linux-kernel - Re: [PATCH] jump_label: Fix anonymous union initialization

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Message-ID: <20170302164200.143b10ff@gandalf.local.home>
Date:   Thu, 2 Mar 2017 16:42:00 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Jason Baron <jbaron@...mai.com>
Cc:     Boris Ostrovsky <boris.ostrovsky@...cle.com>, peterz@...radead.org,
        mingo@...nel.org, linux-kernel@...r.kernel.org,
        Chris Mason <clm@...com>
Subject: Re: [PATCH] jump_label: Fix anonymous union initialization

On Thu, 2 Mar 2017 16:07:19 -0500
Jason Baron <jbaron@...mai.com> wrote:

> On 02/28/2017 11:32 AM, Boris Ostrovsky wrote:
> > Pre-4.6 gcc do not allow direct static initialization of members of
> > anonymous structs/unions. After commit 3821fd35b58d ("jump_label:
> > Reduce the size of struct static_key") STATIC_KEY_INIT_{TRUE|FALSE}
> > definitions cannot be compiled with those older compilers.
> >
> > Placing initializers inside curved brackets works around this problem.
> >
> > Signed-off-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>
> > ---
> >  include/linux/jump_label.h | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/linux/jump_label.h b/include/linux/jump_label.h
> > index 8e06d75..518020b 100644
> > --- a/include/linux/jump_label.h
> > +++ b/include/linux/jump_label.h
> > @@ -166,10 +166,10 @@ extern void arch_jump_label_transform_static(struct jump_entry *entry,
> >   */
> >  #define STATIC_KEY_INIT_TRUE					\
> >  	{ .enabled = { 1 },					\
> > -	  .entries = (void *)JUMP_TYPE_TRUE }
> > +	  { .entries = (void *)JUMP_TYPE_TRUE } }
> >  #define STATIC_KEY_INIT_FALSE					\
> >  	{ .enabled = { 0 },					\
> > -	  .entries = (void *)JUMP_TYPE_FALSE }
> > +	  { .entries = (void *)JUMP_TYPE_FALSE } }
> >
> >  #else  /* !HAVE_JUMP_LABEL */
> >
> >  
> 
> (Adding Steve to 'cc)
> 
> Thanks for the fix.
> 
> Reviewed-by: Jason Baron <jbaron@...mai.com>

Funny, Chris pinged me on IRC telling me that jump labels broke with my
latest tree. And we discovered it was because of anonymous unions and
he was using an older compiler (4.4 or something). I didn't know how to
make it work, and we were just going to say "tough, jump labels are not
for 4.4". Although, didn't goto asm get added into 4.5? Did someone
backport it to the gcc 4.4 compilers? I believe 4.5 handles anonymous
unions.

Since the broken commit went through my tree, I'll take this patch.
I'm getting ready for another git pull request to Linus.

-- Steve