linux-kernel - Re: [PATCH v2 1/2] arm64: implement FTRACE_WITH

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Date:	Fri, 15 Jul 2016 14:36:16 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Torsten Duwe <duwe@....de>
Cc:	Josh Poimboeuf <jpoimboe@...hat.com>,
	Petr Mladek <pmladek@...e.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>, takahiro.akashi@...aro.org,
	Jungseok Lee <jungseoklee85@...il.com>,
	Arnd Bergmann <arnd@...db.de>,
	Li Bin <huawei.libin@...wei.com>,
	Ingo Molnar <mingo@...hat.com>,
	Christopher Li <sparse@...isli.org>,
	Jiri Kosina <jikos@...nel.org>, andrew.wafaa@....com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	live-patching@...r.kernel.org, linux-arch@...r.kernel.org,
	linux-sparse@...r.kernel.org
Subject: Re: [PATCH v2 1/2] arm64: implement FTRACE_WITH_REGS

On Sat, 9 Jul 2016 11:06:32 +0200
Torsten Duwe <duwe@....de> wrote:


> Maybe the code in question can be replaced with the change below, now that
> there is a preprocessor define in V2?
> (untested)
> 
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index 3f743b1..695a646 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -2423,6 +2423,12 @@ ftrace_code_disable(struct module *mod, struct dyn_ftrace *rec)
>  	if (unlikely(ftrace_disabled))
>  		return 0;
>  
> +#ifdef CC_USING_PROLOG_PAD
> +	/* If the compiler already generated NOPs instead of
> +	 * calls to mcount, we're done here.
> +	*/
> +	return 1;
> +#endif

I really hate adding #ifdef's like this in generic code if the arch can
handle it with some other means.

-- Steve


>  	ret = ftrace_make_nop(mod, rec, MCOUNT_ADDR);
>  	if (ret) {
>  		ftrace_bug(ret, rec);