On Wed, 14 Jan 2015, Masami Hiramatsu wrote:
> > diff --git a/arch/x86/include/asm/ftrace.h b/arch/x86/include/asm/ftrace.h
> > index f45acad..29fa417 100644
> > --- a/arch/x86/include/asm/ftrace.h
> > +++ b/arch/x86/include/asm/ftrace.h
> > @@ -4,8 +4,10 @@
> > #ifdef CONFIG_FUNCTION_TRACER
> > #ifdef CC_USING_FENTRY
> > # define MCOUNT_ADDR ((long)(__fentry__))
> > +# define arch_ftrace_ipmodify_compiler_support(void) ({ 1; })
> > #else
> > # define MCOUNT_ADDR ((long)(mcount))
> > +#define arch_ftrace_ipmodify_compiler_support(void) ({ 0; })
>
> Hmm, can we just define ARCH_FTRACE_SUPPORT_IPMODIFY here?
Yup, that's more or less what Steven suggested as well. I'll send v2.
> > diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> > index 929a733..11370fd 100644
> > --- a/kernel/trace/ftrace.c
> > +++ b/kernel/trace/ftrace.c
> > @@ -1809,6 +1809,11 @@ static int __ftrace_hash_update_ipmodify(struct
> > ftrace_ops *ops,
> > if (!(ops->flags & FTRACE_OPS_FL_IPMODIFY))
> > return 0;
> >
> > + if (!arch_ftrace_ipmodify_compiler_support()) {
> > + WARN(1, "Your compiler doesn't support features necessary for
> > IPMODIFY");
> > + return 0;
> > + }
>
> Actually, if ftrace doesn't support IPMODIFY, I would like to just drop
> the entire code for CONFIG_KPROBES_ON_FTRACE(this is a hidden config),
> instead of checking at runtime.
>
> So, there are 2 ifdefs of code in kernel/kprobes.c for
> CONFIG_KPROBES_ON_FTRACE, those should also check
> ARCH_FTRACE_SUPPORT_IPMODIFY too.
Makes sense. Will send that as a followup patch once the way how to do
this in ftrace is settled.
Thanks,
--
Jiri Kosina
SUSE Labs
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