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, 6 insertions, 0 deletions

diff --git a/arch/mips/kernel/Makefile b/arch/mips/kernel/Makefile
index f442de804d8..1340ba3dd38 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