YOyosefk·Feb 17, 2025
Author here - any tips on dirty tricks somehow using %fs + offset from a shared library, without calling __tls_get_addr and without recompiling the executable (for instance, from a Python extension module) are most welcome! (I have one such trick - mmaping an address produced by ORing some high bit into %fs, and accessing that - but it's seriously dirty and I doubt it would survive outside a limited set of use cases.)
Separately, the post describes one of a few aspects of optimizing funtrace (https://github.com/yosefk/funtrace), which I think is the fastest open-source function tracing profiler for C++ today, and which can be ported relatively easily to Rust/other languages producing native code (the runtime is ~1200 LOC of C++; the trace decoder would need very few changes.) A description of how funtrace works as well as why you'd want a
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tracing profiler (as opposed to a sampling profiler like perf) and how you'd use it is here: https://yosefk.com/blog/profiling-in-production-with-functio...