Re: [PATCH 3/4] ftrace: abstract DYNAMIC_FTRACE_WITH_ARGS accesses

[Masami Hiramatsu (Google) <mhiramat@kernel.org>]

Hi Mark,

On Mon, 24 Oct 2022 15:08:45 +0100
Mark Rutland <mark.rutland@arm.com> wrote:

> In subsequent patches we'll arrange for architectures to have an
> ftrace_regs which is entirely distinct from pt_regs. In preparation for
> this, we need to minimize the use of pt_regs to where strictly necessary
> in the core ftrace code.
> 
> This patch adds new ftrace_regs_{get,set}_*() helpers which can be used
> to manipulate ftrace_regs. When CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS=y,
> these can always be used on any ftrace_regs, and when
> CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS=n these can be used when regs are
> available. A new ftrace_regs_has_args(fregs) helper is added which code
> can use to check when these are usable.

Can you also add the ftrace_regs_query_register_offset() as a wrapper of
regs_query_register_offset()? I would like to use it for fprobe_events.

Thank you,

> 
> Co-developed-by: Florent Revest <revest@chromium.org>
> Signed-off-by: Florent Revest <revest@chromium.org>
> Signed-off-by: Mark Rutland <mark.rutland@arm.com>
> Cc: Masami Hiramatsu <mhiramat@kernel.org>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> ---
>  arch/powerpc/include/asm/ftrace.h | 17 +++++++++++++++++
>  arch/s390/include/asm/ftrace.h    | 17 +++++++++++++++++
>  arch/x86/include/asm/ftrace.h     | 14 ++++++++++++++
>  include/linux/ftrace.h            | 27 +++++++++++++++++++++++++++
>  kernel/trace/Kconfig              |  6 +++---
>  5 files changed, 78 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/ftrace.h b/arch/powerpc/include/asm/ftrace.h
> index c3eb48f67566..faecb20d78bf 100644
> --- a/arch/powerpc/include/asm/ftrace.h
> +++ b/arch/powerpc/include/asm/ftrace.h
> @@ -44,6 +44,23 @@ ftrace_regs_set_instruction_pointer(struct ftrace_regs *fregs,
>  	regs_set_return_ip(&fregs->regs, ip);
>  }
>  
> +static __always_inline unsigned long
> +ftrace_regs_get_instruction_pointer(const struct ftrace_regs *fregs)
> +{
> +	return instruction_pointer(&fregs->regs)
> +}
> +
> +#define ftrace_regs_get_argument(fregs, n) \
> +	regs_get_kernel_argument(&(fregs)->regs, n)
> +#define ftrace_regs_get_stack_pointer(fregs) \
> +	kernel_stack_pointer(&(fregs)->regs)
> +#define ftrace_regs_return_value(fregs) \
> +	regs_return_value(&(fregs)->regs)
> +#define ftrace_regs_set_return_value(fregs, ret) \
> +	regs_set_return_value(&(fregs)->regs, ret)
> +#define ftrace_override_function_with_return(fregs) \
> +	override_function_with_return(&(fregs)->regs)
> +
>  struct ftrace_ops;
>  
>  #define ftrace_graph_func ftrace_graph_func
> diff --git a/arch/s390/include/asm/ftrace.h b/arch/s390/include/asm/ftrace.h
> index b8957882404f..5fdc806458aa 100644
> --- a/arch/s390/include/asm/ftrace.h
> +++ b/arch/s390/include/asm/ftrace.h
> @@ -54,6 +54,12 @@ static __always_inline struct pt_regs *arch_ftrace_get_regs(struct ftrace_regs *
>  	return NULL;
>  }
>  
> +static __always_inline unsigned long
> +ftrace_regs_get_instruction_pointer(const struct ftrace_regs *fregs)
> +{
> +	return fregs->regs.psw.addr;
> +}
> +
>  static __always_inline void
>  ftrace_regs_set_instruction_pointer(struct ftrace_regs *fregs,
>  				    unsigned long ip)
> @@ -61,6 +67,17 @@ ftrace_regs_set_instruction_pointer(struct ftrace_regs *fregs,
>  	fregs->regs.psw.addr = ip;
>  }
>  
> +#define ftrace_regs_get_argument(fregs, n) \
> +	regs_get_kernel_argument(&(fregs)->regs, n)
> +#define ftrace_regs_get_stack_pointer(fregs) \
> +	kernel_stack_pointer(&(fregs)->regs)
> +#define ftrace_regs_return_value(fregs) \
> +	regs_return_value(&(fregs)->regs)
> +#define ftrace_regs_set_return_value(fregs, ret) \
> +	regs_set_return_value(&(fregs)->regs, ret)
> +#define ftrace_override_function_with_return(fregs) \
> +	override_function_with_return(&(fregs)->regs)
> +
>  /*
>   * When an ftrace registered caller is tracing a function that is
>   * also set by a register_ftrace_direct() call, it needs to be
> diff --git a/arch/x86/include/asm/ftrace.h b/arch/x86/include/asm/ftrace.h
> index b73e858bd96f..b3737b42e8a1 100644
> --- a/arch/x86/include/asm/ftrace.h
> +++ b/arch/x86/include/asm/ftrace.h
> @@ -51,6 +51,20 @@ arch_ftrace_get_regs(struct ftrace_regs *fregs)
>  #define ftrace_regs_set_instruction_pointer(fregs, _ip)	\
>  	do { (fregs)->regs.ip = (_ip); } while (0)
>  
> +#define ftrace_regs_get_instruction_pointer(fregs) \
> +	((fregs)->regs.ip)
> +
> +#define ftrace_regs_get_argument(fregs, n) \
> +	regs_get_kernel_argument(&(fregs)->regs, n)
> +#define ftrace_regs_get_stack_pointer(fregs) \
> +	kernel_stack_pointer(&(fregs)->regs)
> +#define ftrace_regs_return_value(fregs) \
> +	regs_return_value(&(fregs)->regs)
> +#define ftrace_regs_set_return_value(fregs, ret) \
> +	regs_set_return_value(&(fregs)->regs, ret)
> +#define ftrace_override_function_with_return(fregs) \
> +	override_function_with_return(&(fregs)->regs)
> +
>  struct ftrace_ops;
>  #define ftrace_graph_func ftrace_graph_func
>  void ftrace_graph_func(unsigned long ip, unsigned long parent_ip,
> diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
> index e9905f741916..3b13e3c21438 100644
> --- a/include/linux/ftrace.h
> +++ b/include/linux/ftrace.h
> @@ -125,6 +125,33 @@ static __always_inline struct pt_regs *ftrace_get_regs(struct ftrace_regs *fregs
>  	return arch_ftrace_get_regs(fregs);
>  }
>  
> +/*
> + * When true, the ftrace_regs_{get,set}_*() functions may be used on fregs.
> + * Note: this can be true even when ftrace_get_regs() cannot provide a pt_regs.
> + */
> +static __always_inline bool ftrace_regs_has_args(struct ftrace_regs *fregs)
> +{
> +	if (IS_ENABLED(CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS))
> +		return true;
> +
> +	return ftrace_get_regs(fregs) != NULL;
> +}
> +
> +#ifndef CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS
> +#define ftrace_regs_get_instruction_pointer(fregs) \
> +	instruction_pointer(ftrace_get_regs(fregs))
> +#define ftrace_regs_get_argument(fregs, n) \
> +	regs_get_kernel_argument(ftrace_get_regs(fregs), n)
> +#define ftrace_regs_get_stack_pointer(fregs) \
> +	kernel_stack_pointer(ftrace_get_regs(fregs))
> +#define ftrace_regs_return_value(fregs) \
> +	regs_return_value(ftrace_get_regs(fregs))
> +#define ftrace_regs_set_return_value(fregs, ret) \
> +	regs_set_return_value(ftrace_get_regs(fregs), ret)
> +#define ftrace_override_function_with_return(fregs) \
> +	override_function_with_return(ftrace_get_regs(fregs))
> +#endif
> +
>  typedef void (*ftrace_func_t)(unsigned long ip, unsigned long parent_ip,
>  			      struct ftrace_ops *op, struct ftrace_regs *fregs);
>  
> diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
> index e9e95c790b8e..2c6611c13f99 100644
> --- a/kernel/trace/Kconfig
> +++ b/kernel/trace/Kconfig
> @@ -46,10 +46,10 @@ config HAVE_DYNAMIC_FTRACE_WITH_ARGS
>  	bool
>  	help
>  	 If this is set, then arguments and stack can be found from
> -	 the pt_regs passed into the function callback regs parameter
> +	 the ftrace_regs passed into the function callback regs parameter
>  	 by default, even without setting the REGS flag in the ftrace_ops.
> -	 This allows for use of regs_get_kernel_argument() and
> -	 kernel_stack_pointer().
> +	 This allows for use of ftrace_regs_get_argument() and
> +	 ftrace_regs_get_stack_pointer().
>  
>  config HAVE_DYNAMIC_FTRACE_NO_PATCHABLE
>  	bool
> -- 
> 2.30.2
> 


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>

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