Category Archives: Programming

Programming – C/C++, Java, Ksh, Python, ML

Borland Turbo C++ 3.0 on MacOS

Posted on April 9, 2023 by daveti

The recent post from Hackaday on Borland Turbo C/C++ [1] managed to trigger my nostalgia, when I needed to pass some national programming testing in C as an undergrad in China over 20 years ago, and it was Borland Turbo … Continue reading →

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Hacking Valgrind

Posted on July 7, 2018 by daveti

This post talks about 3 commits I have recently added into my own valgrind tree [1], including the support for fsgsbase instructions, rdrand/rdseed instructions, and adding a new trapdoor (client request) to support gdb-like add-symbol-file command. Note that all these … Continue reading →

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Valgrind trapdoor and fun

Posted on July 7, 2018 by daveti

Valgrind has a client request mechanism, which allows a client to pass some information back to valgrind. This includes asks valgrind to do a logging in its own environment, tells valgrind a range of VA being used as a new … Continue reading →

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Kernel Code Execution Time Measurement (kcetm)

Posted on May 20, 2018 by daveti

This post mainly talks about the correct usage of tsc counters provided by Intel x86/x86-64 architectures to measure the Linux kernel code execution time. Most of the content here is borrowed/inspired from [1]. Note that this is NOT a post … Continue reading →

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Why list and charlist are confusing in Elixir

Posted on October 6, 2017 by daveti

This post talks about list and charlist in Elixir, and discusses one specific issue in Elixir. Let’s look at the confusing thing in Elixir: iex(2)> a = [7] ‘\a’ iex(3)> b = ‘\a’ ‘\a’ iex(4)> a == b true iex(5)> … Continue reading →

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A PoC of DoS attack in Elixir Actor Model

Posted on September 29, 2017 by daveti

The naive way of using the Actor model in Elixir is using “receive” in a loop, which is then “spawn”d as a Erlang process. Unfortunately, a potential DoS attack could happen if the pattern matching is not coded carefully with … Continue reading →

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A pitfall of GenServer programming in Elixir

Posted on September 29, 2017 by daveti

OTP as a programming platform/framework, empowers not only Erlang, but also Elixir. This post looks into a pitfall when programming GenServer in Elixir, and provides a potential solution. All callbacks in the GenServer behavior have a limited and pre-defined possible … Continue reading →

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Pitfalls in negative indexing in C

Posted on August 3, 2017 by daveti

Negative indexing in C, such as a[-1], is legit, although rarely used. There are reasons (pitfalls) why negative indexing is not recommended. This post discusses these pitfalls when using negative indexing (for fun). 1. Negative indexing within the bound In … Continue reading →

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getdelays – get delay accounting information from the kernel

Posted on September 6, 2016 by daveti

Top may be the most common tool in use whenever a preformance issue is hit. It is simple, quick and dumb. Besides the heavy metal stuffs like perf and gprof, another really useful and simple tool is getdelays, which provides … Continue reading →

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Linux kernel I/O Stack Diagram

Posted on August 5, 2015 by daveti

Found this figure online. The title of this diagram may be biased as it is not the complete I/O stack but a concentration on block devices with a focus on SCSI layer. Some important missing stuffs, in my opinion, include … Continue reading →

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