Re: musl on a different syscall layer?

[Rich Felker <dalias@libc.org>]

On Wed, Sep 17, 2014 at 04:57:58PM +0200, u-wsnj@aetey.se wrote:
> An observation, NetBSD libc file looks about 50% bigger than musl
> being used (via Linux ABI) on the same system.
> 
> I am also kind of put off by the NetBSD monolithic build environment,
> musl seems much easier to handle independently of other components of
> the OS than the NetBSD libc.
> 
> Wonder how big effort would be needed to adjust musl to be compilable
> against the NetBSD native syscalls? Unlike Linux, *BSD kernels do not
> promise the stability of the syscall interface, but in practice the
> default compatibility level covers many kernel versions and looks almost
> as stable as in Linux.
> 
> (Linux-ABI-only musl would probably always remain "slightly insufficient"
> for using with OS-specific tools, when the OS is not Linux - as there
> are syscalls which reflect the internals of the kernel and they hardly
> can ever become represented via a foreign ABI)
> 
> How much in musl is fundamentally linux-specific, besides the low level
> syscall interfacing? How feasible would it be to introduce multiple
> "kernel flavour" targets?

The main requirement is having equivalent functionality available. On
the BSD targets I've asked BSD folks about, there's supposedly no
equivalent of futex except inthe Linux compat layer, which is pretty
much a show-stopper unless/until it can be remedied. clone is a big
unknown to me too. The other big potential problem is if the native
syscall API requires a stack to communicate with the kernel (one or
more BSDs require this, IIRC), since at least __unmapself needs to be
able to call SYS_munmap and SYS_exit without a stack.

Rich