ARM C to ASM call

callasm.bin.list

callasm.bin:     file format binary


Disassembly of section .data:

00000000 <.data>:
   0:	e92d4800 	push	{fp, lr}
   4:	e28db004 	add	fp, sp, #4
   8:	e59f0004 	ldr	r0, [pc, #4]	; 0x14
   c:	eb000001 	bl	0x18
  10:	eafffffe 	b	0x10
  14:	00008054 	andeq	r8, r0, r4, asr r0
  18:	e52db004 	push	{fp}		; (str fp, [sp, #-4]!)
  1c:	e28db000 	add	fp, sp, #0
  20:	e24dd00c 	sub	sp, sp, #12
  24:	e59f4024 	ldr	r4, [pc, #36]	; 0x50
  28:	e5905000 	ldr	r5, [r0]
  2c:	e5956000 	ldr	r6, [r5]
  30:	e5846000 	str	r6, [r4]
  34:	e2855001 	add	r5, r5, #1
  38:	e5956000 	ldr	r6, [r5]
  3c:	e3560000 	cmp	r6, #0
  40:	1afffffa 	bne	0x30
  44:	e28bd000 	add	sp, fp, #0
  48:	e49db004 	pop	{fp}		; (ldr fp, [sp], #4)
  4c:	e12fff1e 	bx	lr
  50:	101f1000 	andsne	r1, pc, r0
  54:	6c6c6143 	stfvse	f6, [ip], #-268	; 0xfffffef4
  58:	20676e69 	rsbcs	r6, r7, r9, ror #28
  5c:	6d6f7266 	sfmvs	f7, 2, [pc, #-408]!	; 0xfffffecc
  60:	000a4320 	andeq	r4, sl, r0, lsr #6
-e 

Hexdump

00000000  00 48 2d e9 04 b0 8d e2  04 00 9f e5 01 00 00 eb  |.H-.............|
00000010  fe ff ff ea 54 80 00 00  04 b0 2d e5 00 b0 8d e2  |....T.....-.....|
00000020  0c d0 4d e2 24 40 9f e5  00 50 90 e5 00 60 95 e5  |[email protected]...`..|
00000030  00 60 84 e5 01 50 85 e2  00 60 95 e5 00 00 56 e3  |.`...P...`....V.|
00000040  fa ff ff 1a 00 d0 8b e2  04 b0 9d e4 1e ff 2f e1  |............../.|
00000050  00 10 1f 10 43 61 6c 6c  69 6e 67 20 66 72 6f 6d  |....Calling from|
00000060  20 43 0a 00                                       | C..|
00000064

callasm.c

extern void myprint(char* a);

void _start() {
  myprint("Calling from C\n");
  while(1){}
}

Makefile

CROSS_COMPILE ?= arm-unknown-eabi

AOPS = --warn --fatal-warnings 
COPS = -Wall -Werror -O0 -nostdlib -nostartfiles -ffreestanding

callasm.bin: print.s callasm.c
	$(CROSS_COMPILE)-as $(AOPS) print.s -o print.o
	$(CROSS_COMPILE)-cc -c $(COPS) callasm.c -o callasm.o
	# Caution! The order of the object files is critical
	$(CROSS_COMPILE)-ld callasm.o print.o -o callasm.elf
	$(CROSS_COMPILE)-objdump -D callasm.elf -marm > callasm.elf.list
	$(CROSS_COMPILE)-objcopy -S -O binary callasm.elf callasm.bin
	$(CROSS_COMPILE)-objdump -D -d callasm.bin -b binary -marm > callasm.bin.list
	echo -e "\n\nHexdump\n" >> callasm.bin.list
	hexdump -C callasm.bin >> callasm.bin.list

runfromc: callasm.bin
	qemu-system-arm -M versatilepb -m 128M -nographic -kernel callasm.bin

clean: 
	-rm print.o callasm.o callasm.elf callasm.bin callasm*list

output

$ make clean && make  runfromc 
rm print.o callasm.o callasm.elf callasm.bin callasm*list
arm-unknown-eabi-as --warn --fatal-warnings  print.s -o print.o
arm-unknown-eabi-cc -c -Wall -Werror -O0 -nostdlib -nostartfiles -ffreestanding callasm.c -o callasm.o
# Caution! The order of the object files is critical
arm-unknown-eabi-ld callasm.o print.o -o callasm.elf
arm-unknown-eabi-objdump -D callasm.elf -marm > callasm.elf.list
arm-unknown-eabi-objcopy -S -O binary callasm.elf callasm.bin
arm-unknown-eabi-objdump -D -d callasm.bin -b binary -marm > callasm.bin.list
echo -e "\n\nHexdump\n" >> callasm.bin.list
hexdump -C callasm.bin >> callasm.bin.list
qemu-system-arm -M versatilepb -m 128M -nographic -kernel callasm.bin
pulseaudio: set_sink_input_volume() failed
pulseaudio: Reason: Invalid argument
pulseaudio: set_sink_input_mute() failed
pulseaudio: Reason: Invalid argument
���� ������

QEMU: Terminated

print.s

.global myprint

@ Procedure to print a NULL terminated string through the UART
myprint:
    push {r11}           @Start of the prologue. Saving Frame Pointer onto the stack
    add  r11, sp, #0     @Setting up the bottom of the stack frame
    sub  sp, sp, #12     @End of the prologue. Allocating some buffer (12 bytes) on the stack
    ldr  r4, =0x101f1000 @This address is UART0 in Versatile/PB
    ldr  r5, [r0]        @Load the input string, its in r0 as is the 1st parameter
    ldr  r6, [r5]	     @Load the content of the address pointed by r5 on r6
_printchr:
    str  r6, [r4]        @Print throught the UART
    add  r5, r5, #1      @Point to the next character
    ldr  r6, [r5]        @Load the character to r6
    cmp  r6, #0          @Check if its the last one
    bne  _printchr
    add  sp, r11, #0     @Start of the epilogue. Readjusting the Stack Pointer
    pop  {r11}           @restoring frame pointer
    bx   lr              @End of the epilogue. Jumping back to main via LR register