Hey Guys, this is my first post and I am a beginner with this language. I hope you can help me!
Before, some background
Compiler: gcc
Assembler: gas
objective: open a file, copy the text that is inside, and paste it in a new file.
Problem: function fgets
Error: Segmentation Fault
code where the error appears:
Do you know what the problem is? what am I missing?
thanks in advance
Before, some background
Compiler: gcc
Assembler: gas
objective: open a file, copy the text that is inside, and paste it in a new file.
Problem: function fgets
Error: Segmentation Fault
code where the error appears:
processingfiles: pushl %ebp #prologue
movl %esp, %ebp #prologue
pushl $mode2 #read only
pushl $sourcefilepath
call fopen
addl $8, %esp
mov %eax, fp # fp=file pointer
cmpl $0, fp # if fp==NULL (0) error!
je errors
pushl $sourcefilepath
pushl $10 #amount of data to be pasted
pushl $file #name of the file where the data will be pasted
call fgets #here de problem!
jmp fin
errors: pushl error
call printf
addl $4, %esp
jmp fin
fin: leave
ret
Do you know what the problem is? what am I missing?
thanks in advance
I believe you're using the wrong parameters for fgets:
In order pushed (opposite order listed in C source), you want file descriptor, size, buffer. You appear to be reusing the filename as a buffer(?). Or is "file" supposed to be the buffer? In any case, I think what you want is:
Also, you don't "addl $12, %esp" to remove the parameters. In addition, you seem to be unconditionally jumping over the "error" section. I could be wrong about this - not very familiar with (G)as syntax, nor with the C library's "high level" (buffered) fopen, etc. I'm pretty sure fgets doesn't want any "names", but the "FILE *" returned from fopen (I guess it should be called "stream", not "file descriptor"?). Give it a try and see if it helps.
Best,
Frank
pushl $sourcefilepath
pushl $10 #amount of data to be pasted
pushl $file #name of the file where the data will be pasted
call fgets #here de problem!
In order pushed (opposite order listed in C source), you want file descriptor, size, buffer. You appear to be reusing the filename as a buffer(?). Or is "file" supposed to be the buffer? In any case, I think what you want is:
pushl fp # no '$'! - as returned from fopen
pushl $10
pushl $buffer # call it what you like
call fgets
Also, you don't "addl $12, %esp" to remove the parameters. In addition, you seem to be unconditionally jumping over the "error" section. I could be wrong about this - not very familiar with (G)as syntax, nor with the C library's "high level" (buffered) fopen, etc. I'm pretty sure fgets doesn't want any "names", but the "FILE *" returned from fopen (I guess it should be called "stream", not "file descriptor"?). Give it a try and see if it helps.
Best,
Frank
Just taking a glance, your biggest problem (not including what fbkotler pointed out) is exactly what you're comments state.
Yep! You're right, there is a problem there. You were so diligent about cleaning up after printf and fopen, but you forgot to do the same with fgets!
Also remember that fgets() reads a line at a time, so this will print out the first line from "demo.txt" and you shouldn't leave any hanging pointers out there, so make sure you call fclose() on any fopen()'d descriptor.
P.S. Writing this has reminded me why I hate AT&T Syntax.
call fgets #here de problem!
jmp finYep! You're right, there is a problem there. You were so diligent about cleaning up after printf and fopen, but you forgot to do the same with fgets!
.data
strModeRead:
.ascii "r\0"
strInputFile:
.ascii "demo.txt\0"
strFileError:
.ascii "error: could not open file.\n\0"
.bss
fd:
.space 4
strBuffer:
.space 1025
.text
.globl print_file_out
print_file_out:
enter $0, $0
pushl $strModeRead
pushl $strInputFile
call fopen
addl $0x08, %esp
cmpl $0x00, %eax
je _opn_err
movl %eax, (fd)
pushl %eax # Pointer to File for fgets()
pushl $1024 # Maximum size of buffer.
pushl $strBuffer # Storage buffer.
call fgets
addl $0x0B, %esp
pushl (fd)
call fclose
addl $0x04, %esp
mov $strBuffer, %eax # Return pointer to buffer on success
jmp _ovr_err
_opn_err:
pushl $strFileError
call printf
addl $0x04, %ebp
xorl %eax, %eax # Return zero on error
_ovr_err:
leave
retAlso remember that fgets() reads a line at a time, so this will print out the first line from "demo.txt" and you shouldn't leave any hanging pointers out there, so make sure you call fclose() on any fopen()'d descriptor.
P.S. Writing this has reminded me why I hate AT&T Syntax.
Hi Guys, I really appreciate your answers. You were right, my mistakes were:
I finish my program copying stringbuffer into a new text file... like that
and it worked!
thank you so much for helping me, I am new in assembly language
marcela
pushl $sourcefilepath ---------> instead of $sourcefilepath I should have written the file descriptor....
pushl $10
pushl $file -------------->instead of the filename I should have written a string buffer to save data
call fgets
addl $12, %esp
I finish my program copying stringbuffer into a new text file... like that
pushl $mode1 #write mode
pushl $file #file name
call fopen
addl $8, %esp
movl %eax, fp
pushl $strBuffer
pushl fp
call fprintf
addl $8, %esp
and it worked!
thank you so much for helping me, I am new in assembly language
marcela