[Mesa-dev] [PATCH] glx/dri2: fix use of uninitialized variable "api"

[Kenneth Graunke]

On 01/10/2012 09:32 PM, Vadim Girlin wrote:
> Signed-off-by: Vadim Girlin<vadimgirlin at gmail.com>
> ---
>
> Fixes unigine heaven startup problem for me.
>
>   src/glx/dri2_glx.c |    2 +-
>   1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/src/glx/dri2_glx.c b/src/glx/dri2_glx.c
> index 10b6f52..b4efa40 100644
> --- a/src/glx/dri2_glx.c
> +++ b/src/glx/dri2_glx.c
> @@ -240,7 +240,7 @@ dri2_create_context_attribs(struct glx_screen *base,
>      uint32_t minor_ver = 1;
>      uint32_t major_ver = 2;
>      uint32_t flags = 0;
> -   unsigned api;
> +   unsigned api = __DRI_API_OPENGL;
>      uint32_t ctx_attribs[2 * 4];
>      unsigned num_ctx_attribs = 0;

Ah, I see the problem now:

We pass &api to dri2_convert_glx_attribs, which is supposed to fill it 
in unless it returns false (failure).  However, in the case where 
num_attribs == 0, it does this:

    if (num_attribs == 0)
       return true;

...without setting *api.  I think it would be better to fix the bug in 
dri2_convert_glx_attribs() by changing that to

    if (num_attribs == 0) {
       *api = __DRI_API_OPENGL;
       return true;
    }

rather than working around the broken function here in the caller. 
Notably, drisw_create_context_attribs suffers from the exact same bug; 
fixing it in dri2_convert_glx_attribs would fix both.

Unfortunately, Heaven still gives me bizarre X errors, even with this 
patch.  I'll have to investigate further.