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    SubjectRe: [RFC PATCH 3/4] ftrace: Do not test frame pointers if -mfentry is used
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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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