a5645513db
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
78 lines
2.5 KiB
C++
78 lines
2.5 KiB
C++
//===- SymbolTable.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_SYMBOL_TABLE_H
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#define LLD_MACHO_SYMBOL_TABLE_H
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#include "Symbols.h"
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#include "lld/Common/LLVM.h"
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#include "llvm/ADT/CachedHashString.h"
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#include "llvm/ADT/DenseMap.h"
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#include "llvm/Object/Archive.h"
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namespace lld {
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namespace macho {
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class ArchiveFile;
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class DylibFile;
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class InputFile;
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class ObjFile;
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class InputSection;
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class MachHeaderSection;
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class Symbol;
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class Defined;
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class Undefined;
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/*
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* Note that the SymbolTable handles name collisions by calling
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* replaceSymbol(), which does an in-place update of the Symbol via `placement
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* new`. Therefore, there is no need to update any relocations that hold
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* pointers the "old" Symbol -- they will automatically point to the new one.
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*/
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class SymbolTable {
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public:
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Defined *addDefined(StringRef name, InputFile *, InputSection *,
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uint64_t value, uint64_t size, bool isWeakDef,
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bool isPrivateExtern, bool isThumb,
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bool isReferencedDynamically, bool noDeadStrip);
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Symbol *addUndefined(StringRef name, InputFile *, bool isWeakRef);
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Symbol *addCommon(StringRef name, InputFile *, uint64_t size, uint32_t align,
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bool isPrivateExtern);
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Symbol *addDylib(StringRef name, DylibFile *file, bool isWeakDef, bool isTlv);
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Symbol *addDynamicLookup(StringRef name);
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Symbol *addLazy(StringRef name, ArchiveFile *file,
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const llvm::object::Archive::Symbol &sym);
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Defined *addSynthetic(StringRef name, InputSection *, uint64_t value,
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bool isPrivateExtern, bool includeInSymtab,
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bool referencedDynamically);
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ArrayRef<Symbol *> getSymbols() const { return symVector; }
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Symbol *find(llvm::CachedHashStringRef name);
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Symbol *find(StringRef name) { return find(llvm::CachedHashStringRef(name)); }
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private:
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std::pair<Symbol *, bool> insert(StringRef name, const InputFile *);
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llvm::DenseMap<llvm::CachedHashStringRef, int> symMap;
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std::vector<Symbol *> symVector;
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};
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void treatUndefinedSymbol(const Undefined &, StringRef source = "");
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extern SymbolTable *symtab;
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} // namespace macho
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} // namespace lld
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#endif
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