libasm

A library of standard C functions reimplemented in x86-64 assembly for the 42 libasm project.

Implemented Functions

• ft_strlen - Calculate string length
• ft_strcpy - Copy a string
• ft_strcmp - Compare two strings
• ft_strdup - Duplicate a string (with dynamic memory allocation)
• ft_read - Read from file descriptor
• ft_write - Write to file descriptor

x86-64 Registers Used

Register	Size	Purpose
rax	64-bit	Return value, accumulator
rbx	64-bit	Callee-saved general purpose
rcx	64-bit	General purpose, loop counter
cl	8-bit	Low byte of rcx
rdi	64-bit	First function argument (pointer)
rsi	64-bit	Second function argument (source)
rdx	64-bit	Third function argument / data
rsp	64-bit	Stack pointer

Linux System Calls

The assembly library uses the x86-64 syscall convention. Arguments are passed in rdi, rsi, rdx, r10, r8, r9 and the syscall number goes in rax. The syscall instruction transitions to kernel mode and the kernel dispatches based on rax.

x86-64 System Call Numbers and Argument Registers

rax	Syscall	rdi	rsi	rdx	Notes
0	read	unsigned int fd	void *buf	size_t count	returns ≥0 or -errno
1	write	unsigned int fd	const void *buf	size_t count
60	exit	int status	-	-	no return
2	open	const char *pathname	int flags	mode_t mode
3	close	unsigned int fd	-	-

Build & Test

Makefile Targets

• make / make all - Compile the library (libasm.a)
• make test - Compile library and link with main.c to create test executable
• make clean - Remove object files
• make fclean - Remove object files and library
• make re - Clean and rebuild everything

Usage

# Build the library
make

# Compile and run tests
make test
./test

# Clean build artifacts
make clean

# Full rebuild
make re