I was trying to perf LLVM opt this week and got confused because the perf report showed mangled function calls on the stack traces. So I might as well write an article of it and hope it would get some Google juice and save others from confusion.
To build LLVM with complete stack traces, build with “CMAKE_BUILD_TYPE=Debug“
To allow perf to work on LLVM, build with “LLVM_USE_PERF:=ON“
At the very first place I thought the mangle-ed function call names exist because of perf not recognizing the symbols. It turned out I was wrong. If perf does not recognize the symbol it would simply show Unknown. The mixed-up symbol names are name mangling for function calls. (see more here)
You can remove the mangling simply with llvm-cxxfilt (see more here). For the exact correct mapping you may need to use llvm-cxxmap (see from here).
With the correct build I still get mangled-output. Turned out that the perf I apt-get-ed from is compiled with the de-mangling function turned off. It was a bug filed in linux since 2014 November and I’m still falling into this error on 2021 June 🤢. (on Ubuntu 16.04 linux 4.4.0-131 generic x86_64)
Mangled Output, visualization by FlameGraph
There’s 3 links in the bug thread above that may lead you to the solution. Personally I’ve download the perf tool in mirrors.edge.kernel.org, followed the instructions here to build the correct perf I needed.
NOTE: you may need to apt-get some dependencies to enable some feature in perf. Be sure to checkout the compile messages when you build from source. You can checkout features enabled with perf version --build-options.
PS: Just in case you came in with your perf not working on your self-compiled code with clang or gcc, you may want to look at this stack-overflow answer.
Previously I wrote about basic utility and simple examples of recursive template programming. On this part I will show how to write Find, Remove, PopFront, PopBack.
This article is a writeup to practice on recursive template metaprogramming. It is that may come in handy for compile time operations. I want to thank yoco for giving me a tutorial and introduction to the topic.
