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llvm-project/lld/test/ELF/gc-sections-startstop.s

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[ELF] Default to -z start-stop-gc with a glibc "__libc_" special case 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
2021-04-17 03:18:45 +08:00
## Check that group members are retained or discarded as a unit.
[lld][ELF] __start_/__stop_ refs don't retain C-ident named group sections The special root semantics for identifier-named sections is meant specifically for the metadata sections. In the context of group semantics, where group members are always retained or discarded as a unit, it's natural not to have this semantics apply to a section in a group, otherwise we would never discard the group defeating the purpose of using the group in the first place. This change modifies the GC behavior so that __start_/__stop_ references don't retain C identifier named sections in section groups which allows for these groups to be collected. This matches the behavior of BFD ld. The only kind of existing case that might break is interdependent metadata sections that are all in a group together, but that group doesn't contain any other sections referenced by anything except implicit inclusion in a `__start_` and/or `__stop_`-referenced identifier-named section, but such cases should be unlikely. Differential Revision: https://reviews.llvm.org/D96753
2021-02-16 15:41:16 +08:00
# REQUIRES: x86
# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t.o
# RUN: ld.lld %t.o --gc-sections -o %t
# RUN: llvm-readelf -s %t | FileCheck %s
# RUN: echo ".global __start___data; __start___data:" > %t2.s
# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %t2.s -o %t2.o
[ELF] Default to -z start-stop-gc with a glibc "__libc_" special case 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
2021-04-17 03:18:45 +08:00
# RUN: ld.lld -shared %t2.o --soname=t2 -o %t2.so
[lld][ELF] __start_/__stop_ refs don't retain C-ident named group sections The special root semantics for identifier-named sections is meant specifically for the metadata sections. In the context of group semantics, where group members are always retained or discarded as a unit, it's natural not to have this semantics apply to a section in a group, otherwise we would never discard the group defeating the purpose of using the group in the first place. This change modifies the GC behavior so that __start_/__stop_ references don't retain C identifier named sections in section groups which allows for these groups to be collected. This matches the behavior of BFD ld. The only kind of existing case that might break is interdependent metadata sections that are all in a group together, but that group doesn't contain any other sections referenced by anything except implicit inclusion in a `__start_` and/or `__stop_`-referenced identifier-named section, but such cases should be unlikely. Differential Revision: https://reviews.llvm.org/D96753
2021-02-16 15:41:16 +08:00
# RUN: ld.lld %t.o --gc-sections -o %t2 %t2.so
# RUN: llvm-readelf -s %t2 | FileCheck %s
[ELF] Default to -z start-stop-gc with a glibc "__libc_" special case 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
2021-04-17 03:18:45 +08:00
## The referenced __data is retained.
[lld][ELF] __start_/__stop_ refs don't retain C-ident named group sections The special root semantics for identifier-named sections is meant specifically for the metadata sections. In the context of group semantics, where group members are always retained or discarded as a unit, it's natural not to have this semantics apply to a section in a group, otherwise we would never discard the group defeating the purpose of using the group in the first place. This change modifies the GC behavior so that __start_/__stop_ references don't retain C identifier named sections in section groups which allows for these groups to be collected. This matches the behavior of BFD ld. The only kind of existing case that might break is interdependent metadata sections that are all in a group together, but that group doesn't contain any other sections referenced by anything except implicit inclusion in a `__start_` and/or `__stop_`-referenced identifier-named section, but such cases should be unlikely. Differential Revision: https://reviews.llvm.org/D96753
2021-02-16 15:41:16 +08:00
# CHECK: [[#%x,ADDR:]] {{.*}} __start___data
# CHECK: [[#ADDR + 8]] {{.*}} __stop___data
[ELF] Default to -z start-stop-gc with a glibc "__libc_" special case 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
2021-04-17 03:18:45 +08:00
## __libc_atexit is retained even if there is no reference, as a workaround for
## glibc<2.34 (BZ #27492).
# CHECK: [[#%x,ADDR:]] {{.*}} __start___libc_atexit
# CHECK: [[#ADDR + 8]] {{.*}} __stop___libc_atexit
[lld][ELF] __start_/__stop_ refs don't retain C-ident named group sections The special root semantics for identifier-named sections is meant specifically for the metadata sections. In the context of group semantics, where group members are always retained or discarded as a unit, it's natural not to have this semantics apply to a section in a group, otherwise we would never discard the group defeating the purpose of using the group in the first place. This change modifies the GC behavior so that __start_/__stop_ references don't retain C identifier named sections in section groups which allows for these groups to be collected. This matches the behavior of BFD ld. The only kind of existing case that might break is interdependent metadata sections that are all in a group together, but that group doesn't contain any other sections referenced by anything except implicit inclusion in a `__start_` and/or `__stop_`-referenced identifier-named section, but such cases should be unlikely. Differential Revision: https://reviews.llvm.org/D96753
2021-02-16 15:41:16 +08:00
# CHECK: _start
# CHECK: f
# CHECK-NOT: g
[ELF] Default to -z start-stop-gc with a glibc "__libc_" special case 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
2021-04-17 03:18:45 +08:00
## If -z nostart-stop-gc, sections whose names are C identifiers are retained by
## __start_/__stop_ references.
# RUN: ld.lld %t.o %t2.so --gc-sections -z nostart-stop-gc -o %t3
# RUN: llvm-readelf -s %t3 | FileCheck %s --check-prefix=NOGC
# NOGC: [[#%x,ADDR:]] {{.*}} __start___data
# NOGC: [[#ADDR + 16]] {{.*}} __stop___data
[lld][ELF] __start_/__stop_ refs don't retain C-ident named group sections The special root semantics for identifier-named sections is meant specifically for the metadata sections. In the context of group semantics, where group members are always retained or discarded as a unit, it's natural not to have this semantics apply to a section in a group, otherwise we would never discard the group defeating the purpose of using the group in the first place. This change modifies the GC behavior so that __start_/__stop_ references don't retain C identifier named sections in section groups which allows for these groups to be collected. This matches the behavior of BFD ld. The only kind of existing case that might break is interdependent metadata sections that are all in a group together, but that group doesn't contain any other sections referenced by anything except implicit inclusion in a `__start_` and/or `__stop_`-referenced identifier-named section, but such cases should be unlikely. Differential Revision: https://reviews.llvm.org/D96753
2021-02-16 15:41:16 +08:00
.weak __start___data
.weak __stop___data
[ELF] Default to -z start-stop-gc with a glibc "__libc_" special case 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
2021-04-17 03:18:45 +08:00
.weak __start___libc_atexit
.weak __stop___libc_atexit
[lld][ELF] __start_/__stop_ refs don't retain C-ident named group sections The special root semantics for identifier-named sections is meant specifically for the metadata sections. In the context of group semantics, where group members are always retained or discarded as a unit, it's natural not to have this semantics apply to a section in a group, otherwise we would never discard the group defeating the purpose of using the group in the first place. This change modifies the GC behavior so that __start_/__stop_ references don't retain C identifier named sections in section groups which allows for these groups to be collected. This matches the behavior of BFD ld. The only kind of existing case that might break is interdependent metadata sections that are all in a group together, but that group doesn't contain any other sections referenced by anything except implicit inclusion in a `__start_` and/or `__stop_`-referenced identifier-named section, but such cases should be unlikely. Differential Revision: https://reviews.llvm.org/D96753
2021-02-16 15:41:16 +08:00
.section .text,"ax",@progbits
.global _start
_start:
.quad __start___data - .
.quad __stop___data - .
[ELF] Default to -z start-stop-gc with a glibc "__libc_" special case 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
2021-04-17 03:18:45 +08:00
.quad __start___libc_atexit - .
.quad __stop___libc_atexit - .
[lld][ELF] __start_/__stop_ refs don't retain C-ident named group sections The special root semantics for identifier-named sections is meant specifically for the metadata sections. In the context of group semantics, where group members are always retained or discarded as a unit, it's natural not to have this semantics apply to a section in a group, otherwise we would never discard the group defeating the purpose of using the group in the first place. This change modifies the GC behavior so that __start_/__stop_ references don't retain C identifier named sections in section groups which allows for these groups to be collected. This matches the behavior of BFD ld. The only kind of existing case that might break is interdependent metadata sections that are all in a group together, but that group doesn't contain any other sections referenced by anything except implicit inclusion in a `__start_` and/or `__stop_`-referenced identifier-named section, but such cases should be unlikely. Differential Revision: https://reviews.llvm.org/D96753
2021-02-16 15:41:16 +08:00
call f
.section __data,"axG",@progbits,f
.quad 0
.section .text.f,"axG",@progbits,f
.global f
f:
nop
.section __data,"axG",@progbits,g
.quad 0
.section .text.g,"axG",@progbits,g
.global g
g:
nop
[ELF] Default to -z start-stop-gc with a glibc "__libc_" special case 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
2021-04-17 03:18:45 +08:00
.section __libc_atexit,"a",@progbits
.quad 0