Re: [PATCH v6 6/7] arm64: ftrace: Add CALLER_ADDRx macros

[AKASHI Takahiro]

On 03/14/2014 03:07 AM, Steven Rostedt wrote:
> 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.

I'm going to create a separate RFC, including fixes for other archs.

-Takahiro AKASHI

> -- Steve
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