Re: porting musl to RISCV-64

[Gry Gunvor <gry.gunvor@gmail.com>]

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
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?

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