linux-kernel - Re: [PATCH 1/2] livepatch: fix non-static warnings

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Date:   Fri, 14 Dec 2018 15:51:29 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Joe Lawrence <joe.lawrence@...hat.com>
Cc:     Nicholas Mc Guire <hofrat@...dl.org>, Jessica Yu <jeyu@...nel.org>,
        Jiri Kosina <jikos@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Petr Mladek <pmladek@...e.com>, live-patching@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] livepatch: fix non-static warnings

On Fri, Dec 14, 2018 at 04:34:23PM -0500, Joe Lawrence wrote:
> On 12/14/2018 11:56 AM, Nicholas Mc Guire wrote:
> > Sparse reported warnings about non-static symbols. For the variables a
> > simple static attribute is fine - for those symbols referenced by
> > livepatch via klp_func the symbol-names must be unmodified in the
> > relocation table - to resolve this the __noclone attribute (as 
>   ^^^^^^^^^^
> nit: symbol table
> 
> > suggested by Joe Lawrence <joe.lawrence@...hat.com>) is used
> > for the statically declared functions.
> > 
> > Signed-off-by: Nicholas Mc Guire <hofrat@...dl.org>
> > Link: https://lkml.org/lkml/2018/12/13/827

Needs a:

  Suggested-by: Joe Lawrence <joe.lawrence@...hat.com>


> > 
> > diff --git a/samples/livepatch/livepatch-shadow-fix1.c b/samples/livepatch/livepatch-shadow-fix1.c
> > index 49b1355..eaab10f 100644
> > --- a/samples/livepatch/livepatch-shadow-fix1.c
> > +++ b/samples/livepatch/livepatch-shadow-fix1.c
> > @@ -71,7 +71,7 @@ static int shadow_leak_ctor(void *obj, void *shadow_data, void *ctor_data)
> >  	return 0;
> >  }
> >  
> > -struct dummy *livepatch_fix1_dummy_alloc(void)
> > +static __noclone struct dummy *livepatch_fix1_dummy_alloc(void)
> >  {
> >  	struct dummy *d;
> >  	void *leak;
> > @@ -108,7 +108,7 @@ static void livepatch_fix1_dummy_leak_dtor(void *obj, void *shadow_data)
> >  			 __func__, d, *shadow_leak);
> >  }
> >  
> > -void livepatch_fix1_dummy_free(struct dummy *d)
> > +static __noclone void livepatch_fix1_dummy_free(struct dummy *d)
> >  {
> >  	void **shadow_leak;
> >  
> > diff --git a/samples/livepatch/livepatch-shadow-mod.c b/samples/livepatch/livepatch-shadow-mod.c
> > index 4c54b25..0a72bc2 100644
> > --- a/samples/livepatch/livepatch-shadow-mod.c
> > +++ b/samples/livepatch/livepatch-shadow-mod.c
> > @@ -30,6 +30,11 @@
> >   * memory leak, please load these modules at your own risk -- some
> >   * amount of memory may leaked before the bug is patched.
> >   *
> > + * NOTE - the __noclone attribute to those functions that are to be
> > + * shared with other modules while being declared static. As livepatch
> > + * needs the unmodified symbol names and the usual "static" would
> > + * invoke gccs cloning mechanism that renames the functions this
> > + * needs to be suppressed with the additional __noclone attribute.
> 
> I like the idea of providing the sample code reader this information,
> but since the compiler might also optimize livepatch-callbacks-busymod.c
> :: busymod_work_func(), it too should be annotated __noclone.  Would
> that file deserve a similar comment?
> 
> I don't have a strong opinion, but would throw my vote at leaving this
> in the commit message only.

Agreed, IMO the comment isn't needed.

> BTW, Petr/Miroslav/Josh, should we be annotating the selftests in
> similar fashion?

Probably so.

-- 
Josh