nios2: implement architecture-specific portion of sys_clone3

This commit adds the sys_clone3 entry point for nios2. An
architecture-specific wrapper (__sys_clone3) is required to save and
restore additional registers to the kernel stack via SAVE_SWITCH_STACK
and RESTORE_SWITCH_STACK.

Signed-off-by: Simon Schuster <schuster.simon@siemens-energy.com>
Link: https://lore.kernel.org/20250901-nios2-implement-clone3-v2-4-53fcf5577d57@siemens-energy.com
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: Simon Schuster

arch/nios2/include/asm/syscalls.h

@@ -7,6 +7,7 @@
 
 int sys_cacheflush(unsigned long addr, unsigned long len,
 				unsigned int op);
+asmlinkage long __sys_clone3(struct clone_args __user *uargs, size_t size);
 
 #include <asm-generic/syscalls.h>
 

arch/nios2/include/asm/unistd.h

@@ -7,6 +7,4 @@
 #define __ARCH_WANT_STAT64
 #define __ARCH_WANT_SET_GET_RLIMIT
 
-#define __ARCH_BROKEN_SYS_CLONE3
-
 #endif

arch/nios2/kernel/entry.S

@@ -403,6 +403,12 @@ ENTRY(sys_clone)
 	addi    sp, sp, 4
 	RESTORE_SWITCH_STACK
 	ret
+/* long syscall(SYS_clone3, struct clone_args *cl_args, size_t size); */
+ENTRY(__sys_clone3)
+	SAVE_SWITCH_STACK
+	call	sys_clone3
+	RESTORE_SWITCH_STACK
+	ret
 
 ENTRY(sys_rt_sigreturn)
 	SAVE_SWITCH_STACK

arch/nios2/kernel/syscall_table.c

@@ -13,6 +13,7 @@
 #define __SYSCALL_WITH_COMPAT(nr, native, compat)        __SYSCALL(nr, native)
 
 #define sys_mmap2 sys_mmap_pgoff
+#define sys_clone3 __sys_clone3
 
 void *sys_call_table[__NR_syscalls] = {
 	[0 ... __NR_syscalls-1] = sys_ni_syscall,