Re: [PATCH v10 2/5] powerpc/vdso: Prepare for switching VDSO to generic C implementation.

[Christophe Leroy]

Hi Again,

Le 05/08/2020 à 16:03, Segher Boessenkool a écrit :
> Hi!
>
> On Wed, Aug 05, 2020 at 07:09:23AM +0000, Christophe Leroy wrote:
> > +/*
> > + * The macros sets two stack frames, one for the caller and one for the callee
> > + * because there are no requirement for the caller to set a stack frame when
> > + * calling VDSO so it may have omitted to set one, especially on PPC64
> > + */
>
> If the caller follows the ABI, there always is a stack frame.  So what
> is going on?

Looks like it is not the case. See discussion at 
https://patchwork.ozlabs.org/project/linuxppc-dev/patch/2a67c333893454868bbfda773ba4b01c20272a5d.1588079622.git.christophe.leroy@xxxxxx/

Seems like GCC uses the redzone and doesn't set a stack frame. I guess 
it doesn't know that the inline assembly contains a function call so it 
doesn't set the frame.


Christophe