linux-kernel - Re: [PATCH 2/3] MIPS: Add full ISA emulator.

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Message-ID: <54809C88.8060601@caviumnetworks.com>
Date:	Thu, 4 Dec 2014 09:40:24 -0800
From:	David Daney <ddaney@...iumnetworks.com>
To:	"Maciej W. Rozycki" <macro@...ux-mips.org>
CC:	Leonid Yegoshin <Leonid.Yegoshin@...tec.com>,
	David Daney <ddaney.cavm@...il.com>,
	<linux-mips@...ux-mips.org>, Ralf Baechle <ralf@...ux-mips.org>,
	<Zubair.Kakakhel@...tec.com>, <geert+renesas@...der.be>,
	<peterz@...radead.org>, <paul.gortmaker@...driver.com>,
	<chenhc@...ote.com>, <cl@...ux.com>,
	Ingo Molnar <mingo@...nel.org>, <richard@....at>,
	<zajec5@...il.com>, <james.hogan@...tec.com>,
	<keescook@...omium.org>, <tj@...nel.org>, <alex@...x-smith.me.uk>,
	<pbonzini@...hat.com>, <blogic@...nwrt.org>,
	<paul.burton@...tec.com>, <qais.yousef@...tec.com>,
	<linux-kernel@...r.kernel.org>, <markos.chandras@...tec.com>,
	<dengcheng.zhu@...tec.com>, <manuel.lauss@...il.com>,
	<lars.persson@...s.com>, David Daney <david.daney@...ium.com>
Subject: Re: [PATCH 2/3] MIPS: Add full ISA emulator.

On 12/04/2014 03:49 AM, Maciej W. Rozycki wrote:
> On Wed, 3 Dec 2014, David Daney wrote:
>
>>> but it doesn't support customized instructions,
>>
>> GCC will never put these in the delay slot of a FPU branch, so it is not
>> needed.
>>
>>> multiple ASEs,
>>
>> Same as above.  But any instructions that are deemed necessary can easily be
>> added.
>
>   GAS will happily schedule any instruction into a branch delay slot as
> long as the instruction is not architecturally forbidden there (e.g.
> ERET), there is no data dependency with the branch that would affect the
> result produced and the instruction is not an explicit exception trap
> operation (BREAK, SYSCALL, TEQ, etc.).  For some reason, unknown to me all
> MT ASE instructions are disallowed too.  Anything else -- free to go in!
>
>   Of course instructions can be scheduled into branch delay slots manually
> too, in handcoded assembly, and that has to continue working.
>

It is not difficult to also emulate the trapping instructions.  In order 
to move forward, I will implement the trapping instructions in my 
emulator for the next patch.

Thanks,
David Daney

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