Re: [RFC v5 47/57] arm64: assembler: Add macro to annotate asm function having non standard stack-frame.

[Julien Thierry]

On 1/21/20 10:30 AM, Will Deacon wrote:
> On Thu, Jan 09, 2020 at 04:02:50PM +0000, Julien Thierry wrote:
> > From: Raphael Gault <raphael.gault@xxxxxxx>
> >
> > Some functions don't have standard stack-frames but are intended
> > this way. In order for objtool to ignore those particular cases
> > we add a macro that enables us to annotate the cases we chose
> > to mark as particular.
> >
> > Signed-off-by: Raphael Gault <raphael.gault@xxxxxxx>
> > Signed-off-by: Julien Thierry <jthierry@xxxxxxxxxx>
> > ---
> >   include/linux/frame.h | 19 ++++++++++++++++++-
> >   1 file changed, 18 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/linux/frame.h b/include/linux/frame.h
> > index 02d3ca2d9598..1e35e58ab259 100644
> > --- a/include/linux/frame.h
> > +++ b/include/linux/frame.h
> > @@ -11,14 +11,31 @@
> >    *
> >    * For more information, see tools/objtool/Documentation/stack-validation.txt.
> >    */
> > +#ifndef __ASSEMBLY__
> >   #define STACK_FRAME_NON_STANDARD(func) \
> >   	static void __used __section(.discard.func_stack_frame_non_standard) \
> >   		*__func_stack_frame_non_standard_##func = func
> > +#else
> > +	/*
> > +	 * This macro is the arm64 assembler equivalent of the
> > +	 * macro STACK_FRAME_NON_STANDARD define at
> > +	 * ~/include/linux/frame.h
> > +	 */
> > +	.macro	asm_stack_frame_non_standard	func
> > +	.pushsection ".discard.func_stack_frame_non_standard"
> > +	.quad	\func
> > +	.popsection
> > +	.endm
> >
> > +#endif /* __ASSEMBLY__ */
> >   #else /* !CONFIG_STACK_VALIDATION */
> >
> > +#ifndef __ASSEMBLY__
> >   #define STACK_FRAME_NON_STANDARD(func)
> > -
> > +#else
> > +	.macro	asm_stack_frame_non_standard	func
> > +	.endm
> > +#endif /* __ASSEMBLY__ */
>
> Hmm. Given that we're currently going through the exercise of converting
> a bunch of ENTRY/ENDPROC macros to use the new SYM_{CODE,FUNC}_{START,END}
> macros, I would much prefer for this to be a new flavour of those.
>
> In fact, can you just use SYM_CODE_* for this?

You mean to not introduce the STACK_FRAME_NON_STANDARD() macro and just 
mark the asm callable symbols that don't set up a stackframe as SYM_CODE_* ?

--
Julien Thierry