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

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Message-ID: <20250325071840.7910A12-hca@linux.ibm.com>
Date: Tue, 25 Mar 2025 08:18:40 +0100
From: Heiko Carstens <hca@...ux.ibm.com>
To: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
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 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>