Re: Warning -Wclobbered in PG_TRY(...)

On Thu, 29 May 2025 at 18:26, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

>
> Go there and use the "keyword search" for "longjmp" --- they
> don't seem to make it possible to bookmark individual pages.
>
> Indeed, you are fully correct. I didn't analyse the code well enough. The
equivalent code
for PG_TRY/PG_FINALLY/PG_END_TRY will appear like the following:

do {
jmp_buf *_save_exception_stack = PG_exception_stack;
jmp_buf _local_sigjmp_buf;
bool _do_rethrow = false;

if (setjmp(_local_sigjmp_buf) == 0)
{
PG_exception_stack = &_local_sigjmp_buf;
/* try here */
longjmp(_local_sigjmp_buf, 1); /* elog ERROR */
}
else
_do_rethrow = true;

{
PG_exception_stack = _save_exception_stack;
/* catch */
}

if (_do_rethrow)
pg_re_throw();

PG_exception_stack = _save_exception_stack;
/* finally */
} while (0);

There is no problem here. We only change _do_rethrow after longjmp.
Apparently, we're
dealing with a false positive warning here. Not sure, but it could be
something like [0]. The
correct solution in this case would be to disable clobbered warning.

[0] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=21161

--
Best regards,
Maxim Orlov.