maemo.org - Talk - Plz help me understand what this error means and gdb's bt result

maemo.org - Talk (https://talk.maemo.org/index.php)

- Development (https://talk.maemo.org/forumdisplay.php?f=13)

- - Plz help me understand what this error means and gdb's bt result (https://talk.maemo.org/showthread.php?t=55965)

Plz help me understand what this error means and gdb's bt result

Hi,
I'm getting segmentation fault randomly in my desktop app for fremantle and I just couldn't figure out what's causing it and the exact source code. I'm using gtk+, gdb and maemo-summoner in scratchbox. Following is the error message and the backtrace from gdb: Thanks

Code:

Program received signal SIGSEGV, Segmentation fault.

0xb7ef1db9 in malloc_consolidate () from /lib/libc.so.6

0xb7ef1db9 <malloc_consolidate+137>:        cmp    %edi,0xc(%eax)

(gdb) hildon-desktop[4460]: GLIB WARNING ** ClutterX11 - Failed to get XImage of pixmap: e01040, removing

Quit

(gdb) bt

#0  0xb7ef1db9 in malloc_consolidate () from /lib/libc.so.6

#1  0xb7ef3b4d in _int_malloc () from /lib/libc.so.6

#2  0xb7ef5499 in malloc () from /lib/libc.so.6

#3  0xb7739543 in *INT_cairo_create (target=0x8224800) at cairo.c:154

#4  0xb780b756 in setup_backing_rect_method (method=0xbfffecb4, window=0x806f648, paint=0x4f54535f, x_offset_cairo=0, y_offset_cairo=0)

    at gdkwindow.c:2028

#5  0xb780b891 in gdk_window_clear_backing_rect (window=0x806f648, x=0, y=0, width=800, height=47) at gdkwindow.c:2058

#6  0xb780e07e in IA__gdk_window_begin_paint_region (window=0x806f648, region=0x82245c0) at gdkwindow.c:1153

#7  0xb7972ffe in IA__gtk_main_do_event (event=0xbfffed90) at gtkmain.c:1552

#8  0xb780e42d in gdk_window_process_updates_internal (window=0x806f648) at gdkwindow.c:2599

#9  0xb780eaf0 in IA__gdk_window_process_all_updates () at gdkwindow.c:2665

#10 0xb780eb1b in gdk_window_update_idle (data=0x0) at gdkwindow.c:2509

#11 0xb77f38ac in gdk_threads_dispatch (data=0x81d6150) at gdk.c:473

#12 0xb7d04223 in g_idle_dispatch (source=0x821d5f0, callback=0x5353414d, user_data=0x81d6150)

    at /home/bifh4/fremantle-i386-fremantle1.2.cs2007q3/work/glib2.0-2.20.3/glib/gmain.c:3966

#13 0xb7d05fbc in g_main_context_dispatch (context=0x80708a8)

    at /home/bifh4/fremantle-i386-fremantle1.2.cs2007q3/work/glib2.0-2.20.3/glib/gmain.c:1836

#14 0xb7d09595 in g_main_context_iterate (context=0x80708a8, block=1, dispatch=1, self=0x8055ac0)

    at /home/bifh4/fremantle-i386-fremantle1.2.cs2007q3/work/glib2.0-2.20.3/glib/gmain.c:2467

#15 0xb7d09888 in g_main_loop_run (loop=0x81890f0)

    at /home/bifh4/fremantle-i386-fremantle1.2.cs2007q3/work/glib2.0-2.20.3/glib/gmain.c:2675

#16 0xb7973289 in IA__gtk_main () at gtkmain.c:1200

#17 0xb7cb8d06 in main () from /usr/bin/hildon-home.launch

---Type <return> to continue, or q <return> to quit---

Re: Plz help me understand what this error means and gdb's bt result

Ok, maybe someone can pin-point why I'm getting segmentation fault on this code, rather than the ugly output above :):

Code:

#include <glib.h>

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

#include <assert.h>



char* getUsbMode(void);

gboolean check(gchar*);



int main(){

        gchar *dir = "scratchbox/users/user/home/user/photoapplet/200910a0";

        GMainLoop *loop = NULL;

        loop = g_main_loop_new(NULL, FALSE);

        g_timeout_add_seconds(3, (GSourceFunc)check, dir);

        

        g_main_loop_run(loop);

        

        return 0;

}



gboolean check(gchar *dir){

        if (g_file_test(dir, G_FILE_TEST_EXISTS)){

                printf("Can access %s\n", dir);

        }else{

                printf("Can't access directory.\n");

                char *usb_mode = NULL;

                usb_mode = getUsbMode();

                if (strcmp(usb_mode, "MASS_STORAGE") == 0){

                        printf("USB mass storage mode activated.\n");

                }

        }

        return TRUE;

}



char* getUsbMode(){

        char *file = "/tmp/.current_usb_mode";

        char *mode, val[15];

        mode = (char *) malloc(sizeof(char*));

        assert(mode != NULL);

        FILE *fPtr;

        if ((fPtr = fopen(file, "r")) != NULL){

                fgets(val, 15, fPtr);

                val[strlen(val) - 2] = '\0';

                strcpy(mode, val);

                printf("%s\n", mode);

                fclose(fPtr);

                return mode;

        }else

                return "READ_FAILED";

}

thanks..

Re: Plz help me understand what this error means and gdb's bt result

Code:

mode = (char *) malloc(sizeof(char*));

What are you allocating here?

Re: Plz help me understand what this error means and gdb's bt result

Quote:

Originally Posted by Joorin (Post 712908)

Code:

mode = (char *) malloc(sizeof(char*));

What are you allocating here?

memory to store string which is read from the file and stored in array of char.

EDIT: I can't believe it, I thought it was needed :D but it was the source of problem damn me.... THANK YOU.

Re: Plz help me understand what this error means and gdb's bt result

Quote:

Originally Posted by jaeezzy (Post 712919)

memory to store string which is read from the file and stored in array of char.

Since you're using GLib, here's the cheat way: http://maemo.org/api_refs/5.0/5.0-fi...e-get-contents

Re: Plz help me understand what this error means and gdb's bt result

Ok guys, I'm confused again. I did without malloc() and worked fine in scratchbox(cmdline) and in the device(cmdline). So, thinking it will work, I implemented the same in my real app(Desktop App) but it failed, so I put all the print statements(:D I'm tooo lazy to use gdb unless its completely random) to see where exactly the seg fault is comming from then I found the line strcpy(mode, val) is the source coz the printf statement just before that gets executed and not the one immediately after ;). What do youse have to say about it? Thanks

BTW, I got over it using qwerty's suggestion but just curious to know why it didn't happen that other way....

Re: Plz help me understand what this error means and gdb's bt result

Quote:

Originally Posted by jaeezzy (Post 712919)

memory to store string which is read from the file and stored in array of char.

EDIT: I can't believe it, I thought it was needed :D but it was the source of problem damn me.... THANK YOU.

No. You allocate enough memory to store one pointer to a char. Read the line again and think about what sizeof actually does.

If you're still in doubt, use

Code:

printf("%d\n", sizeof(char *));

to understand more.

sizeof(char *) will return the size of a memory pointer, usually an unsigned int, 4 bytes. This is not what you want to allocate if you are to store something in the allocated memory.