[Mesa-dev] [PATCH] mesa/st: Avoid a NULL-ptr dereference on possible missing callback

[eocallaghan at alterapraxis.com]

Determinism is always better regardless of how you get there. A
null pointer deference `on purpose` is a really poor idea in C.
I am somewhat surprised you are asking if its really better to
rely on undefined behavior vs. an assert.

I thought about using a if branch and just returning but I think
it is better to crash deterministically with a reason rather than
perhaps fail silently. Although I do see in other places a if branch
and a return was used in similar situations so I would be willing to
do the same if I must.

On 2016-03-28 16:08, Ilia Mirkin wrote:
> When would that happen? When a user force-enables
> ARB_query_buffer_object for a driver that's not ready for it? Is
> hitting a deterministic assert in that case any better than hitting a
> null deref?
> 
> On Sun, Mar 27, 2016 at 11:52 PM, Edward O'Callaghan
> <eocallaghan at alterapraxis.com> wrote:
>> Just because we miss a gallium driver callback don't dereference
>> invalid memory.
>> 
>> Signed-off-by: Edward O'Callaghan <eocallaghan at alterapraxis.com>
>> ---
>>  src/mesa/state_tracker/st_cb_queryobj.c | 1 +
>>  1 file changed, 1 insertion(+)
>> 
>> diff --git a/src/mesa/state_tracker/st_cb_queryobj.c 
>> b/src/mesa/state_tracker/st_cb_queryobj.c
>> index cdb9efc..e9abc38 100644
>> --- a/src/mesa/state_tracker/st_cb_queryobj.c
>> +++ b/src/mesa/state_tracker/st_cb_queryobj.c
>> @@ -402,6 +402,7 @@ st_StoreQueryResult(struct gl_context *ctx, struct 
>> gl_query_object *q,
>>        index = 0;
>>     }
>> 
>> +   assert(pipe->get_query_result_resource);
>>     pipe->get_query_result_resource(pipe, stq->pq, wait, result_type, 
>> index,
>>                                     stObj->buffer, offset);
>>  }
>> --
>> 2.5.5
>> 
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