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    SubjectRe: X32 psABI status
    On Sun, Feb 13, 2011 at 7:21 AM, Florian Weimer <> wrote:
    > * H. J. Lu:
    >> On Sun, Feb 13, 2011 at 7:07 AM, Florian Weimer <> wrote:
    >>> * H. J. Lu:
    >>>>> Actually, I'm wondering if you can do the translation in user space.
    >>>>> There already are 32-on-64 implementations in existence, without
    >>>>> kernel changes (recent Hotspot, LuaJIT, and probably some more).
    >>>> Please check out the x32 kernel source and provide feedback.
    >>> I still don't understand why you need a separate syscall table.  You
    >>> should really be able to run on an unmodified amd64 kernel, in 64 bit
    >> That is done on purpose. x32 is designed for environments where the
    >> current ia32 API is sufficient. You can think it as ia32 with register
    >> extended to 64bit plus 8 more registers. Everything else is still 32bit.
    > I think of it as amd64 where all the process memory happens to reside
    > in the first 4 GB of address space, and pointers are stored as 32 bits
    > (and you'd also reduce the size of longs because sizeof(long) !=
    > sizeof(void *) will break too many programs).

    That is what the processor sees in an x32 program.

    > As I said, both LuaJIT and Hotspot are already using this model, with
    > custom memory allocators and a user-space translation layers, so I
    > still don't see what you get by changing the kernel.  LuaJIT has even
    > implemented the amd64 ABI, so you can call C libraries from your
    > 32-bit code.  (Note that LuaJIT uses 64-bit words to store 32-bit
    > pointers with several tag bits, but it does so even on pure 32-bit
    > platforms.)

    They can continue to do so.

    > If you want to make x32 closer to i386, I don't see the point.  Why
    > would it be problematic if it was as close to i386 as, say, armel?

    We are providing a 32bit API with 64bit registers. Current APIs support
    either 32bit or 64bit. I am not talking about pointer or long. I am talking
    other types, like time_t, off_t, ..., defined by API. Adding another API
    is extremely difficult.

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