c - Segmentation Fault when getting the max of three numbers in Assembly x86 -

i trying max of 3 numbers using c call method in assembly 32 bit @ & t. when program runs, segmentation fault(core dumped) error , cannot figure out why. input has been mix of positive/negative numbers , 1,2,3, both same error result.

assembly

# %eax - first parameter # %ecx - second parameter # %edx - third parameter  .code32 .file "maxofthree.s" .text  .global maxofthree .type maxofthree @function  maxofthree:     pushl %ebp # old ebp     movl %esp, %ebp # skip on     movl 8(%ebp), %eax # grab first value     movl 12(%ebp), %ecx # grab second value     movl 16(%ebp), %edx # grab third value     #test first     cmpl %ecx, %eax # compare first , second     jl firstsmaller # first smaller second, exit if     cmpl %edx, %eax # compare first , third     jl firstsmaller # first smaller third, exit if     leave # reset stack pointer , pop old base pointer     ret # return since first > second , first > third     firstsmaller:  # first smaller second or third, resume comparisons     #test second , third against each other     cmpl %edx, %ecx # compare second , third     jg secondgreatest # second greatest, jump end     movl %eax, %edx # third greatest, move third eax     leave # reset stack pointer , pop old base pointer     ret # return third     secondgreatest: # second > third     movl %ecx, %eax #move second eax     leave # reset stack pointer , pop old base pointer     ret # return second 

c code

#include <stdio.h> #include <inttypes.h> long int maxofthree(long int, long int, long int);  int main(int argc, char *argv[]) { if (argc != 4) {     printf("missing command line arguments. instructions to"             " execute  program:- .\a.out <num1> <num2> <num3>");     return 0; }  long int x = atoi(argv[1]); long int y = atoi(argv[2]); long int z = atoi(argv[3]); printf("%ld\n", maxofthree(x, y, z)); // todo change (x, y, z) } 

the code causing segmentation fault because trying jump invalid return address when ret instruction executed. happens 3 different ret instructions.

the reason why occurring because don't pop old base pointer before returning. small change code remove fault. change each ret instruction to:

leave ret 

the leave instruction following:

movl %ebp, %esp popl %ebp 

which reset stack pointer , pop old base pointer saved.

also, comparisons not doing specified in comments. when do:

cmp %eax, %edx jl  firstsmaller 

the jump happen when %edx smaller %eax. want code be

cmpl %edx, %eax jl   firstsmaller 

which jump when %eax smaller %edx, specified in comment.

reference this page details on cmp instruction in at&t/gas syntax.