linux-kernel - Re: [PATCH 04/18] tracing/x86: Add arch_get_func

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Date:   Tue, 6 Feb 2018 01:33:22 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Tom Zanussi <tom.zanussi@...ux.intel.com>,
        linux-rt-users@...r.kernel.org, linux-trace-users@...r.kernel.org,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Clark Williams <williams@...hat.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>
Subject: Re: [PATCH 04/18] tracing/x86: Add arch_get_func_args() function

On Fri, 02 Feb 2018 18:05:02 -0500
Steven Rostedt <rostedt@...dmis.org> wrote:

> From: "Steven Rostedt (VMware)" <rostedt@...dmis.org>
> 
> Add function to get the function arguments from pt_regs.
> 

Can we make it an independent feature in asm/ptrace.h so that
other components (like kprobe-event) share it?
E.g.

static inline unsigned long regs_get_func_arg(struct pt_regs *regs,
                                              unsigned int n)
{
	unsigned int offs[] = {
#ifdef CONFIG_X86_64
	offsetof(typeof(regs),di),
	offsetof(typeof(regs),si),
	offsetof(typeof(regs),dx),
	offsetof(typeof(regs),cx),
	offsetof(typeof(regs),r8),
	offsetof(typeof(regs),r9),
#else
	offsetof(typeof(regs),ax),
	offsetof(typeof(regs),dx),
	offsetof(typeof(regs),cx),
#endif
	};

	if (unlikely(n >= ARRAY_SIZE(offs))
		return 0;
	return *(unsigned long *)((unsigned long)regs + offs[n]);
}

And HAVE_REGS_GET_FUNC_ARG indicates this is defined on that arch.

Thank you,

> Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
> ---
>  arch/x86/kernel/ftrace.c | 28 ++++++++++++++++++++++++++++
>  1 file changed, 28 insertions(+)
> 
> diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
> index 01ebcb6f263e..5e845c8cf89d 100644
> --- a/arch/x86/kernel/ftrace.c
> +++ b/arch/x86/kernel/ftrace.c
> @@ -46,6 +46,34 @@ int ftrace_arch_code_modify_post_process(void)
>  	return 0;
>  }
>  
> +int arch_get_func_args(struct pt_regs *regs,
> +		       int start, int end, long *args)
> +{
> +#ifdef CONFIG_X86_64
> +# define MAX_ARGS 6
> +# define INIT_REGS				\
> +	{	regs->di, regs->si, regs->dx,	\
> +		regs->cx, regs->r8, regs->r9	\
> +	}
> +#else
> +# define MAX_ARGS 3
> +# define INIT_REGS				\
> +	{	regs->ax, regs->dx, regs->cx	}
> +#endif
> +	if (!regs)
> +		return MAX_ARGS;
> +
> +	{
> +		long pt_args[] = INIT_REGS;
> +		int i;
> +
> +		for (i = start; i <= end && i < MAX_ARGS; i++)
> +			args[i - start] = pt_args[i];
> +
> +		return i - start;
> +	}
> +}
> +
>  union ftrace_code_union {
>  	char code[MCOUNT_INSN_SIZE];
>  	struct {
> -- 
> 2.15.1
> 
> 


-- 
Masami Hiramatsu <mhiramat@...nel.org>