Re: Linux, UDI and SCO.

Michael Meissner (meissner@cygnus.com)
Sun, 20 Sep 1998 09:31:38 -0400

You know this UDI debate is amusing, coming about one month after there was
lots of moaning about Linus breaking drivers due to adding a field in the
middle of driver vector table, forcing new versions of the externally supplied
drivers (like PCMCIA for instance). If you go with UDI, you are essentially
tying the hands of the developers to adhere to it, since you don't even have
the choice of a recompile.

This is similar to a problem in userspace land -- on the x86, we use the System
V.4 ABI for setting things up. The V.4 ABI was created in the days of 386's,
and was demands that doubles have *4* byte alignment, not the more natural *8*
byte alignment (and the stack is similarly aligned to a *4* byte boundary).
Ever since the Pentium came out, we compiler folk have been asked to make the
default be the better alignment, but we can't, since we would then be breaking
the ABI (and hence binary compatibility with objects compiled with the old
compiler).

-- 
Michael Meissner, Cygnus Solutions (Massachusetts office)
4th floor, 955 Massachusetts Avenue, Cambridge, MA 02139, USA
meissner@cygnus.com,	617-354-5416 (office),	617-354-7161 (fax)


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