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Message-ID: <20220409133044.GL7074@brightrain.aerifal.cx>
Date: Sat, 9 Apr 2022 09:30:45 -0400
From: Rich Felker <dalias@...c.org>
To: Arnd Bergmann <arnd@...nel.org>
Cc: musl@...ts.openwall.com, Christian Brauner <brauner@...nel.org>
Subject: Re: Re: add loongarch64 port
On Sat, Apr 09, 2022 at 09:19:39AM -0400, Rich Felker wrote:
> On Sat, Apr 09, 2022 at 01:06:13PM +0200, Arnd Bergmann wrote:
> > On Sat, Apr 9, 2022 at 5:55 AM 王洪亮 <wanghongliang@...ngson.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@...ngson.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.
>
> size=4k and passing stack-4k? O_o
>
> This seems like a ridiculous kernel regression to require a size when
> none may be available...
Actually, if there aren't yet archs lacking SYS_clone, this API
regression may be a good argument not to drop SYS_clone on new archs
yet until there's a way for new archs to get the same behavior
(unspecified stack size).
Rich
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