On Sat, 7 Nov 2015, Andy Lutomirski wrote:
> On Nov 7, 2015 3:21 AM, "Thomas Gleixner" <t...@linutronix.de> wrote:
> > +/* ASM jump label support */
> > +#if defined(CC_HAVE_ASM_GOTO) && defined(CONFIG_JUMP_LABEL)
> > +#include <asm/jump_label.h>
> > +
> > + .macro STATIC_CALL_IF_ENABLED fun, key
>
> I think we still need the "def" parameter. But maybe the "static
> call" is a good idea. (By giving 'def' a default value or omitting it
> entirely, it's too easy not to think about it, and that's a huge
> historical source of breakage and it's a good part of the reason for
> the new improved C API. At least these days I *think* we'll diagnose
> the problem on bootup instead of waiting for random breakage later.)
Ok. That's easy to add :)
> > + 1:
> > + jmp.d32 2f
>
> Old binutils will choke on this. But maybe no one has jump labels and
> old binutils.
Good question.
> > + call fun
> > + .pushsection __jump_table, "aw"
> > + _ASM_ALIGN
> > + _ASM_PTR 1b, 2f, \key
> > + .popsection
> > + 2:
> > + .endm
> > +#else
> > + .macro STATIC_CALL_IF_ENABLED fun, key
> > + call fun
> > + .endm
>
> This could result in errors down the road, since this macro is really
> "static call if enabled or if the kernel is built without jump
> labels". enter_from_user_mode is special because it's already a no-op
> if context tracking is off, but I'm not sure that this oddity should
> leak into more generic code.
Hmm. Maybe we need a better name for this macro.
> > +#endif
> > Index: tip/arch/x86/entry/entry_64.S
> > ===================================================================
> > --- tip.orig/arch/x86/entry/entry_64.S
> > +++ tip/arch/x86/entry/entry_64.S
> > @@ -510,7 +510,7 @@ END(irq_entries_start)
> > */
> > SWAPGS
> > #ifdef CONFIG_CONTEXT_TRACKING
> > - call enter_from_user_mode
> > + STATIC_CALL_IF_ENABLED enter_from_user_mode,
> > context_tracking_enabled
> > #endif
>
> This doesn't get rid of the ifdeffery, which I thought was a nice
> feature of my patch.
Right. I was just too lazy to add another macro :)
My main point was to avoid the extra stuff for !HAVE_JUMP_LABEL and
hide this in a header file.
Thanks,
tglx
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