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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
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|---|---|---|
| .. | ||
| Arch | ||
| CMakeLists.txt | ||
| ConcatOutputSection.cpp | ||
| ConcatOutputSection.h | ||
| Config.h | ||
| Driver.cpp | ||
| Driver.h | ||
| DriverUtils.cpp | ||
| Dwarf.cpp | ||
| Dwarf.h | ||
| ExportTrie.cpp | ||
| ExportTrie.h | ||
| InputFiles.cpp | ||
| InputFiles.h | ||
| InputSection.cpp | ||
| InputSection.h | ||
| LTO.cpp | ||
| LTO.h | ||
| MachOStructs.h | ||
| MapFile.cpp | ||
| MapFile.h | ||
| MarkLive.cpp | ||
| MarkLive.h | ||
| ObjC.cpp | ||
| ObjC.h | ||
| Options.td | ||
| OutputSection.cpp | ||
| OutputSection.h | ||
| OutputSegment.cpp | ||
| OutputSegment.h | ||
| Relocations.cpp | ||
| Relocations.h | ||
| Symbols.cpp | ||
| Symbols.h | ||
| SymbolTable.cpp | ||
| SymbolTable.h | ||
| SyntheticSections.cpp | ||
| SyntheticSections.h | ||
| Target.cpp | ||
| Target.h | ||
| UnwindInfoSection.cpp | ||
| UnwindInfoSection.h | ||
| Writer.cpp | ||
| Writer.h | ||