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    SubjectRe: Compat 32-bit syscall entry from 64-bit task!?
    On Thu, Jan 19, 2012 at 11:30 AM, Andrew Lutomirski <luto@mit.edu> wrote:
    >
    > Unless you're writing a debugger and you want to disassemble the code
    > that's being executed (i.e. normal code, not a system call).  I wonder
    > how gdb guesses whether the cpu is in long mode.

    Yes, if you need to disassemble user space you would need to figure
    out the mode.

    I would suggest looking at 'rip/rsp' first, though, and just say that
    if it's >32-bit, it's flat mode. Only if both rsp and rip fit in 32
    bits should you even bother start guessing.

    Because technically I suspect you really do need to look it up in the
    segment descriptors, and I don't think we have that kind of interface
    (nor do I think we really want to expose one).

    Linus
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