linux-kernel - [tip:perf/core] ftrace: Do not test frame pointers if -mfentry is used

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Date:	Mon, 27 Aug 2012 10:05:23 -0700
From:	tip-bot for Steven Rostedt <srostedt@...hat.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...nel.org,
	andi@...stfloor.org, rostedt@...dmis.org, srostedt@...hat.com,
	tglx@...utronix.de, hpa@...ux.intel.com
Subject: [tip:perf/core] ftrace:
  Do not test frame pointers if -mfentry is used

Commit-ID:  781d06248234e221edb560a18461d65808a8a942
Gitweb:     http://git.kernel.org/tip/781d06248234e221edb560a18461d65808a8a942
Author:     Steven Rostedt <srostedt@...hat.com>
AuthorDate: Wed, 9 Feb 2011 13:27:22 -0500
Committer:  Steven Rostedt <rostedt@...dmis.org>
CommitDate: Thu, 23 Aug 2012 11:25:29 -0400

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@...ux.intel.com>
Acked-by: Ingo Molnar <mingo@...nel.org>
Cc: Andi Kleen <andi@...stfloor.org>
Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
---
 kernel/trace/trace_functions_graph.c |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)

diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
index ce27c8b..99b4378 100644
--- 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();
--
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