Could anyone help me to solve "zsh: bus error" - c

Question

On mac OS(which has intel inside), I tried to make a simple x86 hybrid program with main module written in C and a function written in x86 assembly language (NASM assembler).
Then, the following function is to reverse the string of the argument.
My C code is
#include <stdio.h>
char *revstring(char *s);
int main(int argc, char* argv[]){
for (int i=1; i<argc; i++){
printf("%s->", argv[i]);
printf("%s\n", revstring(argv[i]));
}
}
Then my assembly code
section .text
global _revstring
_revstring:
push rbp
mov rbp, rsp
mov rax, [rbp+8]
mov rcx, rax
_find_end:
mov dl, [rax]
inc rax
test dl, dl
jnz _find_end
sub rax, 2
_swap:
cmp rax, rcx
jbe _fin
mov dl, [rax]
xchg dl, [rcx]
mov [rax], dl
dec rax
inc rcx
jmp _swap
_fin:
mov rax, [rbp+8]
pop rbp
ret
Or
section .text
global _revstring
_revstring:
push rbp
mov rbp, rsp
mov rax, [rbp+8]
mov rcx, rax
find_end:
mov dl, [rax]
inc rax
test dl, dl
jnz find_end
sub rax, 2
swap:
cmp rax, rcx
jbe fin
mov dl, [rax]
xchg dl, [rcx]
mov [rax], dl
dec rax
inc rcx
jmp swap
fin:
mov rax, [rbp+8]
pop rbp
ret
Currnt MacOS cannot run 32 bit program, so I built the program by using these commands.
cc -m64 -std=c99 -c revs.c
nasm -f macho64 revstring.s
cc -m64 -o revs revs.o revstring.o
But When I enter
./revs abc123
the following error occured.
zsh: bus error ./revs abc123
I cannot find any solutions, so could anyone help me?