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

[Peter Zijlstra]

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.