30 Sep
2021
30 Sep
'21
9:01 a.m.
On Wed, Sep 29, 2021 at 09:40:23AM -0700, Greg A. Woods wrote:
I think perhaps the problem was that mmap() came too
soon in a narrow
sub-set of the Unix implementations that were around at the time, when
many couldn't support it well (especially on 32-bit systems -- it really
only becomes universally useful with either segments or 64-bit and
larger address spaces). The fracturing of "unix" standards at the time
didn't help either.
Perhaps these "add-on hack" problems are the reason so many people think
fondly of the good old Unix versions where everything was still coming
from a few good minds that could work together to build a cohesive
design. The add-ons were poorly done, not widely implemented, and
usually incompatible with each other when they were adopted by
additional implementations.
mmap() did come from those days and minds.
The first appearance of mmap() was in 32V R3, done by John Reiser in 1981. This is the
version of 32V with full demand paging; it implemented a unified buffer cache. According
to John, that version of mmap() already had the modern 6 argument API. John added mmap()
because he worked with Tenex a lot during his PhD days and missed PMAP. He needed some 6
months to design, implement and debug this version of 32V as a skunkworks project.
I am trying to revert early VAX SVr1/r2 code to get a better view of what 32V R3 looked
like, but unfortunately I did not have much time for this effort in last couple of months.
It would seem that 32V R3 assumed that disk blocks and memory pages were the same size
(true on a 1980 VAX) and with that assumption a unified buffer cache comes natural in this
code base.
For 4.2BSD initially Joy cs. had a different approach to memory mapped files in mind (see
the 1981 tech report #4 from CSRG). By the time of 4.2BSD’s release the manual defined a
mmap() system call, but it was not implemented and it appears to have been largely
forgotten until SunOS 4 and dynamic libraries six years later.
In the SysV lineage it is less clear. For sure mmap() is not there, but the first
implementation of the shmem IPC feature might derive from the 32V R3 code. On the inside,
SVr2 virtual memory appears to implement the segments (now called regions) that Joy
envisaged for 4.2BSD but did not implement.
CB Unix had a precursor to shmem as well, where a portion of system core was reserved for
shared memory purposes and could be accessed either via the /dev/mem device or could be
mapped into the PDP-11 address space (using 1 of the 8 segment registers for each map).
Here too the device and the map were unified.
So far, I have not come across any shared library implementations or precursors in early
Unix prior to SunOS 4.
Paul
30 Sep
30 Sep
10:39 a.m.
New subject: Early shared library implementations
Paul Ruizendaal via TUHS <tuhs(a)minnie.tuhs.org> wrote:
So far, I have not come across any shared library
implementations or
precursors in early Unix prior to SunOS 4.
In more or less the same time frame, the AT&T UnixPC / 3B1, which was
OEM'ed from Convergent, had shared libraries. This was ~ 1986.
I don't know the details of how it worked and how one built the shared
libraries; I am sure that it was an independent implementation from Sun's.
This was done on top of a System V Release 2 kernel. Later versions
of the OS had some bits of the SVR3 user land, but the kernel remained
SVR2 based.
There is a 3B1 emulator and disk images for it available for anyone
who really wants to go back to a system with short filenames and no
job control. :-)
Arnold
2:12 p.m.
New subject: Early shared library implementations
On 9/30/2021 5:39 AM, arnold(a)skeeve.com wrote:
Paul Ruizendaal via TUHS <tuhs(a)minnie.tuhs.org>
wrote:
I'm very hazy on the details, because I wasn't directly involved, but we
had shared libraries in AIX for the RT starting with the initial release
in 1986 (based on SVR1). Larry Loucks did most of the design, with help
from ISC folks and maybe Rick Simpson. Larry mentions this work in our
AIX 2 paper
(https://technologists.com/sauer/Advanced%20Interactive%20Executive%20(AIX)%…)
but I don't see any useful description, nor do I see anything useful
skimming http://www.bitsavers.org/pdf/ibm/pc/rt/ docs. A more
sophisticated shared library design was one of the additions in AIX 3.
Charlie
P.S. That paper and
https://technologists.com/sauer/SA23-1057_IBM_RT_Personal_Computer_Technolo…
do include a bit more discussion of our memory mapped files since
support for those was a primary goal of the 801 virtual memory design
(summarized in the "Rosetta" paragraph of
https://notes.technologists.com/notes/2017/03/08/lets-start-at-the-very-beg…)
--
voice: +1.512.784.7526 e-mail: sauer(a)technologists.com
fax: +1.512.346.5240 Web: https://technologists.com/sauer/
Facebook/Google/Twitter: CharlesHSauer
So far, I have not come across any shared library
implementations or
precursors in early Unix prior to SunOS 4.
In more or less the same time frame, the AT&T UnixPC / 3B1, which was
OEM'ed from Convergent, had shared libraries. This was ~ 1986.
I don't know the details of how it worked and how one built the shared
libraries; I am sure that it was an independent implementation from Sun's.
This was done on top of a System V Release 2 kernel. Later versions
of the OS had some bits of the SVR3 user land, but the kernel remained
SVR2 based.
There is a 3B1 emulator and disk images for it available for anyone
who really wants to go back to a system with short filenames and no
job control. :-) 
11 Oct
11 Oct
6:43 a.m.
New subject: Early shared library implementations
On 9/30/2021 2:01 AM, Paul Ruizendaal via TUHS wrote:
So far, I have not come across any shared library
implementations or
precursors in early Unix prior to SunOS 4.
On 9/30/2021 3:39 AM, arnold(a)skeeve.com wrote:
In more or less the same time frame, the AT&T
UnixPC / 3B1, which was
OEM'ed from Convergent, had shared libraries. This was ~ 1986.
On 9/30/2021 7:12 AM, Charles H Sauer wrote:
... A more > sophisticated shared library design
was one of the additions in AIX 3.
There was also SVR3 (which I believe was the basis for the referenced
AIX 3 shared library work). SVR3 shipped in 1987, SunOS 4 in May 1988.
There was a swarm of UNIX shared library projects during the 1980s. Some
of those preceded or were occurring contemporaneously with SunOS 4. Many
reached at least a running prototype stage, perhaps deployed as specials
for customers, and some reached product status.
Some of the projects had papers published and there are a few old
manuals available through bitsavers.org.
To fill out the history a bit, here are three (including SVR3) that had
papers published. They also serve to illustrate the different approaches
being taken. I can not find on-line copies of the papers, but others may
have better luck or will have access to paper copies of the conference
proceedings. SVR3 has extensive documentation on bitsavers.org, as does
some older editions of UTek.
The three projects are:
1. a 68000-based 7th Edition port;
2. UTek: Tektronix's version of 4BSD for their workstations; and
3. System V Release 3.
The first project had a paper published as part of the USEnix track of a
UniForum Conference in January 1984 and was titled "Transparent
Implementation of Shared Libraries" and authored by C.B. Downing and F.
Farance.
The other two had papers published in the 1986 Atlanta Summer USEnix
proceedings and were: "A New Virtual-Memory Implementation for UNIX" by
E. W. Sznyter, P. Clancy, and J. Crossland (UTek); and "Shared Libraries
on UNIX System V" by J. Q. Arnold.
A very thorough description of the SVR3 shared library mechanism is
available at:
http://bitsavers.org/pdf/att/unix/System_V_Release_3/308-139_UNIX_System_V_…
Some UTek documentation, including their mmap specification but
appearing to pre-date their shared libraries work, is available at:
http://bitsavers.org/pdf/tektronix/6130_4132/
For the "Transparent Implementation..." paper, the "transparent"
referred to a goal that an application's source code not be modified to
link with shared libraries. That, and sharing, were about the only goals
common to all the projects of the era. Nearly every other design choice
varied across the projects as determined by the approach taken or the
constraints under which the project operated.
On the subject of mmap's origins: UTek used mmap, but specified mmap to
take a pid instead of a file descriptor for the source of the mapping.
It appears they contemplated an fmap to map from a file. So for sharing
to occur, there was to be a daemon that scooped up and relocated in its
address space all the libraries to be shared and then advertise what it
had. Client processes would rendezvous with the daemon at runtime and
map the portions of that process they required to accomplish the sharing.
A common characteristic of these 3 projects was that symbols were
resolved at ld-time, necessitating some external coordination about how
address spaces were to be laid out but minimizing run-time overheads.
The referenced SVR3 documentation provides a good description of the
considerations involved.
7:08 a.m.
New subject: Early shared library implementations
My memory is, that at least one model (OSF/1) required reboot, because
it did some intermediate call optimisation to remove/elide indirect
refs. Possibly a mis-remember.
2:22 p.m.
New subject: Early shared library implementations
On Mon, Oct 11, 2021 at 3:09 AM George Michaelson <ggm(a)algebras.org> wrote:
My memory is, that at least one model (OSF/1) required
reboot, because
it did some intermediate call optimisation to remove/elide indirect refs.
Hmm, as far as I know,/my experience was that with OSF/1 was fine with
shared libs, no reboot needed (at least on the 386 reference -- I never
tried it on the PMAX].
I suspect you might be thinking about drivers and kernel modules, which
were not nearly as clean - particularly in the pure (Mach 3.0 based) OSF/1
microkernel implementation [which was hardly 'micro' in size]. IIRC
Rob's
new memory system code for SunOS was one of the first UNIX implementations
that supported loadable kernel modules.
Anyway, for the original OSF/1, I really don't think shared libs caused a
reboot using the original CMU Mach 2.5 memory code, but adding things to
the kernel did. I know that was changed with the MMU rewrite for Tru64, but
I think it was also done in later versions of the OSF RI kernel (but I've
forgotten).
17 Oct
17 Oct
10:19 p.m.
New subject: Early shared library implementations
On Oct 10, 2021, at 11:43 PM, Rob Gingell via TUHS <tuhs(a)minnie.tuhs.org> wrote:
There was also SVR3 (which I believe was the basis for the referenced AIX 3 shared
library work). SVR3 shipped in 1987, SunOS 4 in May 1988.
There was a swarm of UNIX shared library projects during the 1980s. Some of those
preceded or were occurring contemporaneously with SunOS 4. Many reached at least a running
prototype stage, perhaps deployed as specials for customers, and some reached product
status.
I believe NEXTSTEP 1.0 supported shared libraries out of the box too, probably from work
on Mach or the Andrew system at CMU.
— Chris
10:15 p.m.
New subject: Early shared library implementations
On Sep 30, 2021, at 3:39 AM, arnold(a)skeeve.com wrote:
In more or less the same time frame, the AT&T UnixPC / 3B1, which was
OEM'ed from Convergent, had shared libraries. This was ~ 1986.
I don't know the details of how it worked and how one built the shared
libraries; I am sure that it was an independent implementation from Sun's.
This was done on top of a System V Release 2 kernel. Later versions
of the OS had some bits of the SVR3 user land, but the kernel remained
SVR2 based.
Apple A/UX was also SVR2-based and had shared libraries. I wonder if it was a similar
implementation. (The porting work for A/UX was initially done by UniSoft, from what I
recall.)
— Chris
30 Sep
30 Sep
12:56 p.m.
On 9/30/21 5:01 AM, Paul Ruizendaal via TUHS wrote:
For 4.2BSD initially Joy cs. had a different approach
to memory mapped files in mind (see the 1981 tech report #4 from CSRG). By the time of
4.2BSD’s release the manual defined a mmap() system call, but it was not implemented and
it appears to have been largely forgotten until SunOS 4 and dynamic libraries six years
later.
3BSD and I think 4.1BSD had vread() and vwrite(), which looked like
regular read() and write() but accessed pages only on demand. I was a
grad student at Berkeley at the time and remember their genesis. Bill
and I were eating lunch from Top Dog on the Etcheverry Hall plaza, and
were talking about memory-mapped I/O. I remember suggesting the actual
names, perhaps as a parallel to vfork(). I had used both TENEX and
Multics, which both had page mapping. Multics' memory-mapped segments
were quite fundamental, of course. I think we were looking for something
vaguely upward compatible from the existing system calls. We did not
leap to an mmap() right away just because it would have been a more
radical shift than continuing the stream orientation of UNIX. I did not
implement any of this: it was just a brainstorming session.
Dan H
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8 comments
8 participants
participants (8)
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arnold＠skeeve.com -
Charles H Sauer -
Chris Hanson -
Clem Cole -
Dan Halbert -
George Michaelson -
Paul Ruizendaal -
Rob Gingell