ftrace: Do not test frame pointers if -mfentry is used

The function graph has a test to check if the frame pointer is
corrupted, which can happen with various options of gcc with mcount.
But this is not an issue with -mfentry as -mfentry does not need nor use
frame pointers for function graph tracing.

Link: http://lkml.kernel.org/r/20120807194059.773895870@goodmis.org
Acked-by: H. Peter Anvin <hpa@linux.intel.com>
Acked-by: Ingo Molnar <mingo@kernel.org>
Cc: Andi Kleen <andi@firstfloor.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
index ce27c8ba8d318ffa6337f231e12a680f6deb7720..99b4378393d5fae8ea1c8de91032129f52a45216 100644 (file)
--- a/kernel/trace/trace_functions_graph.c
+++ b/kernel/trace/trace_functions_graph.c
@@ -143,7 +143,7 @@ ftrace_pop_return_trace(struct ftrace_graph_ret *trace, unsigned long *ret,
                return;
        }
 
-#ifdef CONFIG_HAVE_FUNCTION_GRAPH_FP_TEST
+#if defined(CONFIG_HAVE_FUNCTION_GRAPH_FP_TEST) && !defined(CC_USING_FENTRY)
        /*
         * The arch may choose to record the frame pointer used
         * and check it here to make sure that it is what we expect it
@@ -154,6 +154,9 @@ ftrace_pop_return_trace(struct ftrace_graph_ret *trace, unsigned long *ret,
         *
         * Currently, x86_32 with optimize for size (-Os) makes the latest
         * gcc do the above.
+        *
+        * Note, -mfentry does not use frame pointers, and this test
+        *  is not needed if CC_USING_FENTRY is set.
         */
        if (unlikely(current->ret_stack[index].fp != frame_pointer)) {
                ftrace_graph_stop();