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Re: [PATCH] MIPS: Add emulation for fpureg-mem unaligned access

To: Lluis Batlle i Rossell <viric@viric.name>
Subject: Re: [PATCH] MIPS: Add emulation for fpureg-mem unaligned access
From: Ralf Baechle <ralf@linux-mips.org>
Date: Tue, 31 Jul 2012 15:40:01 +0200
Cc: linux-mips@linux-mips.org, loongson-dev@googlegroups.com
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On Sat, Jun 16, 2012 at 12:22:53AM +0200, Lluis Batlle i Rossell wrote:

> Reusing most of the code from lw,ld,sw,sd emulation,
> I add the emulation for lwc1,ldc1,swc1,sdc1.
> 
> This avoids the direct SIGBUS sent to userspace processes that have
> misaligned memory accesses.
> 
> I've tested the change in Loongson2F, with an own test program, and
> WebKit 1.4.0, as both were killed by sigbus without this patch.

A misaligned FPU access is a strong indication for broken, non-portable
software.  which means you're likely trying to fix the wrong issue.  It's
quite intentional that there is no unaligned handling for the FPU in the
kernel - and afaics there isn't for any other MIPS UNIX.

  Ralf

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