Category Archives: Programming

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

Hacking Valgrind

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

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)

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

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

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

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

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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