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devel-docs: debugging-tips.md also moved to gimp-web-devel repo.
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There are a few environment variables, options or other more-or-less
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known tricks to debug GIMP. Let's try to add them here for reminder and
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newcomers.
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## Basics ##
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The basic thing is to build babl, GEGL and GIMP with `--enable-debug`.
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Note that if you also built glib from source with `--enable-debug`,
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every pointers of destroyed GObject are overwritten with `0xaa` bytes,
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so dereferencing one after destruction usually leads to a crash, which
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is a good way to find some more vicious bugs. Also it makes pointers of
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destroyed data easy to spot.
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## Debug logs ##
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You can see various GIMP_LOG() calls in the code. These will only be
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outputted when you set GIMP_DEBUG environment variable to a
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comma-separated list of domain.
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For instance, for `GIMP_LOG (XCF, "some string")` to be outputted,
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run GIMP like this:
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> GIMP_DEBUG=xcf gimp-2.10
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Special flags are:
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- "all" to output all domain logs;
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- "list-all" to get a list of available domains.
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## Debugging a warning ##
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If you encounter a CRITICAL or WARNING message on console, you can make
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so that GIMP crashes on it, which will make it very easy to be tracked
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down in a debugger (for instance GDB), by running GIMP with:
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> gimp-2.10 --g-fatal-warnings
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Note that if all you want is a stacktrace, it is not necessary anymore
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to use a debugger and --g-fatal-warnings. In Preferences > Debugging,
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make sure that all type of errors are debugged, and that you have either
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gdb or lldb installed. Then a graphical dialog will automatically appear
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upon encountering any WARNING or CRITICAL with backtraces and variable
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contents.
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Alternatively running GIMP with the CLI option --stack-trace-mode to
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values "query" or "always" will output a stacktrace too on terminal.
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But this happens only for crashes, so it still requires to use
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--g-fatal-warnings for WARNINGs and CRITICALs.
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Note: on Windows, even the debugging GUI happens only for crashes and
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requires that you built with Dr. Mingw dependency.
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## Debugging GTK ##
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You can use GtkInspector by running GIMP with:
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> GTK_DEBUG=interactive gimp-2.99
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Alternatively you may also start it at anytime with ctrl-shift-d
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shortcut, if you first enable with:
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> gsettings set org.gtk.Settings.Debug enable-inspector-keybinding true
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See also: https://wiki.gnome.org/Projects/GTK%2B/Inspector
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Note also that running GIMP with `GDK_SCALE=2` (or other values) allow
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to test the interface in another scaling than your native one. This
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settings is also available in the GtkInspector.
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## Debugging GEGL code ##
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You may encounter this kind of warning upon exiting GIMP:
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> EEEEeEeek! 2 GeglBuffers leaked
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To debug GeglBuffer leaks, make sure you built GEGL with -Dbuildtype=debug
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or -Dbuildtype=debugoptimized, and set the environment variable
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GEGL_DEBUG to "buffer-alloc".
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Your system also needs to have the header "execinfo.h".
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## Debugging babl ##
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Profile conversion is done with babl by default when possible, which is
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much faster.
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Setting GIMP_COLOR_TRANSFORM_DISABLE_BABL environment variable switch
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back to the old lcms implementation, which can be useful for comparison.
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## Debugging X Window System error ##
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Make X calls synchronous so that your crashes happen immediately with:
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> gimp-2.10 --sync
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You can also break on `gdk_x_error()`.
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## Debugging on Windows ##
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Even when run from a `cmd`, the standard and error outputs are not
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displayed in the terminal. For this reason, unstable builds (i.e. with
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odd minor version) pop up a debug console at start.
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If you are building stable versions of GIMP for debugging and want this
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debug console as well, configure with `--enable-win32-debug-console`.
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## Testing older GIMP versions ##
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A useful trick when you want to quickly test a specific GIMP older
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version (e.g. to confirm a behavior change) is to install it with our
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official flatpak. The flathub repository stores past builds (up to 20 at
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the time of writing). You can list them with the following command:
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```
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$ flatpak remote-info --log flathub org.gimp.GIMP
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```
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Each build will have a "Subject" line (a comment to indicate the build
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reason, it may be just dependency updates or build fixes, or sometimes a
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bump in GIMP version) and a commit hash. When you have identified the
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build you want to test, update it like this:
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```
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flatpak update --commit=<hash-of-build> org.gimp.GIMP
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```
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Then just run your older GIMP!
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## Debugging on flatpak
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### Generic flatpak abilities
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If you want to inspect the sandbox environment, you can do so by
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specifying a custom shell instead of the GIMP binary with the following
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command:
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```
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flatpak run --command=bash org.gimp.GIMP
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```
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This will run the exact same environment as the flatpak, which should
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also be identical on all machines.
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Alternatively you can run the GIMP Flatpak using the GNOME SDK as
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runtime (instead of the .Platform) with the `--devel` option. In
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particular, it gives you access to a few additional debug tools, such as
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`gdb`. Therefore running GIMP with --devel will give better stacktrace,
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or you can run explicitly GIMP inside GDB.
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Additionally to install debug symbols in the sandbox, run:
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```
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flatpak install flathub org.gimp.GIMP.Debug
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flatpak install flathub org.gnome.Sdk.Debug
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```
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### Getting accurate traces from reported inaccurate traces
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Even with reporter trace without debug symbols (yet debug symbols
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installed on your side), if you make sure you use exactly the same
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flatpak commit as the reporter (see `Testing older GIMP versions`
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section), you are ensured to use the same binaries. Hence you can trace
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back the code line from an offset.
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For instance, say that your trace has this output:
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```
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gimp-2.10(file_open_image+0x4e8)[0x5637e0574738]
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```
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Here is how you can find the proper code line in the Flatpak (provided
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you use the right flatpak commit):
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```
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$ RUNTIME_VERSION=$(flatpak run org.gimp.GIMP//stable -v |grep runtime=runtime/org.gnome.Platform/ |sed 's$runtime=runtime/org.gnome.Platform/$$')
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$ flatpak install flathub org.gimp.GIMP.Debug org.gnome.Sdk/$RUNTIME_VERSION org.gnome.Sdk.Debug/$RUNTIME_VERSION
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$ flatpak run --devel --command=bash org.gimp.GIMP
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(flatpak) $ gdb /app/bin/gimp-2.10
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(gdb) info line *(file_open_image+0x4e8)
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Line 216 of "file-open.c" starts at address 0x4d5738 <file_open_image+1256> and ends at 0x4d5747 <file_open_image+1271>.
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```
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### Debugging though gdbserver
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In some cases, when GIMP grabs the pointer and/or keyboard, i.e. when
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you debug something happening on canvas in particular, it might be very
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hard to get back to your debugger, since your system won't be responding
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to your keyboard or click events.
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To work around this, you can debug remotely, or simply from a TTY (while
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the desktop doesn't answer properly):
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In your desktop, run GIMP through a debugger server:
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```
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$ flatpak run --devel --command=bash org.gimp.GIMP//beta
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$ gdbserver :9999 /app/bin/gimp-2.99
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```
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Go to a TTY and run
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```
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$ gdb /app/bin/gimp-2.99
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(gdb) target remote localhost:9999
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(gdb) continue
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```
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Of course, before the `continue`, you may add whatever break points or
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other commands necessary for your specific issue. GIMP will start in the
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desktop when you hit `continue` (it will likely be a slower start).
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Then do your issue reproduction steps on GIMP. When you need to debug,
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you can go to the TTY whenever you want, not bothering about any
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keyboard/pointer grabs.
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Note that since copy-pasting is harder in a TTY, you might want to
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redirect your output to a file, especially if you need to upload it or
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read it slowly next to GIMP code. For instance here are commands to
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output a full backtrace into a file from the gdb prompt and exit (to
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force the device ungrab by killing GIMP and go work on desktop again):
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```
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(gdb) set logging file gimp-issue-1234.txt
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(gdb) set logging on
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(gdb) thread apply all backtrace full
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(gdb) quit
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```
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## Debugging icons ##
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See file `devel-docs/icons.txt` to learn more about our icons, and in
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particular the environment variable GIMP_ICONS_LIKE_A_BOSS.
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## Debugging plug-ins ##
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See file `devel-docs/debug-plug-ins.txt` for usage of environment
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variable GIMP_PLUGIN_DEBUG.
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The CLI option --stack-trace-mode also applies to plug-ins, in order to
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output a back trace on terminal.
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## Performance logs ##
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See file `devel-docs/performance-logs/performance-logs.md` for information
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about GIMP performance logs, which can help during optimization.
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