I didn't find the BT that helpful... Although it's possible I've completely forgotten everything I previously knew about gdb and I need to relearn everything from the ground up.
I'm perplexed by the BT because the first of the steps it shows on the way to the segfault is for main.cpp:79.
> (gdb) bt
> #0 xcb_get_setup (c=0x0) at /usr/src/debug/libxcb-1.13.1-7.fc34.x86_64/src/xcb_conn.c:314
> #1 0x00007ffff7f77bd0 in xcb_ewmh_init_atoms (c=<optimized out>, ewmh=0x756540) at /usr/src/debug/xcb-util-wm-0.4.1-20.fc34.x86_64/ewmh/ewmh.c:605
> #2 0x000000000048db12 in LXCB::LXCB (this=this@entry=0x756540) at ../libLumina/LuminaX11.cpp:44
> #3 0x00000000004ab991 in LSession::LSession (this=this@entry=0x7fffffffd9e0, argc=@0x7fffffffd9ac: 1, argv=argv@entry=0x7fffffffdc18) at LSession.cpp:60
> #4 0x0000000000445555 in main (argc=<optimized out>, argv=0x7fffffffdc18) at main.cpp:79
OK Great, except the main.cpp of the program I'm debugging only has 27 lines.
https://github.com/lumina-desktop/lumina/blob/master/src-qt5/desktop-utils/lumina-screenshot/main.cpp So I'm guessing that's a differnet main, and thus I need to figure out how I get from the main in the utility I'm running to whatever that main is.
This is why I was hoping I could just dump everything to a file and then walk the entire process step by step. Yes I know I'd get a ton of info I dont need, but at least then I dont have any questions as to what led to what.
Thanks for the info, I'll see if I glean anything from the links you posted.
On Tue, Dec 28, 2021 at 8:48 AM Ben Beasley <code@xxxxxxxxxxxxxxxxxx> wrote:
Is the backtrace not helpful in figuring out where to set up
breakpoints? As in, “gdb foo”, then “run”, wait for the crash, and type
“bt”?
The darktable development documentation suggests[1] the following to log
useful backtraces:
|$ gdb darktable ... crash dt here ... (gdb) set pagination off
(gdb) set logging file gdb.txt (gdb) set logging on (gdb) thread
apply all bt full|
If you need to do this non-interactively, you can combine it with gdb’s
batch mode. Strangely, I have a spec file that demonstrates this [2].
The debugbreak package is a header-only C library that implements
programmatic breakpoints, so the natural way to test it is with the
debugger.
Hopefully some of that is helpful.
– Ben
[1] https://www.darktable.org/development/
[2]
https://src.fedoraproject.org/rpms/debugbreak/blob/e009ccfac2b8e05a6018921ed6d3e732837a9e52/f/debugbreak.spec#_62
On 12/28/21 08:08, JT wrote:
> Hey all,
> I havent used gdb in a while, so I'm trying to knock the rust off my
> knowledge and pick up a few more skills.
> I'm trying to track down an issue in the Lumina Desktop. One of the
> utilities (lumina-screenshot) segfaults when starting up and I'm
> trying to deduce why. The problem is that it gets pretty far into the
> program starting before it finally dies and I havent been able to step
> through gdb enough manually to find that point.
>
> Is there a way to run gdb in a capture mode of some kind and dump the
> output entirely like I can do with strace?
> I kinda need to know where it's crashing to have an idea of where to
> set up breakpoints.
>
> Unless my memory is off, I was sure there was a way to do this but I
> just can't seem to remember or figure out how to do it.
>
> Any pointers? Thanks!
>
> JT
>
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