If I run a program under gdb, how do I break at an arbitrary point? Pressing Ctrl+C kills the program. Ctrl+Break does nothing.
I can't enter gdb commands because my program is itself sitting in a REPL loop so anything I enter goes to my program, not to gdb.
My program uses linenoise to implement the REPL; I assume that this is hiding Ctrl+C, etc., from gdb.
Ctrl+\ results in a 001C square blob thingy in my program, rather than SIGUSR1.
Pressing Ctrl+C kills the program.
That is not the default GDB behavior.
Did you set handle SIGINT nostop pass?
You can examine current signal disposition with:
(gdb) handle SIGINT
Signal Stop Print Pass to program Description
SIGINT Yes Yes No Interrupt
Update:
My program is using linenoise for console input. I assume that it has done something to Ctrl+C
If your program is modifying terminal settings, you are going to have a very bad time debugging it from the same terminal.
For example, suppose the program sets no echo, and then hits a breakpoint. I think you would get a (gdb) prompt, but would not see any commands you are typing into GDB.
It seems that you would be much better off debugging this program from a different terminal. Use gdb -p $PID to attach to it from "outside".
Related
I am trying to debug an application in gdb running on Ubuntu 18.04.
In some parts of the code, I can set breakpoints and successfully debug problems.
But in other parts, triggering a breakpoint causes the process to exit.
Is there some way I can get debut statements to appear in the gdb console?
I currently use gdb to attach to the process and then debug from that point.
I have code (std::cout) that sends statements to standard out but they are not showing up in the gdb console.
Nor should you expect them to.
When an application is started, its std::cout messages are going to file descriptor 1 (stdout). This can be the terminal window in which the app was started, or a file if the output was redirected. It could also be a pipe or /dev/null.
GDB does not "steal" that output (if it did, it would be harder to debug a program that is the source of input for another program going through a pipe).
Your first task should be to determine where the output is going. On Linux, this is usually as easy as ls -l /proc/$pid/fds/1 (replace $pid with the actual process id of the process you are debugging).
An additional complication is that the stdout can be fully buffered (if it goes into a file, pipe or socket), and may not be flushed by the time your breakpoint is hit.
P.S. In theory, you can "steal" the output from wherever it's going to your current terminal by running the following GDB commands:
(gdb) print open("/dev/tty", 2, 0) # open new fd in the inferior process
# going to current terminal.
# This will print something, e.g. 5
# Now make stdout go to that newly-opened fd
(gdb) call dup2($whatever_last_command_printed, 1)
but I wouldn't recommend this, as it can interfere with the program in unexpected ways.
I've made sure to build my D program with the -g flag (add symbolic debug info) and it looks like I can set simple LOC breakpoints in both GDB and LLDB like this: b SomeModule.d:42 - the debugger replies with a memory address for the new breakpoint.
However when I run the program from the debugger, it gets stopped somewhere completely different than SomeModule.d:42. What am I missing?
D is a safe by default, garbage-collected by default, language.
So in addition to your own breakpoints, programs will often be interrupted by the Garbage Collector Signals (SIGUSR1, SIGUSR2).
In GDB, this can be prevented by:
(gdb) handle SIGUSR1 nostop noprint
Signal Stop Print Pass to program Description
SIGUSR1 No No Yes User defined signal 1
(gdb) handle SIGUSR2 nostop noprint
Signal Stop Print Pass to program Description
SIGUSR2 No No Yes User defined signal 2
Even better, automate by putting the above 2 commands in a file and start GDB with -x gdb_command_file.
The corresponding LLDB-ese sounds different:
(lldb) process handle --stop false --notify false SIGUSR1 SIGUSR2
I'm not sure it's possible to automate it similarly with LLDB alone.
I need to debug a program which segfaults at uneven intervals. The program has a while(true) loop.
While debugging via GDB, it stops and asks for the Enter key to be pressed to continue. However, I want the program to run until it crashes. How do I do that in GDB?
Use set height 0 or set pagination off. Reference
I'm developing an application (a service/daemon, really) on Linux in C++ that needs to interface with a piece of hardware. If my program doesn't release the resources for this peice of hardware cleanly when terminating, then I have to reload the device driver, a process that takes about 10 minutes and for obvious reasons having to wait 10 minutes between each test of the program would be frustrating.
So I have used the sigaction() function to catch a SIGINT (a ctrl-c) so that my program can cleanly shutdown when I'm finished with it. When running the program from the console, this works fine. However, when debugging in Netbeans or Eclipse (I've tried both) things don't work.
In Eclipse, if I hit ctrl-c in the console it provides, it doesn't seem to register that a SIGINT ever occurred
In Eclipse, if I run the program in debug mode and then use kill -SIGINT <pid>, the program just breaks as if it hit a breakpoint
Netbeans actually seems to realise a signal has been sent when I hit ctrl-c in the console, and pops up a dialog asking if I want to forward it to the application. Clicking "Forward and continue" just seems to break the program and the signal is not received by the application. It also says I can configure this stuff in Debug -> Dbx configure, a menu item that doesn't exist
In Netbeans, if I run the program in debug mode and then use kill -SIGINT <pid>, the behaviour is the same as above
I then added a SIGQUIT handler and tried sending that via kill when debugging in Netbeans. This time, no dialog appears and the signal handler is never tripped.
I need some way to cleanly shutdown my app while I'm debugging. Any ideas?
It turns out the problem had nothing to do with Netbeans or Eclipse, but rather gdb.
gdb can be configured to handle signals in a variety of ways. If you run:
gdb
then type:
info signals
You'll get a list of signals and gdb actions on what to do if it receives that signal:
Signal Stop Print Pass to program Description
SIGHUP Yes Yes Yes Hangup
SIGINT Yes Yes No Interrupt
SIGQUIT Yes Yes Yes Quit
SIGILL Yes Yes Yes Illegal instruction
SIGTRAP Yes Yes No Trace/breakpoint trap
etc...
My temporary work around has been to use SIGALRM which gdb defaults to not breaking and sending to the process. However, you can also customise the default gdb settings by creating a .gdbinit file where you can set these
Even this post is old, hope it can help others.
To prevent Eclipse from catching the Ctrl+C, you can configure your gdb using .gbdinit file.
You create a .gdinit with this content
#we want Ctrl+C to be no break, pass to application and printed by the debugger
handle SIGINT nostop
handle SIGINT pass
handle SIGINT print
In your eclipse configuration, you can define where is your .gdbinit file to use in your Debug configuration
Simple solution.. Try using DEBUG macros to handle your situation.
// Register the signal handler to stop service.
#ifdef _DEBUG
signal(SIGKILL, <your signal handler>);
#endif
Also, you may try to clean up your app before exiting.
Is there a way to stop the inferior without using Ctrl+C (or an equivalent signal sent from another process?) I'm using a windows platform and am managing GDB from another process, so with no notion of signals, it seems that there isn't a good way to break execution of my program when it's free running without any breakpoints.
EDIT FOR CLARITY:
There are 2 processes involved here. There's process A, which is the parent of GDB. GDB is managing a process, but it's on a remote host, and we'll call that process C.
When I tell GDB to "run" it kicks off process C on the remote host and blocks either until a breakpoint is hit, process C encounters an error or a fatal signal, or GDB itself receives an interrupt signal. If working interactively, you would simply press CTRL+C at the GDB command console, which GDB interprets as a SIGINT (somehow), triggering GDB to halt process C. Since I'm actually managing GDB with process A (and not dealing with it interactively at the shell) I can't very well press Ctrl+C, and since windows has no native notion of "Signals" like you have in UNIX, I can't figure out how to interrupt GDB when it's blocking waiting for process C to interrupt or hit a breakpoint.
Did you try to take a look at the remote control protocols? for instance, EMACS uses MI to control GDB, you should check how/if they offer such a ctrl-C mechanism, and how they implement it.
EDIT: it seems to be -exec-interrupt which interrupts the execution.