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    SubjectRe: [PATCH] x86: Align jump targets to 1 byte boundaries

    * Josh Triplett <josh@joshtriplett.org> wrote:

    > On Mon, Sep 17, 2001 at 07:00:00AM +0000, Ingo Molnar wrote:
    > > * Denys Vlasenko <dvlasenk@redhat.com> wrote:
    > > > > What do you guys think about this? I think we should seriously
    > > > > consider relaxing our alignment defaults.
    > > >
    > > > Looks like nobody objected. I think it's ok to submit
    > > > this patch for real.
    > >
    > > Yeah, so my plan is to apply the following three changes from that
    > > discussion:
    > >
    > > --- tip.orig/arch/x86/Makefile
    > > +++ tip/arch/x86/Makefile
    > > <at> <at> -77,6 +77,15 <at> <at> else
    > > KBUILD_AFLAGS += -m64
    > > KBUILD_CFLAGS += -m64
    > >
    > > + # Pack jump targets tightly, don't align them to the default 16 bytes:
    > > + KBUILD_CFLAGS += -falign-jumps=1
    > > +
    > > + # Pack functions tightly as well:
    > > + KBUILD_CFLAGS += -falign-functions=1
    > > +
    > > + # Pack loops tightly as well:
    > > + KBUILD_CFLAGS += -falign-loops=1
    > > +
    > > # Don't autogenerate traditional x87 instructions
    > > KBUILD_CFLAGS += $(call cc-option,-mno-80387)
    > > KBUILD_CFLAGS += $(call cc-option,-mno-fp-ret-in-387)
    >
    > It looks like the patch you applied to the tip tree only included one of
    > these (-falign-junmps=1), not the other two.

    It's three separate patches, in case there are any regressions.

    > Also, you've only applied these to 64-bit; could you please apply
    > them to both 32-bit and 64-bit, since many embedded systems aiming
    > for small code size use 32-bit? (Unless 32-bit already defaults to
    > these.)

    First things first - 64-bit is getting far more testing these days
    than 32-bit.

    > Have you considered including -falign-labels=1 as well? Does that
    > make a difference on top of the other three.

    So isn't the default on x86 for -falign-labels already 1?

    Thanks,

    Ingo


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