[systemd-devel] initializing _cleanup_* variables [was: [PATCH 01/12] fsckd daemon for inter-fsckd communication]

[Dimitri John Ledkov]

On 28 January 2015 at 15:47, Martin Pitt <martin.pitt at ubuntu.com> wrote:
> Hey Zbyszek,
>
> Zbigniew Jędrzejewski-Szmek [2015-01-28 15:37 +0100]:
>> > +static int handle_requests(int socket_fd) {
>> > +        Clients *first = NULL;
>> > +        usec_t last_activity = 0;
>> > +        int numdevices = 0, clear = 0;
>> > +        double percent = 100;
>> > +        _cleanup_fclose_ FILE *console = NULL;
>> NULL not necessary (and you don't have it in similar circumstances above ;))
>
> How is that not necessary? Just because the very next line initializes
> it, and there is no exit path before? Because in the general case it
> certainly is necessary, otherwise the _cleanup_ handler will try to
> free/close/clean up a random pointer value and crash.
>
> So IMHO it's a good defensive habit to always init _cleanup_* vars
> with NULL. In the future someone might put some code with "return"
> before the fopen() below, and then get a crash.
>
> Or is there some gcc magic that I missed? (I thought only global
> variables were guaranteed to be NULL, not stack vars).
>

Well, during systemd build there are some -Wmaybe-uninitialized
warnings.... in most cases it is code similar to the above case or
like checking r || check uninitialised variable. Shall we fix all of
them? In most cases it would be of limited gain, but at least it will
be clear to see when -Wmaybe-uninitalized warnings catches a real
thing.

(or is my compiler old and has false positives?)

>>
>> > +
>> > +        console = fopen("/dev/console", "we");
>
> Thanks for clarifying,
>
> Martin
> --
> Martin Pitt                        | http://www.piware.de
> Ubuntu Developer (www.ubuntu.com)  | Debian Developer  (www.debian.org)
>
> _______________________________________________
> systemd-devel mailing list
> systemd-devel at lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/systemd-devel
>



-- 
Regards,

Dimitri.

Intel Corporation (UK) Ltd. - Co. Reg. #1134945 - Pipers Way, Swindon SN3 1RJ.