linux-kernel - Re: [PATCH 1/6] nds32/ftrace: Support static function tracer

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Message-ID: <20180815161121.06c9b531@gandalf.local.home>
Date:   Wed, 15 Aug 2018 16:11:21 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Zong Li <zong@...estech.com>
Cc:     <green.hu@...il.com>, <deanbo422@...il.com>, <mingo@...hat.com>,
        <arnd@...db.de>, <linux-kernel@...r.kernel.org>,
        <zongbox@...il.com>, <greentime@...estech.com>
Subject: Re: [PATCH 1/6] nds32/ftrace: Support static function tracer

On Wed, 15 Aug 2018 17:35:18 +0800
Zong Li <zong@...estech.com> wrote:

> This patch support the static function tracer. On nds32 ABI, we need to
> always push return address to stack for __builtin_return_address can
> work correctly, otherwise, it will get the wrong value of $lp at leaf
> function.
> 
> Signed-off-by: Zong Li <zong@...estech.com>
> ---
>  arch/nds32/Kconfig              |  1 +
>  arch/nds32/Makefile             |  4 ++++
>  arch/nds32/include/asm/ftrace.h | 20 ++++++++++++++++++++
>  arch/nds32/kernel/Makefile      |  6 ++++++
>  arch/nds32/kernel/ftrace.c      | 28 ++++++++++++++++++++++++++++
>  5 files changed, 59 insertions(+)
>  create mode 100644 arch/nds32/include/asm/ftrace.h
>  create mode 100644 arch/nds32/kernel/ftrace.c
> 
> diff --git a/arch/nds32/Kconfig b/arch/nds32/Kconfig
> index 34f7222..af30e1a 100644
> --- a/arch/nds32/Kconfig
> +++ b/arch/nds32/Kconfig
> @@ -40,6 +40,7 @@ config NDS32
>  	select NO_IOPORT_MAP
>  	select RTC_LIB
>  	select THREAD_INFO_IN_TASK
> +	select HAVE_FUNCTION_TRACER
>  	help
>  	  Andes(nds32) Linux support.
>  
> diff --git a/arch/nds32/Makefile b/arch/nds32/Makefile
> index 031c676..3ca8172 100644
> --- a/arch/nds32/Makefile
> +++ b/arch/nds32/Makefile
> @@ -5,6 +5,10 @@ KBUILD_DEFCONFIG := defconfig
>  
>  comma = ,
>  
> +ifdef CONFIG_FUNCTION_TRACER
> +arch-y += -malways-save-lp -mno-relax
> +endif
> +
>  KBUILD_CFLAGS	+= $(call cc-option, -mno-sched-prolog-epilog)
>  KBUILD_CFLAGS	+= -mcmodel=large
>  
> diff --git a/arch/nds32/include/asm/ftrace.h b/arch/nds32/include/asm/ftrace.h
> new file mode 100644
> index 0000000..bac7657
> --- /dev/null
> +++ b/arch/nds32/include/asm/ftrace.h
> @@ -0,0 +1,20 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +
> +#ifndef __ASM_NDS32_FTRACE_H
> +#define __ASM_NDS32_FTRACE_H
> +
> +#ifdef CONFIG_FUNCTION_TRACER
> +
> +#define HAVE_FUNCTION_GRAPH_FP_TEST
> +
> +#define MCOUNT_ADDR ((unsigned long)(_mcount))
> +/* mcount call is composed of three instructions:
> + * sethi + ori + jral
> + */
> +#define MCOUNT_INSN_SIZE 12
> +
> +extern void _mcount(unsigned long parent_ip);
> +
> +#endif /* CONFIG_FUNCTION_TRACER */
> +
> +#endif /* __ASM_NDS32_FTRACE_H */
> diff --git a/arch/nds32/kernel/Makefile b/arch/nds32/kernel/Makefile
> index 4279274..27cded3 100644
> --- a/arch/nds32/kernel/Makefile
> +++ b/arch/nds32/kernel/Makefile
> @@ -21,3 +21,9 @@ extra-y := head.o vmlinux.lds
>  
>  
>  obj-y				+= vdso/
> +
> +obj-$(CONFIG_FUNCTION_TRACER)   += ftrace.o
> +
> +ifdef CONFIG_FUNCTION_TRACER
> +CFLAGS_REMOVE_ftrace.o = $(CC_FLAGS_FTRACE)
> +endif
> diff --git a/arch/nds32/kernel/ftrace.c b/arch/nds32/kernel/ftrace.c
> new file mode 100644
> index 0000000..563f64c
> --- /dev/null
> +++ b/arch/nds32/kernel/ftrace.c
> @@ -0,0 +1,28 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include <linux/ftrace.h>
> +#include <linux/uaccess.h>
> +#include <asm/cacheflush.h>
> +
> +extern void (*ftrace_trace_function)(unsigned long, unsigned long,
> +				     struct ftrace_ops*, struct pt_regs*);
> +
> +noinline void __naked ftrace_stub(unsigned long ip, unsigned long parent_ip,
> +				  struct ftrace_ops *op, struct pt_regs *regs)
> +{
> +	__asm__ ("");  /* avoid to optimize as pure function */
> +}
> +
> +noinline void _mcount(unsigned long parent_ip)
> +{

Wow! The NDS32 arch allows for _mcount to be a C function! That's
nice :-)

-- Steve

> +	/* save all state by the compiler prologue */
> +
> +	unsigned long ip = (unsigned long)__builtin_return_address(0);
> +
> +	if (ftrace_trace_function != ftrace_stub)
> +		ftrace_trace_function(ip - MCOUNT_INSN_SIZE, parent_ip,
> +				      NULL, NULL);
> +
> +	/* restore all state by the compiler epilogue */
> +}
> +EXPORT_SYMBOL(_mcount);