https://sourceware.org/bugzilla/show_bug.cgi?id=26262
Bug ID: 26262
Summary: ld/plugin.c:plugin_notice weak
Product: binutils
Version: unspecified
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: ld
Assignee: unassigned at sourceware dot org
Reporter: i at maskray dot me
Target Milestone: ---
This can be reproduced with clang 10 (likely also 9; and all master commits
before https://reviews.llvm.org/D83967 ). LLVMgold.so is needed.
% cat a.c
int main() {}
% /tmp/Debug/bin/clang -fuse-ld=bfd -fprofile-generate -flto a.c
-Wl,-plugin-opt=save-temps -Wl,-y,__llvm_profile_raw_version
-Wl,-plugin-opt=save-temps
/usr/bin/ld.bfd: /tmp/a-e575a9.o (symbol from plugin): definition of
__llvm_profile_raw_version
/usr/bin/ld.bfd:
/tmp/Debug/lib/clang/12.0.0/lib/linux/libclang_rt.profile-x86_64.a(InstrProfiling.c.o):
definition of __llvm_profile_raw_version
/tmp/a-e575a9.o (symbol from plugin) provides a definition in a prevailing
comdat group.
libclang_rt.profile-x86_64.a(InstrProfiling.c.o) is an weak definition which
should not override the IR definition.
% cat a.out.resolution.txt
/tmp/a-e575a9.o
-r=/tmp/a-e575a9.o,main,plx
-r=/tmp/a-e575a9.o,__llvm_profile_raw_version,l # should be 'plx' instead of
'l'
-r=/tmp/a-e575a9.o,__llvm_profile_filename,plx
Gold and LLD are correct.
% /tmp/Debug/bin/clang -fuse-ld=gold -fprofile-generate -flto a.c
-Wl,-plugin-opt=save-temps -Wl,-y,__llvm_profile_raw_version
/tmp/a-668c9c.o: definition of __llvm_profile_raw_version
/tmp/Debug/lib/clang/12.0.0/lib/linux/libclang_rt.profile-x86_64.a(InstrProfiling.c.o):
definition of __llvm_profile_raw_version
a.out.o: definition of __llvm_profile_raw_version
% cat a.out.resolution.txt
/tmp/a-668c9c.o
-r=/tmp/a-668c9c.o,main,plx
-r=/tmp/a-668c9c.o,__llvm_profile_raw_version,plx
-r=/tmp/a-668c9c.o,__llvm_profile_filename,plx
% /tmp/Debug/bin/clang -fuse-ld=lld -fprofile-generate -flto a.c
-Wl,-plugin-opt=save-temps -Wl,-y,__llvm_profile_raw_version
/tmp/a-afb841.o: definition of __llvm_profile_raw_version
<internal>: reference to __llvm_profile_raw_version
lto.tmp: definition of __llvm_profile_raw_version
% cat a.out.resolution.txt
/tmp/a-afb841.o
-r=/tmp/a-afb841.o,main,plx
-r=/tmp/a-afb841.o,__llvm_profile_raw_version,plx
-r=/tmp/a-afb841.o,__llvm_profile_filename,plx
The ld bug is in ld/plugin.c:plugin_notice . ld somehow drops
bfd_link_hash_defined (provided by "/tmp/a-e575a9.o (symbol from plugin)") in
favor of bfd_link_hash_undefweak. Then bfd_link_hash_undefweak is overridden by
the weak definition in libclang_rt.profile-x86_64.a(InstrProfiling.c.o)
/* Otherwise, it must be a new def.
Ensure any symbol defined in an IR dummy BFD takes on a
new value from a real BFD. Weak symbols are not normally
overridden by a new weak definition, and strong symbols
will normally cause multiple definition errors. Avoid
this by making the symbol appear to be undefined. */
else if (((h->type == bfd_link_hash_defweak
|| h->type == bfd_link_hash_defined)
&& is_ir_dummy_bfd (sym_bfd = h->u.def.section->owner))
|| (h->type == bfd_link_hash_common
&& is_ir_dummy_bfd (sym_bfd = h->u.c.p->section->owner)))
{
h->type = bfd_link_hash_undefweak;
h->u.undef.abfd = sym_bfd;
}
The intended behavior is to let "/tmp/a-e575a9.o (symbol from plugin)" provide
the definition.
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