gdb: Python 3 incompatible with libstdc++ pretty printers.

[Rüdiger Sonderfeld]

gdb is now linked against python 3 but python 3 is incompatible with libstdc++'s pretty printers:

Traceback (most recent call last):
  File "<string>", line 4, in <module>
  File "/usr/share/gcc-4.8/python/libstdcxx/v6/printers.py", line 54
    raise ValueError, "Cannot find type %s::%s" % (str(orig), name)
                    ^
SyntaxError: invalid syntax
/home/ruediger/.gdbinit:7: Error in sourced command file:
Error while executing Python code.

There is a proposed patch but it wasn't upstreamed yet: http://<email address hidden>/msg65185.html

I'd propose either to continue using python2 for gdb, fixing the details to get the patch upstream, or use a patched version downstream for now.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Martin Olsson (mnemo)]

I have the same for trivial hello world program written in go

go build prog.go
gdb prog

  File "/usr/share/go/src/pkg/runtime/runtime-gdb.py", line 358
    print s, ptr['goid'], "%8s" % sts[long((ptr['status']))], blk.function
          ^
SyntaxError: invalid syntax

---

When gdb is switched to use python3 in plugins, then the packaged plugins need to be updated correspondingly as well. Please don't just switch it in gdb and leave stuff like C++ and go pretty printing packages broken.

[Tomasz Ziętkiewicz (tomek-zietkiewicz)]

There are 2 workarounds for this:
1. Convert printers.py to python3 yourself:

$ cd /usr/share/gcc-4.8/python/libstdcxx/v6/
$ 2to3 -w printers.py

2. Use this patch: http://gcc.gnu.org/ml/libstdc++/2013-10/msg00243.html

[John Weldon (johnweldon4)]

@tomek-zietkiewicz I don't have that folder or file on my machine(/usr/share/gcc-4.8, printers.py), but I'm getting the same error.

Is that because I have the packaged binary version of gdb?

If so, is there a workaround in that case, or do I need to build the gdb package from source to fix this?

[Ryan Tandy (rtandy)]

John: The patch is for that particular file. If you get the same error from a different file then you need a different patch.

What's the full path to the file you get the error from? If it comes from a package, that package needs a bug filed against it; if it's a script you supplied, you should contact the script's author about it.

[John Weldon (johnweldon4)]

Thanks Ryan;
You're right. I'll try to fix the specific file I saw the error in. My error was:

S 11:11:34 [0]$ gdb juju.test
GNU gdb (GDB) 7.6.1-ubuntu
Copyright (C) 2013 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law. Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-linux-gnu".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from /mnt/build/go/src/launchpad.net/juju-core/juju.test...done.
  File "/usr/share/go/src/pkg/runtime/runtime-gdb.py", line 358
    print s, ptr['goid'], "%8s" % sts[long((ptr['status']))], blk.function
          ^
SyntaxError: invalid syntax
(gdb)

[Ryan Tandy (rtandy)]

John, the pretty-printer for go is covered by bug 1283626, and it sounds like 2to3 is able to convert that file automatically. Hope that helps.

Adding gcc-4.8 to this bug since that's where the STL pretty-printer comes from, and I think it's more likely to be fixed there than by reverting gdb back to linking against python2.

[John Weldon (johnweldon4)]

Fwiw, running `2to3 -w /usr/share/go/src/pkg/runtime/runtime-gdb.py" fixed my issue.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.