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

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:

quoted

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.

quoted

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.