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

Steven Rostedt
2018-02-05T17:06:12Z

On Tue, 6 Feb 2018 01:33:22 +0900
Masami Hiramatsu <mhiramat@kernel.org> wrote:

> 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?

Most definitely!

> 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]);

I like having the function I used, because it could also handle
arguments in the stack (although I didn't implement that yet). But this
would still be a nice helper function.

-- Steve

> }
>
> 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
> >
> >
>
>