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ftrace: comment arch ftrace code

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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>
This commit is contained in:
Steven Rostedt 2008-10-23 09:33:00 -04:00 committed by Ingo Molnar
parent 593eb8a2d6
commit 76aefee576
1 changed files with 6 additions and 1 deletions
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7
arch/x86/kernel/ftrace.c
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@ -66,18 +66,23 @@ ftrace_modify_code(unsigned long ip, unsigned char *old_code,
/* /*
* Note: Due to modules and __init, code can * Note: Due to modules and __init, code can
* disappear and change, we need to protect against faulting * 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 * No real locking needed, this code is run through
* kstop_machine, or before SMP starts. * kstop_machine, or before SMP starts.
*/ */
/* read the text we want to modify */
if (__copy_from_user_inatomic(replaced, (char __user *)ip, if (__copy_from_user_inatomic(replaced, (char __user *)ip,
MCOUNT_INSN_SIZE)) MCOUNT_INSN_SIZE))
return -EFAULT; return -EFAULT;
/* Make sure it is what we expect it to be */
if (memcmp(replaced, old_code, MCOUNT_INSN_SIZE) != 0) if (memcmp(replaced, old_code, MCOUNT_INSN_SIZE) != 0)
return -EINVAL; return -EINVAL;
/* replace the text with the new text */
if (__copy_to_user_inatomic((char __user *)ip, new_code, if (__copy_to_user_inatomic((char __user *)ip, new_code,
MCOUNT_INSN_SIZE)) MCOUNT_INSN_SIZE))
return -EPERM; return -EPERM;