CODEWITHSUNDEEP
c++linuxgdbgdbserver
Libor Tomsik
Libor Tomsik

Reputation: 718

Remote gdb stops at every event

I'm having remote ARM Linux box which I need to debug.

The server is started:

gdbserver :12345 ./my_app

The client:

./arm-am3354-linux-gnueabihf-gdb ~/
 (gdb) target remote dev_r:12345
 (gdb) continue

Then I'm trying to pause the app with Ctrl+C, but the gdb stops with:

[Inferior 1 (process 2766) exited with code 01]

And on server:

Child exited with status 1 GDBserver exiting

Story: I was trying to use remote debugging in QtCreator, but when setting breakpoints in run-time the gdb was crashing in the same way. Also the breakpoints and pause is not working in QtCreator. I was trying also another gdb like gdb-multiarch and the one from android-sdk.

Update: Debugging small program aka Hello World works. Local Debugging (on x86) works too. The app itself has hundred thousand lines of code, shared and static libraries.

Partial solution: Probably the sysroot for embedded platform that I've got was invalid. After copying /lib/ and /usr/ from the target device and setting it as 

set sysroot /home/karel/sysroot

I'm able to set breakpoints and the app stops at them. The pause however is still stopping the remote app. The same for QtCreator: Tools->Options->Debugger->GDB->Additional Attach Commands

Upvotes: 0

Views: 989

Answers (1)

stjosh
stjosh

Reputation: 1

I had a similar (or even exactly the same?) issue with debugging my application running on the EGLFS platform. Debugging when built with Qt 5.4 was working perfectly fine, debugging with Qt 5.5 did behave as you describe.

After hours of searching, I found that my application on Qt 5.5 exited when receiving a SIGINT, whereas on Qt 5.4, the debugger could pause the application as expected. Since GDB sends SIGINT when trying to pause the application or setting / removing a breakpoint, this was where trouble started.

After some more research, I finally found the following commit to Qt 5.5: Fix up signal handling in QFbVtHandler. At the very end, you see that when receiving SIGINT or SIGTERM, the handleInt() handler is called where we finally run into _exit(1). Setting a breakpoint there confirmed that this is exactly what happens when trying to pause or set a breakpoint with GDB.

Solution that worked for me: I have created a patch to qfbvthandler.cpp, simply removing the #define VTH_ENABLED line.

GDB debugging is now again working like a charm.

Note: Even though qfbvthandler.cpp has been updated in Qt5.6 and upwards, I suspect the behaviour would still be the same. I however don't have a workspace set up in order to test this.

Upvotes: 0

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