Re: [PATCH] tcg/arm: Reduce vector alignment requirement for NEON

[Richard W.M. Jones]

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.

-- 
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