[PATCH v2 1/4] kselftest/arm64: Provide a helper binary and "library" for SVE RDVL

[Dave Martin]

On Thu, Jul 29, 2021 at 05:03:34PM +0100, Mark Brown wrote:
> On Thu, Jul 29, 2021 at 02:27:04PM +0100, Dave P Martin wrote:
> > On Thu, Jul 29, 2021 at 12:22:17PM +0100, Mark Brown wrote:
> 
> > > Yeah, it doesn't seem to be in the slightest bit idiomatic for the arm64
> > > asm code the kernel has.  I don't know if you think it's worth adding
> > > that to SYM_FUNC_START now we have it though?
> 
> > Actually, I think the core definition of SYM_FUNC_END() in
> > <linux/linkage.h> does this.
> 
> Ah, so it does.
> 
> > It would be good to pick up the common linkage macros; if we have to
> > sprinkle .type manually all over the tests people will likely make
> > mistakes, to that's probably not worth it.
> 
> > If picking up the macros isn't trivial to do, I guess it's not that
> > important at this stage.
> 
> They're not exported from the kernel at all at the minute so that'd be a
> whole new block of work that feels out of scope here, we already have a
> stack of asm code in selftests.

Agreed.  Feels like it might be a good idea at some point, but it's
orthogonal to this series, and for now nothing breaks.

> > > that those are outside the kernel either.  We will have to do something
> > > like that if anyone starts building userspace with BTI though (or I
> > > might just shove a BTI C in there unconditionally, I'm sure we'll cope
> > > with the overhead on older systems).
> 
> > I thought about that, but that .S file isn't annotated as supporting
> > BTI, so I guess there's no problem for now(?)
> 
> True, we'll generate linker warnings but it should otherwise sort itself
> out unless someone forced BTI mode.  The whole annotation thing really
> isn't fun to deal with for assembly code, hopefully there'll be some
> toolchain improvements in this area at some point.

Ack

Cheers
---Dave