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by foxfluff 1616 days ago
> Put a breakpoint early on startup, once hit put a data breakpoint on the part of the state which messed up, reproduce the bug, and there's very high chance debugger will take you to the code which broke the state.

Except when you find the data you're after doesn't exist early at startup, it's allocated on the fly as connections come and go, and you need thousands of connections to come and go before the bug manifests, and the data that eventually gets messed up may first be used thousands of times before it's wrong all of a sudden. IME it's precisely these multi-threaded memory corruption bugs that really resist debuggers. And as is often the case, debugger changes timing so much that the bug doesn't even reproduce.

Even if you find the code that corrupts the memory, it might be totally okay, it just somehow got passed the wrong memory long ago through no fault of its own (or you're looking at a use-after-free).
1 comments
Const-me 1616 days ago
Indeed, it can happen too. All software is different, bugs are different, and optimal debugging tactics is very different as well.

But when the one in my comment does work, the saved debugging time can be measured in days.

Speaking about debugging tactics, there’re way more than just two. There’re OS-level tools like process monitor on Windows / strace on Linux. There’re specialized tools like RenderDoc or Wireshark. For different types of bugs, these tools can sometimes also save days of work compared to other methods.

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foxfluff 1616 days ago
Aye. It's also not always obvious what's the optimal tactic, and I believe in many cases there are multiple equally valid approaches and you pick the one you feel most comfortable with. Sometimes the one you start with is a dead end.

That's why I don't really like an absolutist stance (if you rarely use debugger you're dumb / if you always poke around with a debugger you're dumb). I just happen to fall in the "rarely uses debugger" camp myself.

> I’ve done hundreds of interviews like this, and it’s fascinating watching what people do. Do they read the code first? Fire up a debugger? Add print statements and binary search by hand? [..] After hundreds of interviews I still couldn’t tell you which approach is best.

(From https://news.ycombinator.com/item?id=29813036)

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