Messages in this thread | | | Date | Mon, 10 Feb 2014 10:19:43 -0500 | From | Steven Rostedt <> | Subject | Re: [PATCH v3 1/6] arm64: Add ftrace support |
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On Mon, 10 Feb 2014 16:03:21 +0100 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 agree to this. I will admit, this was probably just a copy from my code as I did the same in other Makefiles. I think I added the ifdef statements as more of documenting what the REMOVE was for, when ftrace was just being added to the kernel, and not well known.
I should probably go back and remove the ifdef's from other Makefiles too.
A comment about what the -pg is for wouldn't hurt, though:
# For files that should not have any function tracing done to them, # we must remove the -pg flag.
Something like that.
> > > 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. > > > +/* > > + * 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 wonder if we play linker games and move the _mcount and ftrace_caller and friends into the middle of the kernel? If it is only missing it by a slight overflow of a 32bit jump, then maybe moving it will work.
> > > +#ifdef CONFIG_FUNCTION_GRAPH_TRACER > > Here, again, you an remove the #ifdef by making the entire file built > only for CONFIG_FUNCTION_GRAPH_TRACER.
Interesting. Other archs (at least x86 and powerpc) required this file for function tracing too. Seems this is only needed for function graph tracer.
-- Steve
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