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SubjectRe: [PATCH 1/6] nds32/ftrace: Support static function tracer
On Wed, 15 Aug 2018 17:35:18 +0800
Zong Li <zong@andestech.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@andestech.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);

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