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>

6 files changed, 121 insertions, 1 deletions

diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index 435838ec9591..632dba2ac300 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -5,6 +5,7 @@ config MIPS
         select HAVE_IDE
         select HAVE_OPROFILE
         select HAVE_ARCH_KGDB
+        select HAVE_FUNCTION_TRACER
         # Horrible source of confusion.  Die, die, die ...
         select EMBEDDED
         select RTC_LIB if !MACH_LOONGSON
diff --git a/arch/mips/Makefile b/arch/mips/Makefile
index 0a7e6146bb4b..3725ee923d05 100644
--- a/arch/mips/Makefile
+++ b/arch/mips/Makefile
@@ -48,7 +48,9 @@ ifneq ($(SUBARCH),$(ARCH))
   endif
 endif
 
+ifndef CONFIG_FUNCTION_TRACER
 cflags-y := -ffunction-sections
+endif
 cflags-y += $(call cc-option, -mno-check-zero-division)
 
 ifdef CONFIG_32BIT
diff --git a/arch/mips/include/asm/ftrace.h b/arch/mips/include/asm/ftrace.h
index 40a8c178f10d..5f8ebcf9fa61 100644
--- a/arch/mips/include/asm/ftrace.h
+++ b/arch/mips/include/asm/ftrace.h
@@ -1 +1,24 @@
-/* empty */
+/*
+ * 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 DSLab, Lanzhou University, China
+ * Author: Wu Zhangjin <wuzj@lemote.com>
+ */
+
+#ifndef _ASM_MIPS_FTRACE_H
+#define _ASM_MIPS_FTRACE_H
+
+#ifdef CONFIG_FUNCTION_TRACER
+
+#define MCOUNT_ADDR ((unsigned long)(_mcount))
+#define MCOUNT_INSN_SIZE 4              /* sizeof mcount call */
+
+#ifndef __ASSEMBLY__
+extern void _mcount(void);
+#define mcount _mcount
+
+#endif /* __ASSEMBLY__ */
+#endif /* CONFIG_FUNCTION_TRACER */
+#endif /* _ASM_MIPS_FTRACE_H */
diff --git a/arch/mips/kernel/Makefile b/arch/mips/kernel/Makefile
index f442de804d8a..1340ba3dd38d 100644
--- a/arch/mips/kernel/Makefile
+++ b/arch/mips/kernel/Makefile
@@ -10,6 +10,10 @@ obj-y		+= cpu-probe.o branch.o entry.o genex.o irq.o process.o \
                    ptrace.o reset.o setup.o signal.o syscall.o \
                    time.o topology.o traps.o unaligned.o watch.o
 
+ifdef CONFIG_FUNCTION_TRACER
+CFLAGS_REMOVE_early_printk.o = -pg
+endif
+
 obj-$(CONFIG_CEVT_BCM1480)      += cevt-bcm1480.o
 obj-$(CONFIG_CEVT_R4K_LIB)      += cevt-r4k.o
 obj-$(CONFIG_MIPS_MT_SMTC)      += cevt-smtc.o
@@ -27,6 +31,8 @@ obj-$(CONFIG_SYNC_R4K)		+= sync-r4k.o
 obj-$(CONFIG_STACKTRACE)        += stacktrace.o
 obj-$(CONFIG_MODULES)           += mips_ksyms.o module.o
 
+obj-$(CONFIG_FUNCTION_TRACER)   += mcount.o
+
 obj-$(CONFIG_CPU_LOONGSON2)     += r4k_fpu.o r4k_switch.o
 obj-$(CONFIG_CPU_MIPS32)        += r4k_fpu.o r4k_switch.o
 obj-$(CONFIG_CPU_MIPS64)        += r4k_fpu.o r4k_switch.o
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
diff --git a/arch/mips/kernel/mips_ksyms.c b/arch/mips/kernel/mips_ksyms.c
index 225755d0c1f6..1d04807874db 100644
--- a/arch/mips/kernel/mips_ksyms.c
+++ b/arch/mips/kernel/mips_ksyms.c
@@ -13,6 +13,7 @@
 #include <asm/checksum.h>
 #include <asm/pgtable.h>
 #include <asm/uaccess.h>
+#include <asm/ftrace.h>
 
 extern void *__bzero(void *__s, size_t __count);
 extern long __strncpy_from_user_nocheck_asm(char *__to,
@@ -51,3 +52,7 @@ EXPORT_SYMBOL(csum_partial_copy_nocheck);
 EXPORT_SYMBOL(__csum_partial_copy_user);
 
 EXPORT_SYMBOL(invalid_pte_table);
+#ifdef CONFIG_FUNCTION_TRACER
+/* _mcount is defined in arch/mips/kernel/mcount.S */
+EXPORT_SYMBOL(_mcount);
+#endif