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

Guenter Roeck
2025-04-01T17:55:53Z

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@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.

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

Guenter