[PATCH] S/390: Get rid of warning: the comparision will always evaluate as false

[Stefan Liebler]

ping

On 10/07/2014 05:18 PM, Stefan Liebler wrote:
> Hi,
>
> On s390-32|64 i get the following build warning
> "sysdeps/s390/s390-64/backtrace.c:133:24: warning: the comparison will
> always evaluate as ‘false’ for the address of ‘_Unwind_Backtrace’ will
> never be NULL [-Waddress]" for the non SHARED case.
> In SHARED case, the _Unwind_Backtrace function is loaded via dlsym() and
> thus needs to be NULL-checked (if (unwind_backtrace == NULL)) in order
> to fallback to __backchain_backtrace() function.
>
> In non SHARED case, the #define unwind_backtrace _Unwind_Backtrace was
> introduced with "* sysdeps/s390/s390-32/backtrace.c (init): Guard with
> #ifdef SHARED." (Roland McGrath <roland@gnu.org>  2004-06-11 22:12:55)
> and the NULL-check will never be false for _Unwind_Backtrace() function.
> Thus this NULL-check is now only evaluated in SHARED-case.
>
> The __backchain_backtrace function is only used in the SHARED-case,
> if the unwind-function is not found. Thus it is now only compiled in the
> SHARED-case, to avoid the warning: warning: ‘__backchain_backtrace’
> defined but not used [-Wunused-function].
>
> On s390-32, this function is declared as static, but not on s390-64.
> These functions were introduced in the same patch
> "Update." (Ulrich Drepper <drepper@redhat.com>  2003-12-06 01:20:16)
> and the Changelog from Martin Schwidefsky says:
> * sysdeps/s390/s390-32/backtrace.c (trace_arg): New structure.
> (unwind_backtrace, unwind_getip): New variables.
> (init, __backchain_backtrace, backtrace_helper): New functions.
> (__backtrace): Use unwind info for backtrace instead of backchain
> walking if the unwind functions can be found.
> * sysdeps/s390/s390-64/backtrace.c: Likewise.
>
> On s390-64 it isn´t exported in the shared library, thus on s390-64 it
> is now declared as static too!
>
> Bye Stefan
>
> ---
> 2014-10-07  Stefan Liebler  <stli@linux.vnet.ibm.com>
>
>      * sysdeps/s390/s390-32/backtrace.c (__backtrace):
>      Check for unwind_backtrace ==  NULL only in SHARED case.
>      (__backchain_backtrace): Compile only in SHARED case.
>      * sysdeps/s390/s390-64/backtrace.c (__backtrace):
>      Likewise.
>      (__backchain_backtrace): Declare as static.