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

Masami Hiramatsu
2018-02-05T16:33:22Z

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

> From: "Steven Rostedt (VMware)" <rostedt@goodmis.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@goodmis.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@kernel.org>