I'm facing a segmentation fault. Syslog reports the following:
segfault at 0 ip 00000000f71ff256 sp 00000000f44fee50 error 4 in libprotobuf-c.so.0.0.0[f71f8000+f000]
So, libprotobuf-c.so is loaded at 0xf71f8000. When I loaded the respective core file in gdb and tried info sharedlibrary, it shows FROM address as 0xf71f9f70 which is different from what syslog showed. I'm not able to understand this mismatch. Could someone please help?
0xf71f9f70 0xf7204028 Yes (*) /usr/lib/libprotobuf-c.so.0
So, libprotobuf-c.so is loaded at 0xf71f8000. When I loaded the respective core file in gdb and tried info sharedlibrary, it shows FROM address as 0xf71f9f70 which is different from what syslog showed.
Actually they are the same. GDB shows start of .text as the From address.
If you do readelf -WS /usr/lib/libprotobuf-c.so.0 | grep '\.text', you'll discover that .text starts at 0xf71f9f70 - 0xf71f8000 == 0x1f70.
Related
I'm very new to the C language and have been tasked with modifying GRUB. What a way to learn, right? Anyway, I'm trying to debug my modified GRUB using VMWare and GDB. I've been able to get the debugger working before, but for some reason, every time I load up my VM and connect GDB, during the loading process of GRUB, I get:
.loadsym.gdb:1: Error in sourced command file:
The address where biosdisk.module has been loaded is missing
and I have no idea what to do about it. My first thought was, "Oh, I'll just add-symbol-file <file> and that'll fix it!" but apparently that tells GDB to forget every other symbol it loaded???? So I can't add the symbol-file and set a breakpoint.
My googling only returns one semi-relevant post that doesn't really go all that in-depth on fixing the issue.
This output may also be relevant.
info file biosdisk.module
Symbols from "H:\Workspace\GRUB\Bootloader\Trunk\grub-core\kernel.exec".
Remote serial target in gdb-specific protocol:
Debugging a target over a serial line.
While running this, GDB does not access memory from...
Local exec file:
`H:\Workspace\GRUB\Bootloader\Trunk\grub-core\kernel.exec', file type elf32-i386.
Entry point: 0x9000
0x00009000 - 0x0000e6e0 is .text
0x0000e6e0 - 0x0000f68d is .rodata
0x0000f6a0 - 0x0000fe74 is .data
0x0000fe80 - 0x000175d4 is .bss
Ended up being that my codebase wasn't the same. That is, on my Windows host, I had one copy of my code and on my Ubuntu VM was another.
Using version control solved this issue.
I had a program that was segfaulting.
When I went to investigate and ran dmesg I could see lines like this:
[955.915050] traps: foo_bar[123] general protection ip:7f5fcc2d4306 sp:7ffd9e5868b8 ...
Now the program has been fixed and I'm trying to write some analysis scripts across different systems to find similar messages and was hoping to induce a line in the dmesg log to get a baseline for what to look for and see if there's a difference between, say, a sigbus(10) and a sigill(4)
I tried to do it via kill -11 on the command line . No entry in dmesg
I tried to do it via signal(getpid(), 11) in the code. No entry in dmesg
I tried to do it via signal 11 after attaching in gdb . No entry in dmesg
I tried to do it via writing bad code and it worked for SEGV, but I can't figure out how to trigger a SIGBUS (for example)
I'm guessing that there is more than one path for handling the signal depending on how it occurs and my attempts above just aren't doing it the right way.
How can I trigger/send a signal to my program that'll get a line in dmesg? Is there some kernel or log configuration I can twiddle to get those lines?
Update:
" __builtin_trap: when to use it? " shows how to get a SIGILL but alas doesn't have a signal-agnostic solution)
core.1678,core.1689, how can i resolve this problem using gdb.i have tried gdb bt option but it is not resolving the error.
gdb -bt core.1678
(gdb) core
No core file now.
(gdb) n
The program is not being run.
(gdb) r
Starting program:
No executable file specified.
Use the "file" or "exec-file" command.
(gdb) core.1678
/home/deepak/deepak/mss/.1678: No such file or directory.
(gdb) /home/deepak/deepak/mss/core.1678
help me out
many core files( e.g core.1678 etc )...
This indicates that your same program or different programs in that particular directory is continuously crashing. When your machine is configured to generate dump file, it creates the file in the form of core.(PID). You may refer many useful article regarding the core dump file. You may refer my blog as well which explains about core dump analysis and its internal.
http://mantoshopensource.blogspot.sg/2011/02/core-dump-analysis-part-ii.html
The basic command to load and analyze the core dump file using GDB is as follows:
mantosh#ubuntu:~$ gdb
// This is how you would open the core dump file.
(gdb) core core.23515
(no debugging symbols found)
Core was generated by `./otest LinuxWorldRocks 10'.
Program terminated with signal 11, Segmentation fault.
[New process 23515]
==> Signal 11(SIGSEGV) was the reason for this core-dump file
==> pid of a program is 23515
#0 0x080485f8 in ?? ()
// Load the debug symbol of your program(build with -g option)
(gdb) symbol ./otest
Reading symbols from /home/mantosh/Desktop/otest...done.
// Now you can execute any normal command which you perform while debugging(except breakpoints).
(gdb) bt
#0 0x080485f8 in printf_info (info=0x8ec5008 "LinuxWorld") at test.c:58
#1 0x080485c2 in my_memcpy (dest=0x8ec5012 "", source=0xbfb9c6fe "Rocks",
length=10) at test.c:47
#2 0x0804855d in main (argc=3, argv=0xbfb9b3f4) at test.c:33
EDIT
cored-ump file is the snapshot of that particular program at the time of exception/segmentation fault. So once you load core-dump in GDB you would only be able to execute the command to read
the memory information. You can not use the debugging commands like breakpoints, continue, run ...etc..........
I wanted to start using gdbserver for remote debugging and so I tested-out its functionality on my local machine with a simple test program that generates a segfault shown below:
segfault.c -- compiles to elf named "test"
#define NULL ((void*)0)
int main()
{
int value = *((int*)NULL);
return value;
}
Now when I run:
#gdb test
(gdb)run
I get:
Starting program: /home/awaibel/digiworkspace/test/Debug/test
Program received signal SIGSEGV, Segmentation fault.
0x080483bf in main () at ../segfault.c:4
4 int value = *((int*)NULL);
however if I debug it with gdb server like so:
#gdbserver :65535 test
#gdb test
(gdb)target remote 127.0.0.1:65535
(gdb)continue
it gives me the debug info:
Program received signal SIGSEGV, Segmentation fault.
0x080483bf in ?? ()
it seems to give the same function address for the segfault, but the name and line number is omitted when debugging with the remote debugger. is it possible to have the remote debugger display this information, and if so, how?
I guess I should add that the program was compiled with GCC using the "-g" debug flag
Thanks to markys' comments I was able to figure out the problem. Since the gdb client is what parses the symbols and not the server, I had to make sure the client knew the full path to a copy of the executable. Since 'test' was not in the current directory for the command prompt that was used to run gdbtest it did not have a copy of the symbols to use. adding the the binary to PATH for the terminal running the client solved the problem. Thanks.
Summarizing:
server side:
gdbserver --multi :port "path-to-executable"
client side:
gdb "path-to-executable"
(gdb)> target remote "ip-of-the-remote-device:port"
My program loads a dynamic library, but after it tries to load it (it doesn't seem to, or at least something's amiss with the loading. A free() throws an error, and I commented out that line.)
I get the following in gdb.
Program received signal SIGSEGV, Segmentation fault.
__strlen_ia32 () at ../sysdeps/i386/i686/multiarch/../../i586/strlen.S:99
99 ../sysdeps/i386/i686/multiarch/../../i586/strlen.S: No such file or directory.
in ../sysdeps/i386/i686/multiarch/../../i586/strlen.S
How would I go about addressing this?
EDIT1:
The above issue was due to me not having an xml file where it should have been.
Here's the first error that I covered up to get to the initial error I showed.
(gdb) s
__dlopen (file=0xbfffd03c "/usr/lib/libvisual-0.5/actor/actor_AVS.so", mode=1)
at dlopen.c:76
76 dlopen.c: No such file or directory.
in dlopen.c
(gdb) bt
#0 __dlopen (file=0xbfffd03c "/usr/lib/libvisual-0.5/actor/actor_AVS.so",
mode=1) at dlopen.c:76
#1 0xb7f8680d in visual_plugin_get_references (
pluginpath=0xbfffd03c "/usr/lib/libvisual-0.5/actor/actor_AVS.so",
count=0xbfffd020) at lv_plugin.c:834
#2 0xb7f86168 in plugin_add_dir_to_list (list=0x804e428,
dir=0x804e288 "/usr/lib/libvisual-0.5/actor") at lv_plugin.c:609
#3 0xb7f86b2b in visual_plugin_get_list (paths=0x804e3d8,
ignore_non_existing=1) at lv_plugin.c:943
#4 0xb7f9c5db in visual_init (argc=0xbffff170, argv=0xbffff174)
at lv_libvisual.c:370
#5 0x080494b7 in main (argc=2, argv=0xbffff204) at client.c:32
(gdb) quit
A debugging session is active.
Inferior 1 [process 3704] will be killed.
Quit anyway? (y or n) y
starlon#lyrical:client$ ls /usr/lib/libvisual-0.5/actor/actor_AVS.so
/usr/lib/libvisual-0.5/actor/actor_AVS.so
starlon#lyrical:client$
The file exists. Not sure what's up. Not sure what code to provide either.
Edit2: More info on the file. Permissions are ok.
816K -rwxr-xr-x 1 root root 814K 2011-11-08 15:06 /usr/lib/libvisual-0.5/actor/actor_AVS.so
You didn't tell what dynamic library it is.
If it is a free dynamic library -or a library whose source is accessible to you- you can compile it and use it with debugging enabled.
Several Linux distributions -notably Debian & Ubuntu- provide debugging variant of many libraries (e.g. GLibc, GTK, Qt, etc...), so you don't need to rebuild them. For example, Debian has libgtk-3-0 package (the binary libraries mostly), libgtk-3-dev the development files for it (headers, etc...) and libgtk-3-0-dbg (the debugging variant of the library). You need to set LD_LIBRARY_PATH appropriately to use it (since it is in /usr/lib/debug/usr/lib/libgdk-3.so.0.200.1).
Sometimes, using the debugging variants of system libraries help you to find bugs in your own code. (Of course, you also need to compile with -g -Wall your own code)
Turned out this was due to a faulty hard drive. Looks like I need a new one.