Messages in this thread | | | From | Andy Lutomirski <> | Date | Fri, 12 Dec 2014 12:48:49 -0800 | Subject | Re: [RFC][PATCH 0/8] x86, mpx: Support 32-bit binaries on 64-bit kernels |
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On Fri, Dec 12, 2014 at 12:27 PM, Dave Hansen <dave@sr71.net> wrote: > On 12/12/2014 12:22 PM, Andy Lutomirski wrote: >> On 12/12/2014 11:12 AM, Dave Hansen wrote: >>> This is 3.20 material. I'm hoping to get some comments early >>> in case folks have some issues with the way it's being done. >>> >>> The MPX hardware structures differ in layout in 32 and 64-bit >>> mode. A 32-bit binary running on a 64-bit kernel needs the >>> 32-bit structures, so we need code which switches between >>> the two modes. >> >> The OS community figured out years ago that you aren't supposed to do >> this. Did everyone forget to tell the hardware people? > > What is your concern with it, exactly? > > You want the same size structures with the same format for 32-bit and > 64-bit modes?
Yes. Especially because programs can switch between 32-bit and 64-bit mode entirely in userspace. I don't know whether any do in practice, but programs *can*.
Or better yet: Intel could have skipped supporting it at all in 32-bit mode. Isn't mpx somewhat of an address space hog anyway?
--Andy
-- Andy Lutomirski AMA Capital Management, LLC
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