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.