alpha: use alpha_ni_syscall only for syscall zero

Once upon a time it used to have a C part that printed a warning
about unimplemented OSF syscalls.  That's what it's been doing
all over the OSF syscall range, while the native Linux syscall
range uses sys_ni_syscall().

With those warnings about unimplemented OSF syscalls gone (circa 2.4),
alpha_ni_syscall() has shrunk to that little bit of asm and the
only reason it hasn't been replaced with sys_ni_syscall() everywhere
is that extra twist needed in case of syscall #0.

Let's keep it only for syscall #0 and replace the rest with sys_ni_syscall.
And use sys_ni_syscall for "number out range" in ptraced-call case, as
we'd been doing for normal codepath since 2.1.86...
Acked-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

arch/alpha/kernel/entry.S

@@ -473,7 +473,7 @@ entSys:
 	bne     $3, strace
 	beq	$4, 1f
 	ldq	$27, 0($5)
-1:	jsr	$26, ($27), alpha_ni_syscall
+1:	jsr	$26, ($27), sys_ni_syscall
 	ldgp	$gp, 0($26)
 	blt	$0, $syscall_error	/* the call failed */
 	stq	$0, 0($sp)
@@ -587,7 +587,7 @@ strace:
 	/* get the system call pointer.. */
 	lda	$1, NR_SYSCALLS($31)
 	lda	$2, sys_call_table
-	lda	$27, alpha_ni_syscall
+	lda	$27, sys_ni_syscall
 	cmpult	$0, $1, $1
 	s8addq	$0, $2, $2
 	beq	$1, 1f
@@ -843,15 +843,20 @@ sys_rt_sigreturn:
 .end sys_rt_sigreturn
 
 	.align	4
-	.globl	alpha_ni_syscall
-	.ent	alpha_ni_syscall
-alpha_ni_syscall:
+	.globl	alpha_syscall_zero
+	.ent	alpha_syscall_zero
+alpha_syscall_zero:
 	.prologue 0
-	/* Special because it also implements overflow handling via
-	   syscall number 0.  And if you recall, zero is a special
-	   trigger for "not an error".  Store large non-zero there.  */
+	/* Special because it needs to do something opposite to
+	   force_successful_syscall_return().  We use the saved
+	   syscall number for that, zero meaning "not an error".
+	   That works nicely, but for real syscall 0 we need to
+	   make sure that this logics doesn't get confused.
+	   Store a non-zero there - -ENOSYS we need in register
+	   for our return value will do just fine.
+	  */
 	lda	$0, -ENOSYS
 	unop
 	stq	$0, 0($sp)
 	ret
-.end alpha_ni_syscall
+.end alpha_syscall_zero