Re: [PATCH][BZ #16195] Fix build warnings from systemtap probes in non-systemtap configurations

["Carlos O'Donell" <carlos at redhat dot com>]

On 12/02/2013 09:32 AM, Siddhesh Poyarekar wrote:
> Hi,
> 
> Joseph pointed out in the bug report (and in an earlier thread) that
> systemtap probes cause build time warnings like the following:
> 
> ../sysdeps/ieee754/dbl-64/e_atan2.c:602:4: warning: the address of 'p'
> will always evaluate as 'true' [-Waddress]
> 
> due to the fact that we're now passing non-weak variables to
> LIBC_PROBE in the libm probes.  This happens only on configurations
> that do not enable systemtap.  The macro definition of LIBC_PROBE in
> this case only acts as a sanity checker to ensure that the number
> parameters passed to LIBC_PROBE is equal to the argument count
> parameter passed before it.  This can be done in a much simpler manner
> by just adding a macro definition for each number of arguments.  I am
> assuming here that we don't really want to bother with supporting
> LIBC_PROBE with an indeterminate number of arguments and if there is a
> need for a probe to have more data than what is currently supported (4
> arguments), one could simply add an additional macro here.
> 
> Tested that it gets rid of the warning on i686 and also verified that
> nothing changed on x86_64.  OK to commit?
> 
> Siddhesh
> 
> 	[BZ #16195]
> 	* include/stap-probe.h [!USE_STAP_PROBE && !__ASSEMBLER__]
> 	(LIBC_PROBE): Change definition to call STAP_PROBE* macros.
> 	(STAP_PROBE0): New macro.
> 	(STAP_PROBE1): Likewise.
> 	(STAP_PROBE2): Likewise.
> 	(STAP_PROBE3): Likewise.
> 	(STAP_PROBE4): Likewise.
> 
> diff --git a/include/stap-probe.h b/include/stap-probe.h
> index 5f72556..e296350 100644
> --- a/include/stap-probe.h
> +++ b/include/stap-probe.h
> @@ -61,13 +61,14 @@
>  
>  # ifndef __ASSEMBLER__
>  /* Evaluate all the arguments and verify that N matches their number.  */
> -#  define LIBC_PROBE(name, n, ...)					      \
> -  do {									      \
> -    _Bool __libc_probe_args[] = { 0, ## __VA_ARGS__ };			      \
> -    _Bool __libc_probe_verify_n[(sizeof __libc_probe_args / sizeof (_Bool))   \
> -                                == n + 1 ? 1 : -1];			      \
> -    (void) __libc_probe_verify_n;					      \
> -  } while (0)
> +#define LIBC_PROBE(name, n, ...) STAP_PROBE##n (__VA_ARGS__)
> +
> +#define STAP_PROBE0()
> +#define STAP_PROBE1(a1)
> +#define STAP_PROBE2(a1, a2)
> +#define STAP_PROBE3(a1, a2, a3)
> +#define STAP_PROBE4(a1, a2, a3, a4)
> +
>  # else
>  #  define LIBC_PROBE(name, n, ...)		/* Nothing.  */
>  # endif
> 

OK.

Cheers,
Carlos.