Shared libraries

[William Roberts]

I am currently trying to shoehorn a workable A/UX root partition into
10 Megabytes (well, it keeps me off the streets). During this exercise,
I have noticed that some binaries are nice and small, whilst others
are quite a lot larger for not much more functionality.

For example:

		A/UX 2.0	SunOS 3.5

/bin/chmod	3604 bytes	19292 bytes	(+15688)
/bin/chgrp	32812 bytes	46620 bytes	(+13808)

The A/UX 2.0 version is using the shared libc, but so is the chgrp
and I don't understand why it is so much bigger.

When I do a "what" on these files, I get

/bin/chmod:
         Copyright (c) 1984-85 AT&T-IS, 1985-87 UniSoft Corporation, All Rights
Reserved.  {Apple version 1.3 89/10/10 08:10:18}
        compatmode.c    1.2
/bin/chgrp:
         Copyright (c) 1984-85 AT&T-IS, 1985-87 UniSoft Corporation, All Rights
Reserved.  {Apple version 1.4 90/03/16 13:34:16}
        compatmode.c    1.2
        get_myaddress.c 1.1 86/09/24 Copyr 1984 Sun Micro

The curious thing is that "get_myaddress.c" is part of libc.a, and this
is supposed to be shared.... isn't it?

Turning to my trusty BSD 4.2 source code, I try compiling chmod.c and
chgrp.c, only to discover that I can't seem to match the size that
the distributed /bin/chmod achieves. Furthermore, there are no clear
examples in the A/UX 2.0 distribution (online manuals only) to say
exactly HOW to compile and link for shared libraries.


Looking at the files with "size", I get

Size of /bin/chgrp:  83988

        Section         Size      Physical Address    Virtual Address

        .text             26596             328                328
        .data              5824         4196652            4196652
        .bss              16160         4202476            4202476
        .lbt1206          26156      1206910976         1206910976
        .lbd1207           9108      1207697408         1207697408
        .lbb1207             80      1207706516         1207706516
        .lib                 64               0                  0
Size of /bin/chmod:  38972

        Section         Size      Physical Address    Virtual Address

        .text              2036             328                328
        .data              1176         4196668            4196668
        .bss                352         4197844            4197844
        .lbt1206          26156      1206910976         1206910976
        .lbd1207           9108      1207697408         1207697408
        .lbb1207             80      1207706516         1207706516
        .lib                 64               0                  0

So chgrp is bigger by 24000 bytes of text and 4700 bytes of data.
The sizes of the chmod.o and chgrp.o files are

chmod.o		text=1284	data=156
chgrp.o		text= 852	data=188

so all that extra is coming from unshared text & data extracted from
libc. Running "strings /bin/chgrp | wc" shows that there are 3771 bytes
of printable string (or thereabouts), most of which is the standard
error strings used by perror: chgrp uses perror, chmod doesn't.

Can anyone at Apple shed any light on all this? Have I just found a
way to make the A/UX 2.0 distribution smaller by 20k for most of
the 729 "executable" things listed in /FILES (a modest saving of 14 Meg!)?

PS: gcc makes all string constants part of the text segment (and hence
    non-writeable) by default. The same effect could be achieved with
    ld (I think) and would be valuable if applied to errlst.c in the
    C library - this just defines the standard error strings and would
    put that 2492 bytes of data into somewhere that is truly shared rather
    that "copy-on-write" shared.

    This treatment of string constants would be useful in lots of
    places - just type "strings" on any executable over 40K...


-- 

William Roberts                 ARPA: liam at cs.qmw.ac.uk
Queen Mary & Westfield College  UUCP: liam at qmw-cs.UUCP
Mile End Road                   AppleLink: UK0087
LONDON, E1 4NS, UK              Tel:  071-975 5250 (Fax: 081-980 6533)