a quick demonstration of C inline assembly

inline_asm.c

// re-writing strlen, while certainly doable, isn't the point
#include <string.h>

void print(char* message);
void readLine(int maxBytes, char *dest);

int main(void) {
    char message[] = "Hello world!\n";

    print(message);
    print("What's your name: ");

    char name[128] = {};
    readLine(127, name);
    print("Your name is ");
    print(name);
    print("!\n");
}

// Directly calls sys_write
void print(char *message) {
    int len = strlen(message);
    
    asm("movq $1, %%rax\n\t"
        "movq $1, %%rdi\n\t"
        "syscall"
        :
        : "S"(message), "d"(len)
        : "rax", "rdi");

    return;
}

// Directly calls sys_read
void readLine(int maxBytes, char *dest) {
    asm("movq $0, %%rax\n\t"
        "movq $0, %%rdi\n\t"
        "syscall"
        : "=m"(*dest)
        : "S"(dest), "d"(maxBytes)
        : );

    // strip the trailing newline
    int i = maxBytes - 1;
    while (dest[i] != '\n' && dest[i] >= 0)
        i--;
    if (i != 0)
        dest[i] = 0;
    return;
}

Interestingly if I press the up arrow key during the input prompt I get weird terminal bugs.
Must clobber an escape sequence somewhere in the plumbing.