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.data
.global msg
.global no_arg_msg
.global got_arg_msg
msg:
.ascii "Hello, ARM!\n"
len = . - msg
no_arg_msg:
.ascii "No command line argument...\n"
no_arg_len = . - no_arg_msg
got_arg_msg:
.ascii "Got command line argument(s)...\n"
got_arg_len = . - got_arg_msg
.text
.global do_syscalls
do_syscalls:
/**
* syscall write(int fd, const void *buf, size_t count)
*/
mov %r0, $1 /* fd -> stdout */
ldr %r1, =msg /* buf -> msg */
ldr %r2, =len /* count -> len(msg) */
mov %r7, $4 /* write is syscall #4 */
swi $0 /* invoke syscall */
/**
* syscall write(int fd, const void *buf, size_t count)
*/
mov %r0, $2 /* fd -> stderr */
mov %r7, $4 /* write is syscall #4 */
ldr %r3, [sp] /* argc */
cmp %r3, $1
beq no_arg
ldr %r1, =got_arg_msg /* buf -> msg */
ldr %r2, =got_arg_len /* count -> len(msg) */
b process_arg
no_arg:
ldr %r1, =no_arg_msg /* buf -> msg */
ldr %r2, =no_arg_len /* count -> len(msg) */
process_arg:
swi $0 /* invoke syscall */
/**
* syscall exit(int status)
*/
mov %r0, $123 /* status -> 0 */
mov %r7, $1 /* exit is syscall #1 */
swi $0 /* invoke syscall */
.global _start
_start:
bl do_syscalls
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