On 11 February 2014 00:03, Arnd Bergmann <arnd@arndb.de> wrote:
>
> On Friday 07 February 2014, AKASHI Takahiro wrote:
> > @@ -0,0 +1,23 @@
>
> > +
> > +#ifdef CONFIG_FUNCTION_TRACER
> > +#define MCOUNT_ADDR          ((unsigned long)_mcount)
> > +#define MCOUNT_INSN_SIZE     4 /* sizeof mcount call */
> > +
> > +#ifndef __ASSEMBLY__
> > +extern void _mcount(unsigned long);
> > +#endif /* __ASSEMBLY__ */
> > +#endif /* CONFIG_FUNCTION_TRACER */
>
> We generally like to have as few #ifdef as possible, and I think the
> #ifdef CONFIG_FUNCTION_TRACER here is not needed.

> > +#endif /* __ASM_FTRACE_H */
> > diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
> > index 2d4554b..ca921fb 100644
> > --- a/arch/arm64/kernel/Makefile
> > +++ b/arch/arm64/kernel/Makefile
> > @@ -5,6 +5,11 @@
> >  CPPFLAGS_vmlinux.lds := -DTEXT_OFFSET=$(TEXT_OFFSET)
> >  AFLAGS_head.o                := -DTEXT_OFFSET=$(TEXT_OFFSET)
> >
> > +ifdef CONFIG_FUNCTION_TRACER
> > +CFLAGS_REMOVE_ftrace.o = -pg
> > +CFLAGS_REMOVE_insn.o = -pg
> > +endif
>
> Same here. It never hurts to have the CFLAGS_REMOVE_* statements here, since
> you will not want to build these files for profiling.

I will remove it.

> > diff --git a/arch/arm64/kernel/arm64ksyms.c b/arch/arm64/kernel/arm64ksyms.c
> > index 338b568..7f0512f 100644
> > --- a/arch/arm64/kernel/arm64ksyms.c
> > +++ b/arch/arm64/kernel/arm64ksyms.c
> > @@ -56,3 +56,7 @@ EXPORT_SYMBOL(clear_bit);
> >  EXPORT_SYMBOL(test_and_clear_bit);
> >  EXPORT_SYMBOL(change_bit);
> >  EXPORT_SYMBOL(test_and_change_bit);
> > +
> > +#ifdef CONFIG_FUNCTION_TRACER
> > +EXPORT_SYMBOL(_mcount);
> > +#endif
>
> This one is clearly needed of course.

Sure.

> > +/*
> > + * Gcc with -pg will put the following code in the beginning of each function:
> > + *      mov x0, x30
> > + *      bl _mcount
> > + *   [function's body ...]
> > + * "bl _mcount" may be replaced to "bl ftrace_caller" or NOP if dynamic
> > + * ftrace is enabled.
>
> Unrelated to your patch, I have run into problems with this on arm32, maybe
> someone on Cc to this mail has an idea what to do about it:
>
> If I build a large "randconfig" kernel or "allyesconfig", the kernel image
> size exceeds 32MB, which means I can no longer link callers with a 26
> bit signed immediate argument like the "bl _mcount" here. For any other
> function calls, "gcc -mlong-calls" can be used to work around this, but
> this particular instance is created by inserting assembly statements
> into the output without considering the long-call options. Is there
> a way to get the kernel to link anyway?

I hope that this won't happen on arm64 because a branch offset range is

+/- 128MB.

> > +#ifdef CONFIG_FUNCTION_GRAPH_TRACER
>
> Here, again, you an remove the #ifdef by making the entire file built
> only for CONFIG_FUNCTION_GRAPH_TRACER.

You're right as far as patch [1/6] is concerned, but once patch [2/6] is applied,
this file (ftrace.c) may be compiled even if CONFIG_FUNCTION_GRAPH_TRACER
is not enabled. (That is CONFIG_DYNAMIC_FTRACE.)

Sorry for any confusion by poorly-divided patchset.

-Takahiro AKASHI

>         Arnd