linux-kernel - [PATCH 1/2] MIPS: ftrace.h: Fix the MCOUNT_INSN

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Date:	Mon, 22 Sep 2014 14:32:58 +0100
From:	Markos Chandras <markos.chandras@...tec.com>
To:	<linux-mips@...ux-mips.org>
CC:	Markos Chandras <markos.chandras@...tec.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...hat.com>, <linux-kernel@...r.kernel.org>
Subject: [PATCH 1/2] MIPS: ftrace.h: Fix the MCOUNT_INSN_SIZE definition

The MCOUNT_INSN_SIZE is meant to be used to denote the overall
size of the mcount() call. Since a jal instruction is used to
call mcount() the delay slot should be taken into consideration
as well.
This also replaces the MCOUNT_INSN_SIZE usage with the real size
of a single MIPS instruction since, as described above, the
MCOUNT_INSN_SIZE is used to denote the total overhead of the
mcount() call.

Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: linux-kernel@...r.kernel.org
Signed-off-by: Markos Chandras <markos.chandras@...tec.com>
---
 arch/mips/include/asm/ftrace.h | 2 +-
 arch/mips/kernel/ftrace.c      | 4 +++-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/mips/include/asm/ftrace.h b/arch/mips/include/asm/ftrace.h
index 992aaba603b5..70d4a35fb560 100644
--- a/arch/mips/include/asm/ftrace.h
+++ b/arch/mips/include/asm/ftrace.h
@@ -13,7 +13,7 @@
 #ifdef CONFIG_FUNCTION_TRACER
 
 #define MCOUNT_ADDR ((unsigned long)(_mcount))
-#define MCOUNT_INSN_SIZE 4		/* sizeof mcount call */
+#define MCOUNT_INSN_SIZE 8		/* sizeof mcount call + delay slot */
 
 #ifndef __ASSEMBLY__
 extern void _mcount(void);
diff --git a/arch/mips/kernel/ftrace.c b/arch/mips/kernel/ftrace.c
index 937c54bc8ccc..211460d4617d 100644
--- a/arch/mips/kernel/ftrace.c
+++ b/arch/mips/kernel/ftrace.c
@@ -28,6 +28,8 @@
 #define MCOUNT_OFFSET_INSNS 4
 #endif
 
+#define FTRACE_MIPS_INSN_SIZE 4 /* Size of single MIPS instruction */
+
 #ifdef CONFIG_DYNAMIC_FTRACE
 
 /* Arch override because MIPS doesn't need to run this from stop_machine() */
@@ -395,7 +397,7 @@ void prepare_ftrace_return(unsigned long *parent_ra_addr, unsigned long self_ra,
 	 */
 
 	insns = in_kernel_space(self_ra) ? 2 : MCOUNT_OFFSET_INSNS + 1;
-	trace.func = self_ra - (MCOUNT_INSN_SIZE * insns);
+	trace.func = self_ra - (FTRACE_MIPS_INSN_SIZE * insns);
 
 	/* Only trace if the calling function expects to */
 	if (!ftrace_graph_entry(&trace)) {
-- 
2.1.0

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