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Re: [PATCH resend] MIPS: Allow FPU emulator to use non-stack area.
- From: Andy Lutomirski <luto at amacapital dot net>
- To: David Daney <ddaney at caviumnetworks dot com>
- Cc: Rich Felker <dalias at libc dot org>, David Daney <ddaney dot cavm at gmail dot com>, libc-alpha <libc-alpha at sourceware dot org>, "linux-kernel at vger dot kernel dot org" <linux-kernel at vger dot kernel dot org>, Linux MIPS Mailing List <linux-mips at linux-mips dot org>, David Daney <david dot daney at cavium dot com>
- Date: Mon, 6 Oct 2014 16:54:06 -0700
- Subject: Re: [PATCH resend] MIPS: Allow FPU emulator to use non-stack area.
- Authentication-results: sourceware.org; auth=none
- References: <1412627010-4311-1-git-send-email-ddaney dot cavm at gmail dot com> <20141006205459 dot GZ23797 at brightrain dot aerifal dot cx> <5433071B dot 4050606 at caviumnetworks dot com> <20141006213101 dot GA23797 at brightrain dot aerifal dot cx> <54330D79 dot 80102 at caviumnetworks dot com> <20141006215813 dot GB23797 at brightrain dot aerifal dot cx> <543327E7 dot 4020608 at amacapital dot net> <54332A64 dot 5020605 at caviumnetworks dot com>
On Mon, Oct 6, 2014 at 4:48 PM, David Daney <ddaney@caviumnetworks.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