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Comment by jpc0 | Hacker News Reader

How would you implement this may I ask? C++ does not have reflection in the language so you at best can do that by hooking into the running application, but C++ also aggressively inlines functions on anything except -O0 which mean your function call might never be a function call. Running at -O0 is alsp just generally a bad idea since many many instances of UB will never get caught.

The only way I can see doing this at compile time is with a compiler extension but then you are entirely locked in to 1 compiler.

Maybe if you compile with debug symbols but then well, you are shipping debug symbols...

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gcc has "-finstrument-functions". This calls your code on every function entry and exit. I've used this previously for tracing as described here and to move memory-protection windows around based on the running code.

If you want something passable, most compilers have function prologue/epilogue hooks that you can write in plain code. Realistically, development and test systems are only going to target like 1 or 2 compilers, so it is not very much work. Unless you are distributing a source library and you want to get full-trace telemetry from customer systems in-development, that is probably all you really need to do.

If you want to really zoom, you need to get the hooks inlined and probably just written in straight assembly. You then need to optimize your binary format and recording system. You then need to start optimizing your memory bandwidth usage when that becomes the bottleneck. Your overhead in the end is basically limited by memory bandwidth; you can only shovel so many tens of GB/s of logging into memory. Note that persistence has likely been infeasible for the last 2 or so orders of magnitude; RAM is likely the only storage consistently fast enough for the data rates you want to generate when doing this.

Makes sense and that's for three detailed answer. May put that one on the list of things to play with in the future.

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