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

On Thu, Jul 29, 2021 at 10:52:24AM +0100, Dave Martin wrote:

On Wed, Jul 28, 2021 at 05:33:15PM +0100, Mark Brown wrote:

quoted

+	return 0;

For consistency with the changes in vec-syscfg, we could use
EXIT_SUCCESS here.

0 and EXIT_SUCCESS are defined as equivalent (though they need not be
equal!) and 0 is much more idiomatic.

Although it's hard to see what could go wrong I/O-wise that doesn't
involve vec-syscfg itself having gone wrong, it's probably good
practice to do the final error check:

	if (ferror(stdout) || fclose(stdout))
		return EXIT_FAILURE;

	return EXIT_SUCCESS;

(In reality, people rarely seem to bother with this, so I'm not going
to lose sleep if we don't do it...)

Yeah, I think this is one of those raising more questions than it
answers kind of things.

quoted

+.globl rdvl_sve

Should we stick a

	.type rdvl_sve, @function

here?  This may avoid surprises with future toolchain behaviours.
Probably doesn't matter, but I have bad memories of Thumb-2...

Lacking this annotation is widespread though, as well as being de facto
standard before awkward architectures came along.

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?

If the selftests have access to the ENTRY() macro we could use that, but
I'm guessing that isn't exported for userspace.

We don't use that any more anyway, it's SYM_FUNC_START() and friends not
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).