linux-kernel - Re: [PATCH 1/3 v7] ftrace: Have the callbacks receive a struct ftrace_regs instead of pt

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Message-ID: <X7ZRiPw136nZE3JL@alley>
Date:   Thu, 19 Nov 2020 12:05:44 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-kernel@...r.kernel.org,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Jiri Kosina <jikos@...nel.org>, Miroslav Benes <mbenes@...e.cz>
Subject: Re: [PATCH 1/3 v7] ftrace: Have the callbacks receive a struct
 ftrace_regs instead of pt_regs

On Fri 2020-11-13 12:18:12, 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.
> 
> diff --git a/arch/csky/kernel/probes/ftrace.c b/arch/csky/kernel/probes/ftrace.c
> index f30b179924ef..ae2b1c7b3b5c 100644
> --- a/arch/csky/kernel/probes/ftrace.c
> +++ b/arch/csky/kernel/probes/ftrace.c
> @@ -11,17 +11,19 @@ int arch_check_ftrace_location(struct kprobe *p)
>  
>  /* Ftrace callback handler for kprobes -- called under preepmt disabed */
>  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)
>  {
>  	int bit;
>  	bool lr_saver = false;
>  	struct kprobe *p;
>  	struct kprobe_ctlblk *kcb;
> +	struct pt_regs *regs;
>  
>  	bit = ftrace_test_recursion_trylock(ip, parent_ip);
>  	if (bit < 0)
>  		return;
>  
> +	regs = ftrace_get_regs(fregs);

Should we check for NULL here?
Same in all callers?

>  	preempt_disable_notrace();
>  	p = get_kprobe((kprobe_opcode_t *)ip);
>  	if (!p) {

Otherwise, the patch is pretty strightforard and looks good to me.

Best Regards,
Petr