gdb within emacs: python commands (py and pi)

Question

I want to debug a c++ program using gdb. I use the pi and the py commands to evaluate python commands from within gdb, which works fine when I invoke gdb from the command line. However, when I invoke gdb from within emacs using M-x gdb and then gdb -i=mi file_name, the following errors occur:

• the pi command correctly opens an interactive python shell, but any input to this shell yields the errors like this:

File "stdin", line 1
-interpreter-exec console "2"
SyntaxError: invalid syntax

• the py command works correctly for a single command (like py print 2+2), but not for multiple commands

I can get around those problems by starting gdb with gud-gdb, but then I dont have the support for gdb-many-windows. Maybe the problem is caused by the prompt after typing pi, which is no longer (gdb) but >>> instead?

Answer 1

I am going to go out on a limb and say this is a bug in gud mode. The clue is the -interpreter-exec line in the error.

What happens here is that gud runs gdb in a special "MI" ("Machine Interface") mode. In this mode, commands and their responses are designed to be machine-, rather than human-, readable.

To let GUIs provide a console interface to users, MI provides the -interpreter-exec command, which evaluates a command using some other gdb "interpreter" (which doesn't mean what you may think and in particular has nothing to do with Python).

So, gud sends user input to gdb, I believe, with -interpreter-exec console .... But, in the case of a continuation line for a python command, this is the wrong thing to do.

I tried this out in Emacs and I was able to make it work for the python command when I spelled it out -- but py, pi, and python-interactive all failed.

Answer 2

I had this problem when I build and used emacs 24.5.1 using gdb 7.9.1.

I have no problem with gdb command line, but weird behavior with gdb-emacs.

I get the behavior described by Tom and user280107, depending on the order of commands and operations:

(gdb) pi
>>> print(123)
  File "<stdin>", line 1
    -interpreter-exec console "print(123) "
                            ^
SyntaxError: invalid syntax
>>> 

However, if I run a 'python xxx' command first, it seems to work (some forgotten initialization?):

(gdb) python print(123)
123
(gdb) pi
pi
>>> print(123)
123
>>> 

Anyway, I've sent a note to [email protected].

BTW, I'm sure Tom T. knows way more about this than I do