[Mesa-stable] [PATCH v2 1/2] gallivm: correct channel shift logic on big endian

[Roland Scheidegger]

Am 29.08.2017 um 18:51 schrieb Emil Velikov:
> On 23 August 2017 at 21:32, Ben Crocker <bcrocker at redhat.com> wrote:
>> From: Ray Strode <rstrode at redhat.com>
>>
>> lp_build_fetch_rgba_soa fetches a texel from a texture.
>> Part of that process involves first gathering the element
>> together from memory into a packed format, and then breaking
>> out the individual color channels into separate, parallel
>> arrays.
>>
>> The code fails to account for endianess when reading the packed
>> values.
>>
>> This commit attempts to correct the problem by reversing the order
>> the packed values are read on big endian systems.
>>
>> Bugzilla: https://urldefense.proofpoint.com/v2/url?u=https-3A__bugs.freedesktop.org_show-5Fbug.cgi-3Fid-3D100613&d=DwIBaQ&c=uilaK90D4TOVoH58JNXRgQ&r=_QIjpv-UJ77xEQY8fIYoQtr5qv8wKrPJc7v7_-CYAb0&m=-owfKrLkZG_-D07ad7TcBmuZ0jASKVGMIE-e-E9DLr0&s=zMHob1rOLWVOOgtwdGeaQ_qRwgTRdsKq5wrlSVRyK9o&e= 
>> Cc: "17.2" "17.1" <mesa-stable at lists.freedesktop.org>
>>
>> ---
>>  src/gallium/auxiliary/gallivm/lp_bld_format_soa.c | 8 +++++++-
>>  1 file changed, 7 insertions(+), 1 deletion(-)
>>
>> diff --git a/src/gallium/auxiliary/gallivm/lp_bld_format_soa.c b/src/gallium/auxiliary/gallivm/lp_bld_format_soa.c
>> index 98eb694..22c19b1 100644
>> --- a/src/gallium/auxiliary/gallivm/lp_bld_format_soa.c
>> +++ b/src/gallium/auxiliary/gallivm/lp_bld_format_soa.c
>> @@ -650,7 +650,13 @@ lp_build_fetch_rgba_soa(struct gallivm_state *gallivm,
>>           for (i = 0; i < format_desc->nr_channels; i++) {
>>              struct util_format_channel_description chan_desc = format_desc->channel[i];
>>              unsigned blockbits = type.width;
>> -            unsigned vec_nr = chan_desc.shift / type.width;
>> +            unsigned vec_nr;
>> +
>> +#ifdef PIPE_ARCH_BIG_ENDIAN
>> +            vec_nr = (format_desc->block.bits - (chan_desc.shift + chan_desc.size)) / type.width;
>> +#else
>> +            vec_nr = chan_desc.shift / type.width;
>> +#endif
>>              chan_desc.shift %= type.width;
>>
> Roland, I think you're one of the more knowledgeable people for things gallivm.
> Can you please review this patch?

Well I'm the one who regularly breaks the BE stuff :-).
That said, I already reviewed this:
https://lists.freedesktop.org/archives/mesa-dev/2017-August/167515.html

Roland