On Fri, Jul 24, 2015 at 07:29:05AM +0200, Borislav Petkov wrote:
> On Thu, Jul 23, 2015 at 09:02:14PM +0200, Peter Zijlstra wrote:
> > On Thu, Jul 23, 2015 at 07:54:36PM +0200, Borislav Petkov wrote:
> > > On Thu, Jul 23, 2015 at 07:08:11PM +0200, Peter Zijlstra wrote:
> > > > That would be bad, how can we force it to emit 5 bytes?
> > >
> > > .byte 0xe9 like we used to do in static_cpu_has_safe().
> >
> > Like so then?
> >
> > static __always_inline bool arch_static_branch_jump(struct static_key *key,
> > bool inv)
> > {
> > unsigned long kval = (unsigned long)key + inv;
> >
> > asm_volatile_goto("1:"
> > ".byte 0xe9\n\t .long %l[l_yes]\n\t"
> > ".pushsection __jump_table, \"aw\" \n\t"
> > _ASM_ALIGN "\n\t"
> > _ASM_PTR "1b, %l[l_yes], %c0 \n\t"
> > ".popsection \n\t"
> > : : "i" (kval) : : l_yes);
> >
> > return false;
> > l_yes:
> > return true;
> > }
>
> Yap.
>
> But, we can do even better and note down what kind of JMP the compiler
> generated and teach __jump_label_transform() to generate the right one.
> Maybe this struct jump_entry would get a flags member or so. This way
> we're optimal.
>
> Methinks...
Yes, Jason and Steve already have patches to go do that, but I'd really
like to keep that separate for now, this thing is big enough as is.
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