Limitations for 7th Edition Emulation in Apout 2.2
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Overlay binaries (type 0405) are not recognised.
Floating point is still not emulated (sigh).

The errno values on the native system are not translated back to
the V7 errno values. There is normally a 1-to-1 mapping, but V7
only had 32 errno values; native errno values above this are going
to confuse the emulated application.

The following system calls are not implemented, and return an 
EPERM error to the application: phys(2), prof(2), ptrace(2),
acct(2), mount(2), umount(2), times(2). The following system
calls are ignored: lock(2), stime(2).

The following systems calls are only partially implemented:

    signal(2):		Only SIG_DFL and SIG_IGN are implemented.
    stty(2), gtty(2):	These should work, but V7 stty(1) doesn't work.
    ioctl(2):		Only enough to emulate stty(2) amd gtty(2).

The emulated applications use the native filesystem. Native filenames bigger
than 14 characters are truncated to 14 characters before being passed to
the application. In a similar way, inode numbers bigger than 65,536 are
truncated modulo 65,536 before being passed to the application.
