https://bugzilla.novell.com/show_bug.cgi?id=213892 matz@novell.com changed: What |Removed |Added ---------------------------------------------------------------------------- AssignedTo|matz@novell.com |pbaudis@novell.com ------- Comment #1 from matz@novell.com 2006-10-20 08:32 MST ------- This is a result of the options -std=c99 and -D_FORTIFY_SOURCE=2. That latter makes printf actually be "__printf_chk", and the former switches off the implicit format checking warning for that (not for printf() though). This behaviour is correct from gcc side. As "__printf_chk" is no ISO function, gcc is not allowed to infer any special semantic about it in -std=c99 mode (unlike for printf). The "special semantic" here is the checking of the format string. Hence __printf_chk in -std=c99 mode gets no special treatment. glibc (/usr/include/bits/stdio2.h actually) defines printf as __printf_chk (when fortify level is > 1). And __printf_chk is simply declared like so: extern int __printf_chk (int __flag, __const char *__restrict __format, ...); Note especially the absence of any "printf" attributes. That's why we get no warning here. There are two ways out: 1) define printf to __builtin___printf_chk in bits/stdio2.h or 2) add the necessary attributes to the __printf_chk declaration. The first solution works, because the function "__builtin___printf_chk" is defined as builtin in gcc regardless of the ISO mode, and it will get format checking. GCC itself will then implement this builtin via a call to __printf_chk, so there's no change in runtime behaviour (i.e. gcc itself emits no interesting special code for __builtin___printf_chk, which it doesn't also emit for just __printf_chk). The second solution also would work because of the explicitely added printf attributes (which are implicitely defined for the builtins). I think the first solution would be a bit nicer, but ultimately that's up to the glibc maintainers. Just for reference as testcase: % cat pr.c #include int main(void) { __builtin___printf_chk (2-1, "v = %10.5f %5d - %f %f %d %d\n", 0.5, 1, 0.6, 0.7, 2); __printf_chk (2-1, "v = %10.5f %5d - %f %f %d %d\n", 0.5, 1, 0.6, 0.7, 2); printf ("v = %10.5f %5d - %f %f %d %d\n", 0.5, 1, 0.6, 0.7, 2); (printf) ("v = %10.5f %5d - %f %f %d %d\n", 0.5, 1, 0.6, 0.7, 2); return 0; } % gcc -c -std=c99 -Wall -D_FORTIFY_SOURCE=2 -O1 pr.c pr.c: In function ‘main’: pr.c:5: warning: too few arguments for format pr.c:8: warning: too few arguments for format % gcc -c -Wall -D_FORTIFY_SOURCE=2 -O1 pr.c pr.c: In function ‘main’: pr.c:5: warning: too few arguments for format pr.c:6: warning: too few arguments for format pr.c:7: warning: too few arguments for format pr.c:8: warning: too few arguments for format With -std=c99 at least also line 7 should have given a warning (the normal 'printf' call). In user code there normally won't be explicit calls to __printf_chk, so a warning there is not important. -- Configure bugmail: https://bugzilla.novell.com/userprefs.cgi?tab=email ------- You are receiving this mail because: ------- You are on the CC list for the bug, or are watching someone who is.