ARC: Add the clone3 wrapper

Use the clone3 wrapper on ARC. It doesn't care about stack alignment.
All callers should provide an aligned stack.
It follows the internal signature:

extern int clone3 (struct clone_args *__cl_args, size_t __size,
 int (*__func) (void *__arg), void *__arg);

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

sysdeps/unix/sysv/linux/arc/clone3.S

@@ -0,0 +1,90 @@
+/* The clone3 syscall wrapper.  Linux/arc version.
+   Copyright (C) 2023 Free Software Foundation, Inc.
+
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <sysdep.h>
+#define _ERRNO_H	1
+#include <bits/errno.h>
+
+/* The userland implementation is:
+   int clone3 (struct clone_args *cl_args, size_t size,
+               int (*func)(void *arg), void *arg);
+
+   the kernel entry is:
+   int clone3 (struct clone_args *cl_args, size_t size);
+
+   The parameters are passed in registers from userland:
+   r0: cl_args
+   r1: size
+   r2: func
+   r3: arg  */
+
+ENTRY(__clone3)
+
+	/* Save args for the child.  */
+	mov	r10, r0		/* cl_args  */
+	mov	r11, r2		/* func	 */
+	mov	r12, r3		/* args  */
+
+	/* Sanity check args.  */
+	breq	r10, 0, L (__sys_err)	/* No NULL cl_args pointer.  */
+	breq	r11, 0, L (__sys_err)	/* No NULL function pointer.  */
+
+	/* Do the system call, the kernel expects:
+	   r8: system call number
+	   r0: cl_args
+	   r1: size  */
+	mov	r0, r10
+	mov	r8, __NR_clone3
+	ARC_TRAP_INSN
+
+	cmp	r0, 0
+	beq	thread_start_clone3	/* Child returns.  */
+	blt	L (__sys_err2)
+	j	[blink]			/* Parent returns.  */
+
+L (__sys_err):
+	mov	r0, -EINVAL
+L (__sys_err2):
+	b	__syscall_error
+PSEUDO_END (__clone3)
+
+
+	.align 4
+	.type thread_start_clone3, %function
+thread_start_clone3:
+	cfi_startproc
+	/* Terminate call stack by noting ra is undefined.  */
+	cfi_undefined (blink)
+
+	/* Child jumps off to @fn with @arg as argument.  */
+	jl.d	[r11]
+	mov	r0, r12
+
+	/* exit() with result from @fn (already in r0).  */
+	mov	r8, __NR_exit
+	ARC_TRAP_INSN
+
+	/* In case it ever came back.  */
+	flag	1
+
+	cfi_endproc
+	.size thread_start_clone3, .-thread_start_clone3
+
+libc_hidden_def (__clone3)
+weak_alias (__clone3, clone3)

sysdeps/unix/sysv/linux/arc/sysdep.h

@@ -141,6 +141,8 @@ hidden_proto (__syscall_error)
 
 # define ARC_TRAP_INSN	"trap_s 0	\n\t"
 
+# define HAVE_CLONE3_WRAPPER	1
+
 # undef INTERNAL_SYSCALL_NCS
 # define INTERNAL_SYSCALL_NCS(number, nr_args, args...)	\
   ({								\