Message-ID: <543715D7.1020505@imgtec.com>
Date: Thu, 9 Oct 2014 16:10:15 -0700
From: Leonid Yegoshin <Leonid.Yegoshin@imgtec.com>
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To: James Hogan <james.hogan@imgtec.com>
CC: <linux-mips@linux-mips.org>, <Zubair.Kakakhel@imgtec.com>,
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Subject: Re: [PATCH v2 2/3] MIPS: Setup an instruction emulation in VDSO protected
 page instead of user stack
References: <20141009195030.31230.58695.stgit@linux-yegoshin> <20141009200017.31230.69698.stgit@linux-yegoshin> <20141009224304.GA4818@jhogan-linux.le.imgtec.org>
In-Reply-To: <20141009224304.GA4818@jhogan-linux.le.imgtec.org>
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>> Small stack of emulation blocks is supported because nested traps are possible
>> in MIPS32/64 R6 emulation mix with FPU emulation.
> Could you please clarify how this nesting of emulation blocks could
> happen now that signals are handled more cleanly.
>
> I.e. isn't the emuframe stuff only required for instructions in branch
> delay slots, and branches shouldn't be in branch delay slots anyway, so
> I don't get how they could nest.
>
It may be a case for mix of FPU and MIPS R6 emulations. I just keep both 
emulators separate as much as possible but I assume that without prove 
it may be stackable - some rollback is needed to join both and it may 
(probably) cause a double emulation setup - dsemul may be called twice 
for the same pair of instructions. I didn't see that yet, honestly and 
you may be right.

And as for signals - it is a different issue, some signal may happen 
before or after emulated instruction in emulation block and I see that. 
But I see it only before because of probability for it is a lot of 
higher. Unwinding is need because signal handler may not return but 
longjump to somewhere.
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