Re: How to load C++ pretty-printers

[Simon Marchi <simon dot marchi at polymtl dot ca>]

On 2019-03-16 08:58, Eli Zaretskii wrote:
> > From: asmwarrior <asmwarrior@gmail.com>
> > Date: Sat, 16 Mar 2019 20:41:13 +0800
> >
> > Under My Windows 7 system, I'm using such commands(I put them in a 
> > my.gdb script file) to load and register the pretty printers.
> > I put the libstdcxx folder in the same folder as the my.gdb file.
> >
> >
> > set auto-load safe-path $debugdir;$datadir/auto-load
> > python
> > import sys
> > sys.path.insert(0, '')
> > from libstdcxx.v6.printers import register_libstdcxx_printers
> > # load other pretty printers
> > end
>
> Thanks, but I don't think I understand which part(s) of this are
> necessary in my case.  E.g., is the "set auto-load" command
> needed/relevant?  And what is the my.gdb file, I don't think I have
> such a file on my system.  The pretty-printers that came with GCC are
> installed where the GCC installation puts them, and I'd prefer not to
> change that if possible.
>
> Also, which of the commands you've shown actually loads the
> pretty-printers from their file?
>
> Thanks again for your response.

If it can help, I have something similar to that in my .gdbinit (whereas 
asmwarrior has put the same content in a separate file, my.gdb, which 
they then source by hand).

When libstdc++ is linked dynamically with a program and you debug that 
program, GDB will "auto-load" the file corresponding to the libstdc++ 
shared library.  In my case, it's at 
"/usr/share/gdb/auto-load/usr/lib/libstdc++.so.6.0.25-gdb.py".  This 
file tries to find where the GCC-provided libstdc++ pretty printers are 
installed, and adds this path to the Python import path.  It then calls 
register_libstdcxx_printers, a function provided by the libstdc++ pretty 
printers.

When libstdc++ is linked statically, the auto-load does not happen, as 
you mentioned.  So the idea here is to replicate what the auto-load 
script does, but by hand.

In my case, I have these lines to adjust the Python import path to add 
GCC's pretty printers directory:

  python import sys
  python sys.path.insert(0, '/usr/share/gcc-8.2.1/python')

And then I manually trigger the GDB auto-load script, that would 
normally be sourced automatically when loading the libstdc++ shared lib:

  source /usr/share/gdb/auto-load/usr/lib/libstdc++.so.6.0.25-gdb.py

The "set auto-load safe-path" line is to define it is safe to auto-load 
things from.  If you are missing something, you should know quickly 
enough, as GDB will print you a warning, saying it didn't auto-load X, 
because X is not in a safe path (as well as information about how to 
adjust it).

Hope this helps,

Simon