linux-kernel - Re: [PATCH 1/3 v5] ftrace: Have the callbacks receive a struct ftrace_regs instead of pt

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Message-Id: <1605200348.x55f7x9h4h.naveen@linux.ibm.com>
Date:   Thu, 12 Nov 2020 22:38:53 +0530
From:   "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>
To:     linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 1/3 v5] ftrace: Have the callbacks receive a struct
 ftrace_regs instead of pt_regs

Hi Steven,

Steven Rostedt wrote:
> From: "Steven Rostedt (VMware)" <rostedt@...dmis.org>
> 
> In preparation to have arguments of a function passed to callbacks attached
> to functions as default, change the default callback prototype to receive a
> struct ftrace_regs as the forth parameter instead of a pt_regs.
> 
> For callbacks that set the FL_SAVE_REGS flag in their ftrace_ops flags, they
> will now need to get the pt_regs via a ftrace_get_regs() helper call. If
> this is called by a callback that their ftrace_ops did not have a
> FL_SAVE_REGS flag set, it that helper function will return NULL.
> 
> This will allow the ftrace_regs to hold enough just to get the parameters
> and stack pointer, but without the worry that callbacks may have a pt_regs
> that is not completely filled.
> 
> Reviewed-by: Masami Hiramatsu <mhiramat@...nel.org>
> Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
> ---
>  arch/x86/kernel/kprobes/ftrace.c  |  3 ++-
>  fs/pstore/ftrace.c                |  2 +-
>  include/linux/ftrace.h            | 16 ++++++++++++++--
>  include/linux/kprobes.h           |  2 +-
>  kernel/livepatch/patch.c          |  3 ++-
>  kernel/trace/ftrace.c             | 27 +++++++++++++++------------
>  kernel/trace/trace_event_perf.c   |  2 +-
>  kernel/trace/trace_events.c       |  2 +-
>  kernel/trace/trace_functions.c    |  9 ++++-----
>  kernel/trace/trace_irqsoff.c      |  2 +-
>  kernel/trace/trace_sched_wakeup.c |  2 +-
>  kernel/trace/trace_selftest.c     | 20 +++++++++++---------
>  kernel/trace/trace_stack.c        |  2 +-
>  13 files changed, 55 insertions(+), 37 deletions(-)
> 

<snip>

> diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
> index 629abaf25681..be73350955e4 100644
> --- a/include/linux/kprobes.h
> +++ b/include/linux/kprobes.h
> @@ -345,7 +345,7 @@ static inline void wait_for_kprobe_optimizer(void) 
> { }
>  #endif /* CONFIG_OPTPROBES */
>  #ifdef CONFIG_KPROBES_ON_FTRACE
>  extern void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
> -				  struct ftrace_ops *ops, struct pt_regs *regs);
> +				  struct ftrace_ops *ops, struct ftrace_regs *fregs);

This breaks the build on non-x86 architectures that support 
KPROBES_ON_FTRACE.

- Naveen