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| author | Steven Rostedt <rostedt@goodmis.org> | 2008-10-23 15:33:00 +0200 |
|---|---|---|
| committer | Ingo Molnar <mingo@elte.hu> | 2008-10-23 16:00:17 +0200 |
| commit | 76aefee57657428fb77cbd8624119c1a440bee44 (patch) | |
| tree | 31df8acbe185aeee1515d166d76cf2e85dd0eff6 | |
| parent | ftrace: return error on failed modified text. (diff) | |
| download | linux-76aefee57657428fb77cbd8624119c1a440bee44.tar.xz linux-76aefee57657428fb77cbd8624119c1a440bee44.zip | |
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>
| -rw-r--r-- | arch/x86/kernel/ftrace.c | 7 |
1 files changed, 6 insertions, 1 deletions
diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c index 428291581cb2..783455454d78 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; |