This is a collection of NASM code I have written while learning Assembly. It provides custom implementations of some of the standard C library functionality. I am not trying to be a "purist" here nor am I attempting to teach anyone Assembly. This is merely a repository for me to dump code while I re-learn/refresh my Assembly knowledge. Use at your own risk.
This repository is starting off with code written for 64-bit Ubuntu. I have begun the process of porting it to other Operating Systems/Architectures; namely, 64-bit Windows. I will aim to port at least one of the original 10 folders per week starting today, 2015-10-22.
I am not an Assembly expert. Far from it. Now that is out of the way - can anything here be improved? I am certainly open to improvements or suggestions. Whether they be README, code or comment improvements. This repository is just a bit of fun and purely for learning purposes .. but that doesn't mean I want it to be incorrect.
There is a root level folder for each environment the below samples have been written for. The currently available environments for a given sample are listed in parenthesis next to the sample name.
This project simply writes "Hello world!" to StdOut. The Linux version uses interrupts while the Windows version calls Windows APIs.
This project demonstrates how to call a function and use an argument passed to it. How this is achieved changes for each system/architecture the code is targeting and each folder complies with the specified systems' ABI..
This project also demonstrates stack frame initialization and tear down.
This project demonstrates using a local variable by storing a function argument in it then printing the string pointed to by the local variable. The 64-bit Windows version demonstrates local variables in relation to the local stack frame that contains Shadow Space.
This project reads the user input from StdIn and echoes it back to StdOut. The project itself demonstrates the use of the data segment to pre-allocate a block of memory. This block of memory is used as the buffer for user input.
This project demonstrates an itoa algorithm to print numbers
to StdOut. The algorithm and code is explained in detail on my blog.
This project demonstrates how to determine the length of a NULL-terminated string. It
uses the scasb instruction to scan a string looking for a NULL byte.
This project demonstrates asking the host operating system for some
dynamically allocated memory. It then fills the memory in with "Hello World!"
and prints it to StdOut. This is not a full implementation of malloc, but
it demonstrates dynamic memory allocation.
This project concatenates the strings "Hello " and "World!" before printing them to StdOut. It does so by allocating 16 kilobytes of memory and using it as a string buffer with which to place the result.
This project demonstrates an algorithm for converting ASCII strings to integers. It makes good use of varying register sizes and seems small for what it does. It converts the strings "23" and "32", adds the integer result to 100, then attempts to compare the result to the integer 123. It then prints "Equal" or "Not equal". The tests are performed in the above order.
This project demonstrates separating code into individual files for reuse. It contains a strings and io file for common string and IO operations such as strlen, strcat, readline, print, etc. It makes a few improvements to previous implementations of these and will continue to be used throughout the rest of the learning process (unless significant improvements can be made .. in which case newer versions will be written).
The code itself prompts the user to enter two numbers, adds them together and prints the result to StdOut.