Messages in this thread |  | | | Subject | Re: [RFC PATCH 3/4] ftrace: Do not test frame pointers if -mfentry is used | | From | Steven Rostedt <> | | Date | Wed, 08 Aug 2012 08:49:08 -0400 |
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On Wed, 2012-08-08 at 13:34 +0900, Masami Hiramatsu wrote: > > > -#ifdef CONFIG_HAVE_FUNCTION_GRAPH_FP_TEST > > +#if defined(CONFIG_HAVE_FUNCTION_GRAPH_FP_TEST) && !defined(CC_USING_FENTRY) > > I think CONFIG_HAVE_FENTRY would better unselect > CONFIG_HAVE_FUNCTION_GRAPH_FP_TEST in arch/x86/Kconfig explicitly.
No, CONFIG_HAVE_FENTRY just means fentry is supported, it does not mean that it is being used. It only gets used if CC_USING_FENTRY is set, which is set by the Makefile at time of compile.
If CONFIG_HAVE_FENTRY is defined, a test is done to see if the gcc compiling the kernel supports -mfentry. If it does, then it defines the CC_USING_FENTRY macro, if not, the macro is not defined and the old way is performed.
If the old way is performed, even if CONFIG_HAVE_FENTRY is defined, then we still need the above test. We can not have CONFIG_HAVE_FENTRY unselect CONFIG_HAVE_FUNCTION_GRAPH_FP_TEST.
-- Steve
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