Re: [edk2-devel] [PATCH v2 01/17] MdePkg/ProcessorBind AARCH64: Add asm macro to emit GNU BTI note

["Leif Lindholm" <quic_llindhol@quicinc.com>]

On Mon, Mar 27, 2023 at 14:46:49 +0200, Ard Biesheuvel wrote:
> On Mon, 27 Mar 2023 at 14:45, Leif Lindholm <quic_llindhol@quicinc.com> wrote:
> >
> > On Mon, Mar 27, 2023 at 13:00:56 +0200, Ard Biesheuvel wrote:
> > > Implement a CPP macro that can be called from .S files to emit the .note
> > > section carrying the annotation that informs the linker that the object
> > > file is compatible with BTI control flow integrity checks.
> > >
> > > Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> > > ---
> > >  MdePkg/Include/AArch64/ProcessorBind.h | 31 ++++++++++++++++++++
> > >  1 file changed, 31 insertions(+)
> > >
> > > diff --git a/MdePkg/Include/AArch64/ProcessorBind.h b/MdePkg/Include/AArch64/ProcessorBind.h
> > > index abe2571245c665f3..11814f1ffaef698a 100644
> > > --- a/MdePkg/Include/AArch64/ProcessorBind.h
> > > +++ b/MdePkg/Include/AArch64/ProcessorBind.h
> > > @@ -186,6 +186,37 @@ typedef INT64 INTN;
> > >  #define GCC_ASM_IMPORT(func__)  \
> > >           .extern  _CONCATENATE (__USER_LABEL_PREFIX__, func__)
> > >
> > > +#if defined(__ARM_FEATURE_BTI_DEFAULT) && __ARM_FEATURE_BTI_DEFAULT == 1
> > > +#define AARCH64_BTI(__type)                                        \
> > > +    .ifnc         __type,                                         ;\
> > > +    bti           __type                                          ;\
> > > +    .endif                                                        ;\
> >
> > This didn't jump out at me until looking at the consumer side.
> > This overlays two different sets of functionality depending on whether
> > an option is given to the macro or not, which feels semantically
> > suboptimal to me (i.e. it makes my head hurt).
> >
> > Could we split this into two macros - one that inserts the instruction
> > and one that inserts the note, and expand the latter in the former?
> >
> 
> Yeah, fair point.
> 
> So AARCH64_BTI_NOTE() to emit the note, and AARCH64_BTI() to emit the
> instruction as well as the note.

Yeah, exacty.

> 
> 
>