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Re: New GCC 7 -Wformat-truncation suppressed by (and only by) -Og?


On 02/23/2017 02:51 PM, Stephan Bergmann wrote:
At least with a recent GCC 7 trunk build ("gcc (GCC) 7.0.1 20170221
(experimental)"), I noticed that -Wformat-truncation warnings happen to
not be emitted if and only if -Og is given:

$ cat test.c
#include <stdio.h>
int main() {
    char buf[3];
    snprintf(buf, sizeof buf, "%s", "foo");
    return 0;
}
$ gcc -Wformat-truncation -Og ~/test.c
$ gcc -Wformat-truncation -O ~/test.c
test.c: In function ‘main’:
test.c:4:34: warning: ‘snprintf’ output truncated before the last
format character [-Wformat-truncation=]
     snprintf(buf, sizeof buf, "%s", "foo");
                                  ^
test.c:4:5: note: ‘snprintf’ output 4 bytes into a destination of size 3
     snprintf(buf, sizeof buf, "%s", "foo");
     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Any other optimization level (-O1..3/s/fast) does emit the warning.  The

-O0..3, even

documentation makes it clear that the behavior of that warning may be
coupled to the optimization level, but this difference between -Og and
everything else still looks somewhat odd.  Could it be by mistake?


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