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?

What command were you trying to run when you get that error? It looks like the problem is emacs trying to use the machine interpreter command to run "2" as if it were a command given to the normal GDB command line interface. But Python is parsing input rather than GDB, and it doesn't understand the GDB machine interface. Can you run gdb without the "-i=mi" command (to use the regular human interface)? — Matt
– Matt, Commented Jul 22, 2015 at 21:47

Tom Tromey · Accepted Answer · 2015-07-30 16:19:51Z

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.

Geof Sawaya · Accepted Answer · 2015-12-16 06:46:46Z

0

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

answered Dec 16, 2015 at 6:46

Geof Sawaya

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