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
55 lines
1.5 KiB
ArmAsm
55 lines
1.5 KiB
ArmAsm
# REQUIRES: x86
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# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %s -o %t.o
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# RUN: echo "-sectcreate 1.1" >%t1
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# RUN: echo "-sectcreate 1.2" >%t2
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# RUN: echo "-sectcreate 2" >%t3
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# RUN: %lld \
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# RUN: -sectcreate SEG SEC1 %t1 \
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# RUN: -segcreate SEG SEC2 %t3 \
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# RUN: -sectcreate SEG SEC1 %t2 \
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# RUN: -o %t %t.o
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# RUN: llvm-objdump -s %t | FileCheck %s
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## -dead_strip does not strip -sectcreate sections,
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## but also doesn't set S_ATTR_NO_DEAD_STRIP on them.
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# RUN: %lld -dead_strip \
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# RUN: -sectcreate SEG SEC1 %t1 \
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# RUN: -segcreate SEG SEC2 %t3 \
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# RUN: -sectcreate SEG SEC1 %t2 \
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# RUN: -o %t %t.o
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# RUN: llvm-objdump -s %t | FileCheck --check-prefix=STRIPPED %s
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# RUN: llvm-readobj --sections %t | FileCheck --check-prefix=STRIPPEDSEC %s
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# CHECK: Contents of section __TEXT,__text:
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# CHECK: Contents of section __DATA,__data:
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# CHECK: my string!.
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# CHECK: Contents of section SEG,SEC1:
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# CHECK: -sectcreate 1.1.
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# CHECK: -sectcreate 1.2.
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# CHECK: Contents of section SEG,SEC2:
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# CHECK: -sectcreate 2.
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# STRIPPED: Contents of section __TEXT,__text:
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# STRIPPED-NOT: Contents of section __DATA,__data:
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# STRIPPED-NOT: my string!.
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# STRIPPED: Contents of section SEG,SEC1:
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# STRIPPED: -sectcreate 1.1.
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# STRIPPED: -sectcreate 1.2.
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# STRIPPED: Contents of section SEG,SEC2:
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# STRIPPED: -sectcreate 2.
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# STRIPPEDSEC-NOT: NoDeadStrip
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.text
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.global _main
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_main:
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mov $0, %eax
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ret
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.data
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.global my_string
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my_string:
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.string "my string!"
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.subsections_via_symbols
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