Conditional breakpoints in ceval.c

David Froger david.froger at
Tue Nov 12 09:44:22 CET 2013

Quoting Ned Batchelder (2013-11-09 14:24:34)
> On Friday, November 8, 2013 9:03:51 PM UTC-5, Demian Brecht wrote:
> > Hi all,
> > 
> > I have an .py file with a simple assignment in it:
> > foo = 'bar'
> > 
> > Now, I want to set a conditional breakpoint in gdb, breaking on that
> > assignment (I'm guessing the top of the stack would be breaking on the
> > LOAD_CONST with a value or 'bar'). How would I go about doing that?
> > 
> > b ceval.c:1368 if [?]
> > 
> > Thanks,
> > 
> > -- 
> > Demian Brecht
> >
> I don't know how to use gdb the way you want, but it sounds like you are on a fascinating journey of discovery.  What are you trying to learn?  Perhaps we can talk about how the interpreter works.
> --Ned.
> -- 

Hi all,

In the purpose of debugging C/C++ Python extensions, I've been also looking for
a way to put a gdb breakpoint on a Python line file, like this:
    (gdb) b
But I have no idea how this could be implemented.

To break in a C/C++ extension with gdb, on can declare a function, for
example 'Py_DebugTrap' [1], and call it call in the C/C++ code where he/she
want to break, then in gdb:
    (gdb) b Py_DebugTrap

So a altenative to break into Python could be to do the same: wrap the
Py_DebugTrap in a Python module, then in the Python file, call the trap
function, for example:
    import gdbbreak
    foo = 'bar'

The function gdbbreak.breakpoint_here() would just call the 'Py_DebugTrap'
function, and then in gdb:
    (gdb) b Py_DebugTrap
    (gdb) next # until foo = 'bar' assignement is reach

(I never try this, be it should work.)


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