Re: assertion error in pretty printing

[Jonah Graham <jonah@kichwacoders.com>]

On Wed, 7 Jul 2021 at 17:13, Simon Marchi <simon.marchi@polymtl.ca> wrote:

> On 2021-07-07 2:34 p.m., Jonah Graham wrote:
> > Hi folks.
> >
> > I have an internal error in GDB that AFAICT is down to the python pretty
> > printers. This is being hit by CDT (reported in
> > https://bugs.eclipse.org/bugs/show_bug.cgi?id=574645)
> >
> > Doing a -var-update I get this internal error:
> >
> > ~"/scratch/gdb/binutils-gdb/gdb/c-varobj.c:516: internal-error:
> std::string
> > c_value_of_variable(const varobj*, varobj_display_formats): Assertion
> > `!value_lazy (var->value.get ())' failed.\nA problem internal to GDB has
> > been detected,\nfurther debugging may prove unreliable.\nQuit this
> > debugging session? (y or n) "
> >
> > Steps to reproduce:
> >
> > Get source from
> >
> https://bugzillaattachments.eclipsecontent.org/bugs/attachment.cgi?id=286726
> > curl
> >
> https://bugzillaattachments.eclipsecontent.org/bugs/attachment.cgi?id=286726
> >> bug574645.cpp
> > g++ -std=c++2a -O0 -g3 bug574645.cpp -o bug574645
> > gdb --interpreter=mi2
> >
> > then use these commands:
> > 6-enable-pretty-printing
> > 8-gdb-set print object on
> > 19-file-exec-and-symbols --thread-group i1 bug574645
> > 26-break-insert -f bug574645.cpp:31
> > 27-break-insert -t -f main
> > 29-exec-run --thread-group i1
> > 41-var-create --thread 1 --frame 0 - * data2
> > 44-var-list-children var1 0 1
> > 48-exec-continue --thread 1
> > 51-var-update 1 var1
> >
> > If running with a locally built GDB the python pretty printers need to be
> > pointed at (e.g. add  --data-directory=/usr/share/gdb to gdb command
> line)
> >
> > Where do I start debugging this? I have reproduced with latest HEAD of
> > gdb + the data directory on my Ubuntu 20.04 machine.
>
> Hi Jonah,
>
> First, maybe file a bug with that information.
>
> Then, I'm not sure what to say.  You need to understand why this assert
> is there, why it is failing in this case, what lead up to this.  Classic
> debugging / investigative work.
>
> I can't provide you with pointers in the code without looking at the
> problem myself (which I don't really have time to do), other than "check
> the backtrace at the point of the crash".  Do you need guidance / tips
> on how to debug GDB with GDB?
>

Hi Simon,

My ask was way too wooly - I spent a bunch of time learning about data
directories and python integrations before I understood what the problem
was and asked for help a little too soon. I'll create a ticket and see what
else I can figure out so I can come back with a more specific ask (or a fix
:-). Thanks for taking the time to reply.

Jonah




>
> Thanks,
>
> Simon
>