linux-kernel - Re: [PATCH v6 3/3] x86: paravirt: make native_save

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Date:   Mon, 16 Jul 2018 10:27:04 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     David.Laight@...lab.com
Cc:     mingo@...hat.com, Thomas Gleixner <tglx@...utronix.de>,
        Andrew Morton <akpm@...ux-foundation.org>, hpa@...or.com,
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Subject: Re: [PATCH v6 3/3] x86: paravirt: make native_save_fl extern inline

On Fri, Jul 13, 2018 at 3:15 AM David Laight <David.Laight@...lab.com> wrote:
>
> From: Nick Desaulniers
> > Sent: 21 June 2018 17:23
> >
> > native_save_fl() is marked static inline, but by using it as
> > a function pointer in arch/x86/kernel/paravirt.c, it MUST be outlined.
> >
> > paravirt's use of native_save_fl() also requires that no GPRs other than
> > %rax are clobbered.
> ...
> > diff --git a/arch/x86/include/asm/irqflags.h b/arch/x86/include/asm/irqflags.h
> > index 89f08955fff7..c4fc17220df9 100644
> > --- a/arch/x86/include/asm/irqflags.h
> > +++ b/arch/x86/include/asm/irqflags.h
> > @@ -13,7 +13,7 @@
> > * Interrupt control:
> > */
> >
> > -static inline unsigned long native_save_fl(void)
> > +extern inline unsigned long native_save_fl(void)
>
> This is generating a the compilation warning (that we treat as an error):
> "no previous prototype for 'native_save_fl".
> Fixable by replicating the line with an appended ;

Thanks for the report and sorry for breaking things for you.  Just
curious about more information to try to reproduce the issue to make
sure I fix the issue correctly:
* What compiler and compiler version are you using?
* Are you setting any configs or enabling any warning CFLAGS to see this?
* Do you see this warning for other `extern inline` functions? (It
seems like the few other ones in the kernel are for non-x86 archs)

I would have guessed that extern inline functions with gnu_inline
semantics (gnu89 behavior) should not have a previous declaration, but
it probably doesn't hurt to add it.
-- 
Thanks,
~Nick Desaulniers