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Date: Fri, 12 Jun 2020 13:37:47 -0400
From: Rich Felker <>
Subject: Re: Advocating musl to in windows subsystem and OS X

On Fri, Jun 12, 2020 at 06:56:28PM +0200, Brian Peregrine wrote:
> Hey all,
> after thinking about my previous post (Advocating musl to the chromium
> OS developers ), it struck me that both Microsoft and Apple use some
> sort of libc too (Microsoft has the "subsystem for linux" on windows
> 10 now, and Apple's OS X is based on linux too -I think it was based
> on the "Darwin" linux distro.

No, OSX is in some sense a BSD fork, but with major architectural
changes, and has nothing to do with Linux. Their libc is a BSD one
(FreeBSD I think) with tons of gratuitous changes made that did little
but intentionally break things, basically for NIH purposes/justifying
the existence of the project. (This is much like Google's Fuchsia fork
of musl.)

musl does not run on OSX and while all of the pure-library code and
stdio code could in principle be used, actually making "musl for OSX"
would be a large project that doesn't make sense. What would make much
more sense is either reusing code or making corresponding improvements
based on things that are better in musl.

> Microsoft probably uses glibc (as the subsystem seems to be
> canonical-made and they use glibc in ubuntu), for os x, I'm not sure
> what is being used.
> See
> In either case, Rich, perhaps you can propose to both that they use
> musl,

In some sense WSL doesn't "use" any libc; it's a thin syscall
emulation layer (WSL1) or near-full-linux-vm (WSL2) that's supposed to
be able to run any Linux userspace. My understanding is that they ship
some glibc-based distro, and I don't see that being viable for them to
change because they're supporting whatever users have built on it, but
anyone's free to use whatever they prefer.

On a higher level, I don't really want anyone shipping musl in places
where the end user who receives it doesn't intend to use musl, for
much the same reason that I don't like it when distros ship systemd to
folks who don't intend to use systemd. It leads to gratuitous
complaints from people who are unhappy that it's different from what
they expect, and keep asking for changes to make it more glibc-like.
I'd much rather seek out a user base that *wants* what's different
about musl rather than "puts up with" what's different about musl.

> and point them to your comparison
> ( ) ?
> Also, perhaps that comparison can have Bionic added too and compared
> to that as well ?

The comparison is really out-of-date, and needs some serious
methodological overhaul. Some of the points are quantitative and need
to be pegged to particular versions to be relevant, and need a way of
testing all the libcs with the same hardware/kernel to be able to
update them at all. All of that is beyond the scope of anything I want
to do right now, but I'd be interested in helping someone else who
wants to continue it setup a procedure and revamped test cases.

The qualitative parts are fairly easy to keep up-to-date though, and
Bionic and others could probably be added there. I don't think it
makes sense to include non-Linux libc's, though, since they can't be
used interchangibly -- they're not options you have.

> Perhaps it's most appropriate to do this through posting an issue at
> their relevant repo's (for MS, it's
> , for apple
> ( ), I'm not sure which repo holds the libc.

Unfortunately WSL1 has been broken and can't safely run musl binaries
since forever, and it's apparently not getting fixed despite the fix
being a one-liner if you had the source:

I'm not sure if WSL1 is still an option, but in some sense it "should
be" because it's lighter and cleaner than WSL2 which was basically
just "let's give up and use a VM with a real Linux kernel". If WSL1
ceases to be a thing, using musl on WSL becomes more attractive. I
re-pinged the issue to find out what's up.


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