I'm running my program under gdb, with debuging information and without any optimizations. gdb reports:
Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x7fffeffff700 (LWP 8875)]
0x0000001000000001 in ?? ()
From this message i do not understand where the problem happened. Is it possible to extract stacktrace / problem file and line number?
To get the point where code segmentation fault has happened, you should use backtrace (bt) command.
There are wide range of commands available inside gdb which should be explored to help make you debug your code as efficiently as possible.
e.g. you could record your code flow and replay it in reverse.
explore data types
have breakpoints etc.
Related
When gdb starts in windows 10, error message is received.
Program received signal SIGSEGV, Segmentation fault.
0x00007ffe7c493466 in ntdll!RtlWaitOnAddress () from C:\windows\SYSTEM32\ntdll.dll
enter image description here
Does anyone know how to fix it?
I have web daemon and request that makes it fail with SIGSEGV. So i start daemon, attach with gdb, continuing, send request and getting this:
$ gdb attach -p 630066
(gdb) c
Continuing.
Program terminated with signal SIGSEGV, Segmentation fault.
The program no longer exists.
(gdb)
How to make gdb print stacktrace before killing application? Application do not have subprocesses, just threads.
Thanks.
Your GDB session indicates that you have not attached all threads of the multithreaded process, and some other thread (one you didn't attach) ran into SIGSEGV and terminated the entire process.
Another (somewhat unlikely) possibility is that you are using a very old version of GDB, one which still has this bug in it (the bug was fixed in 2009).
When using gdb -p NNNN you need to be careful and specify correct process id. pgrep daemon-name or ps aux | grep daemon-name should give you a good idea which process to attach.
Just enter backtrace or bt right in the gdb shell after getting SIGSEGV.
To explore stack trace for each separate thread, start with info thread, then choose the thread you need, for example thread 3 and then type bt to see the stack trace for that thread.
Thread 2 received signal SIGBUS, Bus error. 0x00000001001021e0 in ??
()
. What does this mean? GDB does not specify where this occur either
What does this mean?
It means that your program tried to execute instructions at address 0x1001021e0, but page mapped at that address is not mapped with execute permissions.
GDB does not specify where this occur either
Yes it does: it occurred at address 0x1001021e0.
What you want to do is:
Figure out how you got to execute at that address, The GDB where command may help
Figure out how the page at 0x1001021e0 is mapped. On Linux, cat /proc/$pid-of-debugged-program/maps or GDB info proc maps should help. Other OSes may have similar facilities.
I am trying to let my program run continously with GDB.
Currently I have a bash script which starts GDB with my program and when it crashes it prints the backtrace and starts GDB again (endless loop).
Now I added a signal handler for my program which kills specific threads when the handler gets a signal from them. Now I can achieve that GDB does not stop by doing this:
handle SIGSEGV nostop
But this leads me to the problem that I do not get a GDB backtrace which I would like to print automatically without stopping the program (or at least continuing automatically).
Any help would be appreciated!
Continue to use handle to suppress ordinary stops from SEGV. Then set a catchpoint that does what you want:
(gdb) catch signal SIGSEGV
(gdb) commands
> silent # this bit is optional
> bt
> continue
> end
This will print a backtrace on SIGSEGV but not otherwise interfere with normal operation. You may also want handle SIGSEGV noprint.
I will try to be as specific as I can, but so far I have worded this problem so poorly that Google failed to return any useful results (hence my question here).
I am attaching gdb to a multi-threaded c++ server process. All I can say is that strange things have been happening while trying to do the usual set-breakpoint-break-investigate.
First, while waiting for the breakpoint to be hit (in 'Continuing' mode), I suddenly got back the (gdb) prompt with the message:
Continuing.
[Thread 0x54d5b940 (LWP 28503) exited]
[New Thread 0x54d5b940 (LWP 28726)]
Cannot get thread event message: debugger service failed
Second, also while waiting for the breakpoint to be hit, I'm suddenly told the program has received SIGSEGV and - back to the (gdb) prompt - backtrace tells me the segfault happened in pthread_cancel(). Note the process under investigation does not normally segfault.
I clearly lack enough information about how gdb works to even begin guessing what is happening. Am I doing anything wrong? The steps I take are the same each time:
gdb attach
break 'MyFunction()'
continue
Thoughts? Thanks.
I fought with similar gdb issues for a while. My case was having lots of threads spawned that executed few functions and then exited.
It appears if a thread exits too fast and there's lots of these happening sometimes gdb cannot keep up and when it fails, it fails with style as in crashes :) I think it tries to attach to a thread that is already done as per the error message.
I see this as an issue in gdb 6.5 to 7.6 and still happening. Did not try with older versions.
My advice is look for this use case or similar. Once I changed my design to have a thread serving a queue of requests gdb works flawlessly.
Design wise is healthier to have already created threads that digest actions than always spawning new threads.
Still same code debugs without a problem on Visual Studio so I do have to say that is a small disappointment to me with regards to gdb.
I use Eclipse and looking at the GDB traces (usually enabled by default) will give you a better hint of where GDB fails. One of the buttons on the console shows you the GDB trace.