Re: porting musl to RISCV-64

[Szabolcs Nagy <nsz@port70.net>]

* Gry Gunvor <gry.gunvor@gmail.com> [2016-05-11 09:40:42 -0700]:
> Here's another way to put my question: I've already written my own
> ghetto riscv-64 libc for synchronous programming (no threads, signals)
> by writing my own version of what you call syscall_arch.h.  Therefore,
> how hard would it be to factor musl so that syscall_arch.h was all I
> was depending on that is arch dependent?  It seems that should get me

the previous riscv port attempt might be enough for you
https://github.com/lluixhi/musl-riscv
but i've never used any of the riscv stuff.

> a lot of what libc provides.  I would want that if I attempt to
> compile a program that does more than that, say, attempts to use
> threads/signals/something-weird that I just get a compile-time error.
> Here's a naive plan:
> 
>  * grep for the inclusion of the other header files in arch other than
> syscall_arch.h;
> 
>  * for .c files, comment them out in the makefile;
> 
>  * for .h files, insert an #error directive.
> 
> What will go wrong?
> 

there are lot of subtle issues that may or may not matter for you.

> Gry
> 
> 
> On Wed, May 11, 2016 at 9:32 AM, Gry Gunvor <gry.gunvor@gmail.com> wrote:
> > On Wed, May 11, 2016 at 4:25 AM, Szabolcs Nagy <nsz@port70.net> wrote:
> >
> >> newlib is for baremetal development, you don't
> >> need to use threading with it
> >
> > It's attempt at reentrancy support is causing me problems.
> >
> >> musl now has 32bit mips, mips64 and mipsn32 support as well.
> >> these are different abis so they have to be separate ports,
> >> same is true for the riscv targets.
> >
> > Your documentation does not seem to mention the MIPS64 port, but now
> > that I look in arch, I see the directory for it.
> >
> >> there is a google summer of code project to add riscv support
> >> http://www.openwall.com/lists/musl/2016/04/27/3
> >> i think it is supposed to provide a working port within 1-2
> >> months (?) so if you can wait you don't need to do much work.
> >
> > Suppose I can't wait and I attempt this myself.  Right now I'm just
> > trying to get a generic libc working.  I do not want to handle
> > multi-threading or signals.  What can I omit?  Are the
> > non-portabilities isolated in arch/ ?  That is, is there much more to
> > it than cloning the arch/mips64 directory and hacking on it?
> >
> > atomic_arch.h: I think I can make all of these functions empty as I am
> > not going to be using multi-threading, right?
> >
> > crt_arch.h: program startup; what is this doing in a libc
> > implementation?  doesn't the compiler handle this?
> >
> > ksigaction.h: sorry, I'm not a hardware person; I suppose different
> > hardware has a different default layout for a signal object? so this
> > is not a thing determined by kernel software?  I don't care to handle
> > signals right now anyway.
> >
> > pthread_arch.h: again, I think I can make all of these functions empty
> > as I am not going to be using multi-threading.
> >
> > reloc.h: I can't figure out what this is.
> >
> > syscall_arch.h: I've already written this for RISCV-64 (and so have
> > the RISCV people).
> >
> > bits: to what extent is this MIPS64-specific?  since there is *no*
> > inline assembly, how come arch/generic/ doesn't do here?
> >
> > Gry