Segmentation fault in my assembly program - linux

Question

I am getting a segmentation fault from this simple starting program.
I am using Ubuntu 16.10 and kdbg for debugging. Affter reaching starting __int 80h__, it stops moving to the next line.
section .bss ; section containing uninitialized data
BUFFLEN equ 1024 ; length of buffer
Buff: resb BUFFLEN ; text buffer itself
section .data ; section containing initialzed data
section .text ; secttion containing code
global _start ; linker needs to find the entry point!
_start:
nop ; this no-op keeps gdb happy
; read buffer full of text form stdin:
read:
mov eax, 3 ; specify sys_read call
mov ebx, 0 ; specify file descriptor 0 : standard input
mov ecx, Buff ; pass offset of the buffer to read to
mov edx, BUFFLEN ; pass number of bytes to be read at one pass
int 80h ; call sys_read to fill the buffer
mov esi,eax ; copy sys_read return value for safekeeping
cmp eax, 0 ; if eax = 0 , sys_read reached EOF on stdin
je Done ; jump if Equal ( to o, form compare)
; set up the register for the process buffer step:
mov ecx, esi ; place the number of bytes read into ecx
mov ebp, Buff ; pace address of buffer into ebp
dec ebp ; adjust the count to offset
; go through the buffer and cnvert lowercase to uppercase characters:
Scan:
cmp byte [ebp+ecx], 61h ; test input char agaisnst lowercase 'a'
jb Next ; if Below 'a' in ASCII, not lowercase
cmp byte [ebp+ecx], 7Ah ; test against lowercase 'z'
ja Next
sub byte [ebx+ecx], 20h ; subtract 20h to give uppercase..
Next:
dec ecx ; Decrement counter
jnz Scan ; if characters reamin, loop back
; Write the buffer full of processed text to stdout:
Write:
mov eax,4 ; Specify sys_write call
mov ebx, 1 ; Specify file descriptor 1 : stdout
mov ecx, Buff ; pass the offset of the buffer
mov edx, esi ; pass the # of bytes of data in the buffer
int 80h ; make sys_write kernel call
jmp read ; loop back and load another buffer full
Done:
mov eax, 1 ; Code for Exit sys_call
mov ebx, 0 ; return code of Zero
int 80h
I used these commands:
nasm -f elf -g -F stabs uppercaser1.asm
ld -m elf_i386 -o uppercaser1 uppercaser1.o
./uppercaser < inputflie

Answer 1

I think this code is generally public so I am posting with that in mind.
You should use the code as a guide to understanding what may be wrong in your code; however, it does not conform to any coding standard so it is pointless just to copy and paste and turn it in as an assignment; assuming that is the case.
You will never increase your assembly programming skills by merely doing a copy/paste.
lsb_release -a
...
Description: Ubuntu 16.04.3 LTS
nasm -f elf32 -g uppercase1.s -o uppercase1.o && ld -m elf_i386 uppercase1.o -o uppercase1
section .bss
Buff resb 1
section .data
section .text
global _start
_start:
nop
Read:
mov eax, 3 ; read syscall
mov ebx, 0 ; stdin
mov ecx, Buff ; pass address of the buffer to read to
mov edx, 1 ; read one char or one byte
int 0x80 ;
cmp eax, 0 ; if syscall returns returns 0
je Exit ;
cmp byte [Buff], 0x61 ; lower case a
jb Write ; jump if byte is below a in ASCII chart
cmp byte [Buff], 0x7a ; lower case z
ja Write ; jump if byte is above z in ASCII chart
sub byte [Buff], 0x20 ; changes the value in the buffer to an uppercase char
Write:
mov eax, 4 ; write syscall
mov ebx, 1 ; stdout
mov ecx, Buff ; what to print
mov edx, 1 ; length is one byte - each char is a byte
int 0x80
jmp Read ; go back to Read
Exit:
mov eax, 1
mov ebx, 0
int 0x80
Sample output:
david#ubuntuserver00A:~/asm$ ./uppercase1 < uppercase1.s
SECTION .BSS
BUFF RESB 1
SECTION .DATA
SECTION .TEXT
GLOBAL _START
_START:
NOP
READ:
MOV EAX, 3 ; READ SYSCALL
MOV EBX, 0 ; STDIN
MOV ECX, BUFF ; PASS ADDRESS OF THE BUFFER TO READ TO
MOV EDX, 1 ; READ ONE CHAR OR ONE BYTE
INT 0X80 ;
CMP EAX, 0 ; IF SYSCALL RETURNS RETURNS 0
JE EXIT ;
CMP BYTE [BUFF], 0X61 ; LOWER CASE A
JB WRITE ; JUMP IF BYTE IS BELOW A IN ASCII CHART
CMP BYTE [BUFF], 0X7A ; LOWER CASE Z
JA WRITE ; JUMP IF BYTE IS ABOVE Z IN ASCII CHART
SUB BYTE [BUFF], 0X20 ; CHANGES THE VALUE IN THE BUFFER TO AN UPPERCASE CHAR
WRITE:
MOV EAX, 4 ; WRITE SYSCALL
MOV EBX, 1 ; STDOUT
MOV ECX, BUFF ; WHAT TO PRINT
MOV EDX, 1 ; LENGTH IS ONE BYTE - EACH CHAR IS A BYTE
INT 0X80
JMP READ ; GO BACK TO READ
EXIT:
MOV EAX, 1
MOV EBX, 0
INT 0X80