NASM: adding numbers of the main diagonal in a table - string

Question

The program i am writing aims to take in a table from text file. The table is in the following format: The table is NxN, and the first line is the number, N. Each row of the table is then included on its own line. Therefore, the file has N + 1 lines.
The program should read in the table, and grab the numbers along the diagonal, going from top left to bottom right, and add them together, outputting the result to screen.
Currently, i am working on a procedure which takes as input the buffer which holds the row of numbers, along with which number the user wishes to retrieve. The intent is to return this in eax. However, it seems that this procedure currently causes a segfault. I have looked over my code and it seems to make sense to me. Below is both a sample table file and my source.
hw6_1.dat
5
2 45 16 22 4
17 21 67 29 65
45 67 97 35 87
68 34 90 72 7
77 15 105 3 66
hw6_1.asm
; this program demonstrates how to open files for reading
; It reads a text file line by line and displays it on the screen
extern fopen
extern fgets
extern fclose
extern printf
extern exit
global main
segment .data
readmode: db "r",0
filename: db "hw6_1.dat",0 ; filename to open
error1: db "Cannot open file",10,0
format_1: db "%d",10,0
format_2: db "%s",10,0
segment .bss
buflen: equ 256 ; buffer length
buffer: resd buflen ; input buffer
tempBuff: resd buflen
segment .text
main:
pusha
; OPENING FILE FOR READING
push readmode ; 1- push pointer to openmode
push filename ; 2- push pointer to filename
call fopen ; fopen retuns a filehandle in eax
add esp, 8 ; or 0 if it cannot open the file
cmp eax, 0
jnz .L1
push error1 ; report an error and exit
call printf
add esp, 4
jmp .L4
; READING FROM FILE
.L1:
mov ebx, eax ; save filepointer of opened file in ebx
; Get first line and pass to ecx
push ebx
push buflen
push buffer
call fgets
add esp, 12
cmp eax, 0
je .L3
;convert string -> numeric
push buffer
call parseInt
mov ecx, eax
.L2:
push ecx
push ebx ; 1- push filehandle for fgets
push dword buflen ; 2- push max number of read chars
push buffer ; 3- push pointer to text buffer
call fgets ; get a line of text
add esp, 12 ; clean up the stack
cmp eax, 0 ; eax=0 in case of error or EOF
je .L3
push buffer ; output the read string
call printf
add esp, 4
push dword 2
push buffer
call grabNum ;Get the 3rd number in the current line. Space delimited.
;do somehing with the number. For now, lets just output to screen.
push eax
push format_1
call printf
add esp, 8
pop ecx
dec ecx
cmp ecx, 0
jg .L2
;CLOSING FILE
.L3:
push ebx ; push filehandle
call fclose ; close file
add esp, 4 ; clean up stack
.L4:
popa
call exit
parseInt:
push ebp
mov ebp, esp
push ebx
push esi
mov esi, [ebp+8] ; esi points to the string
xor eax, eax ; clear the accumulator
.I1:
cmp byte [esi], 48 ; end of string?
jl .I2
mov ebx, 10
mul ebx ; eax *= 10
xor ebx, ebx
mov bl, [esi] ; bl = character
sub bl, 48 ; ASCII conversion
add eax, ebx
inc esi
jmp .I1
.I2:
pop esi
pop ebx
pop ebp
ret 4
grabNum:
;This method will grab a specified number in a sequence.
;Ex: passed in is buffer and the number 4. The 4th number will be
;returned. It is assumed to be a space delimited buffer.
mov esi, [esp + 4]
mov ecx, [esp + 8]
dec ecx
.skipNum:
;for each number in ecx, advance past a number in esi.
;this is done by decrementing ecx each time a "non-digit" is detected.
;Since the buffer is known to be space delimted, this is a valid strategy.
cmp ecx, 0
je .doneSkipping
cmp byte [esi], 48
jl .numSkipped
cmp byte [esi], 57
jg .numSkipped
inc esi
jmp .skipNum
.numSkipped:
inc esi
dec ecx
jmp .skipNum
.doneSkipping:
;now we grab the number from buffer in its ASCII form. We place it in tempBuff,
;and call parseInt. This should leave the number in integer form waiting in eax
;after the end of the grabNum call.
cmp byte [esi + 1 * ecx], 48
jl .retGrab
cmp byte [esi + 1 * ecx], 57
jg .retGrab
mov ebx, [esi + 1 * ecx]
mov [tempBuff + 1 * ecx], ebx
inc ecx
jmp .doneSkipping
.retGrab:
mov [tempBuff + 1 * ecx], byte 0
push tempBuff
call parseInt
ret 8
To be precise, the program prints out "45", the second number in the first row, as i intend at the moment, but seems to throw the segfault before the second line can be output to the screen.

Answer 1

Accidently used EBX register to hold some temporary data. This trashed the file handle and caused a segfault. EAX was used to hold this data instead, which fixes the issue!
To solve this problem I modified these 2 lines:
mov ebx, [esi + 1 * ecx]
mov [tempBuff + 1 * ecx], ebx
to be:
mov eax, [esi + 1 * ecx]
mov [tempBuff + 1 * ecx], eax