[J-core] The "kernel patch" for sheb-nofpu multi-thread support ?

[Rob Landley]

On 8/5/20 3:55 AM, 蔡傳資 wrote:
> Hi,
> 
> sorry again for making the noise.

No problem. :)

> I was reading the musl-libc wiki, and something caught my eyes :
> https://wiki.musl-libc.org/supported-platforms.html#Supported_target_architectures_(ABIs)
> "sheb-nofpu subarchs (currently this kernel-patch is required for
> multithread usage)"

The linux-next tree gets regularly rebased and thus does not provide stable URLs
to commits. It's ALWAYS been like this https://lwn.net/Articles/289490/
which means a URL to a commit in linux-next will be gone in a week. Whoever
added that URL to the wiki didn't know how linux-next works.

Is this nofpu or nommu? Threading shouldn't need floating point... No, the wiki
link you point to says nofpu. But I don't understand how NOT having an FPU could
cause a problem here? It's more likely a typo than that there was actually a
nofpu issue.

> The kernel-patch link in that page is broken now. [1]
> Yet judging from the URI, I assume that the patch was on the way of
> being merged ?

There were nommu threading issues a while back, kernel commit 00b73d8d1b71 added
basic support that got fixed by 9b7e30ab9753 a year later. But that was years ago.

> Some google search results on this mailing list makes me feel that it
> requires quite a mount of patches to fix the issue.

I'm not a heavy user of threading, but I'm unaware of any current problems in
the 5.x kernel series on nommu sh? As far as I know it works fine?

> So I'm wondering the status of the needed patches for sheb-nofpu
> multi-thread support.
> 
> [1] https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git/commit/arch/sh?id=a37922c1a80663dfb814f3837dc1f2a451707e5f
> [2] https://lists.j-core.org/pipermail/j-core/2016-May/000171.html

The patches attached to that second link were merged several years ago. For
example the MAYSHARE one is upstream as commit 63678c32e209.

> Sincerely,
> Ruinland

Rich just put out a new musl release, I need to rebuild my toolchains and try it
out, but there's a large batch of arch/sh cleanups going into 5.9-rc1 and I'm
waiting to regression test that.

Rob