What does "Duplicate symbol: __fe_def_env" mean? - linker

Question

When building a shared library on AIX with xlc, you see this linker warning:
ld: 0711-224 WARNING: Duplicate symbol: __fe_def_env
To reproduce, use this source file fenvtest.c:
#include <fenv.h>
void exported_func() {
fenv_t f;
(void)fegetenv(&f);
}
Then run the following command:
$ xlc -G -o fenvtest.so -lm -Wl,-bexpfull fenvtest.c
ld: 0711-224 WARNING: Duplicate symbol: __fe_def_env
ld: 0711-345 Use the -bloadmap or -bnoquiet option to obtain more information.

Answer 1

Generally the warning about __fe_def_env occurs when building a shared library and the linker option -bexpfull is used. See the linker documentation for more explanation of -bexpfull.
The symbol __fe_def_env is defined in /usr/include/fenv.h:
const fenv_t __fe_def_env = { FE_TONEAREST, 0, 0, 0, 0 };
so it is included in every object that includes fenv.h. For that reason, if when a shared object is built with -bexpfull or another option that exports __fe_def_env, this symbol will collide with the symbol of the same name in other files.
You can avoid the warning by:
Using -bexpall instead of -bexpfull
Customizing the export list to exclude __fe_def_env
That said, the warning is harmless and may be ignored.