Hi!
> building with compiler flags "-Wall -O2 -D_FORTIFY_SOURCE=2" throws some
> warnings:
>
> [EMAIL PROTECTED]:~/projects/powermanagement/cvs/suspend> make CFLAGS='-Wall
> -O2 -D_FORTIFY_SOURCE=2'
> cc -Wall -O2 -D_FORTIFY_SOURCE=2 -c vt.c -o vt.o
> cc -Wall -O2 -D_FORTIFY_SOURCE=2 -DHAVE_INTTYPES_H -DHAVE_STDINT_H -c md5.c
> -o md5.o
> cc -Wall -O2 -D_FORTIFY_SOURCE=2 -DHAVE_INTTYPES_H -DHAVE_STDINT_H
> -I/usr/local/include -c encrypt.c -o encrypt.o
> cc -Wall -O2 -D_FORTIFY_SOURCE=2 -I/usr/local/include -c config.c -o config.o
> cc -g -Wall -O2 -D_FORTIFY_SOURCE=2 -I/usr/local/include -c bootsplash.c -o
> bootsplash.o
> cc -g -Wall -O2 -D_FORTIFY_SOURCE=2 -I/usr/local/include -c splash.c -o
> splash.o
> cc -g -Wall -O2 -D_FORTIFY_SOURCE=2 -I/usr/local/include vt.o md5.o encrypt.o
> config.o suspend.c -o s2disk splash.o bootsplash.o -L/usr/local/lib
> suspend.c: In function ???prepare_console???:
> suspend.c:816: warning: ignoring return value of ???write???, declared with
> attribute warn_unused_result
> suspend.c: In function ???get_kernel_console_loglevel???:
> suspend.c:886: warning: ignoring return value of ???fscanf???, declared with
> attribute warn_unused_result
> suspend.c: In function ???get_swappiness???:
> suspend.c:919: warning: ignoring return value of ???fscanf???, declared with
> attribute warn_unused_result
> suspend.c: In function ???main???:
> suspend.c:1192: warning: ignoring return value of ???chdir???, declared with
> attribute warn_unused_result
> cc -Wall -O2 -D_FORTIFY_SOURCE=2 -c vbetool/lrmi.c -o vbetool/lrmi.o
> cc -Wall -O2 -D_FORTIFY_SOURCE=2 -c vbetool/x86-common.c -o
> vbetool/x86-common.o
> cc -Wall -O2 -D_FORTIFY_SOURCE=2 -DS2RAM -c vbetool/vbetool.c -o
> vbetool/vbetool.o
> vbetool/vbetool.c: In function ???save_state???:
> vbetool/vbetool.c:347: warning: ignoring return value of ???write???,
> declared with attribute warn_unused_result
> cc -Wall -O2 -D_FORTIFY_SOURCE=2 -DS2RAM -c radeontool.c -o radeontool.o
> cc -Wall -O2 -D_FORTIFY_SOURCE=2 -DS2RAM -c dmidecode.c -o dmidecode.o
> cc -g -Wall -O2 -D_FORTIFY_SOURCE=2 -DCONFIG_BOTH -I/usr/local/include md5.o
> encrypt.o config.o suspend.c s2ram.c -o s2both vt.o vbetool/lrmi.o
> vbetool/x86-common.o vbetool/vbetool.o radeontool.o dmidecode.o splash.o
> bootsplash.o -L/usr/local/lib -lpci
> suspend.c: In function ???prepare_console???:
> suspend.c:816: warning: ignoring return value of ???write???, declared with
> attribute warn_unused_result
> suspend.c: In function ???get_kernel_console_loglevel???:
> suspend.c:886: warning: ignoring return value of ???fscanf???, declared with
> attribute warn_unused_result
> suspend.c: In function ???get_swappiness???:
> suspend.c:919: warning: ignoring return value of ???fscanf???, declared with
> attribute warn_unused_result
> suspend.c: In function ???main???:
> suspend.c:1192: warning: ignoring return value of ???chdir???, declared with
> attribute warn_unused_result
> cc -Wall -O2 -D_FORTIFY_SOURCE=2 -I/usr/local/include md5.o encrypt.o
> config.o vt.o resume.c splash.o bootsplash.o -static -o resume
> -L/usr/local/lib
> resume.c: In function ???main???:
> resume.c:737: warning: ignoring return value of ???fgets???, declared with
> attribute warn_unused_result
> cc -Wall -O2 -D_FORTIFY_SOURCE=2 -g s2ram.c vt.o vbetool/lrmi.o
> vbetool/x86-common.o vbetool/vbetool.o radeontool.o dmidecode.o -lpci -o s2ram
>
> In our build system, _FORTIFY_SOURCE=2 is mandatory and sooner or later those
> warnings will become errors. I can always work around them by casting to void,
> but as was pointed out to me by our toolchain team, some of them are probably
> real errors.
>
> If we _know_ that this write or fscanf cannot fail because we also _know_ what
> we are doing on the kernel side, then we should probably add a comment at the
> appropriate places and maybe just add a (void) cast. This is ugly to look at,
> but tells everybody else that we did not just forget to check for the values.
>
> Even leaving out the void cast, an comment like "this will throw a warning,
> but we know that this cannot fail" is better so i can defend my local patches
> against theevil overlords of the buildsystem :-)
Most of them looks like a real errors, that could bite us when kernel
changes. If (error_detected) { printf("explanation"); exit(17); } is
probably a good solution...
Pavel
--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures)
http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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