[TUHS] v6 debugging

Will Senn will.senn at gmail.com
Sun Jan 24 03:38:06 AEST 2016

On 1/23/16 11:18 AM, Noel Chiappa wrote:
>      > From: Will Senn
>      > How did folks debug assembly routines in Unix v6, back in the day?
> There are three different questions here, although you may not realize it:
>   - How did folks debug assembly routines in user programs in Unix v6
>   - How did folks debug assembly routines in the kernel in Unix v6
>   - How did folks debug assembly routines in PDP-11 standalone code created
>     with Unix v6
> I did all three, and I used different methods for each.
> For user code, there was no source-level debugger, so debugging C programs
> and debugging code written in assembler were the same thing. I used 'adb'
> (which is, stricly speaking, slightly post-V6 - our system at MIT was
> actually sort of an early PWB clone), but V6 itself provides 'db' (and also,
> IIRC, 'cdb'); all three are very similar.
> For standalone code (in my case, a packet switch that ran on PDP-11's), I
> used a version of DDT that was linked in with the rest of the code. The
> original version was one in MACRO-11 which I inherited from Jim Mathis at
> SRI, but I eventually re-wrote it in portable C, and it was used on the 68K,
> uVax and 29K.
> For kernel assembler code... I can't remember what I did! Although I wrote a
> fair amount of it (I modified m45.s very extensively, to work with the Able
> ENABLE card), so I must have done _something_, but I have no idea what. In
> theory I could have linked DDT in with the kernel, but I don't think I ever
> did so?
> Recently I was debugging some kernel code (the splice() system call we were
> discussing here), and I debugged it using... printf()'s! It was written in C,
> but I don't really differentiate between debugging C code, and assembler.
>      > 2. No map file created by ld.
> LD normally includes a symbol table in the output file, which 'nm' can dump.
>      > 3. No debugger that I can find.
> See above.
>      > My workarounds include using OD to view the generated machine code
> Use db/cdb/adb if you want to look at compiled code. Also, for 'cc', use the
> -S flag.
> 	Noel
I have cdb, it works. How do I exit it. %, CTRL-C, CTRL-D, CTRL-Z, 
Break, CTRL-Break, and so on just result in a ? being displayed. I 
checked the man page, no joy. It is possible to use %r to run the 
program at which point it exits, but I'm hoping there's a magic key 

db works too and it's exit is simply %.



More information about the TUHS mailing list