x86, ptrace: Fix block-step

Implement ptrace-block-step using TIF_BLOCKSTEP which will set
DEBUGCTLMSR_BTF when set for a task while preserving any other
DEBUGCTLMSR bits.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20100325135414.017536066@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 20 insertions, 4 deletions

diff --git a/arch/x86/kernel/step.c b/arch/x86/kernel/step.c
index 7beba0769a8c..58de45ee08b6 100644
--- a/arch/x86/kernel/step.c
+++ b/arch/x86/kernel/step.c
@@ -169,9 +169,19 @@ static void enable_step(struct task_struct *child, bool block)
          * So noone should try to use debugger block stepping in a program
          * that uses user-mode single stepping itself.
          */
-        if (!enable_single_step(child))
-                return;
-        /* XXX */
+        if (enable_single_step(child) && block) {
+                unsigned long debugctl = get_debugctlmsr();
+
+                debugctl |= DEBUGCTLMSR_BTF;
+                update_debugctlmsr(debugctl);
+                set_tsk_thread_flag(child, TIF_BLOCKSTEP);
+        } else if (test_tsk_thread_flag(child, TIF_BLOCKSTEP)) {
+                unsigned long debugctl = get_debugctlmsr();
+
+                debugctl &= ~DEBUGCTLMSR_BTF;
+                update_debugctlmsr(debugctl);
+                clear_tsk_thread_flag(child, TIF_BLOCKSTEP);
+        }
 }
 
 void user_enable_single_step(struct task_struct *child)
@@ -189,7 +199,13 @@ void user_disable_single_step(struct task_struct *child)
         /*
          * Make sure block stepping (BTF) is disabled.
          */
-        /* XXX */
+        if (test_tsk_thread_flag(child, TIF_BLOCKSTEP)) {
+                unsigned long debugctl = get_debugctlmsr();
+
+                debugctl &= ~DEBUGCTLMSR_BTF;
+                update_debugctlmsr(debugctl);
+                clear_tsk_thread_flag(child, TIF_BLOCKSTEP);
+        }
 
         /* Always clear TIF_SINGLESTEP... */
         clear_tsk_thread_flag(child, TIF_SINGLESTEP);