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

[David Gow]

On Thu, 13 Mar 2025 at 19:44, Alessandro Carminati <acarmina@xxxxxxxxxx> wrote:
>
> From: Guenter Roeck <linux@xxxxxxxxxxxx>
>
> 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@xxxxxxxxxx>
> Acked-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Borislav Petkov <bp@xxxxxxxxx>
> Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx>
> Signed-off-by: Alessandro Carminati <acarmina@xxxxxxxxxx>
> ---

Reviewed-by: David Gow <davidgow@xxxxxxxxxx>

Cheers,
-- David


>  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)
>
> --
> 2.34.1
>

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