[FFmpeg-devel] [PATCH v6 4/4] lavf/utils: Normalize AVPacket.data to native endian

[Mats Peterson]

On 03/04/2016 03:49 AM, Michael Niedermayer wrote:
> On Fri, Mar 04, 2016 at 03:41:23AM +0100, Mats Peterson wrote:
>> On 03/04/2016 03:30 AM, Michael Niedermayer wrote:
>>>>
>>>> -    if (!*palette && ret == CONTAINS_PAL)
>>>> -        *palette = pkt->data + pkt->size - AVPALETTE_SIZE;
>>>> +    if (!*palette && ret == CONTAINS_PAL) {
>>>> +        uint8_t *pkt_pal = pkt->data + pkt->size - AVPALETTE_SIZE;
>>>> +        int i;
>>>> +        for (i = 0; i < AVPALETTE_COUNT; i++) {
>>>> +            uint8_t *p8 = pkt_pal + 4*i;
>>>
>>>> +            uint32_t *p32 = (uint32_t *)p8;
>>>
>>> undefined behavior, violating alignment requirements, and possibly
>>> aliassing violation
>>>
>>
>> Really? It works just fine, so please elaborate.
>
> you cant cast arbitrary pointers to uint32_t
>
> uint32_t can have platform specific alignment requirements that are
> stricter than what a random 4 uint8_t have.
> pkt->size does not need to be a multiple of 4 so even if pkt->data
> would be aligned enough p8 doesnt have to be
>
>

Whatever. Forget this version 6 of the patch set and use version 5, with 
version 2 of patch 4/4 in it (the one I posted in PM as well). And I 
would be grateful if you could apply it soon. It's extensively tested here.

Mats