adventures in no libc hell, now with library functions xD

// ----------------------------------------------------------------------------
// "THE BEER-WARE LICENSE" (Revision 43):
// <aaronryool@gmail.com> wrote this file. As long as you retain this notice you
// can do whatever you want with this stuff. If we meet some day, and you think
// this stuff is worth it, you can buy me a beer in return Aaron R. Yool
// ----------------------------------------------------------------------------
// the no libc thing is refering to the assembly project this is a probe for, obviously this uses libc :P


#include <dirent.h>
#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <sys/syscall.h>

#include <stddef.h>
#include <stdio.h>
#include <stdint.h>

#define handle_error(msg) \
    do { perror(msg); exit(EXIT_FAILURE); } while (0)


typedef struct linux_dirent {
    long           d_ino;
    off_t          d_off;
    unsigned short d_reclen;
    char           d_name[];
} dent;

print_dent_offsets()
{
    printf("ino: %i\n", offsetof(dent, d_ino));
    printf("off: %i\n", offsetof(dent, d_off));
    printf("reclen: %i\n", offsetof(dent, d_reclen));
    printf("name: %i\n", offsetof(dent, d_name));
}


int Mopendir(const char* dirstr)
{
    int fd;
    asm(
        ".intel_syntax noprefix\n"
        "xor rax, rax\n"
        "mov al, 2\n"
        "mov rdi, %1\n"
        "mov rsi, 0x10000\n"
        "xor rdx, rdx\n"
        "syscall\n"
        :"+a"(fd) : "r"(dirstr)
    );
    return fd;
}

void* Mmalloc(uint64_t size)
{
    void* ptr;
    asm(
        "xor rax, rax\n"    //; char* buf=(char*)sbrk(1024);
        "mov al, 12\n"
        "xor rdi, rdi\n"    //;         //end=brk(0) <- get the current end value
        "syscall\n"
        "lea r9, [rax]\n"
        "xor rax, rax\n"
        "mov al, 12\n"
        "add r9, %1\n"
        "mov rdi, r9\n"     //;         //brk(end+1024) <- get the current end value
        "syscall\n"
        :"+a"(ptr) : "r"(size)
    );
    return ptr;
}

Mgetdents(uint64_t fd, void* buf, uint64_t size)
{
    int nread;
    asm(
        "xor rax, rax\n"    //;     nread = syscall(SYS_getdents, fd, buf, sizeof(buf));
        "mov al, 78\n"
        "mov rdi, %1\n"
        "mov rsi, %2\n"
        "mov rdx, %3\n"
        "syscall\n"
        :"+a"(nread) :"r"(fd), "r"(buf),  "r"(size)
    );
    return nread;
}

main()
{
    int fd, nread;
    // opendir
    fd = Mopendir(".");
    if (fd == -1)
        handle_error("open");

    char* buf = Mmalloc(1024);

    // list dir
    nread = Mgetdents(fd, buf, 1024);
    if (nread == -1)
        handle_error("getdents");


    int bpos = 0;
    for (bpos = 0; bpos < nread;)
    {
        dent* d ;//= (struct linux_dirent *) (buf + bpos);
        asm("lea %0, [%1+%2]" :"=r"(d) : "r"(buf), "r"((uint64_t)bpos));

        int d_type = *(buf + bpos + d->d_reclen - 1);
        if(d_type == DT_REG)
            printf("%8d %s\n", d->d_reclen, d->d_name);

        bpos += d->d_reclen;
    }
    // closedir
    close(fd);
}