Add comments to explain what is happening in the x86 arch ftrace code.

Signed-off-by: Steven Rostedt
---
arch/x86/kernel/ftrace.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)

Index: linux-compile.git/arch/x86/kernel/ftrace.c
================================================== =================
--- linux-compile.git.orig/arch/x86/kernel/ftrace.c 2008-10-22 15:23:20.000000000 -0400
+++ linux-compile.git/arch/x86/kernel/ftrace.c 2008-10-22 15:24:15.000000000 -0400
@@ -66,18 +66,23 @@ ftrace_modify_code(unsigned long ip, uns
/*
* 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;

--
--
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