Tech – eopXD

2021 LLVM Dev Mtg: How to utilize a LoopNest pass

第一次在 LLVM Developer’s Meeting 上做分享！
My first talk on LLVM Developer’s Meeting!

Tutorial: How to contribute to upstream LLVM

As a LLVM Developer, you will have to know how to use the Phabricator if you want to contribute a patch(commit) to the upstream. You can know more about what is upstream here.

Google Summer of Code 2021

這不是一篇技術筆記，主要紀錄今年 Google Summer of Code 的參與。當然，對 LLVM 的參與並不會隨著專案告一個段落而結束。在此分享自己參與的方式與經驗，也想跟大家說 LLVM 社群真的是一個很酷的地方。

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.

Clean Output, visualization by FlameGraph

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.

Plutus Pioneer Program – Week 3 筆記

Plutus Pioneer Program – Lecture #3

Plutus Pioneer Program – Week 2 筆記

Plutus Pioneer Program – Lecture #2

Plutus Pioneer Program – Week 1 筆記

Lecture link: Plutus Pioneer Program – Lecture #1

Recursive template metaprogramming (Part III)

On the previous part, I went through some practice on abstractions when writing recursions.

This part would be the last part of the current topic. I would implement MergeSort with recursive template metaprogramming.

Recursive template metaprogramming (Part II)

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.

Recursive template metaprogramming (Part I)

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.

Category: Tech