Wireshark-dev: Re: [Wireshark-dev] error: logical && with non-zero constant will always evaluat
My (Fedora 10) gcc 4.3.2 was also generating this warning; it would seem
that a fair spread of gcc versions seem to have the problem.
I added a configure check to stop using -Wlogical-op if the compiler is
generating this warning in r46916.
Evan Huus wrote:
While 'separators' is not immediately constant either,
wtap_file_read_till_separator (the function containing the strchr) is
called in only one place, and that call passes in a string constant to
the 'separators' parameter.
GCC is smart enough to figure that out, so __builtin_constant_p [1]
returns 1, leading to the warning you're seeing.
From my perspective, this is a compiler bug. The code as written is
perfectly correct, and GCC is optimizing it and then warning on the
partially-optimized code before completing the optimization (which is
to evaluate the big string of &&'s to false because
__builtin_constant_p(c) is false, resulting in a simple call to
__builtin_strchr (s, c)).
The GCC in squeeze is two patch versions shy of latest in that series
(4.4.5 vs 4.4.7). I don't see any reference to this particular bug in
the changelogs, but it might help to try a newer compiler. If not, I
would suggest filing a bug against Debian's GCC package and let them
figure out who ought to deal with it.
In the meantime, I'm not really sure what the best workaround is...
[1] http://gcc.gnu.org/onlinedocs/gcc-4.4.2/gcc/Other-Builtins.html#index-g_t_005f_005fbuiltin_005fconstant_005fp-2868
On Sat, Dec 29, 2012 at 10:17 AM, Martin Kaiser <lists@xxxxxxxxx> wrote:
Dear all,
I get this warning (error) when I compile svn head
peektagged.c: In function ‘wtap_file_read_till_separator’:
peektagged.c:150: error: logical ‘&&’ with non-zero constant
will always
evaluate as true
make[2]: *** [libwiretap_la-peektagged.lo] Error 1
The offending line is
if (strchr (separators, c) != NULL)
which seems to evaluate on my system (debian squeeze) to something like
(__extension__ (__builtin_constant_p (c) && !__builtin_constant_p (s) \
&& (c) == '\0' \
? (char *) __rawmemchr (s, c) \
: __builtin_strchr (s, c)))
I still don't understand the problem. c is not constant, it's read from
a file.
Commenting out
AC_WIRESHARK_GCC_CFLAGS_CHECK(-Wlogical-op)
in configure.ac will stop the warning.
Any ideas how to fix this properly?
Thanks,
Martin
