SSVE selftests failing unexpectedly

[Mark Brown]

On Wed, Jun 28, 2023 at 04:56:35PM +0100, Will Deacon wrote:

> I did a bit of digging and it looks like this is my libc using a vector
> DUP instruction in memset:

> #0  __memset_generic () at ../sysdeps/aarch64/memset.S:37

> Dump of assembler code for function __memset_generic:
> => 0x0000fffff7edfb00 <+0>:	dup	v0.16b, w1

> The easy option would be to require FA64 for these tests, but I guess it
> would be better to exit streaming mode.

We can't exit streaming mode here since the memset() is done *before* we
collect the signal context, exiting streaming mode would destroy the
context we're trying to collect.  We can, however, open code the
memset() and try to prevent the compiler optimising it I think.  None of
the toolchains/systems I'm using are generating FP instructions though
so can't 100% confirm.
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