mmap.asm

.data

.balign 4
zero_file: .string "/dev/zero"

.balign 4
fail_open_msg: .ascii "cannot open /dev/zero!\n"
.set fail_open_msg_sz, . - fail_open_msg

.balign 4
succ_open_msg: .ascii "successfully opened /dev/zero!\n"
.set succ_open_msg_sz, . - succ_open_msg

.balign 4
fail_mmap_msg: .ascii "mmap failed to allocate memory!\n"
.set fail_mmap_msg_sz, . - fail_mmap_msg

.balign 4
succ_mmap_msg: .ascii "mmap successfully allocated memory!\n"
.set succ_mmap_msg_sz, . - succ_mmap_msg

.text
.global _start

_start:
    ldr r0, =zero_file
    ldr r1, =open_rw
    ldr r2, =open_rusr
    ldr r7, =sys_open

    mov r1, #0
    cmp r0, r1

    ; if less then 0, print message and exit
    ldrlt r0, =stdout
    ldrlt r1, =fail_open_msg
    ldrlt r2, =fail_open_msg_sz
    ldrlt r7, =sys_write
    swilt #0
    blt exit

    ; otherwise print ok message and close file
    push {r0} ; fd
    ldr r0, =stdout
    ldr r1, =succ_open_msg
    ldr r2, =succ_open_msg_sz
    ldr r7, =sys_write
    swi #0

    mov r0, #0
    mov r1, #32 ; allocate 32 bytes
    ldr r2, =mmap_prot_read
    ldr r3, =mmap_prot_write
    orr r2, r3
    ldr r3, =mmap_private
    pop {r4}
    mov r5, #0
    ldr r7, =sys_mmap
    swi #0

    push {r0} ; push mem_ptr to stack

    movs r1, #-1
    cmp r0, r1

    ldr r0, =stdout
    ldrne r1, =succ_mmap_msg
    ldrne r2, =succ_mmap_msg_sz
    ldreq r1, =fail_mmap_msg
    ldreq r2, =fail_mmap_msg_sz
    ldr r7, =sys_write
    swi #0

    pop {r0} ; pop mem_ptr off stack
    mov r1, #32
    ldr r7, =sys_munmap
    swi #0

    mov r0, r4
    ldr r7, =sys_close
    swi #0
exit:
    mov r0, #0
    ldr r7, =sys_exit
    swi #0