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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