x86: clean up ptrace single-stepping, make PT_DTRACE exact.

(This makes the naming of "DTRACE" purely historical, since
on x86 it now means "single step in progress").

arch/i386/kernel/ptrace.c

@@ -138,6 +138,28 @@ static unsigned long getreg(struct task_struct *child,
 	return retval;
 }
 
+static void set_singlestep(struct task_struct *child)
+{
+	long eflags;
+
+	set_tsk_thread_flag(child, TIF_SINGLESTEP);
+	eflags = get_stack_long(child, EFL_OFFSET);
+	put_stack_long(child, EFL_OFFSET, eflags | TRAP_FLAG);
+	child->ptrace |= PT_DTRACE;
+}
+
+static void clear_singlestep(struct task_struct *child)
+{
+	if (child->ptrace & PT_DTRACE) {
+		long eflags;
+
+		clear_tsk_thread_flag(child, TIF_SINGLESTEP);
+		eflags = get_stack_long(child, EFL_OFFSET);
+		put_stack_long(child, EFL_OFFSET, eflags & ~TRAP_FLAG);
+		child->ptrace &= ~PT_DTRACE;
+	}
+}
+
 /*
  * Called by kernel/ptrace.c when detaching..
  *
@@ -145,11 +167,7 @@ static unsigned long getreg(struct task_struct *child,
  */
 void ptrace_disable(struct task_struct *child)
 { 
-	long tmp;
-
-	clear_tsk_thread_flag(child, TIF_SINGLESTEP);
-	tmp = get_stack_long(child, EFL_OFFSET) & ~TRAP_FLAG;
-	put_stack_long(child, EFL_OFFSET, tmp);
+	clear_singlestep(child);
 }
 
 /*
@@ -388,10 +406,8 @@ asmlinkage int sys_ptrace(long request, long pid, long addr, long data)
 		  }
 		  break;
 
-	case PTRACE_SYSCALL: /* continue and stop at next (return from) syscall */
-	case PTRACE_CONT: { /* restart after signal. */
-		long tmp;
-
+	case PTRACE_SYSCALL:	/* continue and stop at next (return from) syscall */
+	case PTRACE_CONT:	/* restart after signal. */
 		ret = -EIO;
 		if ((unsigned long) data > _NSIG)
 			break;
@@ -401,56 +417,39 @@ asmlinkage int sys_ptrace(long request, long pid, long addr, long data)
 		else {
 			clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
 		}
-		clear_tsk_thread_flag(child, TIF_SINGLESTEP);
 		child->exit_code = data;
-	/* make sure the single step bit is not set. */
-		tmp = get_stack_long(child, EFL_OFFSET) & ~TRAP_FLAG;
-		put_stack_long(child, EFL_OFFSET,tmp);
+		/* make sure the single step bit is not set. */
+		clear_singlestep(child);
 		wake_up_process(child);
 		ret = 0;
 		break;
-	}
 
 /*
  * make the child exit.  Best I can do is send it a sigkill. 
  * perhaps it should be put in the status that it wants to 
  * exit.
  */
-	case PTRACE_KILL: {
-		long tmp;
-
+	case PTRACE_KILL:
 		ret = 0;
 		if (child->exit_state == EXIT_ZOMBIE)	/* already dead */
 			break;
 		child->exit_code = SIGKILL;
-		clear_tsk_thread_flag(child, TIF_SINGLESTEP);
 		/* make sure the single step bit is not set. */
-		tmp = get_stack_long(child, EFL_OFFSET) & ~TRAP_FLAG;
-		put_stack_long(child, EFL_OFFSET, tmp);
+		clear_singlestep(child);
 		wake_up_process(child);
 		break;
-	}
-
-	case PTRACE_SINGLESTEP: {  /* set the trap flag. */
-		long tmp;
 
+	case PTRACE_SINGLESTEP:	/* set the trap flag. */
 		ret = -EIO;
 		if ((unsigned long) data > _NSIG)
 			break;
 		clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
-		if ((child->ptrace & PT_DTRACE) == 0) {
-			/* Spurious delayed TF traps may occur */
-			child->ptrace |= PT_DTRACE;
-		}
-		tmp = get_stack_long(child, EFL_OFFSET) | TRAP_FLAG;
-		put_stack_long(child, EFL_OFFSET, tmp);
-		set_tsk_thread_flag(child, TIF_SINGLESTEP);
+		set_singlestep(child);
 		child->exit_code = data;
 		/* give it a chance to run. */
 		wake_up_process(child);
 		ret = 0;
 		break;
-	}
 
 	case PTRACE_DETACH:
 		/* detach a process that was attached. */