linux-kernel - Re: [PATCH] arm64: Add __exception_irq_entry definition for function graph

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Date:	Wed, 12 Aug 2015 17:53:24 +0100
From:	Will Deacon <will.deacon@....com>
To:	Jungseok Lee <jungseoklee85@...il.com>
Cc:	Catalin Marinas <Catalin.Marinas@....com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	AKASHI Takahiro <takahiro.akashi@...aro.org>,
	Marc Zyngier <Marc.Zyngier@....com>,
	Rabin Vincent <rabin@....in>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH] arm64: Add __exception_irq_entry definition for function
 graph

On Wed, Aug 12, 2015 at 04:18:49PM +0100, Jungseok Lee wrote:
> On Aug 13, 2015, at 12:02 AM, Will Deacon wrote:
> > On Wed, Aug 12, 2015 at 03:16:19PM +0100, Jungseok Lee wrote:
> >> diff --git a/arch/arm64/include/asm/traps.h b/arch/arm64/include/asm/traps.h
> >> index 232e4ba..0cc2f29 100644
> >> --- a/arch/arm64/include/asm/traps.h
> >> +++ b/arch/arm64/include/asm/traps.h
> >> @@ -34,13 +34,32 @@ struct undef_hook {
> >> void register_undef_hook(struct undef_hook *hook);
> >> void unregister_undef_hook(struct undef_hook *hook);
> >> 
> >> +#ifdef CONFIG_FUNCTION_GRAPH_TRACER
> >> +static inline int __in_irqentry_text(unsigned long ptr)
> >> +{
> >> +	extern char __irqentry_text_start[];
> >> +	extern char __irqentry_text_end[];
> >> +
> >> +	return ptr >= (unsigned long)&__irqentry_text_start &&
> >> +	       ptr < (unsigned long)&__irqentry_text_end;
> >> +}
> >> +#else
> >> +static inline int __in_irqentry_text(unsigned long ptr)
> >> +{
> >> +	return 0;
> >> +}
> >> +#endif
> >> +
> >> static inline int in_exception_text(unsigned long ptr)
> >> {
> >> 	extern char __exception_text_start[];
> >> 	extern char __exception_text_end[];
> >> +	int in;
> >> +
> >> +	in = ptr >= (unsigned long)&__exception_text_start &&
> >> +	     ptr < (unsigned long)&__exception_text_end;
> >> 
> >> -	return ptr >= (unsigned long)&__exception_text_start &&
> >> -	       ptr < (unsigned long)&__exception_text_end;
> >> +	return in ? : __in_irqentry_text(ptr);
> >> }
> > 
> > On arm64, this function is only called from dump_backtrace, so I'm
> > struggling to see why this change makes any difference to the ftrace
> > output.
> > 
> > What am I missing?
> 
> As you mentioned, the above hunk does not change the ftrace behavior.
> 
> The first diff directly affects the first condition check in print_graph_irq
> function in kernel/trace/trace_functions_graph.c. The code snippet is as follows.
> 
> if (addr < (unsigned long)__irqentry_text_start ||
> 	addr >= (unsigned long)__irqentry_text_end)
> 	return;
> 
> I hope it would be helpful.

Gotcha, thanks for the explanation.

Will
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