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Debugging Octave: Difference between revisions
→Tools for debugging: Restore instructions for attaching gdb to Octave from an "independent" shell.
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(→Tools for debugging: Restore instructions for attaching gdb to Octave from an "independent" shell.) |
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Alternatively, you can attach a debugger to a running Octave session. Current development versions of Octave include the command <code>__debug_octave__</code> to manage the details. Executing this command at the Octave prompt should open a separate window for a debugger session attached to the current Octave process. On Linux systems, the default terminal window is <code>gnome-terminal</code>. On MacOS systems, the default debugger is <code>lldb</code>. | Alternatively, you can attach a debugger to a running Octave session. Current development versions of Octave include the command <code>__debug_octave__</code> to manage the details. Executing this command at the Octave prompt should open a separate window for a debugger session attached to the current Octave process. On Linux systems, the default terminal window is <code>gnome-terminal</code>. On MacOS systems, the default debugger is <code>lldb</code>. | ||
For some kinds of errors on some OS, the last approach might not be useful. The OS might kill the shell that runs gdb as soon as the spawning process (i.e. Octave) crashes. In that case, you can attach to Octave from an "independent" shell. Execute <code>getpid ()</code> in Octave and take note of the displayed *PID*. Open a shell and execute <code>gdb -p *PID*</code> (replace <code>*PID*</code> with the actual PID). On Windows, use the msys2 shell that can be started with the file <code>cmdshell.bat</code> in Octave's installation folder. | |||
Independent of how <code>gdb</code> was started and Octave was attached to it, it is now possible to issue gdb commands on the <code>(gdb)</code> prompt. See e.g. the [https://sourceware.org/gdb/download/onlinedocs/gdb/index.html gdb documentation]. To return to Octave while gdb is still attached to it, execute <code>continue</code> (or <code>c</code>) at the <code>(gdb)</code> prompt. | Independent of how <code>gdb</code> was started and Octave was attached to it, it is now possible to issue gdb commands on the <code>(gdb)</code> prompt. See e.g. the [https://sourceware.org/gdb/download/onlinedocs/gdb/index.html gdb documentation]. To return to Octave while gdb is still attached to it, execute <code>continue</code> (or <code>c</code>) at the <code>(gdb)</code> prompt. | ||
*NOTE | *NOTE: Ubuntu introduced a patch to disallow ptracing of non-child processes by non-root users - i.e. only a process which is a parent of another process can ptrace it for normal users - whilst root can still ptrace every process. | ||
That's why gdb won't be able to link to the octave process if you start gdb from within an Octave session using the <code>__debug_octave__</code> command | That's why gdb won't be able to link to the octave process if you start gdb from within an Octave session using the <code>__debug_octave__</code> command. | ||
You can temporarily disable this restriction by doing: | You can temporarily disable this restriction by doing: | ||
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echo 0 | sudo tee /proc/sys/kernel/yama/ptrace_scope | echo 0 | sudo tee /proc/sys/kernel/yama/ptrace_scope | ||
</syntaxhighlight> | </syntaxhighlight> | ||
and then reopen | and then reopen <code>gdb</code> using the command mentioned above from within an Octave session or if you have admin rights you can simply do: | ||
<syntaxhighlight lang="bash"> | <syntaxhighlight lang="bash"> | ||
__debug_octave__ ("gnome-terminal --command 'sudo gdb -p %d'") | __debug_octave__ ("gnome-terminal --command 'sudo gdb -p %d'") | ||