Messages in this thread | | | Date | Fri, 24 Jul 2015 07:29:05 +0200 | From | Borislav Petkov <> | Subject | Re: Kernel broken on processors without performance counters |
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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...
-- Regards/Gruss, Boris.
ECO tip #101: Trim your mails when you reply. --
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