C assembly implement bubble sort - c

Question

I have to write a bubblesort in C with assembly implement.
My C code looks like :
#include <stdio.h>
extern int arraysort(int array[],int length);
int main () {
int array[]= {7,4,3,6,2,1};
int length = 6;
printf("Unsorted array: %d,%d,%d,%d,%d,%d\n",array[0],array[1],array[2],array[3],array[4],array[5]);
arraysort(array,length);
printf("Sorted array: %d,%d,%d,%d,%d,%d\n",array[0],array[1],array[2],array[3],array[4],array[5]);
return 0;
}
And my assembly code looks like:
.intel_syntax noprefix
.text
.global arraysort
arraysort: # int sortarray(int array[],int length)
#function prologue
push ebp
mov ebp, esp
# function prologue end
push ebx # save ebx for cdecl convection
# 1.argumentum [ebp + 4*2] this is the array
# 2.argumentum [ebp + 4*3] this is the length
mov ecx, [ebp + 12] #array length (6)
dec ecx #array length (5)
mov edx, 1 #variable j
mov esi, [ebp + 8] #array address
loop1:
cmp ecx, 0 # (int i =length; i> length;i--)
jg end
loop2:
mov eax, [esi + 4*ecx] #array[0]
mov ebx, [esi + 4*edx] #array[1]
cmp eax, ebx #if eax > ebx jump to csere
jg swap
dec ecx #i--
inc edx#j++
jz end
jmp loop2
swap:
mov [esi + 4*edx], eax #change the two elements
mov [esi + 4*ecx], ebx
jmp loop2
end:
pop ebx
mov esp, ebp
pop ebp
ret
I dont know what is the problem and I struggling whit this.
If I change in the first loop jg to jl i get infinity loop :/
Sorry for my english and my assembly coding skill but I'm learning this language still.
Please help me! Thank you

Answer 1

Here's the main problem:
mov ecx, [ebp + 12] #array length (6)
dec ecx #array length (5)
mov edx, 1 #variable j
mov esi, [ebp + 8] #array address
loop1:
cmp ecx, 0 # (int i =length; i> length;i--)
jg end
Focus on ecx there. You're basically saying if(--length > 0) goto end;, so you're skipping the entire meat of your function.
Now once you fix that, you'll start getting a segfault. Here's why:
dec ecx #i--
inc edx#j++
jz end
That's equivalent to --i; if(!++j) goto end;. As a result, your loop is going to run way more iterations than you want (until j overflows, but in practice it will segfault first). I'm guessing you meant to switch dec ecx and inc edx, so that the loop would end when i got to 0.
Anyway, with that fixed too, your code will return an updated array, but it will still be wrong. At this point, it's just because your bubble sort is wrong and not because of any assembly-related errors, so I'll stop here.