MIPS: Tracing: Add static function tracer support for MIPS

If -pg of gcc is enabled with CONFIG_FUNCTION_TRACER=y. a calling to
_mcount will be inserted into each kernel function. so, there is a
possibility to trace the kernel functions in _mcount.

This patch add the MIPS specific _mcount support for static function
tracing. by default, ftrace_trace_function is initialized as
ftrace_stub(an empty function), so, the default _mcount will introduce
very little overhead. after enabling ftrace in user-space, it will jump
to a real tracing function and do static function tracing for us.

and -ffunction-sections is incompatible with -pg, so, disable it when
ftracer is enabled.

Signed-off-by: Wu Zhangjin <wuzhangjin@gmail.com>
Reviewed-by: Steven Rostedt <rostedt@goodmis.org>
Cc: Nicholas Mc Guire <der.herr@hofr.at>
Cc: zhangfx@lemote.com
Cc: Wu Zhangjin <wuzhangjin@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: linux-kernel@vger.kernel.org
Cc: linux-mips@linux-mips.org
Patchwork: http://patchwork.linux-mips.org/patch/672/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

1 files changed, 83 insertions, 0 deletions

diff --git a/arch/mips/kernel/mcount.S b/arch/mips/kernel/mcount.S
new file mode 100644
index 000000000000..cebcc3c11305
--- /dev/null
+++ b/arch/mips/kernel/mcount.S
@@ -0,0 +1,83 @@
+/*
+ * MIPS specific _mcount support
+ *
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file "COPYING" in the main directory of this archive for
+ * more details.
+ *
+ * Copyright (C) 2009 Lemote Inc. & DSLab, Lanzhou University, China
+ * Author: Wu Zhangjin <wuzj@lemote.com>
+ */
+
+#include <asm/regdef.h>
+#include <asm/stackframe.h>
+#include <asm/ftrace.h>
+
+        .text
+        .set noreorder
+        .set noat
+
+        .macro MCOUNT_SAVE_REGS
+        PTR_SUBU        sp, PT_SIZE
+        PTR_S   ra, PT_R31(sp)
+        PTR_S   AT, PT_R1(sp)
+        PTR_S   a0, PT_R4(sp)
+        PTR_S   a1, PT_R5(sp)
+        PTR_S   a2, PT_R6(sp)
+        PTR_S   a3, PT_R7(sp)
+#ifdef CONFIG_64BIT
+        PTR_S   a4, PT_R8(sp)
+        PTR_S   a5, PT_R9(sp)
+        PTR_S   a6, PT_R10(sp)
+        PTR_S   a7, PT_R11(sp)
+#endif
+        .endm
+
+        .macro MCOUNT_RESTORE_REGS
+        PTR_L   ra, PT_R31(sp)
+        PTR_L   AT, PT_R1(sp)
+        PTR_L   a0, PT_R4(sp)
+        PTR_L   a1, PT_R5(sp)
+        PTR_L   a2, PT_R6(sp)
+        PTR_L   a3, PT_R7(sp)
+#ifdef CONFIG_64BIT
+        PTR_L   a4, PT_R8(sp)
+        PTR_L   a5, PT_R9(sp)
+        PTR_L   a6, PT_R10(sp)
+        PTR_L   a7, PT_R11(sp)
+#endif
+#ifdef CONFIG_64BIT
+        PTR_ADDIU       sp, PT_SIZE
+#else
+        PTR_ADDIU       sp, (PT_SIZE + 8)
+#endif
+.endm
+
+        .macro RETURN_BACK
+        jr ra
+         move ra, AT
+        .endm
+
+NESTED(_mcount, PT_SIZE, ra)
+        PTR_LA  t0, ftrace_stub
+        PTR_L   t1, ftrace_trace_function /* Prepare t1 for (1) */
+        bne     t0, t1, static_trace
+         nop
+        b       ftrace_stub
+         nop
+
+static_trace:
+        MCOUNT_SAVE_REGS
+
+        move    a0, ra          /* arg1: next ip, selfaddr */
+        jalr    t1      /* (1) call *ftrace_trace_function */
+         move   a1, AT          /* arg2: the caller's next ip, parent */
+
+        MCOUNT_RESTORE_REGS
+        .globl ftrace_stub
+ftrace_stub:
+        RETURN_BACK
+        END(_mcount)
+
+        .set at
+        .set reorder