Subject: Re: [PATCH 3/4] http.c: avoid danging pointer to local variable `finished`

From: Junio C Hamano <[email-masked]>
Date: Tue, 24 May 2022 15:38:50 -0700

Johannes Schindelin <[email-masked]> writes:

> Hi Junio,
>
> On Tue, 24 May 2022, Junio C Hamano wrote:
>
>> The "clear slot->finished", by the way, is what I think is the right
>> thing to do, especially that the objective is to squelch the false
>> positive warning from a new compiler.  If there is a way to annotate
>> the line for the compiler to tell it not to warn about it, that would
>> have been even better.
>
> We could do something like this:

Yuck.

> -- snip --
> diff --git a/http.c b/http.c
> index b08795715f8a..2ac8d51d3668 100644
> --- a/http.c
> +++ b/http.c
> @@ -1365,7 +1365,14 @@ void run_active_slot(struct active_request_slot *slot)
>  	struct timeval select_timeout;
>  	int finished = 0;
>
> +#if __GNUC__ >= 12
> +#pragma GCC diagnostic push
> +#pragma GCC diagnostic ignored "-Wdangling-pointer"
> +#endif
>  	slot->finished = &finished;
> +#if __GNUC__ >= 12
> +#pragma GCC diagnostic pop
> +#endif
>  	while (!finished) {
>  		step_active_slots();
> -- snap --
>
> That's quite ugly, though. And what's worse, it is pretty unreadable, too.

Yes, very ugly.  Would an unconditional

	slot->finished = NULL;

at the end squelch the warning?

Or there is a way to say "we make all warnings into errors with
-Werror, but we do not want to turn this dangling-pointer warning to
an error, because it has false positives"?

Or we could add "-Wno-dangling-pointer" globally, perhaps.