X86-64 ASM Fibonacci

I've been learning x86-64 assembly. Writing a program required actually getting the basics to work:

Working with Intel syntax, not AT&T (most use AT&T)
Working on a 64-bit system (most articles written for 32-bit)
Working on Linux (thankfully fairly standard)
Compiling with NASM (not GCC/GAS)
Linking with LD (not GCC)
Properly linking printf
Remembering calling conventions
Writing logic in assembly
Recreating some control/looping structures

Here's the working code and makefile.

1234567891011121314

TARGET = fibonacci
OBJECTS = fibonacci.o

all: $(OBJECTS)
	ld $(OBJECTS) -o $(TARGET) -lc \
		--dynamic-linker /lib64/ld-linux-x86-64.so.2

%.o: %.asm
	nasm -f elf64 $< -o $@

clean:
	rm -rf *.o;
	rm -rf *.lst;
	rm -rf $(TARGET)

fibonacci.asm (Download)

12345678910111213141516171819202122232425262728293031323334353637383940414243444546474849505152535455565758596061626364656667686970717273747576777879808182838485

section .text			; program test
	global	_start		; _start is default; export for linker
	extern	printf

do_fib:				; do_fib sub/func
	push	r14		; store r14
	push	r15		; store r15
	push	rax		; store rax
	mov	r14, r10	; copy r10 value to r14 for printing
	mov	r15, fib	; copy fib address to r15 for printing
	call	print_int	; print fib str, r10 as param
	mov	rax, r10	; copy r10 to temp
	mov	r10, r11	; set r10 to r11
	add	r11, rax	; new r11 set to old r11 + old r10
	pop	rax		; restore rax
	pop	r15		; restore r15
	pop	r14		; restore r14
	ret			; finished with iteration

for_0_r15:
	push	rcx		; store rcx
	mov	rcx, 0		; set rcx counter to 0
for_loop:
	call	r13		; call function pointer
	inc	rcx		; increment counter
	cmp	rcx, r15	; compare counter to target
	jne	for_loop	; if not equal to target, continue

	pop	rcx		; restore rcx
	ret			; finished for loop

_start:				; _start (default start point) sub/func
	mov	r10, 1		; first initial value: 1
	mov	r11, 1		; second initial value: 1

	mov	r13, do_fib	; execute do_fib in loop
	mov	r15, 10		; execute 10 times
	call	for_0_r15	; call for loop

				; next section is exit routine
	mov	ebx, 0		; exit code: 0 (success)
	mov	eax, 1		; system call: sys_exit
	int	0x80		; call kernel

print_int:
	push	rax		; store all the registers (overkill? yes)
	push	rbx
	push	rcx
	push	rdx
	push	rsi
	push	rdi
	push	rbp
	push	rsp
	push	r8
	push	r9
	push	r10
	push	r11
	push	r12
	push	r13
	mov	rsi, r14	; value stored in r14
	mov	rdi, r15	; string stored in r15
	mov	eax, 0		; no non-int args
	call	printf		; call printf
	pop	r13		; pop all the registers
	pop	r12
	pop	r11
	pop	r10
	pop	r9
	pop	r8
	pop	rsp
	pop	rbp
	pop	rdi
	pop	rsi
	pop	rdx
	pop	rcx
	pop	rbx
	pop	rax
	ret
				

section .data			; program data

ctr db	"Count: %d", 10, 0	; count string
fib db	"Fib: %d", 10, 0	; fib string
dbg db	"Value: %d", 10, 0	; debug string

Ches Koblents