linux-kernel - Re: [PATCH 3/3] selftests: vDSO: chacha: Provide default definition of HWCAP_S390

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Message-ID: <20250325074319-b478adcc-3e04-447f-81b5-c92741c91bfd@linutronix.de>
Date: Tue, 25 Mar 2025 07:48:48 +0100
From: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
To: Heiko Carstens <hca@...ux.ibm.com>
Cc: Shuah Khan <shuah@...nel.org>, "Jason A. Donenfeld" <Jason@...c4.com>, 
	Andy Lutomirski <luto@...nel.org>, Thomas Gleixner <tglx@...utronix.de>, 
	Vincenzo Frascino <vincenzo.frascino@....com>, linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH 3/3] selftests: vDSO: chacha: Provide default definition
 of HWCAP_S390_VXRS

On Mon, Mar 24, 2025 at 04:55:13PM +0100, Heiko Carstens wrote:
> On Mon, Mar 24, 2025 at 03:03:17PM +0100, Thomas Weißschuh wrote:
> > s390 does not provide a hwcap.h UAPI header.
> > 
> > Add an inline definition for the constant HWCAP_S390_VXRS until a proper
> > UAPI header is introduced.
> > 
> > Fixes: 210860e7f733 ("selftests: vDSO: check cpu caps before running chacha test")
> > Signed-off-by: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
> > ---
> >  tools/testing/selftests/vDSO/vdso_test_chacha.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/tools/testing/selftests/vDSO/vdso_test_chacha.c b/tools/testing/selftests/vDSO/vdso_test_chacha.c
> > index fd5c5108b42f04ec459d39b74f33edc2ceafbba1..0ce5189718ce35b0a4d69b71559db8379b598b93 100644
> > --- a/tools/testing/selftests/vDSO/vdso_test_chacha.c
> > +++ b/tools/testing/selftests/vDSO/vdso_test_chacha.c
> > @@ -19,6 +19,9 @@ static bool cpu_has_capabilities(void)
> >  	return getauxval(AT_HWCAP) & HWCAP_ASIMD;
> >  }
> >  #elif defined(__s390x__)
> > +#ifndef HWCAP_S390_VXRS
> > +#define HWCAP_S390_VXRS	(1 << 11)
> > +#endif
> >  static bool cpu_has_capabilities(void)
> >  {
> >  	return getauxval(AT_HWCAP) & HWCAP_S390_VXRS;
> 
> How did this cause a problem?
> 
> Did you use something different than glibc(-devel) on your test
> system? Just wondering since glibc-devel provides the define since
> ages and is also required for getauxval().

I used nolibc (from the kernel tree at tools/include/nolibc/) to make cross
platform usage of the tests easier. See also [0].
I got confused by the existence of hwcap.h in the kernel UAPI headers for
various architectures and didn't check the libc headers.
So this isn't really a bug right now, and the hwcap changes will only really be
necessary once my other work goes upstream.

[0] https://lore.kernel.org/lkml/20250217-kunit-kselftests-v1-0-42b4524c3b0a@linutronix.de/