[Qt-creator] Remote debugging with GDB-multiarch not sending command line arguments

[Pablo Rogina]

Hi, this is a follow up to my issue. I guess I found what's happening
but I was not able to fix it...

I did run an external gdb-multiarch remote debug session in MI mode
using all the commands QtCreator passes to the debugger. However, I
skipped the unset environment commands for all the env variables as
QtCreator does, and the session run very well.
Then I realized that one of the variables being unset by QtCreator is
DISPLAY, so I repeated a new external gdb-multiarch remote session in
MI mode, sending all the commands as QtCreator and unset environment
variable DISPLAY and session crashes.

And that behavior makes sense as I now realized that the same is
happening when pressing F5, see the Output Application pane below, Qt
app cannot connect to display since the env variable was unset.

qt.qpa.xcb: could not connect to display
qt.qpa.plugin: Could not load the Qt platform plugin "xcb" in "" even
though it was found.

So looking in source code (src/plugins/debugger/gdb/gdbengine.cpp)
method void GdbEngine::setEnvironmentVariables() there's a loop that
sets or unsets every variable. But I couldn't understand what's the
criteria for any variable to have operation as EnvironmentItem::Unset

if (item.operation == EnvironmentItem::Unset)
runCommand({"unset environment " + name});
else
runCommand({"-gdb-set environment " + name + '=' + item.value});

In addition, I tried adding set environment DISPLAY = :0 in the Attach
Additional Commands but it has the same effect: app crashes since
could not attach to display...

Thanks. Pablo

On Thu, Jul 2, 2020 at 12:17 PM Pablo Rogina <pablojr at gmail.com> wrote:
>
> Christian,
>
> again, by looking at the Application Output pane, where I can see
> gdbserver starting on remote device, the port number, etc.
> But mostly by the fact that the debug session for my Qt application
> CRASHES since the xcb plugin isn't loaded.
> So somehow even when the proper -exec-args command is sent from
> QtCreator to the debugger is not being used or properly setup, I don't
> know.
>
> On the other hand I am able to debug the same Qt app/device etc. by
> using option Debug/Start Debugging/Attach to Running Debug Server or
> if I run the debug session externally to QtCreator.
> So I am confident that remote debugging for that Qt app with X
> forwarding does work
>
> Thanks. Pablo
>
> On Thu, Jul 2, 2020 at 12:11 PM Christian Kandeler
> <christian.kandeler at qt.io> wrote:
> >
> > On Thu, 2 Jul 2020 09:37:51 -0300
> > Pablo Rogina <pablojr at gmail.com> wrote:
> >
> > > I see. I'm not familiar with GDB/MI mode so that could be the right
> > > approach then, but the end result at least for me is that the
> > > arguments don't reach the remote program under debug
> >
> > Again, how do you know that?
> >
> >
> > Christian
> > _______________________________________________
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> > Qt-creator at qt-project.org
> > https://lists.qt-project.org/listinfo/qt-creator