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authorSteven Rostedt <rostedt@goodmis.org>2008-10-23 09:33:00 -0400
committerIngo Molnar <mingo@elte.hu>2008-10-23 16:00:17 +0200
commit76aefee57657428fb77cbd8624119c1a440bee44 (patch)
tree31df8acbe185aeee1515d166d76cf2e85dd0eff6 /arch/x86/kernel/ftrace.c
parent593eb8a2d63e95772a5f22d746f18a997c5ee463 (diff)
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>
Diffstat (limited to 'arch/x86/kernel/ftrace.c')
-rw-r--r--arch/x86/kernel/ftrace.c7
1 files changed, 6 insertions, 1 deletions
diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index 428291581cb..783455454d7 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -66,18 +66,23 @@ ftrace_modify_code(unsigned long ip, unsigned char *old_code,
/*
* 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;