linux-kernel - Re: [PATCH resend] MIPS: Allow FPU emulator to use non-stack area.

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Message-ID: <CALCETrXt4xNCW9+UbEzhST5Eo6s9ymNOc16C+EGi2Pr=GrEZuA@mail.gmail.com>
Date:	Mon, 6 Oct 2014 16:54:06 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	David Daney <ddaney@...iumnetworks.com>
Cc:	Rich Felker <dalias@...c.org>, David Daney <ddaney.cavm@...il.com>,
	libc-alpha <libc-alpha@...rceware.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linux MIPS Mailing List <linux-mips@...ux-mips.org>,
	David Daney <david.daney@...ium.com>
Subject: Re: [PATCH resend] MIPS: Allow FPU emulator to use non-stack area.

On Mon, Oct 6, 2014 at 4:48 PM, David Daney <ddaney@...iumnetworks.com> wrote:
> On 10/06/2014 04:38 PM, Andy Lutomirski wrote:
>>
>> On 10/06/2014 02:58 PM, Rich Felker wrote:
>>>
>>> On Mon, Oct 06, 2014 at 02:45:29PM -0700, David Daney wrote:
>
> [...]
>>>
>>> This is a huge ill-designed mess.
>>
>>
>> Amen.
>>
>> Can the kernel not just emulate the instructions directly?
>
>
> In theory it could, but since there can be implementation defined
> instructions, there is no way to achieve full instruction set coverage for
> all possible machines.

Can modern user code just avoid constructs that require this kind of
trampoline hack?  If so, can this be solved the same way that x86
added no-exec stacks?  (I.e. mark all the binaries as supporting
non-executable stacks and letting them crash if they screw it up.)

Knowing very little about MIPS, it sounds like this is the kernel
compensating for a dumb assembler.

--Andy
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