Quick sort using ARM assembly - segmentation error - c

Question

I'm trying to make a Quick Sort function using ARM assembly (Raspberry pi),
but it shows me segmentation error.
I think recursion process makes that error, while storing or loading with stacks.
Can you tell me how can I fix it?
I used ARM assembly code in https://en.wikibooks.org/wiki/Algorithm_Implementation/Sorting/Quicksort#ARM_Assembly
here,
I just typed it same. Just changing registers like 'r3'->'r2', 'r2'->'r1', 'r1'->'r0' ...
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#define SIZE 32
int main()
{
int arr[SIZE];
int max, min;
int i;
for (i = 0; i < SIZE; i++) {
arr[i] = rand() % 100;
}
asm(
"mov r0, #0\n\t"
"mov r1, #128\n\t"
"Loop3:\n\t"
"stmfd sp!, {r3, r5, lr}\n\t"
"mov r5, r1\n\t"
"Loop4:\n\t"
"sub r6, r5, r0\n\t"
"cmp r6, #4\n\t"
"ldmlefd sp!, {r3, r5, pc}\n\t"
"ldr r6, [%[arr],r0]\n\t"
"add r1, r0, #4\n\t"
"mov r3, r5\n\t"
"Loop5:\n\t"
"ldr r2, [%[arr],r1]\n\t"
"cmp r2, r6\n\t"
"addle r1, r1, #4\n\t"
"ble Loop6\n\t"
"sub r3, r3, #4\n\t"
"ldr r4, [%[arr],r3]\n\t"
"str r4, [%[arr],r1]\n\t"
"str r2, [%[arr],r3]\n\t"
"Loop6:\n\t"
"cmp r1, r3\n\t"
"blt Loop5\n\t"
"Loop7:\n\t"
"sub r1, r1, #4\n\t"
"ldr r2, [%[arr],r1]\n\t"
"str r2, [%[arr],r0]\n\t"
"str r6, [%[arr],r1]\n\t"
"bl Loop3\n\t"
"mov r0, r3\n\t"
"b Loop4\n\t"
:
:
[arr] "r"(arr)
:
"r0", "r1", "r2", "r3", "r4", "r5", "r6"
);
return 0;
}

Answer 1

You inline asm can never reach the end of the asm template. Presumably you're trying to return out of the C function, not just the internal recursive calls. That's obviously unsafe because there's zero guarantee about stack layout or the contents of LR, and that will change with/without optimization.
Don't write a whole recursive in the middle of a C function.
Use a debugger to single-step the resulting program and see where your code breaks the compiler-generated asm that surrounds it.
Also your inline asm is broken: you dereference arr without specifying it as a memory read/write input or a "memory" clobber. A pointer input does not imply that the pointed-to memory is also an operand.