I am running my Qt app from gdb, and i want to stop when new threads creates.
(when gdb prints message [New Thread address (LPW number)].
I have set breakpoint b __pthread_create_2_1.
That allows me to catch most of new threads prints. but i still got few new threads that are not catched.
What else can i do to catch their creation?
Probably what you want is
catch syscall clone (see here https://sourceware.org/gdb/onlinedocs/gdb/Set-Catchpoints.html)
Also by default gdb let other threads continue their execution if a breakpoint or catchpoint event occurs.
So maybe you want to take a look at the All-Stop mode (https://sourceware.org/gdb/onlinedocs/gdb/Thread-Stops.html)
Related
I have a double-free bug. I am able to reproduce it using a debug build with Address Sanitizer (AS) detects but when I run under GDB, AS kills the GDB session.
I found this Address Sanitizer page with instructions how to keep GDB:
https://github.com/google/sanitizers/wiki/AddressSanitizerAndDebugger
but when I do:
(gdb) break __asan::ReportGenericError
at the beginning of the session, the GDB state still disappears after the problem is detected:
(gdb) bt
No stack.
the GDB state still disappears after the problem is detected
There are several possible reasons for this:
Somehow you didn't set the breakpoint correctly
It's actually a child process that is dying
Somehow the thread in which the error is detected is not attached by GDB.
To eliminate 1, use catch syscall exit_group (and possibly also catch syscall exit) -- this way GDB is sure to stop before the process disappears.
For 2, AddressSanitizer message should indicate the thread id in which the error is detected, and that id should match one of the threads in GDB info thread output.
For 3, we'd need to understand more about how that thread was created.
got some big real time project to deal with (multiple processes (IPCs), multi Everything in short).
My working on process is started as service on Linux. I have the root access.
Here is the problem:
I'm trying to attach to a running proc, tried starting it through/with gdb but the result is the same: it stops the executable once I "touched" it with gdb or sometimes it throws:
Program received signal SIGUSR1, User defined signal 1. [Switching to Thread 0x7f9fe869f700 (LWP 2638)]
of course from there nothing can be done.
Tried:
handle all nostop
attach to launched as service (daemon) or launched as regular proc
started from gdb
thought maybe forking/multi-threaded problem - implemented in the very beginning sleep for 10 seconds - attached to it with "continue"
Guys, all I want it is to debug, hit the breakpoints, etc.
Please help! Share ideas.
Editing actual commands:
1) gdb attach myProcId. Then after reading symbols, I hit "c" which results:
Program received signal SIGUSR1, User defined signal 1.
[Switching to Thread 0x7f9fe869f700 (LWP 2638)]
0x00007f9fec09bf73 in select () from /lib64/libc.so.6
2) If I make the first line 10 seconds sleep in the code, attaching to the process, hit "c", result: it runs, shows info threads, backtrace of main, but never hits the breakpoint (for sure the code runs there - I get logs and different behaviour if I change code there), meaning the process is stuck.
3) All other combinations like gdb path/to/my/proc args list, then start. Where arg list played with different related options gdb gives us.
Maybe worth to mention: process network packets related, timers driven also.
But for me the important thing is a current snapshot on break, i don't care what will happen to the system after timers expired.
Since you mentioned that you are debugging a multiprocessing program, I think the underlying program you have is to set the breakpoint in the correct subprocess.
Try break fork and set follow-fork-mode child/parent. What you want to achieve is have gdb attached to the process that is running the code you want to debug.
Refer to this link.
Another thought is to generate a crash, since you can compile the programe. For example add a int i = *(int*)NULL and that will generate a core dump. You can then debug the core dump with gdb <program> <core dump>. You can refer to this page for how to configure core dump.
Is it possible to disable gdb breakpoints on a per-thread basis?
I have a breakpoint which triggers every 100 milliseconds in the background worker thread. But I need to debug the same location in any other threads. So it would be cool to disable breakpoint only in the background worker thread. Is it possible?
Maybe I can disable thread by adding some specially crafted condition to this breakpoint when I know thread's number?
Gdb provides two convenience variables, $_thread and $_gthread (the latter being pretty new), which can be used in conditions to refer to the current thread.
So, once the worker thread has started, you can use info thread to find its number. Then you can change your breakpoint (supposing for this example that it is breakpoint 2) like:
(gdb) cond 2 $_thread != 57
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.