[PATCH 1/2] bsps/aarch64: Ensure FPU trap state is consistent

[Chris Johns]

On 28/10/2022 9:57 am, Kinsey Moore wrote:
> 
> On Thu, Oct 27, 2022 at 5:46 PM Chris Johns <chrisj at rtems.org
> <mailto:chrisj at rtems.org>> wrote:
> 
>     On 28/10/2022 9:25 am, Kinsey Moore wrote:
>     > On Thu, Oct 27, 2022 at 5:10 PM Chris Johns <chrisj at rtems.org
>     <mailto:chrisj at rtems.org>
>     > <mailto:chrisj at rtems.org <mailto:chrisj at rtems.org>>> wrote:
>     >
>     >     On 28/10/2022 9:05 am, Kinsey Moore wrote:
>     >     > RTEMS may be booted from a dirty environment. Ensure that FPU trap
>     >     > settings are consistent.
>     >     > ---
>     >     >  bsps/aarch64/shared/start/start.S | 10 ++++++++++
>     >     >  1 file changed, 10 insertions(+)
>     >     >
>     >     > diff --git a/bsps/aarch64/shared/start/start.S
>     >     b/bsps/aarch64/shared/start/start.S
>     >     > index 8bd4f86f4e..de0fdf4c80 100644
>     >     > --- a/bsps/aarch64/shared/start/start.S
>     >     > +++ b/bsps/aarch64/shared/start/start.S
>     >     > @@ -307,6 +307,16 @@ _el1_start:
>     >     > 
>     >     >    /* FPU does not need to be enabled on AArch64 */
>     >     > 
>     >     > +  /* Ensure FPU traps are disabled by default */
>     >     > +  mrs x0, FPCR
>     >     > +  bic x0, x0, #(1 << 8)
>     >     > +  bic x0, x0, #(1 << 9)
>     >     > +  bic x0, x0, #(1 << 10)
>     >     > +  bic x0, x0, #(1 << 11)
>     >     > +  bic x0, x0, #(1 << 12)
>     >     > +  bic x0, x0, #(1 << 15)
>     >
>     >     Does `bic x0, x0, #((1 << 8) | (1 << 9) | (1 << 10) | ...)` work?
>     >
>     > The assembler complains about the operand being out of range. I can split it
>     > into 8-12 in one and 15 by itself and everything seems to work.
> 
>     Huh? If you use a hex value does it work?
> 
> I think the equivalent value would be 0x9f00. That generates the same error as
> putting all the components on the same line. I think there's a 6-bit immediate
> involved that's the limitation.

Ah, must be an aarch64 thing. I have been using ARM and thumb mode asm this week :)

I will leave this with you to sort out which is best.

Chris