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

[Kinsey Moore]

On Thu, Oct 27, 2022 at 5:46 PM Chris Johns <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>> 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.

Kinsey
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