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

[AKASHI Takahiro]

On 03/14/2014 07:09 PM, Will Deacon wrote:
> On Fri, Mar 14, 2014 at 03:00:14AM +0000, AKASHI Takahiro wrote:
> > On 03/14/2014 12:54 AM, 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?
> >
> > arm64 selects ARCH_WANT_FRAME_POINTERS, then FRAME_POINTER is on (lib/Kconfig.debug)
> > and so -fno-omit-frame-pointer is appended (${TOP}/Makefile).
> > (stacktrace.c also assumes FRAME_POINTER.)
> >
> > Do you think I should remove the comment above?
>
> Yes please, it sounds like everything is taken care of automatically, so
> there's no need to scare people in the commit message!

OK, I will do so.

Thanks,
-Takahiro AKASHI

> > > > diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h
> > > > index ed5c448..c44c4b1 100644
> > > > --- a/arch/arm64/include/asm/ftrace.h
> > > > +++ b/arch/arm64/include/asm/ftrace.h
> > > > @@ -18,6 +18,7 @@
> > > >
> > > >    #ifndef __ASSEMBLY__
> > > >    extern void _mcount(unsigned long);
> > > > +extern void *return_address(unsigned int);
> > > >
> > > >    struct dyn_arch_ftrace {
> > > >    	/* No extra data needed for arm64 */
> > > > @@ -33,6 +34,16 @@ static inline unsigned long ftrace_call_adjust(unsigned long addr)
> > > >    	 */
> > > >    	return addr;
> > > >    }
> > > > -#endif /* __ASSEMBLY__ */
> > > > +
> > > > +#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?
> >
> > I think I understand what you mean, and will try to post a separate RFC,
> > but I also want to hold off this change on this patch since such a change
> > may raise a small controversy from other archs' maintainers.
>
> I don't see anything controversial here, but ok. Steve already posted
> something you can get started with.
>
> Will
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