-Wformat-overflow works strangely with struct members

[Xi Ruoyao]

On 2017-07-07 09:35 -0600, Martin Sebor wrote:
> On 07/07/2017 07:05 AM, Basin Ilya wrote:
> > 	#include <stdio.h>
> > 
> > 	extern struct {
> > 		char s[142];
> > 	} x;
> > 
> > 	extern char s[142];
> > 
> > 	int main(int argc, char *argv[]) {
> > 		char buf[12];
> > 		sprintf(buf, "%c%s", 'x', x.s); // why warning?
> > 		sprintf(buf, "%s", x.s); // why no warning then?
> > 		sprintf(buf, "%c%s", 'x', s); // why no warning then?
> > 		return 0;
> > 	}
> With GCC 8 I get a warning for the second call to sprintf for
> the same reason at both -Wformat-overflow levels.  I'm not sure
> what prevents it in your case.  Please open a new bug for it and
> either attach the translation unit for your test case (obtained
> by preprocessing it with with -E) or remove the #include and
> declare sprintf or use __builtin_sprintf.  (This should tell
> us if the sprintf declaration in <stdio.h> is causing it.)

No.  Using __builtin_sprintf still produces no warning with
GCC 7.  I think it's a GCC 7 bug.

-- 
Xi Ruoyao <ryxi@stu.xidian.edu.cn>
School of Aerospace Science and Technology, Xidian University