Subject: Re: [PATCH v2 12/14] sh: Add support for suppressing warning backtraces

From: Simon Horman <[email-masked]>
Date: Wed, 27 Mar 2024 19:39:20 +0000

On Wed, Mar 27, 2024 at 08:10:51AM -0700, Guenter Roeck wrote:
> On 3/27/24 07:44, Simon Horman wrote:
> > On Mon, Mar 25, 2024 at 10:52:46AM -0700, Guenter Roeck wrote:
> > > 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 <[email-masked]>
> > > Acked-by: Dan Carpenter <[email-masked]>
> > > Signed-off-by: Guenter Roeck <[email-masked]>
> > > ---
> > > - Rebased to v6.9-rc1
> > > - Added Tested-by:, Acked-by:, and Reviewed-by: tags
> > > - Introduced KUNIT_SUPPRESS_BACKTRACE configuration option
> > > 
> > >   arch/sh/include/asm/bug.h | 26 ++++++++++++++++++++++----
> > >   1 file changed, 22 insertions(+), 4 deletions(-)
> > > 
> > > diff --git a/arch/sh/include/asm/bug.h b/arch/sh/include/asm/bug.h
> > > index 05a485c4fabc..470ce6567d20 100644
> > > --- a/arch/sh/include/asm/bug.h
> > > +++ b/arch/sh/include/asm/bug.h
> > > @@ -24,21 +24,36 @@
> > >    * The offending file and line are encoded in the __bug_table section.
> > >    */
> > >   #ifdef CONFIG_DEBUG_BUGVERBOSE
> > > +
> > > +#ifdef CONFIG_KUNIT_SUPPRESS_BACKTRACE
> > > +# define HAVE_BUG_FUNCTION
> > > +# define __BUG_FUNC_PTR	"\t.long %O2\n"
> > > +#else
> > > +# define __BUG_FUNC_PTR
> > > +#endif /* CONFIG_KUNIT_SUPPRESS_BACKTRACE */
> > > +
> > 
> > Hi Guenter,
> > 
> > a minor nit from my side: this change results in a Kernel doc warning.
> > 
> >       .../bug.h:29: warning: expecting prototype for _EMIT_BUG_ENTRY(). Prototype was for HAVE_BUG_FUNCTION() instead
> > 
> > Perhaps either the new code should be placed above the Kernel doc,
> > or scripts/kernel-doc should be enhanced?
> > 
> 
> Thanks a lot for the feedback.
> 
> The definition block needs to be inside CONFIG_DEBUG_BUGVERBOSE,
> so it would be a bit odd to move it above the documentation
> just to make kerneldoc happy. I am not really sure that to do
> about it.

FWIIW, I agree that would be odd.
But perhaps the #ifdef could also move above the Kernel doc?
Maybe not a great idea, but the best one I've had so far.

> I'll wait for comments from others before making any changes.
> 
> Thanks,
> Guenter
> 
> > >   #define _EMIT_BUG_ENTRY				\
> > >   	"\t.pushsection __bug_table,\"aw\"\n"	\
> > >   	"2:\t.long 1b, %O1\n"			\
> > > -	"\t.short %O2, %O3\n"			\
> > > -	"\t.org 2b+%O4\n"			\
> > > +	__BUG_FUNC_PTR				\
> > > +	"\t.short %O3, %O4\n"			\
> > > +	"\t.org 2b+%O5\n"			\
> > >   	"\t.popsection\n"
> > >   #else
> > >   #define _EMIT_BUG_ENTRY				\
> > >   	"\t.pushsection __bug_table,\"aw\"\n"	\
> > >   	"2:\t.long 1b\n"			\
> > > -	"\t.short %O3\n"			\
> > > -	"\t.org 2b+%O4\n"			\
> > > +	"\t.short %O4\n"			\
> > > +	"\t.org 2b+%O5\n"			\
> > >   	"\t.popsection\n"
> > >   #endif
> > > +#ifdef HAVE_BUG_FUNCTION
> > > +# define __BUG_FUNC	__func__
> > > +#else
> > > +# define __BUG_FUNC	NULL
> > > +#endif
> > > +
> > >   #define BUG()						\
> > >   do {							\
> > >   	__asm__ __volatile__ (				\
> > 
> > ...
>