Re: [PATCH] m4: Remove ternary operator from extern-inline

[Bruno Haible]

Hi,

Martin Kletzander wrote:
> When compiling libvirt with updated GCC (v7.1.0), the following warning
> pops out (which then ends up treated like an error):
> 
> ../config.h:2994:48: error: this use of "defined" may not be portable 
> [-Werror=expansion-to-defined]
>              || (defined _FORTIFY_SOURCE && 0 < _FORTIFY_SOURCE \
> 
> If I remove the ternary operator, the warning/error goes away.

This warning (-Wexpansion-to-defined) is documented in [1]:

   Warn whenever ‘defined’ is encountered in the expansion of a macro
   (including the case where the macro is expanded by an ‘#if’ directive).

What is the expansion of _FORTIFY_SOURCE in your case?
(You can use "gcc -E -dM" to determine it.)

If it does contain the 'defined' keyword, please fix that.

If not, you have found a GCC bug. Please report it at [2].
And disable -Werror until it gets fixed. Gnulib does *not* support the use of
-Werror. [3]

Bruno

[1] https://gcc.gnu.org/onlinedocs/gcc-7.1.0/gcc/Warning-Options.html
[2] https://gcc.gnu.org/bugs/
[3] https://www.gnu.org/software/gnulib/manual/html_node/warnings.html