Re: [musl] Re: add loongarch64 port

[Arnd Bergmann <arnd@kernel.org>]

On Sat, Apr 9, 2022 at 5:55 AM 王洪亮 <wanghongliang@loongson.cn> wrote:
> 在 2022/4/8 下午2:46, Arnd Bergmann 写道:
> > On Fri, Apr 8, 2022 at 4:21 AM 王洪亮 <wanghongliang@loongson.cn> wrote:
> >
> > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=fa729c4df5589
> >
> > What happens in the clone() syscall in the kernel is that the size
> > gets added to the initial pointer on normal architectures (parisc and ia64
> > being the exceptions). If you already have the stack pointer, I think you can
> > just pass size=0 as we do internally in the kernel.
> >
> > If there was a port of musl to one of the architectures that does it
> > differently,
> > then changing callers such as
> >
> >          pid = __clone(child, stack+sizeof stack,
> >                  CLONE_VM|CLONE_VFORK|SIGCHLD, &args);
> >
> > would be required, and the separate size argument in clone3() could
> > help keep that hidden from musl.
> >
> >           Arnd
>
>
> In LoongArch,the stack is grows down.
>
> As previous suggested,I implement __NR_clone3 syscall within __clone()
> in loongarch port,based on __clone() interface unchanged and the
> architecture-independent code of call __clone() unchanged.
>
> In __NR_clone3 syscall,I need pass the lowest address of memory area to
> clone_args.stack,and pass stack_size to clone_args.stack_size(stack_size
> must not be 0)
>          if (kargs->stack_size == 0)
>              return false;
>
> current,the __clone()'s input parameters have no "stack_size",so I can't
> pass valid(must be size!=0) stack_size to clone3.
>
> your meaning is pass stack_size=0 when the input parameter "stack" of
> __clone()
> is already stack point? but pass stack_size=0 is illegal.

Ah, you are right, that doesn't work at the moment. You dropped Christian
from the Cc list, adding him back because he probably has an idea
for how to address that.

It looks like it could be fixed for the internal callers of __clone() by
adding a __clone3() call that takes the size argument, and falls back
to calling __clone() on architectures that have that. I don't see how
one would do it for the generic clone() library function call though.

         Arnd