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

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:

quoted

On Tue, Jul 27, 2021 at 07:06:47PM +0100, Mark Brown wrote:

quoted

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

quoted

quoted

+.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

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