Author: eopXD

Hi 我是 eop ，希望人生過得有趣有挑戰XD

畢業

畢業了。畢業對我來說其實不太像是離開台大。台大是何等模糊抽象的概念。更像是離開辛亥、溫州、泰順、汀州、大安。

在這裡經歷過不少荒謬的事，也因為這樣的地利之便才容納得下許多強說愁的騷年們。半夜的溫州仍然散發出蓬勃的生命力。

離開應該是代表新的階段的開始，但思緒還是常常把自己帶回這裡，或許就是這邊的穩定不變， 每次經過時的既視感才會如此強烈。告白、拒絕、牽手、滑板、熬夜、嘔吐、一起聞嘔吐過後的臭味、被老鼠嚇爛、醉到怎麼回青田街都忘記。

當時結交的朋友也都不再聯絡了。我該檢討為什麼至今的人生充滿告別，少了一些對維持的努力。這些痕跡為什麼除了在我們腦海裡之外沒能繼續留著。

我該多寫字，要不然又發生這種自以為片刻即永恆的慘劇。

的確是來來去去，但究竟什麼是長遠，什麼是從長計議，如今畢業似乎也沒有比較明瞭。如今心中仍然沒有一個穩定的狀態，伴隨而來勢必不是穩定的生活與交友圈，但似乎還不到真心為自己這樣擔心的時候，所幸前方仍然還是迷霧。

這份文章確實有存在的必要。是為了希望。希望來自未來，未來需要現在，現在需要這篇文章對過去的。到最後就算不留下這些外在性的事件，也要歸功於這些，才能打磨出通往內心的鑰匙。

疫情記事

人之間的疏離是一個過程，先是訊息的差異，差異構成了不同的敘事。不同的敘事導致不同的價值判斷，日積月累形成迥異的信仰。是什麼使我們得以立足於生活，而有了生活這樣的形狀與語境。不管如何社群與社會總是作為源源不絕的養份存在。當脫離人所組成所組成的社群和社會，失去生活中鮮活細節的激發與覺察，自然很難再站在同樣的脈絡上。

畢竟抽象化與推論似乎是根深蒂固於大腦內部的本能。經過了抽象化，道路中街景號誌等各式的細節，僅僅是數學模型一個小黑點。省去冗贅的細節可以幫助我們大腦思考，而過度的省略，資訊與細節的遺失就會發生。

社會運行的前進有它的節奏，怎麼樣也太大了，永遠超出了個體的感官所能覺察。即便還沒消化完今天的感受，明天仍要片刻不緩地出門，簡直與飛蛾撲火別無二致。金錢作為介質抽象化了將近所有的交換行為，生活的細節被換算成每日開銷，又進一步推估出年度預算。理性預先描繪了感官所能感知的範圍，寸步不逾。

疫情來了。機器停擺，機制必須改變。大家被推回各自的蝸居之中，每日推進自己的快節奏停下來了，被下來了。視野變小的情況下，也許生活可以被重新聚焦。行為的單向性不再遠超出自己的邏輯思考之外而被轉成結論。過多的物質勢必再次重新氾濫進生活之中。但總覺得這次的疫情對個人的精神來說是非常特別的過程。物質帶來的愉悅或許能不再只是金錢的增減。重新走過一次抽象化的過程，或許也能把生活的節奏重新放回自己雙手上，牢牢抓住。

If your perf is not working…

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.

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.

Continue reading “Recursive template metaprogramming (Part III)”