linux-kernel - Re: [PATCH 1/3] ftrace: introdue ftrace_call

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Message-ID: <alpine.LSU.2.21.1908201118190.9536@pobox.suse.cz>
Date:   Tue, 20 Aug 2019 11:27:38 +0200 (CEST)
From:   Miroslav Benes <mbenes@...e.cz>
To:     Jisheng Zhang <Jisheng.Zhang@...aptics.com>
cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mark Rutland <mark.rutland@....com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Torsten Duwe <duwe@...e.de>
Subject: Re: [PATCH 1/3] ftrace: introdue ftrace_call_init

Hi,

On Mon, 19 Aug 2019, Jisheng Zhang wrote:

> On some arch, the FTRACE_WITH_REGS is implemented with gcc's
>  -fpatchable-function-entry (=2), gcc adds 2 NOPs at the beginning
> of each function, so this makes the MCOUNT_ADDR useless. In ftrace
> common framework, MCOUNT_ADDR is mostly used to "init" the nop, so
> let's introcude ftrace_call_init().
> 
> Signed-off-by: Jisheng Zhang <Jisheng.Zhang@...aptics.com>
> ---
>  include/linux/ftrace.h | 1 +
>  kernel/trace/ftrace.c  | 4 ++++
>  2 files changed, 5 insertions(+)
> 
> diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
> index 8a8cb3c401b2..8175ffb671f0 100644
> --- a/include/linux/ftrace.h
> +++ b/include/linux/ftrace.h
> @@ -458,6 +458,7 @@ extern void ftrace_regs_caller(void);
>  extern void ftrace_call(void);
>  extern void ftrace_regs_call(void);
>  extern void mcount_call(void);
> +extern int ftrace_call_init(struct module *mod, struct dyn_ftrace *rec);
>  
>  void ftrace_modify_all_code(int command);
>  
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index eca34503f178..9df5a66a6811 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -2500,7 +2500,11 @@ ftrace_code_disable(struct module *mod, struct dyn_ftrace *rec)
>  	if (unlikely(ftrace_disabled))
>  		return 0;
>  
> +#ifdef MCOUNT_ADDR
>  	ret = ftrace_make_nop(mod, rec, MCOUNT_ADDR);
> +#else
> +	ret = ftrace_call_init(mod, rec);
> +#endif
>  	if (ret) {
>  		ftrace_bug_type = FTRACE_BUG_INIT;
>  		ftrace_bug(ret, rec);

I may be missing something, but the patch does not seem to be complete. 
There is no ftrace_call_init() implemented. MCOUNT_ADDR is still defined, 
so it does not change much. I don't think it is what Mark had in his mind.

Miroslav