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

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Message-ID: <ddc7939f-fb98-43af-aed1-0bc0594ecc41@roeck-us.net>
Date: Tue, 1 Apr 2025 10:53:46 -0700
From: Guenter Roeck <linux@...ck-us.net>
To: Peter Zijlstra <peterz@...radead.org>,
 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>,
 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 4/1/25 10:08, Peter Zijlstra wrote:
> 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.

Only if CONFIG_KUNIT_SUPPRESS_BACKTRACE is enabled. Why does that warrant a NACK ?

Guenter