gistfile1.txt

Trying to compile open-mpi on macOS Sonoma with Xcode 15 (or CLT 15) Release Candidate fails, because the new linker has a behaviour inconsistent with the previous (classic) linker. The error occurs during configure:

checking prefix for global symbol labels... none
configure: error: Could not determine global symbol label prefix

I have been able to reduce it to a simple example. Take the following C and ASM files:

$ cat a.c
#ifdef __cplusplus
extern "C" {
#endif
void gsym_test_func(void);
#ifdef __cplusplus
}
#endif
int
main()
{
    gsym_test_func();
    return 0;
}

$ cat b.s
.text
# _gsym_test_func
.globl _gsym_test_func
_gsym_test_func:
# _gsym_test_func
fx@admins-Mac-mini openmpi-4.1.5 % clang a.c b.s -Wl,-ld_classic                    
fx@admins-Mac-mini openmpi-4.1.5 % clang a.c b.s                
ld: Undefined symbols:
  _gsym_test_func, referenced from:
      _main in a-822851.o
clang: error: linker command failed with exit code 1 (use -v to see invocation)

Compile them with the classic linker, it works:

$ clang a.c b.s -Wl,-ld_classic

Compile them with the new linker, it fails:

$ clang a.c b.s                 
ld: Undefined symbols:
  _gsym_test_func, referenced from:
      _main in a-92d1f8.o
clang: error: linker command failed with exit code 1 (use -v to see invocation)

I am not sure why, because the symbols are clearly defined in the object files:

$ clang a.c b.s -save-temps   
ld: Undefined symbols:
  _gsym_test_func, referenced from:
      _main in a.o
clang: error: linker command failed with exit code 1 (use -v to see invocation)
$ nm a.o                   
                 U _gsym_test_func
0000000000000000 T _main
0000000000000000 t ltmp0
0000000000000030 s ltmp1
$ nm b.o                   
0000000000000000 T _gsym_test_func
0000000000000000 t ltmp0