ftrace: comment arch ftrace code
Add comments to explain what is happening in the x86 arch ftrace code.
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index 4282915..7834554 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -66,18 +66,23 @@
/*
* Note: Due to modules and __init, code can
* disappear and change, we need to protect against faulting
- * as well as code changing.
+ * as well as code changing. We do this by using the
+ * __copy_*_user functions.
*
* No real locking needed, this code is run through
* kstop_machine, or before SMP starts.
*/
+
+ /* read the text we want to modify */
if (__copy_from_user_inatomic(replaced, (char __user *)ip,
MCOUNT_INSN_SIZE))
return -EFAULT;
+ /* Make sure it is what we expect it to be */
if (memcmp(replaced, old_code, MCOUNT_INSN_SIZE) != 0)
return -EINVAL;
+ /* replace the text with the new text */
if (__copy_to_user_inatomic((char __user *)ip, new_code,
MCOUNT_INSN_SIZE))
return -EPERM;