[Info-vax] C History on VMS (was Re: C... the only winning move is not to play...)

[Stephen Hoffman]

On 2014-02-12 15:34:35 +0000, JohnF said:

> ...I think dcl is what all those str$functions we discussed were really 
> written for. That is, but for digital's desire to provide string 
> manipulation in dcl, they never would have bothered with that 
> str$library. The C headers and stuff were more of an afterthought, 
> i.e., as long as the library's there, might as well let C link it. But 
> all other things equal, when writing C you're better advised to use 
> standard C stuff if possible.

Some history and discssions of general and related structures...

DCL has its own supervisor-mode world; getting stuff compiled and 
linked into that environment is a little odd.    (It and the XQP are 
probably two of the weirder parts of VMS, in terms of its general 
run-time environment, and around debugging it.)

FWIW, none of the VMS and none of the (user-mode) language RTLs are 
intended to be callable from any inner-mode code.   (There were (are) 
some security-clobbering hacks latent in the RTL calls that allowed 
inner-mode to sort-of kind-of work, for those folks that were inclined 
to open up leaks across the per-mode memory management protections.  
Not recommended.)

I don't have the OpenVMS source listings handy to confirm it, but I'd 
be surprised if there were RTL calls around.

As for the include files, the VMS-provided header files are common 
source.  The same SDL source file generates C, BASIC, Fortran and 
others, and — with the most recent versions of SDL — also now DCL 
symbolic constants.  C was added to this list over time, and 
particularly around the addition of the SYS$STARLET_C and SYS$LIB_C 
libraries into OpenVMS.  STARLETSD.TLB was also used by various 
languages.

In terms of the per-language support within OpenVMS, C was effectively 
an afterthought for most of the environments, as the first C compiler 
and VAXCRTL library support only arrived somewhere around V4.4 IIRC.  
That was well after the other languages.   C is also somewhat weird on 
OpenVMS in that it now has two libraries; the traditional user-mode 
library that most languages have, and also its own kernel-mode library 
that was implemented as part of the C system programming support that 
arrived around OpenVMS V6.1 IIRC.

The STR$ and LIB$ calls are generally old.  Many of the core routines 
are older than V4.4.  It wouldn't surprise me to learn that the history 
of this stuff goes back further than VAX-11/VMS too, as here's the 
XPORT library for TOPS 
<http://bitsavers.informatik.uni-stuttgart.de/pdf/dec/pdp10/TOPS10_softwareNotebooks/vol08/AA-J201A-TK_XPORT_Programmers_Guide_Apr81.pdf> 


The STR$ and LIB$ calls are useful in Macro, Bliss, Fortran and various 
other languages.  (Various Fortran code was is still fond of using 
space-padded fixed-length strings, too.)  The OTS$ calls was largely 
for the compilers, but was and is available for other use.

More to make it a little easier for me to find these details for some 
hypothetical next time a discussion of ancient VMS calls and ancient 
run-time libraries (RTLs) arises, there are all sorts of related 
shenanigans around the break-up of the VMSRTL run-time library are in 
play here, too.  The ancient VMSRTL omnibus library has a long and 
checkered career: 
<http://archive.org/stream/bitsavers_decvaxvms2ReleaseNotesMar80_3242450/AA-D015C-TE_VMS_2.0_Release_Notes_Mar80_djvu.txt> 
<http://archive.org/stream/bitsavers_decvaxvms3leaseNotesV3.0May82_5458871/AA-D015D-TE_VAX-VMS_Release_Notes_V3.0_May82_djvu.txt> 
<http://www.ibiblio.org/pub/academic/computer-science/history/pdp-11/hardware/micronotes/numerical/micronote36.txt>. 
 This VMSRTL stuff was in common use prior to VAX/VMS V4.0, when that 
RTL was broken up into hunks; into separate RTLs.  For completeness, 
this was all before C existed on VMS, too.


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