below...
On Fri, Aug 25, 2023 at 3:51 PM segaloco via TUHS <tuhs@tuhs.org> wrote:
Hello, I've been doing some research on the history of disassembly lately, tools available historically, today, and what sorts of developments have been made regarding utilities and systems for taking a machine-code binary and working it back to some semblance of source code.
So in the early days UNIX had das(I), a PDP-11 disassembler I believe written by Ken (he's OWNER in the manual) with very little information other than "it exists". Fast forward to the UNIX 4.1 manual in 1981 for the 3B20S and there is dis(1), a 3B20 disassembler. Other such manuals feature dis(1) versions for other 3B targets.
Was a disassembler ever considered part of the standard binary objects toolkit with the assembler, linker, etc.
not to my memory - although some of the debuggers could. IIRC, the DDT that was on the Harvard tape knew about it. I also remember on that tape was a PDP-11 disassembler. Phil Karn wrote a table-based one for UNIX when we were students - but it was aimed at 8-bit micros. It could do 8080/8085 and Z80; if I remember, it could also do MOS6502 and M6800. It had a feature that it could take an external symbol table and turn out code that was reasonable to reassemble. [ I may have a copy if it squirreled away ].
That said, while they we not part of the core tool kit, by the time of BSD4.2 there were a couple of disassemblers kicking around the USENET. I remember one for the Vax and another for the 68000. You might do a grep for dis-assembler in the USENET archives for comp.sources
or was that the sort of thing that was more niche and therefore just kinda cropped up when/if someone decided to write one?
exactly - need driven. Phil wrote his when we were trying to pull apart a ROM for a tape controller. It had a funky interface on it that was not well documented and what we did have, was wrong. So, disassembled enough of the ROM that we could changed it.
Were there legal concerns to be grappled with when producing a disassembler?
Mumble ... by the mid-80s/late-90 people we disassembling code for game controllers and PCs. So many manufacturers started adding words in the EULA saying that was a no-no. But I don't remember worrying about it much when I was a student 10-15 years before that.
Were such tools ever shipped or did they only appear in the manuals as they were technically up in the code base, just not commonly distributed or used? Also, was there any thought given during the development of C to producing "decompilers" as has been becoming more common lately? Or was it a foregone conclusion that C to assembly is a "lossy" conversion and going the other direction couldn't be fully automated.
Again - in V6/V7 with DMR's compiler, it was not always easy, but the code generally was pretty straightforward.
Post Wulf's 'Green Book' on compiler optimization and we started to have a generation of BLISS-style optimizers pretty much everywhere, I think those compilers really started refactoring code plus instruction sets got more sophisticated, so I think it started to get harder and harder to reconstruct.
But I'll defer to someone like Paul W or Steve Johnson who loved building those style of tools.
Thank you for any insights!
- Matt G.
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