[TUHS] 2.11 BSD question... (exe sizes)

Tom Ivar Helbekkmo tih at hamartun.priv.no
Fri Sep 3 21:22:07 AEST 2010

Jason Stevens <neozeed at gmail.com> writes:

> I'll admit I'm not all that swift on the pdp-11, but I get the impression
> that the maximum exe size is 128kb with 64kb of instructions, and 64kb of
> data?  Isn't there something that can be done with overlays or some other
> linker thing to act like an 8086/80286 with the large memory model (ie
> multiple segments...?)

There is. :)

> I've been trying to build ircII-4.4 and I can't figure out how to link
> something that big... I've tried the -Z and -O flags to ld to no avail.
> Clearly I'm doing either something wrong, or impossible or stupid.

IIRC, you want something along the lines of:

ld -i -o irc -Z a.o b.o -Z c.o d.o -Z e.o f.o -Y g.o h.o -lc

where -i says to use split I/D (64KB for each), each -Z introduces a set
of object modules to go into one overlay, and the -Y introduces the
object modules that are not to be overlaid.  You'll want your main() to
be in the -Y group, ideally along with the most used parts of the code.
Each -Z group should ideally contain object modules that are all used at
the same time; the idea is to minimize the number of overlay swaps that
have to be done.

There are binaries in 2.11BSD that are built in this way.  Look for the
-Z flag in the Makefiles.

Use size(1) on the a.out to see the sizes of the various overlays and
the main area: you'll get error messages from ld(1), and size(1) will
help you figure out how you need to move objects around to keep the main
area under 56KB, and each overlay under 8KB.  (Actually, I seem to
recall that those limits can also be 48 and 16, or 40 and 24, and so
on.  'man ld' might be of help.)

> FWIW, here is the size of the same program on the VAX
> myname# ls -l irc-4.4
> -rwxr-xr-x  1 root       413696 Jun  8 08:46 irc-4.4*
> myname# size irc-4.4
> text    data    bss     dec     hex
> 293888  67584   20784   382256  5d530
> I have a feeling that 300kb of text, along with 67kb of data is just too
> much...?

You might be able to squeeze it in.  Your data space usage will be less
on a 16-bit system, and you may be able to reduce the sizes of arrays
and allocations here and there by accepting limitations in the resulting

I don't believe that souls or bodies can be changed by incantation.
                                            --Christopher Hitchens

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