Re: [kvm-unit-tests PATCH] s390x: snippets: c: Load initial cr0

[Claudio Imbrenda <imbrenda@linux.ibm.com>]

On Thu, 31 Mar 2022 12:55:15 +0000
Janosch Frank <frankja@linux.ibm.com> wrote:

> As soon as we use C we need to set the AFP bit in cr0 so we can use
> all fprs.
> 

seems like a good idea

> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>

Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>

> ---
>  s390x/snippets/c/cstart.S | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/s390x/snippets/c/cstart.S b/s390x/snippets/c/cstart.S
> index aaa5380c..a7d4cd42 100644
> --- a/s390x/snippets/c/cstart.S
> +++ b/s390x/snippets/c/cstart.S
> @@ -12,6 +12,8 @@
>  .section .init
>  	.globl start
>  start:
> +	larl	%r1, initial_cr0
> +	lctlg	%c0, %c0, 0(%r1)
>  	/* XOR all registers with themselves to clear them fully. */
>  	.irp i, 0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15
>  	xgr \i,\i
> @@ -34,3 +36,7 @@ exit:
>  	/* For now let's only use cpu 0 in snippets so this will always work. */
>  	xgr	%r0, %r0
>  	sigp    %r2, %r0, SIGP_STOP
> +
> +initial_cr0:
> +	/* enable AFP-register control, so FP regs (+BFP instr) can be used */
> +	.quad	0x0000000000040000