4 ms·

Even if the rest of GDB remains a mystery to you, you can learn the two simplest and most useful functions: 1) how to create a backtrace, and 2) how to create a

Even if the rest of GDB remains a mystery to you, you can learn the two simplest and most useful functions: 1) how to create a backtrace, and 2) how to create a core dump. That way you can always send a bug report with lots of detail to somebody else for analysis.

jmclnx 5y ago
> 2) how to create a core dump This is a PITA under Linux, I figured this out but nor happy I had to look. I wish Linux was like OpenBSD, where you get core files by default. This give me yet another reason to switch to OpenBSD, I only wish some other issues I am having with OpenBSD could get solved.
- mark_undoio 5y ago
  What did you figure out as a solution? I've previously configured `/proc/sys/kernel/core_pattern` to generate core dumps by default (and not pipe them to a core dump collection program, which may be useful for error reporting but is rarely what I want). There's also `gcore` for doing on-demand core dumps. I wish it were possible to configure core dump behaviour per-process (or something similar).
  - jmclnx 5y ago
    This is what I did: ulimit -S -c unlimited sudo sysctl -w kernel.core_pattern=core took me a while to figure this out, HTH
    - mark_undoio 5y ago
      Thanks! I also see there's a `/proc/sys/kernel/core_uses_pid` that will make you get `core.PID` files, without having to mess around with core patterns - seems useful.
- begriffs 5y ago
  > OpenBSD, where you get core files by default By this, are you referring to the behavior: "By default, this memory image is written to a file named programname.core in the working directory, provided the terminated process had write permission in the directory[...]" (from https://man.openbsd.org/core.5 https://man.openbsd.org/core.5) ? Also, do you know if there's a way to obtain a core file from a running process on OpenBSD? I don't see a port of gcore, and (e)gdb on OpenBSD doesn't support the generate-core-file command (it says, "Can't create a corefile").
  - jmclnx 5y ago
    Yes, kill -ABRT pid should do it
    - begriffs 5y ago
      Good idea to just abort it. :) However, I tried your suggestion from another terminal, and gdb appears to shield the program somehow. What ended up working is running "signal SIGABRT" from within gdb. One thing that's still lacking is gcore's ability to take a snapshot of the core without killing the program. "Unlike after a crash, after gcore finishes its job the program remains running without any change." https://www.man7.org/linux/man-pages/man1/gcore.1.html https://www.man7.org/linux/man-pages/man1/gcore.1.html

jmclnx 5y ago

> 2) how to create a core dump This is a PITA under Linux, I figured this out but nor happy I had to look. I wish Linux was like OpenBSD, where you get core files by default. This give me yet another reason to switch to OpenBSD, I only wish some other issues I am having with OpenBSD could get solved.

mark_undoio 5y ago
What did you figure out as a solution? I've previously configured `/proc/sys/kernel/core_pattern` to generate core dumps by default (and not pipe them to a core dump collection program, which may be useful for error reporting but is rarely what I want). There's also `gcore` for doing on-demand core dumps. I wish it were possible to configure core dump behaviour per-process (or something similar).
- jmclnx 5y ago
  This is what I did: ulimit -S -c unlimited sudo sysctl -w kernel.core_pattern=core took me a while to figure this out, HTH
  - mark_undoio 5y ago
    Thanks! I also see there's a `/proc/sys/kernel/core_uses_pid` that will make you get `core.PID` files, without having to mess around with core patterns - seems useful.
begriffs 5y ago
> OpenBSD, where you get core files by default By this, are you referring to the behavior: "By default, this memory image is written to a file named programname.core in the working directory, provided the terminated process had write permission in the directory[...]" (from https://man.openbsd.org/core.5 https://man.openbsd.org/core.5) ? Also, do you know if there's a way to obtain a core file from a running process on OpenBSD? I don't see a port of gcore, and (e)gdb on OpenBSD doesn't support the generate-core-file command (it says, "Can't create a corefile").
- jmclnx 5y ago
  Yes, kill -ABRT pid should do it
  - begriffs 5y ago
    Good idea to just abort it. :) However, I tried your suggestion from another terminal, and gdb appears to shield the program somehow. What ended up working is running "signal SIGABRT" from within gdb. One thing that's still lacking is gcore's ability to take a snapshot of the core without killing the program. "Unlike after a crash, after gcore finishes its job the program remains running without any change." https://www.man7.org/linux/man-pages/man1/gcore.1.html https://www.man7.org/linux/man-pages/man1/gcore.1.html