linux-kernel - Re: [PATCH v4 06/14] x86: Add support for suppressing warning backtraces

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Message-ID: <20250401170829.GO5880@noisy.programming.kicks-ass.net>
Date: Tue, 1 Apr 2025 19:08:29 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Alessandro Carminati <acarmina@...hat.com>
Cc: 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>,
	Guenter Roeck <linux@...ck-us.net>,
	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>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH v4 06/14] x86: Add support for suppressing warning
 backtraces

On Thu, Mar 13, 2025 at 11:43:21AM +0000, Alessandro Carminati wrote:
> From: Guenter Roeck <linux@...ck-us.net>
> 
> Add name of functions triggering warning backtraces to the __bug_table
> object section to enable support for suppressing WARNING backtraces.
> 
> To limit image size impact, the pointer to the function name is only added
> to the __bug_table section if both CONFIG_KUNIT_SUPPRESS_BACKTRACE and
> CONFIG_DEBUG_BUGVERBOSE are enabled. Otherwise, the __func__ assembly
> parameter is replaced with a (dummy) NULL parameter to avoid an image size
> increase due to unused __func__ entries (this is necessary because __func__
> is not a define but a virtual variable).
> 
> Tested-by: Linux Kernel Functional Testing <lkft@...aro.org>
> Acked-by: Dan Carpenter <dan.carpenter@...aro.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> Signed-off-by: Guenter Roeck <linux@...ck-us.net>
> Signed-off-by: Alessandro Carminati <acarmina@...hat.com>
> ---
>  arch/x86/include/asm/bug.h | 21 ++++++++++++++++-----
>  1 file changed, 16 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/include/asm/bug.h b/arch/x86/include/asm/bug.h
> index e85ac0c7c039..f6e13fc675ab 100644
> --- a/arch/x86/include/asm/bug.h
> +++ b/arch/x86/include/asm/bug.h
> @@ -35,18 +35,28 @@
>  
>  #ifdef CONFIG_DEBUG_BUGVERBOSE
>  
> +#ifdef CONFIG_KUNIT_SUPPRESS_BACKTRACE
> +# define HAVE_BUG_FUNCTION
> +# define __BUG_FUNC_PTR	__BUG_REL(%c1)
> +# define __BUG_FUNC	__func__
> +#else
> +# define __BUG_FUNC_PTR
> +# define __BUG_FUNC	NULL
> +#endif /* CONFIG_KUNIT_SUPPRESS_BACKTRACE */
> +
>  #define _BUG_FLAGS(ins, flags, extra)					\
>  do {									\
>  	asm_inline volatile("1:\t" ins "\n"				\
>  		     ".pushsection __bug_table,\"aw\"\n"		\
>  		     "2:\t" __BUG_REL(1b) "\t# bug_entry::bug_addr\n"	\
>  		     "\t"  __BUG_REL(%c0) "\t# bug_entry::file\n"	\
> -		     "\t.word %c1"        "\t# bug_entry::line\n"	\
> -		     "\t.word %c2"        "\t# bug_entry::flags\n"	\
> -		     "\t.org 2b+%c3\n"					\
> +		     "\t"  __BUG_FUNC_PTR "\t# bug_entry::function\n"	\
> +		     "\t.word %c2"        "\t# bug_entry::line\n"	\
> +		     "\t.word %c3"        "\t# bug_entry::flags\n"	\
> +		     "\t.org 2b+%c4\n"					\
>  		     ".popsection\n"					\
>  		     extra						\
> -		     : : "i" (__FILE__), "i" (__LINE__),		\
> +		     : : "i" (__FILE__), "i" (__BUG_FUNC), "i" (__LINE__),\
>  			 "i" (flags),					\
>  			 "i" (sizeof(struct bug_entry)));		\
>  } while (0)
> @@ -92,7 +102,8 @@ do {								\
>  do {								\
>  	__auto_type __flags = BUGFLAG_WARNING|(flags);		\
>  	instrumentation_begin();				\
> -	_BUG_FLAGS(ASM_UD2, __flags, ANNOTATE_REACHABLE(1b));	\
> +	if (!KUNIT_IS_SUPPRESSED_WARNING(__func__))			\
> +		_BUG_FLAGS(ASM_UD2, __flags, ANNOTATE_REACHABLE(1b));	\
>  	instrumentation_end();					\
>  } while (0)

NAK, this grows the BUG site for now appreciable reason.