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Date: Mon, 26 Jun 2006 17:35:14 +0200
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Subject: Re: [Qemu-devel] Pending MIPS patches
References: <449EB5FA.6070405@gmail.com> <449EBC39.3050701@bellard.org>
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From: Dirk Behme <dirk.behme@googlemail.com>
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To: qemu-devel@nongnu.org

Fabrice Bellard wrote:
>> 2. [PATCH][MIPS] add "lwu" instruction
>> http://lists.gnu.org/archive/html/qemu-devel/2006-04/msg00326.html
> 
> 
> On which MIPS CPU is it defined ? Need to track instruction sets exactly 
> to be able to select a given MIPS CPU at compile time or dynamically.
> 
>> 3. [PATCH] Add special MIPS multiply instructions
>> http://lists.gnu.org/archive/html/qemu-devel/2006-04/msg00375.html
> 
> 
> Same remark.

These are NEC VR54xx specific extensions to the MIPS 
instruction set.

They are used if you use GCC's -march=vr5400 option. See

www.necelam.com/docs/files/1375_V2.pdf

as well.

>> 9. [PATCH] Update MIPS status register with EXL and ERL bits at exception
>> http://lists.gnu.org/archive/html/qemu-devel/2006-06/msg00329.html
> 
> 
> OK but the following lines are suspicious:

Yes, I see. I mixed two fixes, let me explain below:

> -        env->hflags = MIPS_HFLAG_ERL;
> +        env->hflags |= MIPS_HFLAG_ERL;

This is a typo fix for a missing "or" (it should be "|=" 
instead of only "="). hflags is used as a shadow of the 
status register and there not the whole value should be set, 
only the corresponding flag. See for example correct usage 
of  MIPS_HFLAG_EXL or MIPS_HFLAG_ERL in helper.c or op.c of 
target-mips. There, they are correctly used everywhere with 
"|=" or "&= ~", except at this place.

> +       env->CP0_Status &= (1 << CP0St_ERL);

This is part of the "Update status register EXL and ERL 
flags directly, entering or leaving exception, not only hflags".

So this two added lines fix the missing "or" and set the 
flag in the status register as well, not only in hflags.

If you like you can apply the single "|=" line as a typo 
fix, and the rest as an additional fix to update status 
register as well with ERL and EXL.

Regards

Dirk

Btw: Many thanks for commenting all patches!