origin of alloca(3) (was: Undocumented systems/standards PWB and 32V)

["G. Branden Robinson" <g.branden.robinson@gmail.com>]

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Hi Alex,

At 2026-01-01T14:17:35+0100, Alejandro Colomar wrote:
> Hi Branden, Seth,
> 
> On Wed, Dec 31, 2025 at 11:46:32PM -0600, G. Branden Robinson wrote:
> > Hi Seth,
> > 
> > At 2026-01-01T04:45:28+0000, Seth McDonald wrote:
> > > Starting the year off strong, here's a classic bug report.  The man
> > > page for alloca(3) lists two systems/standards in its HISTORY: PWB and
> > > 32V.
> > > 
> > > $ man ./man3/alloca.3 | sed -n '/HISTORY/,/^$/p'
> > > HISTORY
> > >        PWB, 32V.
> > > 
> > > After some Googling, I assume these are referring to the PWB/UNIX and
> > > UNIX/32V operating systems, respectively.
> > 
> > Yes.  Most likely.  I have some remarks on nomenclature, orthography,
> > and history.
> > 
> > PWB stands for "Programmer's Workbench".  It was a flavor of Unix
> > maintained and sustained outside of the Bell Labs Computing Science
> > Research Center (CSRC) in Murray Hill, New Jersey.  The CSRC is where
> > Unix was born and where famous names like Ken Thompson, Dennis Ritchie,
> > and Brian Kernighan worked.  Eventually, the flavor of Unix produced by
> > the CSRC came to be known as "Research Unix".  In the late 1980s the
> > CSRC decided that the Unix system was an unrewarding vehicle for further
> > _research_, and shifted its emphasis to Plan 9.  Over time, the Jack
> > Welch-ification of AT&T[1] meant that research at Bell Labs became less
> > ambitious and eventually halted.
> > 
> > PWB came in at least two revisions--the original, retro-branded PWB1,
> > and a second, sometimes called "PWB/UNIX 2.0".
> 
> It would be good to check in which one alloca(3) was present.

There's _an_ `alloca()` in PWB/Unix 1.0.

https://minnie.tuhs.org/cgi-bin/utree.pl?file=PWB1/sys/source/s4/util/alloca.s

It's not declared in any header file I can find, and as you can see it's
written in PDP-11 assembly, but it's there, and appears to do what a
modern C programmer would expect of it.[1]

It appeared to get stuck into a library called "libpw.a".

Static, of course, because there were no shared libraries back then.

https://minnie.tuhs.org/cgi-bin/utree.pl?file=PWB1/sys/source/s4/util/makefile

Close enough?  :)

Regards,
Branden

[1] I see some other familiar stuff here...

https://minnie.tuhs.org/cgi-bin/utree.pl?file=PWB1/sys/source/s4/stdio

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