linux-kernel - Re: [PATCH v3 3/3] kselftest/arm64: Add lsfe to the hwcaps test

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Message-ID: <aMnTm59nrA5lBxN5@willie-the-truck>
Date: Tue, 16 Sep 2025 22:16:11 +0100
From: Will Deacon <will@...nel.org>
To: Mark Brown <broonie@...nel.org>
Cc: Catalin Marinas <catalin.marinas@....com>,
	Jonathan Corbet <corbet@....net>, Marc Zyngier <maz@...nel.org>,
	Oliver Upton <oliver.upton@...ux.dev>,
	Joey Gouly <joey.gouly@....com>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Shuah Khan <shuah@...nel.org>, linux-arm-kernel@...ts.infradead.org,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	kvmarm@...ts.linux.dev, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v3 3/3] kselftest/arm64: Add lsfe to the hwcaps test

On Mon, Aug 18, 2025 at 08:21:20PM +0100, Mark Brown wrote:
> This feature has no traps associated with it so the SIGILL is not reliable.
> 
> Signed-off-by: Mark Brown <broonie@...nel.org>
> ---
>  tools/testing/selftests/arm64/abi/hwcap.c | 21 +++++++++++++++++++++
>  1 file changed, 21 insertions(+)
> 
> diff --git a/tools/testing/selftests/arm64/abi/hwcap.c b/tools/testing/selftests/arm64/abi/hwcap.c
> index 002ec38a8bbb..941890f69df6 100644
> --- a/tools/testing/selftests/arm64/abi/hwcap.c
> +++ b/tools/testing/selftests/arm64/abi/hwcap.c
> @@ -17,6 +17,8 @@
>  #include <asm/sigcontext.h>
>  #include <asm/unistd.h>
>  
> +#include <linux/auxvec.h>
> +
>  #include "../../kselftest.h"
>  
>  #define TESTS_PER_HWCAP 3
> @@ -169,6 +171,18 @@ static void lse128_sigill(void)
>  		     : "cc", "memory");
>  }
>  
> +static void lsfe_sigill(void)
> +{
> +	float __attribute__ ((aligned (16))) mem = 0;
> +	register float *memp asm ("x0") = &mem;
> +
> +	/* LDFADD H0, H0, [X0] */
> +	asm volatile(".inst 0x7c200000"
> +		     : "+r" (memp)

Doesn't this corrupt H0 without the compiler knowing? It's probably
easier to use STFADD.

> +		     :
> +		     : "cc", "memory");

Why do you need the "cc" clobber?

Will