Re: [PATCH 04/18] tracing/x86: Add arch_get_func_args() function

[Masami Hiramatsu]

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

> From: "Steven Rostedt (VMware)" <rostedt@xxxxxxxxxxx>
> 
> 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@xxxxxxxxxxx>
> ---
>  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@xxxxxxxxxx>