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    Subject[PATCH v7 04/17] tracing: add static function tracer support for MIPS
    Date
    From: Wu Zhangjin <wuzhangjin@gmail.com>

    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 deafult, 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 to support module tracing, we need to enable -mlong-calls for the
    long call from modules space to kernel space. -mlong-calls load the
    address of _mcount to a register and then jump to it, so, the address is
    allowed to be 32bit long, but without -mlong-calls, for the instruction
    "jal _mcount" only left 26bit for the address of _mcount, which is not
    enough for jumping from the module space to kernel space.

    Reviewed-by: Steven Rostedt <rostedt@goodmis.org>
    Signed-off-by: Wu Zhangjin <wuzhangjin@gmail.com>
    ---
    arch/mips/Kconfig | 1 +
    arch/mips/Makefile | 4 ++
    arch/mips/include/asm/ftrace.h | 25 +++++++++++-
    arch/mips/kernel/Makefile | 2 +
    arch/mips/kernel/mcount.S | 83 ++++++++++++++++++++++++++++++++++++++++
    arch/mips/kernel/mips_ksyms.c | 5 ++
    6 files changed, 119 insertions(+), 1 deletions(-)
    create mode 100644 arch/mips/kernel/mcount.S

    diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
    index 03bd56a..6b33e88 100644
    --- a/arch/mips/Kconfig
    +++ b/arch/mips/Kconfig
    @@ -4,6 +4,7 @@ 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 !LEMOTE_FULOONG2E
    diff --git a/arch/mips/Makefile b/arch/mips/Makefile
    index 77f5021..041deca 100644
    --- a/arch/mips/Makefile
    +++ b/arch/mips/Makefile
    @@ -48,7 +48,11 @@ ifneq ($(SUBARCH),$(ARCH))
    endif
    endif

    +ifndef CONFIG_FUNCTION_TRACER
    cflags-y := -ffunction-sections
    +else
    +cflags-y := -mlong-calls
    +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 40a8c17..5f8ebcf 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 f228868..38e704a 100644
    --- a/arch/mips/kernel/Makefile
    +++ b/arch/mips/kernel/Makefile
    @@ -10,6 +10,7 @@ obj-y += cpu-probe.o branch.o entry.o genex.o irq.o process.o \

    ifdef CONFIG_FUNCTION_TRACER
    CFLAGS_REMOVE_trace_clock.o = -pg
    +CFLAGS_REMOVE_early_printk.o = -pg
    endif

    obj-$(CONFIG_CEVT_BCM1480) += cevt-bcm1480.o
    @@ -29,6 +30,7 @@ obj-$(CONFIG_STACKTRACE) += stacktrace.o
    obj-$(CONFIG_MODULES) += mips_ksyms.o module.o

    obj-$(CONFIG_FTRACE) += trace_clock.o
    +obj-$(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
    diff --git a/arch/mips/kernel/mcount.S b/arch/mips/kernel/mcount.S
    new file mode 100644
    index 0000000..cebcc3c
    --- /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 225755d..1d04807 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
    --
    1.6.2.1


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