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Date: Tue, 1 Jul 2014 14:25:01 -0400
From: Rich Felker <dalias@...c.org>
To: musl@...ts.openwall.com
Subject: Re: AArch64 merge back

On Tue, Jul 01, 2014 at 10:41:10AM -0700, Weiming Zhao wrote:
> Hi Isaac,
> 
> So if I just want to use some arch-independent functions, then I just need
> to build the main musl repo with aarch64 compiler. Is my understanding
> correct?

No. I didn't really understand what you were asking before, but it
might be more clear if you read the porting documents on the wiki.
Rather than trying to answer point by point I'll try to explain a few
things:

It's not possible to use musl on a new arch simply by compiling the
arch-independent C. This is partly because there are a number of
components of libc that fundamentally cannot be expressed in C, and
partly because the kernel (gratuitously) has a different set of
constants, struct definitions, etc. for each architecture.

Generally ports are not merged (in the "git merge" sense) because most
of the early work on them is a mess of incompleteness,
trial-and-error, etc. Also merging would be a lot of work since we
normally rebase all merges, whereas master has often diverged quite a
bit before a port is ready to merge. Instead, once the port is
working, we usually just add it as a single commit, followed by any
fixes for issues that weren't found before commit.

I'm not clear on the status of the aarch64 port right now. It was
stalled for a while because of changes needed in many of the
arch-independent files to accomodate the way the kernel does things on
newer archs (omitting lots of simple syscalls that can be emulated
using more complex ones). That work is done in mainline musl now
though, so it's no longer blocking ports. Further progress is up to
the people working on those ports (or anyone else who wants to build
on their work). I'm really hoping it will be finished during this
release cycle so we can have aarch64 support in 1.1.4.

If you or anyone else wants to play around with trying to get it to
work based on the in-progress ports, the best approach would be to
simply copy over the new files added in the aarch64 musl git tree into
a more recent musl (1.1.2 or later).

Rich

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