Do you expect an IAP peddler to support free software?

Although that was true at the time, it was before the creation of modern omniscient debuggers like Pernosco (<https://pernos.co/>).

This doesn't sound like a particularly difficult problem for some scenarios.

It's definitely convoluted as it comes to memory obtained from the stack, but for heap allocations, a debugger could trace the returns of the allocator APIs, use that as a beginning point of some data's lifetime, and then trace any access to that address, and then gather the high-level info on the address of the reader/writer.

Global variables should also be trivial (fairly so) as you'll just need to track memory accesses to their address.

(Of course, further work is required to actually apply this.)

For variables on the stack, or registers, though, you'll possibly need heuristics which account for reusage of memory/variables, and maybe maintain a strong association with the thread this is happening in (for both the thread's allocated stack and the thread context), etc.

Sounds like you want a time travel debugger, eg. rr.

Sophisticated live debuggers are great when you can use them but you have to be able to reproduce the bug under the debugger. Particularly in distributed systems, the hardest bugs aren't reproducible at all and there are multiple levels of difficulty below that before you get to ones that can be reliably reproduced under a live debugger, which are usually relatively easy. Not being able to use your most powerful tools on your hardest problems rather reduces their value. (Time travel debuggers do record/replay, which expands the set of problems you can use them on, but you still need to get the behaviour to happen while it's being recorded.)

Sounds like you want time travel debugging [1]. Then you can just run forwards and backwards as needed and look at the full evolution of state and causality. You usually want to use a integrated history visualization tool to make the most of that since the amount of state you are looking at is truly immense; identifying the single wrong store 17 billion instructions ago can be a pain without it.

[1] https://en.wikipedia.org/wiki/Time_travel_debugging

Here's another one

https://scrutinydebugger.com/

It's for embedded systems though, which is where I come from. In embedded we have this concept called instruction trace where every instruction executed with the target gets sent over to the host. The host can reconstruct part of what's been going on in the target system. But there's usually so much data, I've always assumed a live view is kind of impractical and only used it for offline debugging. But maybe that's not a correct assumption. I would love to see better observability in embedded systems.