From: "Richard W.M. Jones" <rjones@redhat.com>
To: Richard Henderson <richard.henderson@linaro.org>
Cc: peter.maydell@linaro.org, qemu-devel@nongnu.org
Subject: Re: [PATCH] tcg/arm: Reduce vector alignment requirement for NEON
Date: Mon, 13 Sep 2021 09:07:38 +0100 [thread overview]
Message-ID: <20210913080738.GC26415@redhat.com> (raw)
In-Reply-To: <20210912174925.200132-1-richard.henderson@linaro.org>
On Sun, Sep 12, 2021 at 10:49:25AM -0700, Richard Henderson wrote:
> With arm32, the ABI gives us 8-byte alignment for the stack.
> While it's possible to realign the stack to provide 16-byte alignment,
> it's far easier to simply not encode 16-byte alignment in the
> VLD1 and VST1 instructions that we emit.
>
> Remove the assertion in temp_allocate_frame, limit natural alignment
> to the provided stack alignment, and add a comment.
>
> Reported-by: Richard W.M. Jones <rjones@redhat.com>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>
> I haven't seen the assertion with the various arm kernels that I happen
> to have laying about. I have not taken the time to build the combo
> from the bug report:
>
> [ 0.000000] Linux version 5.14.0-60.fc36.armv7hl (mockbuild@buildvm-a32-12.iad2.fedoraproject.org) (gcc (GCC) 11.2.1 20210728 (Red Hat 11.2.1-1), GNU ld version 2.37-9.fc36) #1 SMP Mon Aug 30 14:08:34 UTC 2021
>
> I thought about parameterizing this patch further, but I can't think of
> another ISA that would be affected. (i686 clumsily changed its abi 20
> years ago to avoid faulting on vector spills; other isas so far have
> allowed vectors to be unaligned.)
You should be able to download the Fedora kernel that I am using from
https://koji.fedoraproject.org/koji/packageinfo?packageID=8
I added the patch to Fedora qemu and will do a test build once it
becomes available to build against - currently there's some problem
with new builds not propagating to the new buildroot.
Rich.
--
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
Fedora Windows cross-compiler. Compile Windows programs, test, and
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next prev parent reply other threads:[~2021-09-13 8:11 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-12 17:49 [PATCH] tcg/arm: Reduce vector alignment requirement for NEON Richard Henderson
2021-09-13 8:07 ` Richard W.M. Jones [this message]
2021-09-13 11:07 ` Richard W.M. Jones
2021-09-13 16:19 ` Richard Henderson
2021-09-13 16:28 ` Richard W.M. Jones
2021-09-13 17:01 ` Peter Maydell
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