Messages in this thread | | | From | Linus Torvalds <> | Date | Sat, 30 Jun 2018 12:01:20 -0700 | Subject | Re: [GIT PULL] x86 fixes |
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On Sat, Jun 30, 2018 at 1:49 AM Ingo Molnar <mingo@kernel.org> wrote: > > --- a/arch/x86/entry/entry_32.S > +++ b/arch/x86/entry/entry_32.S > @@ -477,7 +477,7 @@ ENTRY(entry_SYSENTER_32) > * whereas POPF does not.) > */ > addl $PT_EFLAGS-PT_DS, %esp /* point esp at pt_regs->flags */ > - btr $X86_EFLAGS_IF_BIT, (%esp) > + btrl $X86_EFLAGS_IF_BIT, (%esp) > popfl
Ho humm. Just looking at this patch, my reaction was "why isn't this an 'andl $~X86_EFLAGS_IF' instead"?
Yeah, I guess the 'andl' is two bytes longer (due to the 32-bit constant - because IF is bit 9, you can't use a byte constant, and you don't want to get a partial word write just before the popfl).
But btr is really pretty heavy operation for older CPU's (it's gotten better, but 32-bit code presumably cares more about the older CPUs).
It really doesn't matter, I guess. The btr goes back to commit c2c9b52fab0d ("x86/entry/32: Restore FLAGS on SYSEXIT").
Andy?
Linus
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