[PATCH v1 1/3] kselftest/arm64: Provide a helper binary and "library" for SVE RDVL

[Dave Martin]

On Wed, Jul 28, 2021 at 11:20:35AM +0100, Mark Brown wrote:
> On Wed, Jul 28, 2021 at 10:41:30AM +0100, Dave Martin wrote:
> > On Tue, Jul 27, 2021 at 07:06:47PM +0100, Mark Brown wrote:
> > > SVE provides an instruction RDVL which reports the currently configured
> > > vector length. In order to validate that our vector length configuration
> > > interfaces are working correctly without having to build the C code for
> 
> > > +.globl rdvl_sve
> > > +rdvl_sve:
> > > +	rdvl	x0, #1
> > > +	ret
> > 
> > This works, but can we use an ACLE intrinsic for this?  I'm pretty GCC
> > and LLVM have been up to date with that stuff for some time, though
> > you'd have to check with the compiler folks.
> 
> If we put SVE into C source files we need to build the C code with SVE
> support enabled, I felt it was safer to avoid any possibility that we
> might get some interference with the tests due to interactions with SVE
> code generated by the compiler.  It should be fine, but it's even easier
> to not have to think about it at all.

Good point, stick with the out-of-line asm in that case.

(Also saves having to find out about the intrinsics!)

Cheers
---Dave