Tao's Fragments: RiscV Linux lib ELF Generation

Today is Jan 1st, 2026. And I will be back with what is meaningful. Years ago, I decide to start a new journey. After working on Rust, Linux OS, ELF file format, RiscV chip/ABI, and assembler and linker, and started C language compiler. Let's see how compiler tech and latest AI can change how technology can make programmer's life easier. 

I feel I can start blog again and share some fragments of my work and ready for open source. 

I've done the ELF executable with dynamic link support, it means that I can use my assembler+linker to generate ELF binary to invoke printf in libc. I've to say the RISCV's PLT/GOT RELA is really a headache, which can be topic for another fragemnt of mine. 😉

Today I finished the .so file generation and it can generate a library can be linked with gcc. Now I know why F# choose to support library after executable is done. And I know why F# library has its own printf. But anyway. 

The .so ELF generation is simple, my test .s file is listed below. Please note that i added my own pseudo instruction for RiscV assembly language. 

.data

.extern printf

tt_fmt: .string "%d\n"

const_float_or_string_value_104:

.string "Array index access test, expected value 42 and actual value: %d\n"

.text 

    .globl  add2               

    .type   add2, @function

add2:

    add     a0, a0, a1

    ret

    .size   add2, .-add2

    exit 42

The .extern will trigger dynamic symbol structure generation. The key here is the add2 function related instruction which is in bold font. 

• globl add2 is to add "add2" to the dynamic symbol (.dynsym) table.
• add2 shows the starting point of add2 function and it will be used to compute the size of the add2 function. 
• .size show the add2's size is equal to current (the small dot) minus add2. 

After these info being added to dynamic symbol table, the readelf -a shows the following:

the riscv64 gcc link can link this shared library with c code and command is listed below:

#include <stdio.h>

int add2(int a, int b);

int main() {

    printf("%d\n", add2(20, 22));

    return 0;

} 

and the exeuction result shows 42 which is 20 + 22 from add2(20, 22). 

Thanks to ChatGPT's which helps me to generate Linux command. Being a long time windows guy, I am still struggle to use correct Linux language, but let's see if this can change when I add more feature.

Compiler AST & Mermaid

I'm interested in RISC compiler for a while. One of the challenge of a compiler is to process AST. Being a visual person, I am interested in seeing the structure in an image. So I generate the mermaid state diagram and can visualize the tree. 

SelfNote: Enable Python in Visual Studio Interactive

This note is to document how to configure Python interactive window in Visual Studio (not VS Code)

Reference a local library

When I added a new .py file in the project, I cannot add it to the python interact window. The reason is the default path for python interact is under "program files". The following command is to change the current working folder to a new folder:

import os

os.chdir(r"c:\mycode\xyz\")

Make sure the string is started with "r". 

Reload a library

After change a library, the new content is not loaded to the python interactive session by default. The following command is to reload the library into the session.

import myModule #import my module

 

#the following is to reload myModule

import importlib

importlib.reload(myModule )

Please note: myModule does not need quote or double quote 

 

Matrix Multiplication & Graph Reachable

I have been struggling to find a good way to represent graph structure. There are number of graph library where Node and Edge are defined. I found that matrix can be used to represent a graph. 

The row and column of the matrix represent the node in a graph. The element in the matrix is connection between two nodes. In a graph, this connection is called Edge. The following diagram represents a graph with 3 nodes and 3 edges. 

 

In a matrix representation, it can be written as a matrix. Row and column are named A, B, and C. If there is an edge between two nodes, the corresponding cell is set to 1. For example, edge AB shows 1 in cell (A, B) in the grid. We can denote this matrix as M

Matrix "multiplication" to itself can reveal if a certain node can reach the other nodes in two steps. The "multiplication" operation is different from the linear algebra matrix multiplication.  

K = M ⊗ M

 Each element b in N can be calculated by the following formula, where N is the number of the nodes (or the column number of the matrix M).

Two nodes i and j. If there j is reachable from i, either of the following two conditions are met:

• there is a direct edge between i and j 
• there is a node p which is reachable from i and p can reach j

Written as math language in the matrix M

• M(i, j) = 1
• 彐p, M(i, p) = 1 and M(p, j) = 1

Repeat the "multiplication" operation logN times, it can calculate any node in a graph can be reachable from other nodes. 

Finally, I can move away from a complicated node/edge definition into a formal math world. Hopefully the existing linear algebra can help me down the road. 

SelfNote: VSCode setup

Recently I started to use the Azure cloud machine to do my coding work. I can still do my coding in my laptop using full Visual Studio but an Azure VM with VSCode will be much convenient. Low tech but works. :)

The following VSCode setup script helps me set up a new machine:

1. open PowerShell 
2. copy extension names to the clipboard (yes, Ctrl+C)
3. run get-clipboard | % { code --install-extension $_ }

DavidAnson.vscode-markdownlint

eamodio.gitlens

ms-azuretools.vscode-docker

ms-python.python

ms-vscode-remote.remote-wsl

ms-vscode.cpptools

ms-vscode.powershell

npclaudiu.vscode-gn

yzhang.markdown-all-in-one

Docker Image build clean up using PowerShell on local PC

When I run the docker image to do the debug on PC, I was struggling to keep the hard disk space consumption low and running the recent binary in "Docker on Windows Desktop". This development stage, so I won't consider the Azure cloud for hosting.

I need a script to reclaim hard disk, remove the currently running container, build and run the new image in docker on windows desktop. 

The following code first removes unused images and then gets the image running on the port 5555. I will have to play the string replace tricks using PowerShell. Please check "-replace" part for details. 

#prune unused image

docker image prune -f

#remove existing running docker image

$a = docker container ls --filter expose=5555

$a2 = $a | foreach-object {$_ -replace '\s{3,}', '  '} | foreach-object {$_ -replace '  ', "`t"}

$obj = ConvertFrom-Csv -InputObject $a2 -Delimiter "`t"

if ($obj -ne $null)

{

    docker rm -f  $obj.names

}

else

{

    Write-Verbose "cannot find running container image so won't remove"

}

#build flask app and set its version to 1

docker build -t flaskapp:1 .

docker run -d -p 5555:5555 flaskapp:1

#test running instance

sleep -s 4

invoke-restmethod "http://localhost:5555/api/health"

SelfNote: Setup Spacy Module in Visual Studio

I guess not so many people use Visual Studio doing NLP with Python. I have been searching for a solution on how to add a Spacy module in Visual Studio. I kept getting cannot find en_core_web_sm module error and the only solution I could find is to run python -m spacy download en_core_web_sm. I was struggling to find where in the UI to run the Python command. And finally, the solution came.

you noticed the "Admin" icon? yes, that is the key to solve the problem. With admin permission, you can open PowerShell and run python -m spacy download en_core_web_sm.

I installed en_core_web_sm, but it shows a warning message. And the en_core_web_lg module can eliminate the warning.