Commit 76aefee5 authored by Steven Rostedt's avatar Steven Rostedt Committed by Ingo Molnar
Browse files

ftrace: comment arch ftrace code 



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

Signed-off-by: default avatarSteven Rostedt <srostedt@redhat.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 593eb8a2

arch/x86/kernel/ftrace.c

+6 −1
Original line number Diff line number Diff line
@@ -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;