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gdb: fix the extension to be loaded with Python 2
There was a mystic error when the extension was loaded by the old gdb versions built against Python 2: | (gdb) source luajit-gdb.py | Traceback (most recent call last): | File "luajit-gdb.py", line 702, in <module> | load(None) | File "luajit-gdb.py", line 699, in load | 'lj-gc': LJGC, | File "luajit-gdb.py", line 687, in init | command(name) | File "luajit-gdb.py", line 468, in __init__ | gdb.write('{} command initialized\n'.format(name)) | ValueError: sequence.index(x): x not in sequence I made a little investigation (for more info see the mentioned issue) and found the next fun fact: the exception was raised much earlier to <str.format>, more precisely in <gdb.events.new_objfile.disconnect>. However, the handled exception is preserved until <str.format> call and hits the condition underneath leading to the extension load failure. As a result to avoid the exception, the special global variable is introduced for legacy (i.e. Python 2) environment. It checks whether any callback is associated with new_objfile event prior to disconnecting it. This variable usage is encapsulated within two introduced routines: <connect> and <disconnect> which are wrappers for ones provided by gdb. Furthermore, after diving to gdb sources related to Python embedding, I found that callbacks are grouped into an internal list. Previous implementation appended the <load> function to this callback list on each its unsuccessful call, but only the successful one is removes it from the list. Thereby disconnect action is moved prior to connect one so there is no more than one <load> instance kept in callback list. Fixes tarantool/tarantool#4828 Reported-by: Oleg Babin <olegrok@tarantool.org> Reviewed-by: Oleg Babin <olegrok@tarantool.org> Reviewed-by: Sergey Ostanevich <sergos@tarantool.org> Signed-off-by: Igor Munkin <imun@tarantool.org>
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