6d2d3bd0a6
Change the default to facilitate GC for metadata section usage, so that they don't need SHF_LINK_ORDER or SHF_GROUP just to drop the unhelpful rule (if they want to be unconditionally retained, use SHF_GNU_RETAIN (`__attribute__((retain))`) or linker script `KEEP`). The dropped SHF_GROUP special case makes the behavior of -z start-stop-gc and -z nostart-stop-gc closer to GNU ld>=2.37 (https://sourceware.org/PR27451). However, we default to -z start-stop-gc (which actually matches more closely to GNU ld before 2015-10 https://sourceware.org/PR19167), which is different from modern GNU ld (which has the unhelpful rule to work around glibc). As a compensation, we special case `__libc_` sections as a workaround for glibc<2.34 (https://sourceware.org/PR27492). Since -z start-stop-gc as the default actually matches the traditional GNU ld behavior, there isn't much to be aware of. There was a systemd usage which has been fixed by https://github.com/systemd/systemd/pull/19144
65 lines
1.7 KiB
ArmAsm
65 lines
1.7 KiB
ArmAsm
## Check that group members are retained or discarded as a unit.
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# REQUIRES: x86
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# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t.o
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# RUN: ld.lld %t.o --gc-sections -o %t
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# RUN: llvm-readelf -s %t | FileCheck %s
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# RUN: echo ".global __start___data; __start___data:" > %t2.s
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# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %t2.s -o %t2.o
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# RUN: ld.lld -shared %t2.o --soname=t2 -o %t2.so
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# RUN: ld.lld %t.o --gc-sections -o %t2 %t2.so
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# RUN: llvm-readelf -s %t2 | FileCheck %s
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## The referenced __data is retained.
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# CHECK: [[#%x,ADDR:]] {{.*}} __start___data
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# CHECK: [[#ADDR + 8]] {{.*}} __stop___data
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## __libc_atexit is retained even if there is no reference, as a workaround for
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## glibc<2.34 (BZ #27492).
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# CHECK: [[#%x,ADDR:]] {{.*}} __start___libc_atexit
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# CHECK: [[#ADDR + 8]] {{.*}} __stop___libc_atexit
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# CHECK: _start
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# CHECK: f
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# CHECK-NOT: g
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## If -z nostart-stop-gc, sections whose names are C identifiers are retained by
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## __start_/__stop_ references.
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# RUN: ld.lld %t.o %t2.so --gc-sections -z nostart-stop-gc -o %t3
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# RUN: llvm-readelf -s %t3 | FileCheck %s --check-prefix=NOGC
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# NOGC: [[#%x,ADDR:]] {{.*}} __start___data
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# NOGC: [[#ADDR + 16]] {{.*}} __stop___data
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.weak __start___data
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.weak __stop___data
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.weak __start___libc_atexit
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.weak __stop___libc_atexit
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.section .text,"ax",@progbits
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.global _start
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_start:
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.quad __start___data - .
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.quad __stop___data - .
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.quad __start___libc_atexit - .
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.quad __stop___libc_atexit - .
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call f
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.section __data,"axG",@progbits,f
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.quad 0
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.section .text.f,"axG",@progbits,f
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.global f
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f:
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nop
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.section __data,"axG",@progbits,g
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.quad 0
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.section .text.g,"axG",@progbits,g
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.global g
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g:
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nop
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.section __libc_atexit,"a",@progbits
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.quad 0
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