Hello!
I have a piece of code here that I just can't get to work. I get segmentation fault and now I'm trying to apply a ddd tool to understand the problem. I haven't used ddd before but there seem to be some kind of a problem around the subroutines fgets or gettext. I have been putting a breakpoint at various places but I guess I'm doing some mistake here.
fgets reads what comes from the keyboard and then I'm supposed to transfer that piece of text(in this case, for the moment, 2 numbers ) into a buffer (INBUFFERT ) with gettext. But I'm obviously doing something wrong here.
Putting a breakpoint at fgets and then stepi I get the message "a syntax error in expression, near 0x123d30"
Here's the code:
.equ MAXPOS, 40
.equ POS, 44
.equ MINPOS, 48
.data
Head: .asciz "Start of testprogram.Put in 2 numbers!"
Show_Integ: .asciz "%d\n"
Buf: .skip 64
N: .long 0
T: .long 0
Show: .asciz "%s\n"
Intg: .long 0
UTBUFFERT: .skip 128
INBUFFERT: .skip 128
.text
.globl main, puttext, outimage, inimage, getint
main:
pushl $Head /*Head lagras på stacken*/
call puttext /*Denna text läggs nu in i UTBUFFERT*/
call outimage /*Texten tas från UTBUFFERT och skrivs nu ut på skärmen*/
call inimage
movl $5, N
call getint
call printgetint_end
call exit
printgetint_end:
pushl %eax
pushl $Show_Integ
call printf
addl $8, %esp
movl $0, %eax
ret
puttext:
pushl %ebp
movl %esp, %ebp
movl $UTBUFFERT, %ecx
movl 8(%ebp), %ebx
next: movb (%ebx), %al
cmpb $0, %al
je puttextLoopEnd
movb %al, (%ecx)
incb %cl
incb %bl
jmp next
puttextLoopEnd:
movl %ebp, %esp
popl %ebp
ret
outimage:
pushl $UTBUFFERT
pushl $Show
call printf
addl $8, %esp
ret
inimage:
pushl stdin
pushl $79
pushl Buf
call fgets
addl $12,%esp
xorl %ecx, %ecx /*position = 0*/
gettext: pushl %ebp
movl %esp, %ebp
movl $INBUFFERT, %ebx
gettext_loop:
movb (%eax), %dl
cmpb $13, %dl
je end_gettext
movb %dl, (%ebx)
incl %eax
incl %ebx
incl %ecx
jmp gettext_loop
end_gettext:
movl %ecx, MAXPOS(%ebp)
movl $0, %ecx
movl %ebp, %esp
popl %ebp
ret
getint:
popl %ebp
movl %esp, %ebp
movl $1, %edi
call getinpos
getchar:
movl $INBUFFERT, (%ebx)
cmpb $45, (%ebx) /*check to see if the character = '-'*/
je increase_charN /*if so, jump to increase_charN*/
jmp getchar_loop /*if not, jump to getchar_loop*/
getchar_loop:
cmpb $32, (%ebx)
je increase_char
movzx (%ebx), %eax
pushl %eax
incl %ecx
incl %ebx
jmp getchar_loop
increase_char: incl %ecx
incl %ebx
jmp setinpos
getint_loop:
popl %eax
subl $48, %eax
imul %edi, %eax
addl %eax, Intg
imul $10, %edi
decl %ecx
cmpl $0, %ecx
je getint_end
jmp getint_loop
getint_end:
xorl %eax, %eax
movl Intg, %eax
movl %ebp, %esp
popl %ebp
ret
setinpos:
cmpl $0, %ecx
jb setinpos_zero
cmpl MAXPOS(%ebp), %ecx
jg setinpos_max
movl %ecx, POS(%ebp)
jmp getint_loop
setinpos_zero:
movl $0, %ecx
movl %ecx, MINPOS(%ebp)
jmp getint_loop
setinpos_max:
movl MAXPOS(%ebp), %ecx
movl %ecx, POS(%ebp)
jmp getint_loop
getinpos:
cmpl $0, %ecx
je getchar
movl POS(%ebp), %ecx
movl %ecx, %ebx
ret
getint_loopN:
popl %eax
subl $48, %eax
imul %edi, %eax
addl %eax, Intg
imul $10, %edi
decl %ecx
cmpl $0, %ecx
je getint_end
jmp getint_loopN
getint_endN:
xorl %eax, %eax
movl Intg, %eax
movl %ebp, %esp
popl %ebp
ret
setinposN:
cmpl $0, %ecx
jb setinpos_zeroN
cmpl MAXPOS(%ebp), %ecx
jg setinpos_maxN
movl %ecx, POS(%ebp)
jmp getint_loopN
setinpos_zeroN:
movl $0, %ecx
movl %ecx, MINPOS(%ebp)
jmp getint_loopN
setinpos_maxN:
movl MAXPOS(%ebp), %ecx
movl %ecx, POS(%ebp)
jmp getint_loopN
increase_charN:
incl %ecx
incl %ebx
jmp setinposN
getchar_loopN:
cmpb $32, (%ebx)
je increase_charN
movzx (%ebx), %eax
pushl %eax
incl %ecx
incl %ebx
jmp getchar_loopNWith the code I just want to take the first number and print it out. If it's a negative number there are subroutines to take care of that. At least I hope they do.
Since I get the error message "Segmentation fault" I thought that with the ddd tool it should be easy to find out this problem but I don't think so. I understand that there is some kind of problem with the stack so I'm looking up the source - backtrace in order to see the stack but it doesn't help me. What shall I do in order to solve this problem?
Can anyone please help me out here?
Anders