[Mesa-dev] [PATCH] radeonsi: correct si_vgt_param_key on big endian machines

[Gert Wollny]

Am Dienstag, den 20.03.2018, 15:33 +0100 schrieb Nicolai Hähnle:
> Nice, did you actually get it to work entirely on a big endian
> machine?
> 
> Bit fields aren't super portable, [...]
Indeed, the order of the bits in a bit field is compiler implementation
dependent. To make sure that changing the compiler doesn't change the
behaviour of the code I'd suggest that instead of using a bit field the
index should be created by explicitly shifting the bits into the right
positions.

Best,
Gert 

> However, I 
> think we should use the PIPE_ARCH_LITTLE_ENDIAN define from
> u_endian.h
> 
> Cheers,
> Nicolai
> 
> On 20.03.2018 15:21, Bas Vermeulen wrote:
> > Using mesa OpenCL failed on a big endian PowerPC machine because
> > si_vgt_param_key is using bitfields and a 32 bit int for an
> > index into an array.
> > 
> > Fix si_vgt_param_key to work correctly on both little endian
> > and big endian machines.
> > 
> > Signed-off-by: Bas Vermeulen <bas at daedalean.ai>
> > ---
> >   src/gallium/drivers/radeonsi/si_pipe.h | 13 +++++++++++++
> >   1 file changed, 13 insertions(+)
> > 
> > diff --git a/src/gallium/drivers/radeonsi/si_pipe.h
> > b/src/gallium/drivers/radeonsi/si_pipe.h
> > index 2053dcb9fc..32dbdf6e2c 100644
> > --- a/src/gallium/drivers/radeonsi/si_pipe.h
> > +++ b/src/gallium/drivers/radeonsi/si_pipe.h
> > @@ -385,6 +385,7 @@ struct si_shader_ctx_state {
> >    */
> >   union si_vgt_param_key {
> >   	struct {
> > +#if (__BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__)
> >   		unsigned prim:4;
> >   		unsigned uses_instancing:1;
> >   		unsigned
> > multi_instances_smaller_than_primgroup:1;
> > @@ -395,6 +396,18 @@ union si_vgt_param_key {
> >   		unsigned tess_uses_prim_id:1;
> >   		unsigned uses_gs:1;
> >   		unsigned _pad:32 - SI_NUM_VGT_PARAM_KEY_BITS;
> > +#else /* __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__ */
> > +		unsigned _pad:32 - SI_NUM_VGT_PARAM_KEY_BITS;
> > +		unsigned uses_gs:1;
> > +		unsigned tess_uses_prim_id:1;
> > +		unsigned uses_tess:1;
> > +		unsigned line_stipple_enabled:1;
> > +		unsigned count_from_stream_output:1;
> > +		unsigned primitive_restart:1;
> > +		unsigned multi_instances_smaller_than_primgroup:1;
> > +		unsigned uses_instancing:1;
> > +		unsigned prim:4;
> > +#endif
> >   	} u;
> >   	uint32_t index;
> >   };
> > 
> 
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