linux-kernel - Re: [PATCH v6 6/7] arm64: ftrace: Add CALLER

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Date:	Thu, 13 Mar 2014 14:07:50 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Will Deacon <will.deacon@....com>
Cc:	AKASHI Takahiro <takahiro.akashi@...aro.org>,
	"fweisbec@...il.com" <fweisbec@...il.com>,
	"mingo@...hat.com" <mingo@...hat.com>,
	Catalin Marinas <Catalin.Marinas@....com>,
	"tim.bird@...ymobile.com" <tim.bird@...ymobile.com>,
	"gkulkarni@...iumnetworks.com" <gkulkarni@...iumnetworks.com>,
	"dsaxena@...aro.org" <dsaxena@...aro.org>,
	"arndb@...db.de" <arndb@...db.de>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 6/7] arm64: ftrace: Add CALLER_ADDRx macros

On Thu, 2014-03-13 at 15:54 +0000, Will Deacon wrote:
> On Thu, Mar 13, 2014 at 10:13:49AM +0000, AKASHI Takahiro wrote:
> > CALLER_ADDRx returns caller's address at specified level in call stacks.
> > They are used for several tracers like irqsoff and preemptoff.
> > Strange to say, however, they are refered even without FTRACE.
> > 
> > Please note that this implementation assumes that we have frame pointers.
> > (which means kernel should be compiled with -fno-omit-frame-pointer.)
> 
> How do you ensure that -fno-omit-frame-pointer is passed?

Perhaps -pg does the same thing?

> > +#define HAVE_ARCH_CALLER_ADDR
> > +
> > +#define CALLER_ADDR0 ((unsigned long)__builtin_return_address(0))
> > +#define CALLER_ADDR1 ((unsigned long)return_address(1))
> > +#define CALLER_ADDR2 ((unsigned long)return_address(2))
> > +#define CALLER_ADDR3 ((unsigned long)return_address(3))
> > +#define CALLER_ADDR4 ((unsigned long)return_address(4))
> > +#define CALLER_ADDR5 ((unsigned long)return_address(5))
> > +#define CALLER_ADDR6 ((unsigned long)return_address(6))
> 
> Could we change the core definitions of these macros (in linux/ftrace.h) to
> use return_address, then provide an overridable version of return_address
> that defaults to __builtin_return_address, instead of copy-pasting this
> sequence?

We could add a new macro:

/* All archs should have this, but we define it for consistency */
#ifndef ftrace_return_address0
# define ftrace_return_address0  __builtin_return_address(0)
#endif
/* Archs may use other ways for ADDR1 and beyond */
#ifndef ftrace_return_address
# define ftrace_return_address(n) __builtin_return_address(n)
#endif

And then have:

#define CALLER_ADDR0 ((unsigned long)ftrace_return_address0)
#define CALLER_ADDR1 ((unsigned long)ftrace_return_address(1))
[...]

And then you would only need to redefine ftrace_return_address.

-- Steve


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