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

From: Heiko Carstens <hca@linux.ibm.com>
To: Alessandro Carminati <acarmina@redhat.com>
Cc: "Guenter Roeck" <linux@roeck-us.net>,
	linux-kselftest@vger.kernel.org,
	"David Airlie" <airlied@gmail.com>,
	"Arnd Bergmann" <arnd@arndb.de>,
	"Maíra Canal" <mcanal@igalia.com>,
	"Dan Carpenter" <dan.carpenter@linaro.org>,
	"Kees Cook" <keescook@chromium.org>,
	"Daniel Diaz" <daniel.diaz@linaro.org>,
	"David Gow" <davidgow@google.com>,
	"Arthur Grillo" <arthurgrillo@riseup.net>,
	"Brendan Higgins" <brendan.higgins@linux.dev>,
	"Naresh Kamboju" <naresh.kamboju@linaro.org>,
	"Maarten Lankhorst" <maarten.lankhorst@linux.intel.com>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Maxime Ripard" <mripard@kernel.org>,
	"Ville Syrjälä" <ville.syrjala@linux.intel.com>,
	"Daniel Vetter" <daniel@ffwll.ch>,
	"Thomas Zimmermann" <tzimmermann@suse.de>,
	"Alessandro Carminati" <alessandro.carminati@gmail.com>,
	"Jani Nikula" <jani.nikula@intel.com>,
	dri-devel@lists.freedesktop.org, kunit-dev@googlegroups.com,
	linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
	linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
	linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org,
	linux-sh@vger.kernel.org, loongarch@lists.linux.dev,
	x86@kernel.org,
	"Linux Kernel Functional Testing" <lkft@linaro.org>,
	"Vasily Gorbik" <gor@linux.ibm.com>,
	"Alexander Gordeev" <agordeev@linux.ibm.com>
Subject: Re: [PATCH v4 10/14] s390: Add support for suppressing warning backtraces
Date: Mon, 24 Mar 2025 11:47:02 +0100	[thread overview]
Message-ID: <20250324104702.12139E73-hca@linux.ibm.com> (raw)
In-Reply-To: <CAGegRW4GinPmsav5=VBfjXBKy4cUEs5FWv-ixXODk7ajZ69vYg@mail.gmail.com>

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.