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Re: [PATCH for-6.2 12/43] target/sh4: Implement do_unaligned_access for

From: Richard Henderson
Subject: Re: [PATCH for-6.2 12/43] target/sh4: Implement do_unaligned_access for user-only
Date: Thu, 29 Jul 2021 14:01:15 -1000
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0

On 7/29/21 3:52 AM, Peter Maydell wrote:
sh4 kernel default for unaligned accesses seems to be "warn and fixup",
not SIGBUS, unless the user changes that by writing to /proc/cpu/alignment
or the process changes it via prctl().

We will still need this for load-locked/store-conditional (MOVLI/MOVCO).

It appears that the sh4 kernel fails to decode these properly, and will do something ugly, like interpreting MOVLI as a multiple-store instead of a load.

There are also other instructions that the kernel does not attempt to handle, such as MAC. I suppose we could begin with turning off TARGET_ALIGNED_ONLY for sh4-linux-user, then re-enabling MO_ALIGN for the atomics (at least).


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