microblaze: ftrace: add static function tracer

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 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.

Commit message from Wu Zhangjin <wuzhangjin@gmail.com>

Signed-off-by: Michal Simek <monstr@monstr.eu>

1 files changed, 105 insertions, 0 deletions

diff --git a/arch/microblaze/kernel/mcount.S b/arch/microblaze/kernel/mcount.S
new file mode 100644
index 000000000000..a257a1b75ed2
--- /dev/null
+++ b/arch/microblaze/kernel/mcount.S
@@ -0,0 +1,105 @@
+/*
+ * Low-level ftrace handling
+ *
+ * Copyright (C) 2009 Michal Simek <monstr@monstr.eu>
+ * Copyright (C) 2009 PetaLogix
+ *
+ * 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.
+ */
+
+#include <linux/linkage.h>
+
+#define NOALIGN_ENTRY(name)     .globl name; name:
+
+/* FIXME MS: I think that I don't need to save all regs */
+#define SAVE_REGS               \
+        addik   r1, r1, -120;   \
+        swi     r2, r1, 4;      \
+        swi     r3, r1, 8;      \
+        swi     r4, r1, 12;     \
+        swi     r5, r1, 116;    \
+        swi     r6, r1, 16;     \
+        swi     r7, r1, 20;     \
+        swi     r8, r1, 24;     \
+        swi     r9, r1, 28;     \
+        swi     r10, r1, 32;    \
+        swi     r11, r1, 36;    \
+        swi     r12, r1, 40;    \
+        swi     r13, r1, 44;    \
+        swi     r14, r1, 48;    \
+        swi     r16, r1, 52;    \
+        swi     r17, r1, 56;    \
+        swi     r18, r1, 60;    \
+        swi     r19, r1, 64;    \
+        swi     r20, r1, 68;    \
+        swi     r21, r1, 72;    \
+        swi     r22, r1, 76;    \
+        swi     r23, r1, 80;    \
+        swi     r24, r1, 84;    \
+        swi     r25, r1, 88;    \
+        swi     r26, r1, 92;    \
+        swi     r27, r1, 96;    \
+        swi     r28, r1, 100;   \
+        swi     r29, r1, 104;   \
+        swi     r30, r1, 108;   \
+        swi     r31, r1, 112;
+
+#define RESTORE_REGS            \
+        lwi     r2, r1, 4;      \
+        lwi     r3, r1, 8;      \
+        lwi     r4, r1, 12;     \
+        lwi     r5, r1, 116;    \
+        lwi     r6, r1, 16;     \
+        lwi     r7, r1, 20;     \
+        lwi     r8, r1, 24;     \
+        lwi     r9, r1, 28;     \
+        lwi     r10, r1, 32;    \
+        lwi     r11, r1, 36;    \
+        lwi     r12, r1, 40;    \
+        lwi     r13, r1, 44;    \
+        lwi     r14, r1, 48;    \
+        lwi     r16, r1, 52;    \
+        lwi     r17, r1, 56;    \
+        lwi     r18, r1, 60;    \
+        lwi     r19, r1, 64;    \
+        lwi     r20, r1, 68;    \
+        lwi     r21, r1, 72;    \
+        lwi     r22, r1, 76;    \
+        lwi     r23, r1, 80;    \
+        lwi     r24, r1, 84;    \
+        lwi     r25, r1, 88;    \
+        lwi     r26, r1, 92;    \
+        lwi     r27, r1, 96;    \
+        lwi     r28, r1, 100;   \
+        lwi     r29, r1, 104;   \
+        lwi     r30, r1, 108;   \
+        lwi     r31, r1, 112;   \
+        addik   r1, r1, 120;
+
+ENTRY(ftrace_stub)
+        rtsd    r15, 8;
+        nop;
+
+ENTRY(_mcount)
+        SAVE_REGS
+        swi     r15, r1, 0;
+        /* MS: test function trace if is taken or not */
+        lwi     r20, r0, ftrace_trace_function;
+        addik   r6, r0, ftrace_stub;
+        cmpu    r5, r20, r6; /* ftrace_trace_function != ftrace_stub */
+        beqid   r5, end; /* MS: not taken -> jump over */
+        nop;
+/* static normal trace */
+        lwi     r6, r1, 120; /* MS: load parent addr */
+        addik   r5, r15, 0; /* MS: load current function addr */
+        /* MS: here is dependency on previous code */
+        brald   r15, r20; /* MS: jump to ftrace handler */
+        nop;
+end:
+        lwi     r15, r1, 0;
+        RESTORE_REGS
+
+        rtsd    r15, 8; /* MS: jump back */
+        nop;