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

Peter Zijlstra
2025-04-01T17:10:41Z

On Thu, Mar 13, 2025 at 11:43:21AM +0000, Alessandro Carminati wrote:
> From: Guenter Roeck <linux@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@linaro.org>
> Acked-by: Dan Carpenter <dan.carpenter@linaro.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: Dave Hansen <dave.hansen@linux.intel.com>
> Signed-off-by: Guenter Roeck <linux@roeck-us.net>
> Signed-off-by: Alessandro Carminati <acarmina@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.