linux-kernel - Re: [PATCH v4 10/14] s390: Add support for suppressing warning backtraces

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Message-ID: <20250324104702.12139E73-hca@linux.ibm.com>
Date: Mon, 24 Mar 2025 11:47:02 +0100
From: Heiko Carstens <hca@...ux.ibm.com>
To: Alessandro Carminati <acarmina@...hat.com>
Cc: Guenter Roeck <linux@...ck-us.net>, linux-kselftest@...r.kernel.org,
        David Airlie <airlied@...il.com>, Arnd Bergmann <arnd@...db.de>,
        Maíra Canal <mcanal@...lia.com>,
        Dan Carpenter <dan.carpenter@...aro.org>,
        Kees Cook <keescook@...omium.org>,
        Daniel Diaz <daniel.diaz@...aro.org>, David Gow <davidgow@...gle.com>,
        Arthur Grillo <arthurgrillo@...eup.net>,
        Brendan Higgins <brendan.higgins@...ux.dev>,
        Naresh Kamboju <naresh.kamboju@...aro.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Maxime Ripard <mripard@...nel.org>,
        Ville Syrjälä <ville.syrjala@...ux.intel.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Alessandro Carminati <alessandro.carminati@...il.com>,
        Jani Nikula <jani.nikula@...el.com>, dri-devel@...ts.freedesktop.org,
        kunit-dev@...glegroups.com, linux-arch@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-parisc@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-riscv@...ts.infradead.org,
        linux-s390@...r.kernel.org, linux-sh@...r.kernel.org,
        loongarch@...ts.linux.dev, x86@...nel.org,
        Linux Kernel Functional Testing <lkft@...aro.org>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>
Subject: Re: [PATCH v4 10/14] s390: Add support for suppressing warning
 backtraces

On Fri, Mar 21, 2025 at 10:05:42PM +0100, Alessandro Carminati wrote:
> > > +#ifdef CONFIG_KUNIT_SUPPRESS_BACKTRACE
> > > +# define HAVE_BUG_FUNCTION
> > > +# define __BUG_FUNC_PTR      "       .long   %0-.\n"
> > > +# define __BUG_FUNC  __func__
> >
> > gcc 7.5.0 on s390 barfs; it doesn't like the use of "__func__" with "%0-."

...

> GCC makes significant efforts to handle this, and for several
> architectures, it manages to solve the problem.
> However, this is not universally the case.
> Additionally, -fPIC is not widely used in kernel code... I have only
> seen it used for VDSO, the x86 boot piggyback decompressor, PowerPC
> boot, and the s390x architecture.
> 
> That said, GCC has been mitigating this issue, allowing us to treat a
> non-compile-time constant as if it were one.
> A proof of this is that, at least since GCC 11, the s390x version of
> GCC is able to build this code.
> Before that... certainly in GCC 7.5 it couldn't.
> 
> A simple fix would be to restrict usage to GCC versions greater than
> 11 for s390.

But please add that dependency only for this new feature for the time
being. Right now I would not like to see that s390 is the only architecture
(besides parisc) which requires a much higher minimum gcc level than every
other architecture. Unless there are specific reasons.