Device tree is for describe the peripheral HW. It not noly can describe the detectable devices, but also can be used for ==non-detectable== devices :::info non-detectable device: Like memory information, flash information, UARTs, GPIOs ...etc. ::: Device Tree Source (.dts) root /: This is root for device tree. / {

What is "Address Sanitizer"？ Address Sanitizer is a tool for detection memory error, like stack over flow, buffer over follw, memory leak...etc. How to use it ? set the compiler flag​​​​-fsanitize=address -fno-omit-frame-pointer ​​​​-fsanitize=address including the LSan, so when you enable ASan, the LSan also be enabled. :::info You can use

Overview Compiler Linker Elf LivePatch

ASan TSan MSan others

What is linker What does the linker do? Collect together all pieces of a program Coalesce like segments Fix addresses of code and data so the program can run So linker is for linking object code and library to elf file, like the following figure. 擷取選取區域_090 :::info

If there is a problem when the process is running, we stop the process and observe the debugging log, and then update the code to try to reproduce the problem. But when you stop this process, it means that the current environment may change. So in this case livepatch can be used LivePatch repo Theory When a program be loaded to memory, it will be loaded by elf format into the VMA. Loader will also link the dynamci lib to support it.

symptom When executing the following cmd echo "run:touch file1" touch file1 echo "run:ln -s file1 symlink" ln -s file1 symlink echo "run:rm -f symlink"

simplefs Kernel panic root is not show “.” and “..” simplefs Slab cache remaining Cache leak issues solve

Repo. Auxiliary Tool kmodleak : eBpf for slab memoroy tracing leak tracing ls/ mv cmd leaking commit 0 [<ffffffffa5d2f98e>] __alloc_pages+0x24e

source code repo simplefs Cache leak when remove simplefs module When we remove the kernel module, the kernel message shows =="Objects remaining in .... on __kmem_cache_shutdown()"==, that means some cache leaks in slab when the module be removed. [97834.762774] BUG simplefs_cache (Tainted: G B W OE ): Objects remaining in simplefs_cache on __kmem_cache_shutdown() [97834.766579] ----------------------------------------------------------------------------- [97834.771620] Slab 0x00000000cabe2244 objects=12 used=1 fp=0x00000000805ab4f7 flags=0xfffffc0010200(slab|head|node=0|zone=1|lastcpupid=0x1fffff) [97834.775969] CPU: 0 PID: 28304 Comm: rmmod Tainted: G B W OE 5.15.0-94-generic #104-Ubuntu

source code repo simplefs ls make kernel panic By execute the kernel module and use =="ls"== to show the list, we will get the kernel panic [ 2679.036002] usercopy: Kernel memory exposure attempt detected from SLUB object 'simplefs_cache' (offset 0, size 5)! [ 2679.038088] ------------[ cut here ]------------ [ 2679.038091] kernel BUG at mm/usercopy.c:102! [ 2679.039056] invalid opcode: 0000 [#1] PREEMPT SMP PTI [ 2679.040065] CPU: 0 PID: 167958 Comm: ls Tainted: G B W OE 6.2.0-39-generic #40-Ubuntu

source code repo - simplefs root directory do not show "." and ".." As we know the "." is a symbol link to currnet directory, and ".." point to it's parent When the file system is root for kernel system, the 'ls' do not show the =='.' / ".."==, but if the file system is mounted to other file system, this file system's root should has '.' and ".." test simplefs test environmet:

What is "Thread Sanitizer"？ Thread Sanitizer is a tool for detection race conditions or deadlocks in multi-thread How to use it ? set the compiler flag -fsanitize=thread: enable thread sanitize suggestion add "fPIE" and ""-pie" -g: create racing line number

3 kinds of real time task Head real-time The hard real-time definition considers any missed deadline to be a system failure. This scheduling is used extensively in mission critical systems where failure to conform to timing constraints results in a loss of life or property. Firm real-time Firm real-time tasks are such type of real-time tasks which are associated with time bound and the task need to produce the result within the deadline. Although firm real-time task is different from hard real-time task as in hard real-time once deadline is crossed and task is not completed, system fails but in case of firm real-time task even after the passing of deadline, system does not fail. :::infoVideo conferencing Satellite based tracking ::: Soft real-time

contributed by <RoyWFHuang> futex introduction futex(fast user-space locking), 用來減少 user space 使用競爭資源時, 對於 lock 的 kernel 系統呼叫. :::success 舉例來說, 兩個 process, 一個是網路程式, 另一個是檔案 io 操作. P1: socket 使用 write 動作時候, 會對於 buffer 做一次的 lock. P2: fd write 對於 disk block 進行 io, 此時也會對 kernel 呼叫一次 lock 但兩個 processes 資源是沒有衝突的, 所以 lock 就變成是多餘的 kernel lock. :::

linux2023 summer ref: 2023 年暑期 Linux 核心課程第 1 次測驗/作業檢討 測驗 α 測驗 α − 1 測驗 β 測驗 β - 1 static inline uintptr_t align_up(uintptr_t sz, size_t alignment) {

10 minutes for some coding skill How to check if an integer is divisible by 3/ 5/ 15? Intro. For this purpose, you might be think: That's too easy, Use modulus to resolve, see the pseudo code if $nr modulus 15 is 0 print $nr is divided by 15 else if $nr modulus 3 is 0 print $nr is divided by 3 else if $nr modulus 5 is 0

Install outline digraph G { rankdir=LR; compound=true node [shape=record]; label="Auto test framework" subgraph cluster_NN{ label = "Name Node";

\ test case test software Target just for test Like pg tool using software arch[^0-6] developing fast

contributed by < RoyWFHuang > 2022q1 第 2 週測驗題 開發環境為: OS: ubuntu 20.04 kernel ver: 5.4.0-99-generic CPU arch: x86_64 roy@roy-ThinkPad-T460s:$ lsb_release -a