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Date: Wed, 12 Apr 2017 14:47:20 -0700
From: Andre McCurdy <>
Cc: Jaydeep Patil <>
Subject: Re: microMIPS32R2 O32 port

On Wed, Apr 12, 2017 at 1:27 PM, Rich Felker <> wrote:
> On Wed, Apr 12, 2017 at 09:25:35PM +0200, Szabolcs Nagy wrote:
>> * Jaydeep Patil <> [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 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:

"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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