Re: [PATCH] http.c: clear the 'finished' member once we are done with it

From: Junio C Hamano <gitster@pobox.com>
Date: May 7, 2022, 18:42 UTC
Message-ID: <xmqq4k21gp6g.fsf@gitster.g>
In-Reply-To: <20220507054017.fnvb6xisr6s7m2l5@carlos-mbp.lan>

Carlo Marcelo Arenas Belón <carenas@gmail.com> writes:

Show 16 quoted lines

> On Fri, May 06, 2022 at 02:17:01PM -0700, Junio C Hamano wrote:
>> diff --git a/http.c b/http.c
>> index 229da4d148..85437b1980 100644
>> --- a/http.c
>> +++ b/http.c
>> @@ -1367,6 +1367,9 @@ void run_active_slot(struct active_request_slot *slot)
>>  			select(max_fd+1, &readfds, &writefds, &excfds, &select_timeout);
>>  		}
>>  	}
>> +
>> +	if (slot->finished == &finished)
>> +		slot->finished = NULL;
>
> I am not completely sure yet (since I looked at it long ago and got
> sidetracked) but I think this might be optimized out (at least by gcc12)
> since it is technically UB, which is why it never "fixed" the warning.

UB meaning "undefined behaviour"? Which part is? Taking the address of an on-stack variable "finished"? Comparing it with a pointer that may or may not have been assigned/overwritten elsewhere in a structure? Not clearing the member in the struct unconditionally?

Puzzled.