Reading from STDIN and printing to STDOUT with nasm assembly? - gcc

Question

As the title suggest I seem to be having a hard time converting the below code to do the exact same thing, which is to read from stdin and stdout. My professor wants us to stop using int 80h and switch over to using gcc. I've had no problems with reading input with the below code however, switching over to gcc is where I start getting segmentation core dump errors.
section .bss
buf resb 1 ; 1000-byte buffer (in data section)
section .text
global _start
_start:
loop1: mov edx, 1 ; max length
mov ecx, buf ; buffer
mov ebx, 0 ; stdin
mov eax, 3 ; sys_read
int 80h
cmp eax, 0 ; end loop if read <= 0
jle lpend1
mov edx, eax ; length
mov ecx, buf ; buffer
mov ebx, 1 ; stdout
mov eax, 4 ; sys_write
int 80h
jmp loop1 ; go back for more
lpend1:
mov eax, 1
mov ebx, 0
int 80h
My attempt at converting the above to perform the same task
SECTION .data
format: db "%c",0
SECTION .bss
buff: resb 1
SECTION .text
extern printf
extern scanf
global main
main:
loop1:
push buff ;buff will hold the characters in the string/file
push format ;expect character for every buff
call scanf
add esp, 8 ;clear stack
cmp eax, 0 ;if eax is equal to 0 then EOF
je lpend1 ;jump to end main func
xor eax, eax ;clear eax
mov eax, buff ;mov buff to eax register
push eax ;push eax onto the stack
mov eax, format ;mov the string format to eax
push eax ;push onto the stack
call printf ;call printf, prints to screen
add esp, 8 ;clear the stack
jmp loop1 ;jump back to top and repeat
lpend1:
ret ;end of main