Logan's Note

Thoughts on the Developement of PyPy RISC-V JIT Backend

Logan — Mon, 30 Dec 2024 23:21:00 +0800

After eight years of development, my patch implementing a RISC-V JIT backend for PyPy was merged upstream in 2024. This work is now included in the PyPy v7.3.17 release in this August. To share my journey and my insights, I decided to write this article.

A brief introduction …

Django: Count Aggregates with Conditions

Logan — Sun, 06 Jan 2019 18:39:00 +0800

In Django, One-to-Many relations are modeled by the ForeignKey. Under some circumstances, we may wish to collect some information (e.g. count, min, max, avg, etc) from related objects. For example, in a blog app, we may wish to build a table which lists the title and the number of …

Manage Chroot Environments with Schroot

Logan — Sat, 24 Feb 2018 22:33:00 +0800

Schroot allows users to switch between different Linux distributions or releases conveniently. As a software developer, I have to test software between different Debian and Ubuntu releases. Schroot perfectly fits my use case.

Besides, schroot has good balance between isolation and convenience. By default, it will mount the home directory …

Build qemu-user-static from source code

Logan — Sun, 18 Feb 2018 15:50:00 +0800

qemu-user-static is an important tool for cross-architecture developers. It allows developers to create a chroot environment and run the cross-compiled programs. For example, a developer may run an AArch64 executable without the overhead of system-level emulation.

I usually install the qemu-user-static binaries from Ubuntu apt repository. However, I encountered some …

Find Undefined Behavior with Clang UBSan

Logan — Sat, 27 Jan 2018 20:01:00 +0800

Two weeks ago, I came across an interesting bug. The convert() function below returns 0x80000001 when p points to 0x01, 0x00, 0x00, 0x80, but the expected return value is 0x00000001 instead.

int32_t convert(const uint8_t *restrict p) {
  uint32_t x = (                  p[0] +
                256 *             p[1] +
                256 * 256 *       p[2] +
                256 * 256 …

POSIX Shared Memory

Logan — Sun, 07 Jan 2018 08:23:00 +0800

POSIX shared memory is an inter-process communication (IPC) mechanism defined in POSIX specification. After setting up the shared memory, two (or more) processes may read from and write to the shared memory region. Compared to other IPC mechanisms (e.g. pipe, socket, etc), POSIX shared memory does not impose copy …

Full-text Search with Django and PostgreSQL

Logan — Sat, 30 Dec 2017 19:50:00 +0800

Django has several PostgreSQL database functions to support full-text search. If you are using PostgreSQL as the database backend, then it is easy to add full-text search to your Django app.

In this post, I would like to build an demo app with full-text search. This post covers several PostgreSQL-specific …

Introduction to qemu-debootstrap

Logan — Sat, 21 Jan 2017 22:49:00 +0800

User-mode QEMU translates the instructions and the system calls. To run a static executable, you may wrap the command line with qemu-${arch}. For example, you may wrap an ARM64 static executable with qemu-aarch64:

$ qemu-aarch64 /path/to/static-executable

However, running a dynamically linked executable requires more efforts. To run a …

Django ORM and Updating Counters

Logan — Sat, 03 Dec 2016 22:04:00 +0800

Counters are common in website development. Most websites collect the number of page views with counters. E-commerce websites keep track of the quantity of a commodity with counters. However, it is hard to implement a correct counter with Django ORM.

In this post, I would like to cover three ways …

Connect to Freenode with Irssi through SSL and SASL

Logan — Sat, 19 Mar 2016 16:47:00 +0800

My dynamic IP address, which is provided by my ISP, seems to be blocked by Freenode (because it is easy for us to get another IP.) According to the error message, I should connect and login with SASL. It took me a while to figure out a solution, thus I …

Python Property Decorator

Logan — Sat, 12 Mar 2016 20:09:00 +0800

Recently, I was tracing the source code of PyPy, and a special decorator named @property caught my attention. It seems to be a mechanism for Python programmers to create a getter, a setter, and a deleter for an instance variable. For example, how could we intercept the access to a …

Experience with Atom Editor

Logan — Sat, 05 Mar 2016 11:02:00 +0800

I have been a Vim user for a long time. However, I found that Vim is not good enough for me to write blog with Pelican. I need a good reStructuredText previewer, but I am not very satisfied with InstantRst. I wish to have a two-panel editor that I can …

Colon Built-in in Bash

Logan — Sat, 27 Feb 2016 15:17:00 +0800

I came across a weird line in a shell script:

: ${parameter:=word}

It is so weird that I don't even know how to search for further information. Fortunately, I found a post after searching bash colon. It is a built-in utility which simply exits with 0. In the other words …

Open and Close Files in Bash

Logan — Sat, 20 Feb 2016 16:05:00 +0800

In a shell script, file descriptor 0 stands for stdin, file descriptor 1 stands for stdout, and file descriptor 2 stands for stderr. In addition, programmers can open, close, or duplicate file descriptors with the exec built-in command and the I/O redirection operator:

Syntax	Description
`exec $fd< "${filepath}"`	Open …

JavaScript Object.defineProperty()

Logan — Sat, 30 Jan 2016 21:01:00 +0800

In Javascript, we can add a property to an object with:

obj.property = value;

However, sometimes we would like to have fine-grained control over properties. With Object.defineProperty(), we can decide:

Descriptor	Purpose	Default
value	Property value	`undefined`
writable	Whether the property can be assigned	`false`
get	Getter of the …

NPM Package Manager

Logan — Sun, 24 Jan 2016 20:04:00 +0800

NPM package manager plays an important role in Node.js ecosystem. Every serious Javascript developers should learn how to create a package with npm. In this post, I am going to cover several important npm commands.

Initialize a NPM Package

To start a project, we have to create package.json …

Flask and Socket.IO

Logan — Sat, 16 Jan 2016 15:03:00 +0800

Under some scenarios, we would like to push a message from an HTTP server to clients. For example, in a group messaging application, whenever a user sends a message to the server, the server has to push such message to everyone. Since 2001, several techniques have been proposed. Eventually, WebSocket …

Vim Ctrl-P Plug-in

Logan — Sat, 09 Jan 2016 09:21:00 +0800

Ctrl-P plug-in allows us to open files with fuzzy names or regular expression matches. It boosts my productivity at lot! I am glad to know about this plug-in and I would like to share my experience with you.

Installation

If you are managing Vim plug-ins with Vundle [1], you can …

Python New Style Class

Logan — Sat, 02 Jan 2016 19:08:00 +0800

Recently, I am curious about this code snippet:

class Test(object):
    def __init__():
        pass

Why do we have to extend or inherit from object type?

There are no differences with or without (object) in Python 3. But there are significant differences in Python 2. If a class inherits (either directly …

A Quick Guide to Grunt

Logan — Sat, 26 Dec 2015 17:34:00 +0800

Grunt is a task runner for Javascript development. Grunt automates the process to bundle, transpile, uglify, and compress the Javascript source code. This post would like to give a quick guide to Grunt.

Installation

Our first step is to create a package.json. We will need a package.json to …

JavaScript Prototype and Object Oriented

Logan — Sat, 19 Dec 2015 23:21:00 +0800

Javascript is a prototype-based object-oriented programming language. Unlike the conventional class-based object-oriented programming languages (e.g. C++ or Java), which ask programmers to write a class and then instantiate several similar objects from the class, Javascript adopts a different approach. In the world of Javascript, we have to craft a …

Read Lines from stdin in Node.js

Logan — Sat, 12 Dec 2015 22:13:00 +0800

It is easy to write a hello world program in Node.js:

console.log("Hello world!")

However, due to the asynchronous nature of Javascript, reading inputs and writing outputs are less straight-forward. We have to pass the callback functions or register event listeners.

First Attempt

For example, to read some …

Browserify

Logan — Sat, 05 Dec 2015 19:30:00 +0800

It is common to organize the code in several modules when we are developing Javascript applications. In Node.js ecosystem, we can import a module with the require() function and export symbols by adding them to the module.exports object. On the other hand, ES2015 adds import statements and export …

Run ES2015 with Babel 6

Logan — Sun, 29 Nov 2015 18:45:00 +0800

ECMAScript 2015 (also known as ES2015 or informally ES6) is the latest standard for JavaScript. It has been released for a while. However, V8, the JavaScript engine for Node.js, has only limited ES2015 support. As of writing, according to ECMAScript 6 compatibility table, the feature coverage of each Javascript …

Bash Signal Handler and Traps

Logan — Mon, 16 Nov 2015 01:25:00 +0800

I would like to launch ssh-agent and add my private key at the beginning of my shell script and stop it before leaving the shell script. How do I guarantee that ssh-agent will be shutted down properly? What will happen if the user press Ctrl-C or even kill the shell …

Autossh and Systemd Service

Logan — Sun, 15 Nov 2015 22:35:00 +0800

Several months ago, I wrote a post to describe how to setup an autossh daemon with upstart. Since Ubuntu 15.04 has switched to systemd, I would like to do the same with systemd. I will give a brief introduction to systemd in this post.

Systemd Unit File

Systemd services …

Fix Nautilus Video Thumbnails

Logan — Sun, 08 Nov 2015 15:19:00 +0800

I have a clean Ubuntu 15.10 installation these days. However, I noticed that video thumbnails (or previews) do not show up in Gnome Nautilus:

I prefer thumbnails to icons. Besides, I remember that Nautilus will generate a thumbnail for each video in Ubuntu 14.04. Thus, I took some …

Debug Multithreaded Program with GDB

Logan — Sun, 01 Nov 2015 20:37:00 +0800

GDB is a powerful debugger. Without a doubt, we can debug multi-threaded programs with gdb. In particular, we can switch between threads, inspect the stack, and dump the registers. In this post, I would like to start with the Dining Philosophers Problem, which was first coined by Edsger Dijkstra.

Here …

Discourse Installation Notes

Logan — Sun, 13 Sep 2015 22:28:00 +0800

Discourse is a new generation discussion forum. I found that Discourse is very suitable for personal note taking. One notable feature of Discourse is that the users can focus on conversations. Besides, it supports Markdown as the message markup language. This is the reason why I like it very much …

Global Git Ignore File

Logan — Sat, 27 Jun 2015 21:19:00 +0800

There are some files that shouldn't be tracked by Git at all. For example, the temporary files created by the text editors, the Python bytecode, and etc.

How could we ignore those files? In the previous post, I have mentioned that we can create a .gitignore file and list the …

Comparison and Sorting in Python3

Logan — Sun, 14 Jun 2015 23:45:00 +0800

Although I have written Python for several years, I am still not very familiar with its idioms. In particular, I don't quite understand how to compare and sort the objects in Python. That's the reason why I am writing this article.

The rest of this article consists of following sections …

Troubleshooting adb No Permissions Problem

Logan — Mon, 25 May 2015 21:59:00 +0800

I got an Android Nexus 7 (2013, Wi-Fi) device a short while ago. I attached the device to my computer and tried to list the devices with adb devices command. But, unfortunately, I got the following error message:

$ adb devices
List of devices attached
????????????    no permissions

In the following of …

Grub Install and Btrfs Root File System

Logan — Sun, 17 May 2015 01:44:00 +0800

Recently, the Linux operating system on my laptop no longer boots. It seems that the boot sector for GRUB bootloader is corrupted. I tried to reinstall GRUB with an Ubuntu LiveCD; however, I have encountered some problem related to Btrfs file system (which is the file system for my root …

Check Code Coverage with Clang and LCOV

Logan — Tue, 28 Apr 2015 01:28:00 +0800

Code coverage is a metric to show the code being untested. It can be considered as a hint to add more test cases. When we are writing C/C++, the most notable code coverage testing tool is gcov, which is a GCC built-in coverage testing tool. Besides, we can collect …

Trace Source Code with Vim and Ctags

Logan — Tue, 10 Mar 2015 23:01:00 +0800

Ctags is a source code indexing tool. With ctags, we can easily find the definitions of the classes, functions, and variables. According to my experiences, ctags can significantly reduce the time to browse the source code. In this post, I would like to give a brief introduction to ctags and …

Git Ignore File

Logan — Sat, 28 Feb 2015 14:19:00 +0800

In some circumstances, we would like to ignore the files (or directories) under the Git repository base directory. How could we do this? For example, assume that we have a Git repository with following files:

out/bin/conv
preprocessed/out/gen-case1.h
preprocessed/out/gen-case2.h
preprocessed/input.txt
conv …

Using Aria2 Download Manager

Logan — Sat, 21 Feb 2015 23:02:00 +0800

I used to download the large files with wget because I can simply resume the download tasks with -c option. This option will check the size of the output file, and download the rest of the file from the server. I can even restart the download task with a different …

C++11 Unique Pointer

Logan — Sat, 31 Jan 2015 23:04:00 +0800

C++11 introduced three new smart pointer class templates: std::unique_ptr, std::shared_ptr, and std::weak_ptr. These smart pointer class templates are designed to replace the old std::auto_ptr smart pointer, which is known to have some defect and deprecated now. In this post, I would like to give a …

C++ std::multimap and Equal Range

Logan — Tue, 20 Jan 2015 23:17:00 +0800

Today I have encountered a problem: Given that there are multiple equivalent keys in an instance of std::multimap, how could we list all of the corresponding values? For example:

#include <map>
#include <iostream>

int main() {
  std::multimap<int, int> xs;
  xs.insert(std::make_pair(1, 12));
  xs.insert(std …

Waliki Installation

Logan — Fri, 02 Jan 2015 11:20:00 +0800

Waliki is a simple wiki app for Django. We can write wiki contents with reStructuredText and the contents will be stored in a Git repository. In this post, I would like to introduce the instructions to install Waliki.

Getting Started

First, install the related Ubuntu packages:

$ sudo apt-get install git …

Python Package Manager: PIP

Logan — Thu, 01 Jan 2015 00:14:00 +0800

The Python package manager pip is a tool to manage the installed site packages. With pip, we don't have to be worried about the package dependencies anymore. pip will download the required packages from Python Package Index automatically.

Install Packages

To download and install the packages from Python Package Index …

2014 Year End Review

Logan — Wed, 31 Dec 2014 23:54:00 +0800

It's the end of 2014. It has been an amazing year with a lot of astonishing moments!

This is my first year to work as a full-time software engineer. I have learned a lot from the real world software development, including the PMD, annaul planning, software schedule estimation, and etc …

Debian Backports

Logan — Sat, 20 Dec 2014 22:04:00 +0800

It is well-known that Debian stable release is very stable, i.e. the packages are very old and well-tested. However, this become a problem to me.

Since Git 1.9, we have to run the following command to silence a warning when we are running git push.

$ git config --global …

Count Trailing Zeros

Logan — Wed, 17 Dec 2014 23:34:00 +0800

How to count the number of trailing zeros of an integer? The simplest way is to use the built-in function __builtin_ctz():

uint64_t count(uint64_t n) {
  return __builtin_ctz(n);
}

What will happen if we don't have __builtin_ctz()? If we have another built-in function __popcount(), which can compute the Hamming weight (the …

RISC-V Microprocessor

Logan — Tue, 16 Dec 2014 23:20:00 +0800

RISC-V is an instruction set architecture (ISA) released by UC Berkeley. Besides, a high performance, power efficient, and royalty-free open source implementation Rocket Chip is available.

RISC-V was developed by Krste Asanović and David A. Patterson. In their technical report, they claimed that an open instruction set can benefit both …

Autossh and Ubuntu Upstart Daemon

Logan — Mon, 15 Dec 2014 18:04:00 +0800

Since I am sharing the network without public IP, I would like to maintain a SSH tunnel so that I can connect to my desktop from the remote site. After searching the web, I found that Autossh fits my needs. Autossh is a utility that can start and monitor the …

LLVM Obfuscator

Logan — Tue, 09 Dec 2014 23:18:00 +0800

I came across the LLVM obfuscator today. It is a code obfuscator working mostly on LLVM IR level. This means that most LLVM supported target platforms are supported by the LLVM obfuscator as well.

Also, I have also read an article which mentioned how to disassemble and deobfuscate the binaries …

C++ Virtual Destructor and Inheritence

Logan — Tue, 09 Dec 2014 19:00:00 +0800

It is a well-known idiom to define a virtual destructor for the classes with virtual functions. If we don't define a virtual destructor, then the base class destructor will be invoked when you are deleting the object through the base class pointer even if the object is an instance of …

LLVM Bugpoint

Logan — Wed, 26 Nov 2014 23:03:00 +0800

In this post, I would like to introduce the bugpoint command line tool. This is a automatic test case reduction tool which can help us generate minimal test case.

As a compiler developer, the first step to debug is to create a minimal test case which can still reproduce the …

Vim Vundle

Logan — Tue, 25 Nov 2014 22:41:00 +0800

In the past, I didn't like to install the Vim plug-ins or new syntax highlight because all of the files were messed up in the .vim directory which makes it difficult to uninstall a plug-in.

Recently, I have come across with Vim Vundle. It is a vim plug-in manager which …

Let's Encrypt

Logan — Mon, 24 Nov 2014 23:32:00 +0800

According to the post by Andreas Gal, EFF, Mozilla, Cisco, Akamai, and IdenTrust are going to form Internet Security Research Group which will start the Let's Encrypt ceritificate authority service in 2015 Q2.

Let's Encrypt is expected to become a free, automated, and open SSL sertificate authority which aims to …

Ubuntu Bluetooth Headset

Logan — Mon, 24 Nov 2014 23:04:00 +0800

I have bought a Bluetooth headset recently. After connecting the device, I was quite disappointed with the sound quality. Fortunately, after searching on the web, it seems that I am using the "Telphony Duplex" mode, which has low quality.

Here are the steps to switch to the mode with better …

Install GCIN on Ubuntu 14.04

Logan — Sun, 23 Nov 2014 14:36:00 +0800

I decided to look for some alternatives to IBus input method after tolerating its long latency to switch between input methods for a long time. As a Taiwanese, both gcin and hime came up to my mind. Unfortunately, both of them need extra configuration after apt-get. Here's my note to …

Pre-compile the OpenCL Kernel Program - Part 2

Logan — Sat, 22 Nov 2014 12:22:00 +0800

In the part 1 of this article, we have mentioned how to pre-compile the OpenCL kernel program and load the pre-compiled binaries with the OpenCL API.

However, I was using the ioc64 command from the Intel OpenCL SDK to pre-compile the kernel program. This command might be unavailable in the …

Pre-compile the OpenCL Kernel Program - Part 1

Logan — Fri, 21 Nov 2014 21:22:00 +0800

In the previous post, we have written a simple vector addition OpenCL program. We were compiling the OpenCL kernel program from source code at run-time, thus we have to distribute the OpenCL source code to our users.

However, in some cases, we may prefer to pre-compile the OpenCL kernel program …

C++ Private Inheritence and Using Directive

Logan — Thu, 20 Nov 2014 11:52:00 +0800

I used to feel that the private inheritence is useless. Although we can implement the has-a semantics with private inheritence, it provides little benefits compared with object composition. Besides, in order to expose the privately inherited members to public, C++ introduced an awkward syntax, i.e. the using directives. These …

OpenCL 1.2 Manual Pages

Logan — Wed, 19 Nov 2014 22:37:00 +0800

There is a package for OpenCL 1.2 manual pages in the Ubuntu repository. To install the opencl-1.2-man-doc package, please run this command:

$ sudo apt-get install opencl-1.2-man-doc

After installing this package, we can check the OpenCL API with man command. For example, run man 3 clGetPlatformIDs to read …

Getting Started with OpenCL

Logan — Tue, 18 Nov 2014 23:05:00 +0800

I have heard of OpenCL for a long time, but I haven't tried it until recently. Here's my note to write and run a simple vector addition OpenCL program.

The following source code is compiled and tested with Intel SDK for OpenCL Applications. The code should work with other OpenCL …

Fix GRUB2 Warning

Logan — Mon, 17 Nov 2014 23:50:00 +0800

It has been for a while that my desktop PC was not showing the GRUB2 menu. Besides, I noticed that there was a warning message during the execution of update-grub:

Warning: Setting GRUB_TIMEOUT to a non-zero value when GRUB_HIDDEN_TIMEOUT is set is no longer supported.

After checking the manual, I …

GitHub Pages and HTTPS

Logan — Sun, 16 Nov 2014 23:31:00 +0800

GitHub Pages supports HTTPS protocol. It will be good to prefer HTTPS to HTTP. However, I found that if the URLs are not written carefully, the user might be redirected to HTTP URLs.

For unknown reason, GitHub Pages are redirecting the directories without trailing slash to the HTTP URLs. For …

Pelican and GitHub Pages

Logan — Sun, 16 Nov 2014 23:01:00 +0800

Pelican has built-in support for GitHub Pages. However, I noticed that the ghp-import command might screw up the commit log if your GitHub Pages and your Pelican source code share the same branch name.

According to the document of GitHub Pages, the user pages should be committed to master branch …

SSL Certificate

Logan — Sat, 15 Nov 2014 02:30:00 +0800

I would like to run shellinabox and my private blog system through HTTPS protocol. However, an SSL certificate is really expensive, thus I decided to run our own certificate authority and distribute my cacert.pem through GitHub Pages.

In general, running a certificate authority requires three steps:

Create a RSA …

C++ std::list Operations

Logan — Fri, 14 Nov 2014 23:53:00 +0800

To sort the doubly linked list std::list, we can simply call the sort() member function. For example,

#include <iostream>
#include <list>

int main() {
  std::list<int> xs{5, 4, 3, 2, 1};

  xs.sort();  // Sort the std::list!

  for (auto &x : xs) {
    std::cout << x << std::endl;
  }
}

We can't …

C++ Associative Container and Iterator Validness

Logan — Thu, 13 Nov 2014 22:38:00 +0800

I used to believe that iterators will be invalidated after calling the member functions insert() or erase() of containers. Thus, I would adopt a conservative approach:

Create a temporary container.
Copy the elements which I would like to keep to the temporary container.
Swap the container.

For example, to remove …

Git Merge Base and Checkout

Logan — Thu, 13 Nov 2014 22:04:00 +0800

Today I have learned two different usages of git command. First, to list the least common ancestor of two refs, we may use following command:

$ git merge-base --octopus <commit_1> <commit_2> ... <commit_n>

Please notice that --octopus is mandatory; otherwise, git will create a hypothetical commit M, which merges commit_2 .. commit_n, and …

Soundness and Completeness of the Type System

Logan — Wed, 12 Nov 2014 21:26:00 +0800

In the section 6 of Programming Languages course, Dan Grossman discussed about the soundness and the completeness of the type system. He said that:

A type-system is sound implies that all of type-checked programs are correct (in the other words, all of the incorrect program can't be type checked), i …

First Post

Logan — Tue, 11 Nov 2014 23:38:00 +0800

After using Blogger for several years, I decided to switch to Pelican and GitHub Pages. I feel it will be much easier to write down my thoughts, notes, and ideas with reStructuredText. As a result, I can update the blog more frequently.

In the foreseeable future, I will start to …