[PATCH v4 06/14] x86: Add support for suppressing warning backtraces

[Guenter Roeck]

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 at roeck-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 at linaro.org>
>> Acked-by: Dan Carpenter <dan.carpenter at linaro.org>
>> Cc: Thomas Gleixner <tglx at linutronix.de>
>> Cc: Ingo Molnar <mingo at redhat.com>
>> Cc: Borislav Petkov <bp at alien8.de>
>> Cc: Dave Hansen <dave.hansen at linux.intel.com>
>> Signed-off-by: Guenter Roeck <linux at roeck-us.net>
>> Signed-off-by: Alessandro Carminati <acarmina at redhat.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