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>
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@ -66,18 +66,23 @@ ftrace_modify_code(unsigned long ip, unsigned char *old_code,
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/*
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* Note: Due to modules and __init, code can
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* disappear and change, we need to protect against faulting
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* as well as code changing.
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* as well as code changing. We do this by using the
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* __copy_*_user functions.
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*
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* No real locking needed, this code is run through
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* kstop_machine, or before SMP starts.
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*/
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/* read the text we want to modify */
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if (__copy_from_user_inatomic(replaced, (char __user *)ip,
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MCOUNT_INSN_SIZE))
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return -EFAULT;
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/* Make sure it is what we expect it to be */
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if (memcmp(replaced, old_code, MCOUNT_INSN_SIZE) != 0)
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return -EINVAL;
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/* replace the text with the new text */
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if (__copy_to_user_inatomic((char __user *)ip, new_code,
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MCOUNT_INSN_SIZE))
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return -EPERM;
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