> Von: Gabriel Paubert [paub...@iram.es]
> Gesendet: Freitag, 30. Januar 2015 09:49
> An: Markus Stockhausen
> Cc: Scott Wood; linuxppc-dev@lists.ozlabs.org; Herbert Xu
> Betreff: Re: AW: SPE & Interrupt context (was how to make use of SPE
> instructions)
>
> > ...
> > - I must already save several non-volatile registers. Putting the 64 bit
> > values
> > into them would require me to save their contents with evstdd instead of
> > stw. Of course stack alignment to 8 bytes required. So only a few alignment
> > instructions needed additionally during initialization.
>
> On most PPC ABI the stack is guaranteed to be aligned to a 16 byte
> boundary. In some it may be only 8, but I can't remember any 4 byte
> only alignment.
>
> I checked my 32 bit kernel images with:
>
> objdump -d vmlinux |awk '/stwu.*r1,/{print $6,$7}'|sort -u
>
> and the stack seems to always be 16 byte aligned.
> For 64 bit, use stdu instead of stwu.
>
> I've also found a few stwux/stdux which are hopefully known
> to be harmless.
>
> Gabriel
A helpful annotation. But now I'm unsure about function usage. SPE seems to be
32bit only and I would use their evxxx instructions. Do you think the following
sequence will be the right way?
_GLOBAL(ppc_spe_sha256_transform)
stwu r1,-128(r1); /* create stack frame */
stw r24,8(r1); /* save normal registers */
stw r25,12(r1);
evstdw r14,16(r1); /* We must save non volatile */
evstdw r15,24(r1); /* registers. Take the chance */
evstdw r16,32(r12); /* and save the SPE part too */ \
...
lwz r24,8(r1); /* restore normal registers */ \
lwz r25,12(r1);
evldw r14,16(r12); /* restore non-v. + SPE registers */
evldw r15,24(r12);
evldw r16,32(r12);
addi r1,r1,128; /* cleanup stack frame */
Or must I use the kernel provided defines with PPC_STLU r1,-INT_FRAME_SIZE(r1)
plus SAVE_GPR/SAVE_EVR/REST_GPR/REST_EVR?
Markus
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