Merge branch 'x86/for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip...

[pandora-kernel.git] / arch / x86 / kernel / step.c

diff --git a/arch/x86/kernel/step.c b/arch/x86/kernel/step.c
index 92c20fe..e8b9863 100644 (file)
--- a/arch/x86/kernel/step.c
+++ b/arch/x86/kernel/step.c
@@ -105,6 +105,20 @@ static int is_setting_trap_flag(struct task_struct *child, struct pt_regs *regs)
 static int enable_single_step(struct task_struct *child)
 {
        struct pt_regs *regs = task_pt_regs(child);
+       unsigned long oflags;
+
+       /*
+        * If we stepped into a sysenter/syscall insn, it trapped in
+        * kernel mode; do_debug() cleared TF and set TIF_SINGLESTEP.
+        * If user-mode had set TF itself, then it's still clear from
+        * do_debug() and we need to set it again to restore the user
+        * state so we don't wrongly set TIF_FORCED_TF below.
+        * If enable_single_step() was used last and that is what
+        * set TIF_SINGLESTEP, then both TF and TIF_FORCED_TF are
+        * already set and our bookkeeping is fine.
+        */
+       if (unlikely(test_tsk_thread_flag(child, TIF_SINGLESTEP)))
+               regs->flags |= X86_EFLAGS_TF;
 
        /*
         * Always set TIF_SINGLESTEP - this guarantees that
@@ -113,11 +127,7 @@ static int enable_single_step(struct task_struct *child)
         */
        set_tsk_thread_flag(child, TIF_SINGLESTEP);
 
-       /*
-        * If TF was already set, don't do anything else
-        */
-       if (regs->flags & X86_EFLAGS_TF)
-               return 0;
+       oflags = regs->flags;
 
        /* Set TF on the kernel stack.. */
        regs->flags |= X86_EFLAGS_TF;
@@ -126,9 +136,22 @@ static int enable_single_step(struct task_struct *child)
         * ..but if TF is changed by the instruction we will trace,
         * don't mark it as being "us" that set it, so that we
         * won't clear it by hand later.
+        *
+        * Note that if we don't actually execute the popf because
+        * of a signal arriving right now or suchlike, we will lose
+        * track of the fact that it really was "us" that set it.
         */
-       if (is_setting_trap_flag(child, regs))
+       if (is_setting_trap_flag(child, regs)) {
+               clear_tsk_thread_flag(child, TIF_FORCED_TF);
                return 0;
+       }
+
+       /*
+        * If TF was already set, check whether it was us who set it.
+        * If not, we should never attempt a block step.
+        */
+       if (oflags & X86_EFLAGS_TF)
+               return test_tsk_thread_flag(child, TIF_FORCED_TF);
 
        set_tsk_thread_flag(child, TIF_FORCED_TF);