parisc: split syscall_trace into two halves

Instead of fiddling with gr[20], restructure code to return whether
or not to -ENOSYS. (Also do a bit of fiddling to let them take
pt_regs directly instead of re-computing it.)

Signed-off-by: Kyle McMartin <kyle@mcmartin.ca>
diff --git a/arch/parisc/kernel/syscall.S b/arch/parisc/kernel/syscall.S
index 07de1bb..f5f9602 100644
--- a/arch/parisc/kernel/syscall.S
+++ b/arch/parisc/kernel/syscall.S
@@ -288,19 +288,23 @@
 	STREG	%r18,PT_GR18(%r2)
 	/* Finished saving things for the debugger */
 
-	ldi	0,%r26				/* syscall entry */
-	ldil	L%syscall_trace,%r1
+	copy	%r2,%r26
+	ldil	L%do_syscall_trace_enter,%r1
 	ldil	L%tracesys_next,%r2
-	be	R%syscall_trace(%sr7,%r1)
+	be	R%do_syscall_trace_enter(%sr7,%r1)
 	ldo	R%tracesys_next(%r2),%r2
 	
-tracesys_next:	
+tracesys_next:
+	/* do_syscall_trace_enter either returned the syscallno, or -1L,
+	 *  so we skip restoring the PT_GR20 below, since we pulled it from
+	 *  task->thread.regs.gr[20] above.
+	 */
+	copy	%ret0,%r20
 	ldil	L%sys_call_table,%r1
 	ldo     R%sys_call_table(%r1), %r19
 
 	ldo     -THREAD_SZ_ALGN-FRAME_SIZE(%r30),%r1      /* get task ptr */
 	LDREG	TI_TASK(%r1), %r1
-	LDREG   TASK_PT_GR20(%r1), %r20
 	LDREG   TASK_PT_GR26(%r1), %r26		/* Restore the users args */
 	LDREG   TASK_PT_GR25(%r1), %r25
 	LDREG   TASK_PT_GR24(%r1), %r24
@@ -337,8 +341,8 @@
 #ifdef CONFIG_64BIT
 	ldo	-16(%r30),%r29			/* Reference param save area */
 #endif
-	ldi	1,%r26				/* syscall exit */
-	bl	syscall_trace, %r2
+	ldo	TASK_REGS(%r1),%r26
+	bl	do_syscall_trace_exit,%r2
 	STREG   %r28,TASK_PT_GR28(%r1)          /* save return value now */
 	ldo     -THREAD_SZ_ALGN-FRAME_SIZE(%r30),%r1      /* get task ptr */
 	LDREG	TI_TASK(%r1), %r1
@@ -359,8 +363,8 @@
 #ifdef CONFIG_64BIT
 	ldo	-16(%r30),%r29			/* Reference param save area */
 #endif
-	bl	syscall_trace, %r2
-	ldi	1,%r26				/* syscall exit */
+	bl	do_syscall_trace_exit,%r2
+	ldo	TASK_REGS(%r1),%r26
 
 	ldil	L%syscall_exit_rfi,%r1
 	be,n	R%syscall_exit_rfi(%sr7,%r1)