ls

ls.o

ls.s

/*#!as --gstabs+ -o ls.o ls.s && ld -o ls -e _start ls.o && objdump -d -j .text -j .data ls && ./ls
 */

.global _start
.macro sys_exit
    mov r7, $0x01 /* set system call number to 1 (exit) */
    svc $0x00     /* supervisor call  */
.endm

O_RDONLY = 0x0000
.macro sys_open
    mov r7, $0x05
    svc $0x00     /* supervisor call  */
.endm

.macro sys_write
    mov r7, $0x04
    svc $0x00     /* supervisor call  */
.endm

.macro sys_close
    mov r7, $0x06
    svc $0x00     /* supervisor call  */
.endm

.macro sys_getdents
    mov r7, $0x8d
    svc $0x00     /* supervisor call  */
.endm

.section .text
_start:
        bl main

        /* not reached */
        mov r0, $0xff
        sys_exit

main:
        /* open */
        ldr r0, =current_dir
        mov r1, #O_RDONLY
        sys_open
        cmp r0, $0x00
        rsble r0, r0, #0
        blle error
        mov v1, r0

1:
        /* getdents */
        mov r0, v1
        ldr r1, =dentry_buffer
        mov r2, #dentry_buffer_len
        sys_getdents
        cmp r0, $0x00
        beq 2f
        mov v2, r0 /* read bytes */
        rsblt r0, r0, #0
        bllt error


        ldr v3, =dentry_buffer
3:
        ldrh v5, [v3, #8] /* linux_dirent d_reclen */

        mov r0, $0x00
        add r1, v3, #10
        sub r2, v5, #12
        sys_write
        mov r0, $0x0a

        push {r0}
        mov r0, $0x00
        mov r1, sp
        mov r2, #1
        sys_write
        pop {r0}

        sub v2, v2, v5 /* len -= d_reclen */
        add v3, v3, v5 /* buffer += d_reclen */
        cmp v2, $0x00
        bne 3b

        b 1b

2:
        /* close */
        mov r0, v1
        sys_close

        mov r0, $0x00 /* set exit status to 0 */
        sys_exit

current_dir:
    .asciz "."
    .align 2

error:
        cmp r0, $0x00
        moveq r0, $0x01
        sys_exit

.section .bss
    .align 2

buffer: .skip 4096
dentry_buffer:
    .skip 4096
    dentry_buffer_len = . - dentry_buffer