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    SubjectRe: [PATCH 2/5] livepatch: Allow architectures to specify an alternate ftrace location
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    On Thu, 2016-04-14 at 14:01 +0200, Miroslav Benes wrote:
    > On Wed, 13 Apr 2016, Michael Ellerman wrote:
    > > diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
    > > index d68fbf63b083..b0476bb30f92 100644
    > > --- a/kernel/livepatch/core.c
    > > +++ b/kernel/livepatch/core.c
    > > @@ -298,6 +298,19 @@ unlock:
    > > rcu_read_unlock();
    > > }
    > >
    > > +/*
    > > + * Convert a function address into the appropriate ftrace location.
    > > + *
    > > + * Usually this is just the address of the function, but on some architectures
    > > + * it's more complicated so allow them to provide a custom behaviour.
    > > + */
    > > +#ifndef klp_get_ftrace_location
    > > +static unsigned long klp_get_ftrace_location(unsigned long faddr)
    > > +{
    > > + return faddr;
    > > +}
    > > +#endif
    >
    > Whoah, what an ugly hack :)

    Hey it's a "cool trick" ;)

    > Note to my future self - This is what you want to do if you need a weak
    > static inline function.
    >
    > static inline is probably unnecessary here so __weak function would be
    > enough. It would introduce powerpc-specific livepatch.c though because of
    > it and this is not worth it.

    Yeah that was my logic, at least for now. We can always change it in future
    to be weak if anyone cares deeply.

    > > static void klp_disable_func(struct klp_func *func)
    > > {
    > > struct klp_ops *ops;
    > > @@ -312,8 +325,14 @@ static void klp_disable_func(struct klp_func *func)
    > > return;
    > >
    > > if (list_is_singular(&ops->func_stack)) {
    > > + unsigned long ftrace_loc;
    >
    > This is a nit, but could you move the definition up to have them all in
    > one place to be consistent with the rest of the code? The same applies to
    > klp_enable_func() below.

    Hmm, actually I moved it in there because you pointed out we only needed it
    inside the if:

    http://lkml.kernel.org/r/alpine.LNX.2.00.1603151113020.20252@pobox.suse.cz

    Thinking about it, we need ftrace_loc only in cases where we call
    ftrace_set_filter_ip() right? So we can move klp_get_ftrace_location()
    call to appropriate if branch both in klp_disable_func() and
    klp_enable_func().

    But I guess you meant the function call, not the variable declaration.

    Personally I think it's better this way, as the variable is in scope for the
    shortest possible amount of time, but I can change it if you want me to.

    cheers

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