Core dump accessing some $[monitor] variables

[afhp-2020]

Just exploring and checking out the manpage, accessing some of the monitor-related variables will crash fvwm3 and dump core, e.g. Echo $[monitor.whatever] at the FvwmConsole.

The following work: $[monitor.primary], $[monitor.current], $[monitor.count]

On the other hand, $[monitor.output] and all monitor-specific geometry-related variables crash.

Compiled from today's master (76b8e2e) on FreeBSD 12.1-RELEASE-p5 amd64.

Latest core dump, accessing $[monitor.$[monitor.current].x] available if that helps (also crashes if monitor name is specified explicitly).

[ThomasAdam]

Hi @afhp-2020,

Yeah, not surprised.

Please can you get me a bt full backtrace from gdb?

[afhp-2020]

I have no idea how to do that. Last time I used a debugger on compiled code must have been in the Turbo Pascal timeframe :)

I'll be glad to follow any instructions you could provide.

[ThomasAdam]

@afhp-2020,

Sure. If you can recompile FVWM3 with:

make clean
make CFLAGS="-O0 -ggdb"
sudo make install

... then reproduce your problem, you'll find the coredump in the same place you did before.

Then install gdb, and run:

gdb /path/to/fvwm3 /path/to/corefile

... then you'll find a prompt like this:

(gdb)

... in there, type:

bt full

... and send me the output here.

Thanks!

[afhp-2020]

Thank you. This and a quick lookup of SO (about redirecting output) helped.

Here it is, running Echo $[monitor.output] at the FvwmConsole.

For some reason, the debug version would not start my MainPanel but it doesn't really matter.

fvwm3-gdb.log.txt

[ThomasAdam]

Hi @afhp-2020,

Thanks. Please can you have a look at #102 (ta/gh-101 branch). Hopefully that'll fix the segfault.

Kindly,
Thomas

[afhp-2020]

Fixed.

All geometry-related monitor variables respond normally, including incomplete references, e.g.
Echo $[monitor.$[monitor.current]] → [fvwm][Echo]: $[monitor.DVI-I-1]
Echo $[monitor.$[monitor.current].height] → [fvwm][Echo]: 1200

What exactly is the meaning of output in this context ?
Echo $[monitor.output] → [fvwm][Echo]: $[monitor.output]
Echo $[monitor.$[monitor.current].output] → [fvwm][Echo]: 733
About this one, the manpage should be fixed, 1) to explain output and 2) to specify the call format $[monitor.<n>.output].

Thanks again for such a prompt fix.

[ThomasAdam]

@afhp-2020,

output refers to the number RandR assigns the monitor, which is an identifier FVWM3 uses internally. It'll be used more for when FvwmEvent learns about RandR events (#26).

I'll take a look at the man page, although patches welcome! ;)