I’m trying to open my Xbox Gamepad at /dev/input/js0 using syscall 56. I have verified the devices’ existence at the given path. Including through a test program written in C with open(). However, the program continues to branch FailExit.

.global main

.section .text
.align 2
main:
    ldr x0, =GamepadPath
    mov x1, #0
    mov x8, #56
    svc #0

    cmp x0, #0
    blt FailExit 

    mov x0, #1
    ldr x1, =SuccessMsg
    mov x2, #25
    mov x8, #64
    svc #0 

    mov x0, #0
    mov x8, #93
    svc #0

FailExit:
    mov x0, #1
    ldr x1, =ErrorMsg
    mov x2, #25
    mov x8, #64
    svc #0
    mov x0, #0
    mov x8, #93
    svc #0

.section .data

.section .rodata
GamepadPath: .asciz "/dev/input/js0"
SuccessMsg: .asciz "Gamepad Connectednn"
ErrorMsg: .asciz "Gamepad Not Availablenn"

.section .bss

I’ve attempt to understand several references including:

openat(2) – Linux man page

ARM64.Syscall.sh

What leaves me confused is that Syscall 56, OpenAt‘s first argument at x0 is suppose to be a return value set by syscall Open, which I cannot find on any reference for ARMv8 Linux.

Side Note: Software assembled with GCC. Which expects main rather than
start…