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Date: Thu, 13 Apr 2017 04:29:10 +0000
From: Jaydeep Patil <Jaydeep.Patil@...tec.com>
To: Andre McCurdy <armccurdy@...il.com>, "musl@...ts.openwall.com"
	<musl@...ts.openwall.com>
Subject: RE: microMIPS32R2 O32 port

Hi,

With this branch (micromips32r2_v2) we are supporting microMIPS cores that co-exist with MIPS. The MUSL library must be built with -minterlink-compressed option as there are couple of hand-written MIPS only functions. For microMIPS only cores we will create a different subarch.

Thanks,
Jaydeep

>-----Original Message-----
>From: Andre McCurdy [mailto:armccurdy@...il.com]
>Sent: 13 April 2017 AM 03:17
>To: musl@...ts.openwall.com
>Cc: Jaydeep Patil
>Subject: Re: [musl] [MUSL] microMIPS32R2 O32 port
>
>On Wed, Apr 12, 2017 at 1:27 PM, Rich Felker <dalias@...c.org> wrote:
>> On Wed, Apr 12, 2017 at 09:25:35PM +0200, Szabolcs Nagy wrote:
>>> * Jaydeep Patil <Jaydeep.Patil@...tec.com> [2017-04-12 11:54:10 +0000]:
>>> > Hi Rich,
>>> >
>>> > We can reuse existing MIPS code for microMIPS. There are places where
>we read from $ra must be compiled for MIPS.
>>> > Please refer to https://github.com/JaydeepIMG/musl-
>1/tree/micromips32r2_v2 for modifications.
>>> >
>>>
>>> is micromips a different encoding for mips instructions that works on
>>> some cpus but not others?
>>
>> Yes, it's something like thumb or thumb2 on arm, or the riscv
>> compressed isa. What I'm not clear on is whether there are
>> micromips-only cpu models that can't execute normal mips.
>
>According to:
>
>  https://imagination-technologies-cloudfront-
>assets.s3.amazonaws.com/documentation/MIPS_Architecture_microMIPS32
>_InstructionSet_AFP_P_MD00582_06.04.pdf
>
>"microMIPS is also an alternative to the MIPSĀ® instruction encoding and can
>be implemented in parallel or stand-alone."
>
>"If only one ISA mode exists (either MIPS or microMIPS) then this mode
>switch mechanism does not exist"
>
>> If so we probably need the ability to build musl as micromips, but as
>> long as cpus which support both support interworking (calls between
>> the two type of code in the same process) reasonably, I don't think
>> there's any reason to consider it a different subarch.
>>
>> If not (that is, if all cpus that support micromips also support the
>> normal mips isa) then I fail to see why there's any need to compile
>> musl's asm files as micromips. They're not size or performance
>> bottlenecks.
>>
>> Rich

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