From 76aefee57657428fb77cbd8624119c1a440bee44 Mon Sep 17 00:00:00 2001 From: Steven Rostedt <rostedt@goodmis.org> Date: Thu, 23 Oct 2008 09:33:00 -0400 Subject: [PATCH] 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> --- arch/x86/kernel/ftrace.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) 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; -- 2.41.3