[TUHS] v6 debugging

[Will Senn]

All,

I'm finally returning to my study of v6 after digging a bit further into 
assembly language and "other" pdp-11 operating systems. I even managed 
to get hello, world working in assembly in v6 and interestingly enough, 
I actually see how it works... for the most part :). Mini-note here:

http://decuser.blogspot.com/2016/01/hello-world-in-assembly-on-research.html

My question for y'all today is as follows (asked previously with a much 
larger gap in understanding):

How did folks debug assembly routines in Unix v6, back in the day?

I realize that most folks didn't do assembly, but some did and I'm 
curious what their approach might have been.

After having worked with RT-11 for a bit, I can see how I might develop 
using RT-11 and then "port" a program across, but that seems less than 
ideal. Here is my short list of missing features as I see them:

1. No listing file/cross reference list created by as.
2. No map file created by ld.
3. No debugger that I can find.
4. This is not a missing feature, but it deserves inclusion in the list, 
the command as has possibly the most terse error messages I have ever 
seen - B 12? Really? Thankfully, the awesome man command comes to the 
rescue with the list of error codes.

My workarounds include using OD to view the generated machine code and 
adding mesg calls.

Thoughts?

Will