Re: [Qemu-devel] cirrus_vga: uninitialized variable warnings

[Blue Swirl]

On Thu, Jan 6, 2011 at 9:13 PM, Aurelien Jarno <address@hidden> wrote:
> On Thu, Jan 06, 2011 at 07:45:01PM +0000, Blue Swirl wrote:
>> There are a few variables which appear uninitialized to GCC 4.6.0:
>
> It's due to my commit 92d675d1c1f23f3617e24b63c825074a1d1da44b
>
>>   CC    i386-softmmu/cirrus_vga.o
>> /src/qemu/hw/cirrus_vga.c: In function 'cirrus_bitblt_start':
>> /src/qemu/hw/cirrus_vga.c:678: warning: 'depth' may be used
>> uninitialized in this function
>> /src/qemu/hw/cirrus_vga.c:678: note: 'depth' was declared here
>> /src/qemu/hw/cirrus_vga.c:677: warning: 'dx' may be used uninitialized
>> in this function
>> /src/qemu/hw/cirrus_vga.c:677: note: 'dx' was declared here
>> /src/qemu/hw/cirrus_vga.c:676: warning: 'sx' may be used uninitialized
>> in this function
>> /src/qemu/hw/cirrus_vga.c:676: note: 'sx' was declared here
>> /src/qemu/hw/cirrus_vga.c:676: warning: 'sy' may be used uninitialized
>> in this function
>> /src/qemu/hw/cirrus_vga.c:676: note: 'sy' was declared here
>> /src/qemu/hw/cirrus_vga.c:677: warning: 'dy' may be used uninitialized
>> in this function
>> /src/qemu/hw/cirrus_vga.c:677: note: 'dy' was declared here
>>
>> I don't think they are, since the variable use is conditional to
>> notify variable:
>>      if (notify)
>>       qemu_console_copy(s->vga.ds,
>>                         sx, sy, dx, dy,
>>                         s->cirrus_blt_width / depth,
>>                         s->cirrus_blt_height);
>
> Strangely neither GCC 4.4 nor GCC 4.5 trigger such a warning, though
> they are usually catching cases like that. Could it be a regression in
> GCC 4.6, or do you think it's just that it wasn't detected in previous
> versions?

It also happens with GCC 4.2.1 but not with 4.3.2.

>
>> Perhaps the code could be rearranged to avoid the warnings? Otherwise
>> we could add zero initializers.
>>
>
> Rearranging the code doesn't seems easy, so we should probably go to
> zero initializers, as in the patch below.
>
> From: Aurelien Jarno <address@hidden>
>
> cirrus: delete GCC 4.6 warnings
>
> Commit 92d675d1c1f23f3617e24b63c825074a1d1da44b triggered uninitialized
> variables warning with GCC 4.6. Fix them by adding zero initializers.
>
> Signed-off-by: Aurelien Jarno <address@hidden>

Acked-by: Blue Swirl <address@hidden>

> ---
>  hw/cirrus_vga.c |    6 +++---
>  1 files changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/hw/cirrus_vga.c b/hw/cirrus_vga.c
> index 833a2eb..75d1cc6 100644
> --- a/hw/cirrus_vga.c
> +++ b/hw/cirrus_vga.c
> @@ -673,9 +673,9 @@ static int 
> cirrus_bitblt_videotovideo_patterncopy(CirrusVGAState * s)
>
>  static void cirrus_do_copy(CirrusVGAState *s, int dst, int src, int w, int h)
>  {
> -    int sx, sy;
> -    int dx, dy;
> -    int depth;
> +    int sx = 0, sy = 0;
> +    int dx = 0, dy = 0;
> +    int depth = 0;
>     int notify = 0;
>
>     /* make sure to only copy if it's a plain copy ROP */
>
> --
> Aurelien Jarno                          GPG: 1024D/F1BCDB73
> address@hidden                 http://www.aurel32.net
>