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

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Message-ID: <20250325115127-0eaf5fcb-202d-4aaa-bfd2-fede68f8e7b4@linutronix.de>
Date: Tue, 25 Mar 2025 11:54:59 +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 Tue, Mar 25, 2025 at 08:18:40AM +0100, Heiko Carstens wrote:
> On Tue, Mar 25, 2025 at 07:48:48AM +0100, Thomas Weißschuh wrote:
> > 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(+)
> 
> ...
> 
> > > >  #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.
> 
> Thanks for explaining!
> 
> Acked-by: Heiko Carstens <hca@...ux.ibm.com>

Thanks!

I'll wait for some more feedback and then resend the series with some better
explanations, and without the incorrect Fixes: tags.
If there is pushback for applying any of the patches now, I'll carry them
downstream and will resubmit them as part of the later series which integrates
more of the vDSO selftests with nolibc.