Re: musl risc-v port & gsoc - resources & ideas

[Rich Felker <dalias@libc.org>]

On Thu, Mar 03, 2016 at 10:58:12PM -0500, Rich Felker wrote:
> lowrisc.org has been accepted into Google Summer of Code 2016, and has
> porting musl to risc-v as one of the suggested projects:
> 
> http://www.lowrisc.org/docs/gsoc-2016-ideas/
> 
> I'm very hopeful that we'll make the port happen this year. In this
> email I'd like to go over some resources that may be helpful to
> students interested in applying, and some ideas for other tasks that
> could be included in proposals.
> 
> The musl wiki contains a porting page with some useful but
> not-entirely-up-to-date information on porting musl to a new arch.
> This is a good starting point, and updating it could actually be part
> of the gsoc project. See http://wiki.musl-libc.org/wiki/Porting
> 
> Some information on recent changes can be found in the mailing list
> archives. These threads pertain to changes to how ports are expected
> to provide atomic primitives:
> 
> http://www.openwall.com/lists/musl/2015/05/17/2
> http://www.openwall.com/lists/musl/2015/05/20/1
> http://www.openwall.com/lists/musl/2016/01/10/6
> 
> which was committed here:
> 
> http://git.musl-libc.org/cgit/musl/commit/?id=1315596b510189b5159e742110b504177bdd4932
> 
> and other subsequent commits with per-arch improvements.
> 
> And these cover the bits deduplication:
> 
> http://www.openwall.com/lists/musl/2016/01/25/1
> http://www.openwall.com/lists/musl/2016/01/27/9
> 
> which was committed here:
> 
> http://git.musl-libc.org/cgit/musl/commit/?id=4dfac11538cb20c848c30d754863800061ee8c81
> 
> Threads on the recent mips64 port work, which is almost ready for
> merging, may also be helpful to read. It's broken up across several
> threads but you can find most of the content in the January-March 2016
> archives.
> 
> Since a port of musl to a new arch does not actually involve much
> code, mainly attention to detail to make sure that all of the type
> definitions/ABI/etc. are correct, I think that for a proposal to be
> big enough to make a reasonable GSoC project, it should go beyond just
> the basic porting. Some ideas for things to include would be:
> 
> - Improvement of porting documentation
> 
> - Feedback/patches on where there's too much redundancy between ports
>   and how to reduce it (i.e. making improvements to musl that reduce
>   the amount of code/headers needed for a new port).
> 
> - Patches for musl-cross and/or musl-cross-make (build systems for
>   generating a cross-compiler toolchain) to make it easy to build a
>   musl/riscv cross compiler.
> 
> - Optimizing performance-critical code like memcpy or floating point
>   math functions for riscv.
> 
> - Improving test coverage, especially for things that are easy to get
>   wrong in a new port.
> 
> I'll follow up with more ideas if I think of any.
> 
> Students interested in the project are welcome (and encouraged!) to
> ask questions and discuss here on the musl list. Obviously everyone
> should have in mind writing their own proposals but I want everyone to
> have access to knowledge/resources/community for ideas.

One more thing: the current test suite we use is here:

http://nsz.repo.hu/git/?p=libc-test

It replaces the old one on the musl git site, which has not been
updated in a long time and has nowhere near the coverage. Having this
could be useful to familiarize yourself with the types of testing that
we have and to get ideas for coverage areas you could propose to add.

Also, while we don't have any formal requirement for sample
problems/tasks to go with applications, looking for interesting bug
reports on the mailing list (or bugs fixes in musl's git log) and
writing some simple regression tests or broader tests of the affected
code to add to libc-test would be a nice way to demonstrate your
ability, especially if you don't already have existing FOSS project
contributions to cite, and would actually produce something of value.

Rich