x86/entry/64: Move sys_ni_syscall stub to common.c

so it can be available to multiple syscall tables.  Also directly return
-ENOSYS instead of bouncing to the generic sys_ni_syscall().
Signed-off-by: Brian Gerst <brgerst@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20200313195144.164260-7-brgerst@gmail.com

arch/x86/entry/common.c

@@ -438,3 +438,10 @@ __visible long do_fast_syscall_32(struct pt_regs *regs)
 #endif
 }
 #endif
+
+#ifdef CONFIG_X86_64
+SYSCALL_DEFINE0(ni_syscall)
+{
+	return -ENOSYS;
+}
+#endif

arch/x86/entry/syscall_64.c

@@ -8,13 +8,6 @@
 #include <asm/asm-offsets.h>
 #include <asm/syscall.h>
 
-extern asmlinkage long sys_ni_syscall(void);
-
-SYSCALL_DEFINE0(ni_syscall)
-{
-	return sys_ni_syscall();
-}
-
 #define __SYSCALL_64(nr, sym, qual) extern asmlinkage long sym(const struct pt_regs *);
 #define __SYSCALL_X32(nr, sym, qual) __SYSCALL_64(nr, sym, qual)
 #include <asm/syscalls_64.h>

arch/x86/include/asm/syscall_wrapper.h

@@ -8,6 +8,9 @@
 
 struct pt_regs;
 
+extern asmlinkage long __x64_sys_ni_syscall(const struct pt_regs *regs);
+extern asmlinkage long __ia32_sys_ni_syscall(const struct pt_regs *regs);
+
 /* Mapping of registers to parameters for syscalls on x86-64 and x32 */
 #define SC_X86_64_REGS_TO_ARGS(x, ...)					\
 	__MAP(x,__SC_ARGS						\