Function call with more than 4 registers ARM assembly - function

Question

I am trying to pass r0-r5 into the function check. However only the registers r0-r3 are copied by reference. In my main function i have this code.
push {lr}
mov r0, #1
mov r1, #2
mov r2, #3
mov r3, #4
mov r4, #5
mov r5, #6
bl check
pop {lr}
bx lr
Inside my check function i have this code. This is in a separate file also not sure if that matters
m: .asciz "%d, %d ~ (%d, %d, %d)
...
push {lr}
ldr r0, =m
bl printf
pop {lr}
bx lr
The output for this is 2, 3 ~ (4, 33772, 1994545180). I am trying to learn assembly so can you please explain the answer with some googling i know i need to use the stack but, I am not sure how to use it and would like to learn how. Thanks in advance.

Answer 1

you could just try it and see
void check ( unsigned int, unsigned int, unsigned int, unsigned int, unsigned int );
void call_check ( void )
{
check(1,2,3,4,5);
}
arm-linux-gnueabi-gcc -c -O2 check.c -o check.o
arm-linux-gnueabi-objdump -D check.o
00000000 <call_check>:
0: e52de004 push {lr} ; (str lr, [sp, #-4]!)
4: e3a03005 mov r3, #5
8: e24dd00c sub sp, sp, #12
c: e58d3000 str r3, [sp]
10: e3a00001 mov r0, #1
14: e3a01002 mov r1, #2
18: e3a02003 mov r2, #3
1c: e3a03004 mov r3, #4
20: ebfffffe bl 0 <check>
24: e28dd00c add sp, sp, #12
28: e8bd8000 ldmfd sp!, {pc}
now of course this could be hand optimized and still work just fine. Maybe they are keeping the stack aligned on a 16 byte/4 word/64 bit boundary is the reason for the additional 12 byte modification to the stack pointer? dont know. but other than that you can see that you naturally need to save the link register since you are calling another function. r0 - r3 are obvious and then per the eabi the first thing on the stack is the 5th word worth of parameters.
Likewise for your check function you can simply let the compiler get you started. If you look at your code, r0 is coming in as your first parameter and then you trash it by changing it to the first parameter for printf. you need 6 parameters for printf to pass in. you need to move them over one the first parameter to check is the second parameter to printf, the second to check is third to printf and so on. so the code has to do that shift (two of which now are on the stack).