hello.c

#include "d64.h"

int
main()
{
	cputs("Hello 6502 world from C!\n");

	return 0;
}

hello.c.s

;
; File generated by cc65 v 2.14 - Git a0c4ca9
;
	.fopt		compiler,"cc65 v 2.14 - Git a0c4ca9"
	.setcpu		"6502"
	.smart		on
	.autoimport	on
	.case		on
	.debuginfo	off
	.importzp	sp, sreg, regsave, regbank
	.importzp	tmp1, tmp2, tmp3, tmp4, ptr1, ptr2, ptr3, ptr4
	.macpack	longbranch
	.forceimport	__STARTUP__
	.import		_cputs
	.export		_main

.segment	"RODATA"

L0003:
	.byte	$48,$65,$6C,$6C,$6F,$20,$36,$35,$30,$32,$20,$77,$6F,$72,$6C,$64
	.byte	$20,$66,$72,$6F,$6D,$20,$43,$21,$0A,$00

; ---------------------------------------------------------------
; int __near__ main (void)
; ---------------------------------------------------------------

.segment	"CODE"

.proc	_main: near

.segment	"CODE"

	lda     #<(L0003)
	ldx     #>(L0003)
	jsr     _cputs
	ldx     #$00
	txa
	rts

.endproc

hello.s

; hello.s
; Hello World example using syscalls
;

.segment "CODE"

.macro		sys				; syscall
.byte		$02
.endmacro

main:
			tsx				; save the stack pointer
			lda #<message
			pha
			lda #>message
			pha
			lda #$11		; put string
			sys
			txs				; restore the stack

			lda #$00		; terminate program
			pha				; also: success (0)
			sys

			jmp *			; never gets here

message:
			.byte "Hello world from 6502!", $0a, 0