c-nostdlib-assembly

We define own _start point without using glibc runtime library using ASM.

Support both x86_64 and i386 architecture.

$ gcc asm.c -o asm -nostdlib

This program dates back to probably 2019. I remember getting help from several people to prepare this. But unfortunately I do not remember their names.

Extra Draft

.data
msg: .ascii "Hello World\n"

.text
.global _start


_start:
    movl $4, %eax   ; use the write syscall
    movl $1, %ebx   ; write to stdout
    movl $msg, %ecx ; use string "Hello World"
    movl $12, %edx  ; write 12 characters
    int $0x80       ; make syscall
    
    movl $1, %eax   ; use the _exit syscall
    movl $0, %ebx   ; error code 0
    int $0x80       ; make syscall

As defined in $build/usr/include/asm/unistd_32.h, the syscall numbers for write and _exit are:

#define __NR_exit 1
#define __NR_write 4

In $build/usr/include/asm/unistd_64.h, the syscall numbers are defined as following:

#define __NR_write 1
#define __NR_exit 60

Thanks