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. LD normally includes a symbol table in the output file, which 'nm' can dump. See above. Use db/cdb/adb if you want to look at compiled code. Also, for 'cc', use the -S flag. Noel