[systemd-devel] [PATCH 2/5] libsystemd:terminal :fix uninitialized warning

[David Herrmann]

Hi

On Thu, Oct 16, 2014 at 11:43 PM,  <philippedeswert at gmail.com> wrote:
> From: Philippe De Swert <philippedeswert at gmail.com>
>
> Remove the following warning during the compilation:
> src/libsystemd-terminal/grdev-drm.c: In function 'grdrm_card_hotplug':
> src/libsystemd-terminal/grdev-drm.c:1087:45: warning: 'fb' may be used uninitialized in this function [-Wmaybe-uninitialized]
> src/libsystemd-terminal/grdev-drm.c:1035:19: note: 'fb' was declared here
> ---
>  src/libsystemd-terminal/grdev-drm.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/src/libsystemd-terminal/grdev-drm.c b/src/libsystemd-terminal/grdev-drm.c
> index dba6db2..415755e 100644
> --- a/src/libsystemd-terminal/grdev-drm.c
> +++ b/src/libsystemd-terminal/grdev-drm.c
> @@ -1032,7 +1032,7 @@ error:
>
>  static void grdrm_crtc_expose(grdrm_crtc *crtc) {
>          grdrm_pipe *pipe;
> -        grdrm_fb *fb;
> +        grdrm_fb *fb  = NULL;

Ewww, this is not nice. It does fix the warning, indeed, but the
underlying problem is more generic. Lets look at this:

int some_function(void **out) {
...
        r = ioctl(...);
        if (r < 0)
                return -errno;
...
}

gcc has no guarantee that "errno" is <0 if r is <0. Therefore,
whenever it inlines those functions (-O2 etc.), it will spew a warning
that "out" might be uninitialized if r<0 but errno==0. With -O0 gcc
doesn't complain as it probably does not optimize across functions.
However, with -O2 I get those warnings for "static" functions all the
time.

Not sure what to do here. I dislike initializing the pointer to NULL
as it might hide other real warnings. I'd prefer something like:

r = -SANE_ERRNO;

with:

#define SANE_ERRNO (abs(errno) ? : EMAGIC)

...not sure what we do in other places, though. Lennart? Tom?

Thanks
David

>          size_t i;
>          int r;
>
> --
> 1.8.3.2
>
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