Messages in this thread | | | Date | Sat, 7 Nov 2015 17:58:14 +0100 (CET) | From | Thomas Gleixner <> | Subject | Re: [PATCH 3/4] x86/asm: Add asm macros for static keys/jump labels |
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On Sat, 7 Nov 2015, Andy Lutomirski wrote: > On Nov 7, 2015 3:21 AM, "Thomas Gleixner" <tglx@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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