Without getting into to to much detail, I'm working on a program that consists of several separate processes all running on embedded QNX RTOS. They don't have a parent-child relationship, they are all spawned using spawnlp(P_NOWAIT, ...) and they all communicate with each other using the IPC mechanism provided by the OS.
When I'm debugging with GDB and I hit a breakpoint in the process I'm working in, all of my threads are paused, which is great. But is there a way to also have it pause execution of my other processes? Right now what's happening is all the other processes keep on truckin' while my process is paused and so all the IPC queues get full etc. etc.
Thanks in advance,
HF
You can associate a list of GDB commands with each breakpoint. So when you hit a breakpoint in process A, you can for example send a SIGTRAP to process B, which should drop it into the debugger:
(gdb) b main
Breakpoint 1 at 0x804834a: file testA.c, line 40.
(gdb) command
Type commands for when breakpoint 1 is hit, one per line.
End with a line saying just "end".
>shell kill -s TRAP `pidof testB`
>end
(gdb)
More info at Breakpoint Command Lists
Related
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.
Let say I want to debug 2 instances of my program "Program.exe", each one with a different argument ("one" and "two"). Also I need to run both process at the same time (or at least within 1 second).
I've read that GDB's inferiors lets you run and debug multiple programs in a single session. And this is my try:
file Program.exe
set args one
add-inferior
inferior 2
file Program.exe
set args two
run
But not success. Only one inferior is running
Any idea?
I'm considering these two options:
Creating a new program that forks the process, then GDB can handle both processes through "set detach-on-fork off" but this approach seems to me a bit ugly...
Launching two processes normally and then attach them by PID in GDB. But my environment is Windows and I don't know how to do that nor how to find PID by command line argument.
Thanks in advance!
I'm having a tough time figuring this one out; I have a program, iverilog that executes a system() call to invoke another program, ivl. I want to debug the second program, ivl in gdb, but I can't get gdb to set any breakpoints in the child process when I invoke gdb with the parent process. Here's what the programs look like:
//iverilog-main.cpp (Parent process)
int main(){
//...
system("ivl arg1 arg2");
//...
return 0;
}
.
//ivl-main.cpp (child process)
int main(){
//...
//stuff I want to debug
//...
return 0;
}
.
The gdb commands I'm running are: gdb iverilog -x cmds.gdb
# cmds.gdb
set args hello.v
set follow-fork-mode child
set breakpoint pending on
break ivl-main.cpp:main
run
Unfortunately, gdb doesn't break at ivl-main.cpp:main,it just completes without ever breaking; the output I get is:
Starting program: /usr/local/bin/iverilog hello.v
[New process 18117]
process 18117 is executing new program: /bin/dash
[Inferior 2 (process 18117) exited normally]
I'm certain ivl-main.cpp:main is being called because when I run the ivl program in gdb it successfully breaks there.
My thinking is that gdb doesn't recognize ivl-main.cpp as a source file when its running gdb iverilog, and it's not setting that breakpoint when it enters the child process which does contain ivl-main.cpp as a source file. So I think if I set the breakpoint for ivl-main.cpp when gdb enters the child process, it should work. The only way I can think of doing this is to manually break at the system() call and step into the child process, then set the breakpoint. Is there a more elegant approach that would force gdb to break whenever entering a child process?
Normally GDB only debugs one process at a time- if your program forks then you will debug the parent or the child, but not both simultaneously. By default, GDB continues debugging the parent after a fork, but you can change this behavior if you so desire with the following command:
set follow-fork-mode child
Alternately, you can tell GDB to keep both the parent and the child under its control. By default GDB only follows one process, but you can tell it to follow all child processes with this command:
set detach-on-fork off
GDB refers to each debugged process as an "inferior". When debugging multiple processes you can examine and interact each process with the "inferiors" command similar to how you would use "threads" to examine or interact with multiple threads.
See more documentation here:
https://sourceware.org/gdb/onlinedocs/gdb/Forks.html
This answer provides one way to achieve what you want.
In theory, set follow-fork-mode child should work.
In practice, the iverilog is likely itself a shell script that runs (forks) multiple commands, so at every fork you will need to decide whether you want to continue debugging the parent or the child. One wrong decision and you've lost control of the process that will eventually execute your program. This very likely explains why it didn't work for you.
If I have some multithreaded process and want to trace it with gdb using attach command, to which thread it will connect (e.g. current running or main)? I know that I can discover it with info threads but I want to know which thread it will choose by default.
For Linux, all of the threads are stopped by the ptrace command when gdb attaches.
It has been my experience that gdb defaults to the main thread for C/C++ applications. If you attach to a process and do a 'bt' it will list the stack for 'main'.
Information is available for all threads however. gdb can look at the thread(s) information in the /proc filesystem. The proc contains information about each thread in the tasks area. Details about the stack address is located in the stat file as well as the maps file. Details are also available regarding the register values for each thread.
Along the lines of your question, I've often wondered why stepping through a multithreaded application will cause gdb to jump from thread to thread. I think that gdb is still at the mercy of the kernel scheduler so that a step on a thread may lead to a different thread getting the CPU resource and a breakpoint being triggered.
On Linux, where thread ids exist in the same space as process ids, it appears you can run gdb -p tid to attach to the thread with given tid and its owning process, without knowing the pid. Because the main thread of a process has tid == pid, it makes sense that running gdb -p pid connects to the main thread.
Example code that connects gdb to the currently executing thread, e.g. for generating a pretty stack trace: https://github.com/facebook/rocksdb/pull/11150
I attached to my multithread application with gdb and after that type cont to continue execution.
Is there any way to stop execution at any time on cont gdb state and check what every thread do?
How to check state of every thread and get execution line number of each? (commands)
Here's what I do, (taken from here )
Create a little gdb script stackdumper.gdb that dumps the stack trace of all threads:
thread apply all backtrace
Then repeatedly attach gdb and run the dumper:
for i in $(seq 1 10) ; do
gdb -batch -x stackdumper.gdb ./a.out 123456 > stack.$i
sleep 10
done
where ./a.out is the binary you are interested and 123456 is the PID.
Adjust the sleep to match your sampling needs.
thread apply all bt
Or
info threads
t <threadid from above trace >
Followed by
where or bt
To get the backtrace for all of the stopped threads type the
thread apply all bt
command (the output is exactly the same that one might see in the MacOSX crash report box).
Usually the threads are stopped simultaneously in gdb.
Reference: http://www.delorie.com/gnu/docs/gdb/gdb_40.html
And here's about "all-stop" mode, which is default: http://sourceware.org/gdb/onlinedocs/gdb/All_002dStop-Mode.html
Is this any way to stop execution at any time on cont gdb state and check what every thread do
If you ask about ways to check what threads do without gdb the you can just run pstask <pid-of-your application>
Is it "pstack" because i don't think "pstask" is any command in linux, If it is please provide some more info