x86: be a lot more careful about TF handling.

This should fix Wine for some games that otherwise
seem to think that they run under a debugger.

arch/i386/kernel/ptrace.c

@@ -42,6 +42,12 @@
  */
 #define EFL_OFFSET ((EFL-2)*4-sizeof(struct pt_regs))
 
+static inline struct pt_regs *get_child_regs(struct task_struct *task)
+{
+	void *stack_top = (void *)task->thread.esp0;
+	return stack_top - sizeof(struct pt_regs);
+}
+
 /*
  * this routine will get a word off of the processes privileged stack. 
  * the offset is how far from the base addr as stored in the TSS.  
@@ -140,22 +146,35 @@ static unsigned long getreg(struct task_struct *child,
 
 static void set_singlestep(struct task_struct *child)
 {
-	long eflags;
+	struct pt_regs *regs = get_child_regs(child);
 
+	/*
+	 * Always set TIF_SINGLESTEP - this guarantees that 
+	 * we single-step system calls etc..  This will also
+	 * cause us to set TF when returning to user mode.
+	 */
 	set_tsk_thread_flag(child, TIF_SINGLESTEP);
-	eflags = get_stack_long(child, EFL_OFFSET);
-	put_stack_long(child, EFL_OFFSET, eflags | TRAP_FLAG);
+
+	/*
+	 * If TF was already set, don't do anything else
+	 */
+	if (regs->eflags & TRAP_FLAG)
+		return;
+
+	/* Set TF on the kernel stack, and set the flag to say so */
+	regs->eflags |= TRAP_FLAG;
 	child->ptrace |= PT_DTRACE;
 }
 
 static void clear_singlestep(struct task_struct *child)
 {
-	if (child->ptrace & PT_DTRACE) {
-		long eflags;
+	/* Always clear TIF_SINGLESTEP... */
+	clear_tsk_thread_flag(child, TIF_SINGLESTEP);
 
-		clear_tsk_thread_flag(child, TIF_SINGLESTEP);
-		eflags = get_stack_long(child, EFL_OFFSET);
-		put_stack_long(child, EFL_OFFSET, eflags & ~TRAP_FLAG);
+	/* But touch TF only if it was set by us.. */
+	if (child->ptrace & PT_DTRACE) {
+		struct pt_regs *regs = get_child_regs(child);
+		regs->eflags &= ~TRAP_FLAG;
 		child->ptrace &= ~PT_DTRACE;
 	}
 }

arch/i386/kernel/signal.c

@@ -270,7 +270,6 @@ setup_sigcontext(struct sigcontext __user *sc, struct _fpstate __user *fpstate,
 		 struct pt_regs *regs, unsigned long mask)
 {
 	int tmp, err = 0;
-	unsigned long eflags;
 
 	tmp = 0;
 	__asm__("movl %%gs,%0" : "=r"(tmp): "0"(tmp));
@@ -292,16 +291,7 @@ setup_sigcontext(struct sigcontext __user *sc, struct _fpstate __user *fpstate,
 	err |= __put_user(current->thread.error_code, &sc->err);
 	err |= __put_user(regs->eip, &sc->eip);
 	err |= __put_user(regs->xcs, (unsigned int __user *)&sc->cs);
-
-	/*
-	 * Iff TF was set because the program is being single-stepped by a
-	 * debugger, don't save that information on the signal stack.. We
-	 * don't want debugging to change state.
-	 */
-	eflags = regs->eflags;
-	if (current->ptrace & PT_DTRACE)
-		eflags &= ~TF_MASK;
-	err |= __put_user(eflags, &sc->eflags);
+	err |= __put_user(regs->eflags, &sc->eflags);
 	err |= __put_user(regs->esp, &sc->esp_at_signal);
 	err |= __put_user(regs->xss, (unsigned int __user *)&sc->ss);
 
@@ -424,11 +414,9 @@ static void setup_frame(int sig, struct k_sigaction *ka,
 	 * The tracer may want to single-step inside the
 	 * handler too.
 	 */
-	if (regs->eflags & TF_MASK) {
-		regs->eflags &= ~TF_MASK;
-		if (current->ptrace & PT_DTRACE)
-			ptrace_notify(SIGTRAP);
-	}
+	regs->eflags &= ~TF_MASK;
+	if (test_thread_flag(TIF_SINGLESTEP))
+		ptrace_notify(SIGTRAP);
 
 #if DEBUG_SIG
 	printk("SIG deliver (%s:%d): sp=%p pc=%p ra=%p\n",
@@ -519,11 +507,9 @@ static void setup_rt_frame(int sig, struct k_sigaction *ka, siginfo_t *info,
 	 * The tracer may want to single-step inside the
 	 * handler too.
 	 */
-	if (regs->eflags & TF_MASK) {
-		regs->eflags &= ~TF_MASK;
-		if (current->ptrace & PT_DTRACE)
-			ptrace_notify(SIGTRAP);
-	}
+	regs->eflags &= ~TF_MASK;
+	if (test_thread_flag(TIF_SINGLESTEP))
+		ptrace_notify(SIGTRAP);
 
 #if DEBUG_SIG
 	printk("SIG deliver (%s:%d): sp=%p pc=%p ra=%p\n",

arch/i386/kernel/traps.c

@@ -717,8 +717,17 @@ fastcall void do_debug(struct pt_regs * regs, long error_code)
 		 */
 		if ((regs->xcs & 3) == 0)
 			goto clear_TF_reenable;
-		if ((tsk->ptrace & (PT_DTRACE|PT_PTRACED)) == PT_DTRACE)
-			goto clear_TF;
+
+		/*
+		 * Was the TF flag set by a debugger? If so, clear it now,
+		 * so that register information is correct.
+		 */
+		if (tsk->ptrace & PT_DTRACE) {
+			regs->eflags &= ~TF_MASK;
+			tsk->ptrace &= ~PT_DTRACE;
+			if (!tsk->ptrace & PT_DTRACE)
+				goto clear_TF;
+		}
 	}
 
 	/* Ok, finally something we can handle */