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>

arch/parisc/kernel/ptrace.c

@@ -264,20 +264,19 @@ long compat_arch_ptrace(struct task_struct *child, compat_long_t request,
 }
 #endif
 
+long do_syscall_trace_enter(struct pt_regs *regs)
+{
+	if (test_thread_flag(TIF_SYSCALL_TRACE) &&
+	    tracehook_report_syscall_entry(regs))
+		return -1L;
+
+	return regs->gr[20];
+}
 
-void syscall_trace(int why)
+void do_syscall_trace_exit(struct pt_regs *regs)
 {
-	struct pt_regs *regs = &current->thread.regs;
+	int stepping = !!(current->ptrace & (PT_SINGLESTEP|PT_BLOCKSTEP));
 
-	if (!test_thread_flag(TIF_SYSCALL_TRACE))
-		return;
-	/*
-	 * Report the system call for tracing.  Entry tracing can
-	 * decide to abort the call.  We handle that by setting an
-	 * invalid syscall number (-1) to force an ENOSYS error.
-	 */
-	if (why)
-		tracehook_report_syscall_exit(regs, 0);
-	else if (tracehook_report_syscall_entry(regs))
-		regs->gr[20] = -1;	/* force ENOSYS */
+	if (stepping || test_thread_flag(TIF_SYSCALL_TRACE))
+		tracehook_report_syscall_exit(regs, stepping);
 }

arch/parisc/kernel/syscall.S

@@ -288,19 +288,23 @@ tracesys:
 	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:
+	/* 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 @@ tracesys_exit:
 #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 @@ tracesys_sigexit:
 #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)