_names::unwindInfo) {
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align = 4;
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}
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2020-12-07 14:33:38 +08:00
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2021-05-26 02:57:16 +08:00
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ConcatOutputSection *compactUnwindSection = nullptr;
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2020-08-21 04:05:13 +08:00
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uint64_t unwindInfoSize = 0;
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};
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2021-04-16 09:14:33 +08:00
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UnwindInfoSection *makeUnwindInfoSection();
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2021-02-09 02:47:33 +08:00
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2020-08-21 04:05:13 +08:00
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} // namespace macho
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} // namespace lld
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#endif
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