linux-kernel - Re: [PATCH v2 12/14] sh: Add support for suppressing warning backtraces

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Message-ID: <320aacc6-b7e5-4c3d-948e-d0743ab26c5d@roeck-us.net>
Date: Wed, 27 Mar 2024 08:10:51 -0700
From: Guenter Roeck <linux@...ck-us.net>
To: Simon Horman <horms@...nel.org>
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>, 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, netdev@...r.kernel.org,
 Linux Kernel Functional Testing <lkft@...aro.org>
Subject: Re: [PATCH v2 12/14] sh: Add support for suppressing warning
 backtraces

On 3/27/24 07:44, Simon Horman wrote:
> On Mon, Mar 25, 2024 at 10:52:46AM -0700, Guenter Roeck wrote:
>> 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>
>> Signed-off-by: Guenter Roeck <linux@...ck-us.net>
>> ---
>> - Rebased to v6.9-rc1
>> - Added Tested-by:, Acked-by:, and Reviewed-by: tags
>> - Introduced KUNIT_SUPPRESS_BACKTRACE configuration option
>>
>>   arch/sh/include/asm/bug.h | 26 ++++++++++++++++++++++----
>>   1 file changed, 22 insertions(+), 4 deletions(-)
>>
>> diff --git a/arch/sh/include/asm/bug.h b/arch/sh/include/asm/bug.h
>> index 05a485c4fabc..470ce6567d20 100644
>> --- a/arch/sh/include/asm/bug.h
>> +++ b/arch/sh/include/asm/bug.h
>> @@ -24,21 +24,36 @@
>>    * The offending file and line are encoded in the __bug_table section.
>>    */
>>   #ifdef CONFIG_DEBUG_BUGVERBOSE
>> +
>> +#ifdef CONFIG_KUNIT_SUPPRESS_BACKTRACE
>> +# define HAVE_BUG_FUNCTION
>> +# define __BUG_FUNC_PTR	"\t.long %O2\n"
>> +#else
>> +# define __BUG_FUNC_PTR
>> +#endif /* CONFIG_KUNIT_SUPPRESS_BACKTRACE */
>> +
> 
> Hi Guenter,
> 
> a minor nit from my side: this change results in a Kernel doc warning.
> 
>       .../bug.h:29: warning: expecting prototype for _EMIT_BUG_ENTRY(). Prototype was for HAVE_BUG_FUNCTION() instead
> 
> Perhaps either the new code should be placed above the Kernel doc,
> or scripts/kernel-doc should be enhanced?
> 

Thanks a lot for the feedback.

The definition block needs to be inside CONFIG_DEBUG_BUGVERBOSE,
so it would be a bit odd to move it above the documentation
just to make kerneldoc happy. I am not really sure that to do
about it.

I'll wait for comments from others before making any changes.

Thanks,
Guenter

>>   #define _EMIT_BUG_ENTRY				\
>>   	"\t.pushsection __bug_table,\"aw\"\n"	\
>>   	"2:\t.long 1b, %O1\n"			\
>> -	"\t.short %O2, %O3\n"			\
>> -	"\t.org 2b+%O4\n"			\
>> +	__BUG_FUNC_PTR				\
>> +	"\t.short %O3, %O4\n"			\
>> +	"\t.org 2b+%O5\n"			\
>>   	"\t.popsection\n"
>>   #else
>>   #define _EMIT_BUG_ENTRY				\
>>   	"\t.pushsection __bug_table,\"aw\"\n"	\
>>   	"2:\t.long 1b\n"			\
>> -	"\t.short %O3\n"			\
>> -	"\t.org 2b+%O4\n"			\
>> +	"\t.short %O4\n"			\
>> +	"\t.org 2b+%O5\n"			\
>>   	"\t.popsection\n"
>>   #endif
>>   
>> +#ifdef HAVE_BUG_FUNCTION
>> +# define __BUG_FUNC	__func__
>> +#else
>> +# define __BUG_FUNC	NULL
>> +#endif
>> +
>>   #define BUG()						\
>>   do {							\
>>   	__asm__ __volatile__ (				\
> 
> ...