[PATCH v9 02/10] um: use execveat to create userspace MMs

[David Gow]

On Thu, 17 Oct 2024 at 20:05, Benjamin Berg <benjamin at sipsolutions.net> wrote:
>
> Hi,
>
> On Thu, 2024-10-17 at 10:18 +0200, Johannes Berg wrote:
> > [SNIP]
> >
> > I wonder now if the SSE instructions generated are memset() and that
> > goes away with the patches that Nathan just sent to not have the memset
> > (which was due to -ftrivial-auto-var-init) in the first place?
>
> I am guessing it would not fix it. I can reproduce the problem if I add
>   __attribute__((aligned(16)))
> to the "stack" variable. That is sufficient for GCC to emit an
> offending movaps instruction for me. The -ftrivial-auto-var-init=
> option will not affect that initialization.
>

Yeah, that seems to be what's happening here: the SSE use is all in
the 'stack' and 'sa' variable initialisation. Nathan's patch doesn't
fix it for me, but then again, I can't reproduce it with clang, just
gcc 13.2.0.

> > But anyway all of these pretty much sound reasonable. We don't need much
> > to happen in the stub here, simpler is better.
>
> Yeah, and I guess c) really is sufficient by itself.

I've sent (c) out here:
https://lore.kernel.org/linux-um/20241017231007.1500497-2-davidgow@google.com/T/#u

Thanks,
-- David
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