https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94659
Bug ID: 94659
Summary: Missing symbol with LTO and target_clones
Product: gcc
Version: 9.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: lto
Assignee: unassigned at gcc dot gnu.org
Reporter: yyc1992 at gmail dot com
CC: marxin at gcc dot gnu.org
Target Milestone: ---
This is basically the same as
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80732 except now it only happens
with LTO enabled.
It seems that if a function with `target_clones` attribute isn't used in the
final library and if LTO is enabled, the function will be missing from the
resulting library. Only the `.resolver` symbol appears.
The test code is
```
// b.c
__attribute__((target_clones("default,avx")))
int f1()
{
return 2;
}
```
when compiled with `gcc -g -flto -O3 -fPIC b.c -shared -o libb-lto.so`, the
exported symbols available are,
```
$ objdump -T libb-lto.so
libb-lto.so: file format elf64-x86-64
DYNAMIC SYMBOL TABLE:
0000000000000000 w D *UND* 0000000000000000
_ITM_deregisterTMCloneTable
0000000000000000 w D *UND* 0000000000000000 __gmon_start__
0000000000000000 w D *UND* 0000000000000000
_ITM_registerTMCloneTable
0000000000000000 w DF *UND* 0000000000000000 GLIBC_2.2.5 __cxa_finalize
0000000000001730 g DF .text 000000000000002b Base f1.resolver
```
Compared to the output lilbrary from `gcc -g -O3 -fPIC b.c -shared -o libb.so`
```
$ objdump -T libb.so
libb.so: file format elf64-x86-64
DYNAMIC SYMBOL TABLE:
0000000000000000 w D *UND* 0000000000000000
_ITM_deregisterTMCloneTable
0000000000000000 w D *UND* 0000000000000000 __gmon_start__
0000000000000000 w D *UND* 0000000000000000
_ITM_registerTMCloneTable
0000000000000000 w DF *UND* 0000000000000000 GLIBC_2.2.5 __cxa_finalize
0000000000001730 w DF .text 000000000000002b Base f1.resolver
0000000000001730 g iD .text 000000000000002b Base f1
```
The exported symbol has the wrong name for the LTO version. `dlsym` result
confirms the difference.
If the function is used somewhere else in the library, the resulting symbol
will then looks the same as the non-LTO version.
