[TUHS] SDB debugger

Paul Winalski paul.winalski at gmail.com
Mon May 4 03:35:19 AEST 2020

On 5/3/20, Clem Cole <clemc at ccc.com> wrote:
> Paul W -- do you remember if DEC TLG did a version of dbx for Ultrix
> (Leslie might remember)?  FWIW: I know that DEC had a number of different
> debugger projects so on the UNIX side over the years, and I really don't
> remember what was done for the VAX, as I was not there at the time.  By
> MIPS/Alpha in the mid-late 90's there was a whole new debugger stream that
> had been developed at part of GEM, but there was another one that came from
> MIPs too which was based on dbx.

DEC's Technical Languages & Environments (TLE) group was responsible
for compilers for BLISS, Fortran, Pascal, PL/I, and Ada, on the
languages side, and the Language-Sensitive Editor (LSE) and debugger
on the software tools side.  All for VMS on the VAX and RSX-11, RT-11,
and RSTS on the PDP-11.  When VAX Ultrix came along, TLE ported the
VMS Fortran compiler and runtime to run on Ultrix.  It was a rush-rush
project and it was decided that there wasn't enough time to modify the
Fortran compiler to produce a.out object files or as assembler files
directly.  Instead Caroline Davidson and I modified the VMS linker to
run on Ultrix and to accept a.out and .a archive files as well as VMS
object files, and to produce a.out executables.  This linker was
called lk.  Part of this project was code to translate the debug
information in VMS object files to a.out stabs.  That work was done by
two members of the Ultrix development team (I don't recall their

So VAX Fortran for Ultrix used the off-the-shelf Ultrix debugger.
DEC's MIPS and Alpha Unix offerings used COFF as the object file and
executable format, and the GEM common back end emitted COFF-style
stabs for those platforms.  I was the project leader for the group
that developed and maintained the object file emission code in the GEM
compiler back end, but Ron Brender, who did a LOT of research on
debugging highly-optimized code and parallel programs, maintained the
GEM code that generated debug information.  I know that all of Ron's
work ended up in the VMS debugger.  I don't know how much of it went
into the Unix side of things.

I wasn't paying too much attention at the time, but I believe TLE also
did its own debugger for the Alpha Unix platform.  John Bishop can
tell you more about that.  When Microsoft sold Visual Fortran to DEC,
TLE took over the toolchain and interactive development environment
and released it as Digital Visual Fortran (DVF).  When Compaq sold the
Alpha technology to Intel, DVF went with it and became Intel Visual
Fortran, although the Intel compiler back end was chosen and GEM was
abandoned.  An Intel debugger, idb, was offered on Linux, although not
on Unix IIRC.  It was based on the DEC Alpha debugger technology.
This was later replaced by a debugger based on gdb.

-Paul W.

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