Wireshark mailing list archives
Re: error: logical && with non-zero constant will always evaluate as true
From: Jeff Morriss <jeff.morriss.ws () gmail com>
Date: Thu, 03 Jan 2013 11:52:52 -0500
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 isperfectly 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 () kaiser cx> 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
___________________________________________________________________________ Sent via: Wireshark-dev mailing list <wireshark-dev () wireshark org> Archives: http://www.wireshark.org/lists/wireshark-dev Unsubscribe: https://wireshark.org/mailman/options/wireshark-dev mailto:wireshark-dev-request () wireshark org?subject=unsubscribe
Current thread:
- Re: error: logical && with non-zero constant will always evaluate as true Jeff Morriss (Jan 03)
- Re: error: logical && with non-zero constant will always evaluate as true Jeff Morriss (Jan 03)
- Re: error: logical && with non-zero constant will always evaluate as true Guy Harris (Jan 03)
- Re: error: logical && with non-zero constant will always evaluate as true Jeff Morriss (Jan 04)
- Re: error: logical && with non-zero constant will always evaluate as true Guy Harris (Jan 03)
- <Possible follow-ups>
- Re: error: logical && with non-zero constant will always evaluate as true Jakub Zawadzki (Jan 03)
- Re: error: logical && with non-zero constant will always evaluate as true Jeff Morriss (Jan 03)