On Sun, 2024-01-28 at 21:33 -0800, Yonghong Song wrote:
[...]
> I tried below example with the above prog/dynptr_fail.c case with gcc 11.4
> for native x86 target and didn't trigger the warning. Maybe this requires
> latest gcc? Or test C file is not sufficient enough to trigger the warning?
>
> [~/tmp1]$ cat t.c
> struct t {
> char a;
> short b;
> int c;
> };
> void init(struct t *);
> long foo() {
> struct t dummy;
> init(&dummy);
> return *(int *)&dummy;
> }
> [~/tmp1]$ gcc -Wall -Werror -O2 -g -Wno-compare-distinct-pointer-types -c t.c
> [~/tmp1]$ gcc --version
> gcc (GCC) 11.4.1 20230605 (Red Hat 11.4.1-2)
I managed to trigger this warning for gcc 13.2.1:
$ gcc -fstrict-aliasing -Wstrict-aliasing=1 -c test-punning.c -o /dev/null
test-punning.c: In function ‘foo’:
test-punning.c:10:19: warning: dereferencing type-punned pointer might break strict-aliasing rules [-Wstrict-aliasing]
10 | return *(int *)&dummy;
| ^~~~~~
Note the -Wstrict-aliasing=1 option, w/o =1 suffix it does not trigger.
Grepping words "strict-aliasing", "strictaliasing", "strict_aliasing"
through clang code-base does not show any diagnostic related tests or
detection logic. It appears to me clang does not warn about strict
aliasing violations at all and -Wstrict-aliasing=* are just stubs at
the moment.
