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    Subject[tip:perf/core] ftrace: Add -mfentry to Makefile on function tracer
    Commit-ID:  a2546fae01124fb8063747439300fcf39bac033a
    Gitweb: http://git.kernel.org/tip/a2546fae01124fb8063747439300fcf39bac033a
    Author: Steven Rostedt <srostedt@redhat.com>
    AuthorDate: Wed, 9 Feb 2011 13:15:59 -0500
    Committer: Steven Rostedt <rostedt@goodmis.org>
    CommitDate: Thu, 23 Aug 2012 11:25:02 -0400

    ftrace: Add -mfentry to Makefile on function tracer

    Thanks to Andi Kleen, gcc 4.6.0 now supports -mfentry for x86
    (and hopefully soon for other archs). What this does is to have
    the function profiler start at the beginning of the function
    instead of after the stack is set up. As plain -pg (mcount) is
    called after the stack is set up, and in some cases can have issues
    with the function graph tracer. It also requires frame pointers to
    be enabled.

    The -mfentry now calls __fentry__ at the beginning of the function.
    This allows for compiling without frame pointers and even has the
    ability to access parameters if needed.

    If the architecture and the compiler both support -mfentry then
    use that instead.

    Link: http://lkml.kernel.org/r/20120807194059.392617243@goodmis.org

    Acked-by: H. Peter Anvin <hpa@linux.intel.com>
    Acked-by: Ingo Molnar <mingo@kernel.org>
    Cc: Michal Marek <mmarek@suse.cz>
    Cc: Andi Kleen <andi@firstfloor.org>
    Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
    ---
    Makefile | 6 +++++-
    kernel/trace/Kconfig | 5 +++++
    2 files changed, 10 insertions(+), 1 deletions(-)

    diff --git a/Makefile b/Makefile
    index ddf5be9..e7ca93f 100644
    --- a/Makefile
    +++ b/Makefile
    @@ -609,7 +609,11 @@ KBUILD_CFLAGS += $(call cc-option, -femit-struct-debug-baseonly)
    endif

    ifdef CONFIG_FUNCTION_TRACER
    -KBUILD_CFLAGS += -pg
    +ifdef CONFIG_HAVE_FENTRY
    +CC_USING_FENTRY := $(call cc-option, -mfentry -DCC_USING_FENTRY)
    +endif
    +KBUILD_CFLAGS += -pg $(CC_USING_FENTRY)
    +KBUILD_AFLAGS += $(CC_USING_FENTRY)
    ifdef CONFIG_DYNAMIC_FTRACE
    ifdef CONFIG_HAVE_C_RECORDMCOUNT
    BUILD_C_RECORDMCOUNT := y
    diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
    index 8c4c070..9301a0e 100644
    --- a/kernel/trace/Kconfig
    +++ b/kernel/trace/Kconfig
    @@ -49,6 +49,11 @@ config HAVE_SYSCALL_TRACEPOINTS
    help
    See Documentation/trace/ftrace-design.txt

    +config HAVE_FENTRY
    + bool
    + help
    + Arch supports the gcc options -pg with -mfentry
    +
    config HAVE_C_RECORDMCOUNT
    bool
    help

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