linux-kernel - Re: [PATCH 3/3] kprobes/x86: stacktool: ignore kretprobe_trampoline

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Date:	Fri, 18 Sep 2015 09:04:30 -0500
From:	Josh Poimboeuf <jpoimboe@...hat.com>
To:	Chris J Arges <chris.j.arges@...onical.com>
Cc:	x86@...nel.org, tglx@...utronix.de, mingo@...hat.com,
	hpa@...or.com, live-patching@...r.kernel.org,
	linux-kernel@...r.kernel.org, mmarek@...e.cz, peterz@...radead.org,
	luto@...nel.org, bp@...en8.de, torvalds@...ux-foundation.org,
	andi@...stfloor.org, palves@...hat.com, namhyung@...il.com,
	bernd@...rovitsch.priv.at, akpm@...ux-foundation.org,
	konrad.wilk@...cle.com, boris.ostrovsky@...cle.com,
	david.vrabel@...rix.com, jeremy@...p.org, chrisw@...s-sol.org,
	akataria@...are.com, rusty@...tcorp.com.au,
	herbert@...dor.apana.org.au, davem@...emloft.net, pavel@....cz,
	rjw@...ysocki.net, len.brown@...el.com, matt.fleming@...el.com,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Petr Mladek <pmladek@...e.cz>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Eugene Shatokhin <eugene.shatokhin@...alab.ru>,
	"Steven Rostedt (Red Hat)" <rostedt@...dmis.org>
Subject: Re: [PATCH 3/3] kprobes/x86: stacktool: ignore
 kretprobe_trampoline_holder

On Thu, Sep 17, 2015 at 05:14:37PM -0500, Chris J Arges wrote:
> The function kretprobe_trampoline_holder isn't called explicility and therefore
> should be ignored by stacktool.
> 
> Signed-off-by: Chris J Arges <chris.j.arges@...onical.com>
> ---
>  arch/x86/kernel/kprobes/core.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
> index 1deffe6..3ade909 100644
> --- a/arch/x86/kernel/kprobes/core.c
> +++ b/arch/x86/kernel/kprobes/core.c
> @@ -49,6 +49,7 @@
>  #include <linux/kdebug.h>
>  #include <linux/kallsyms.h>
>  #include <linux/ftrace.h>
> +#include <linux/stacktool.h>
>  
>  #include <asm/cacheflush.h>
>  #include <asm/desc.h>
> @@ -704,6 +705,7 @@ static void __used kretprobe_trampoline_holder(void)
>  }
>  NOKPROBE_SYMBOL(kretprobe_trampoline_holder);
>  NOKPROBE_SYMBOL(kretprobe_trampoline);
> +STACKTOOL_IGNORE_FUNC(kretprobe_trampoline_holder);
>  
>  /*
>   * Called from kretprobe_trampoline
> -- 
> 1.9.1

The kretprobe trampoline isn't called directly but it can still be
executed at runtime.  I think we should make sure it does the "right
thing" with respect to frame pointers and CFI before telling stacktool
to ignore it.

-- 
Josh
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