Re: [patch] [python] Implement stop_p for gdb.Breakpoint

Phil Muldoon
2011-03-11T11:39:26Z

Tom Tromey <tromey@redhat.com> writes:

> Tom> My reason is that the Python method is an implementation detail of some
> Tom> kind of "stop point" provided by a Python script.  It is not readily
> Tom> mutable by the user.  On the other hand, the condition is something
> Tom> explicitly under the user's control.
>
> Doug> That sounds a bit weird.
> Doug> The python method is part of an API.
> Doug> APIs are not implementation details.
>
> I think we are using the same words to mean different things.

Here is the latest patch. I've added the mutual exclusion to setting
the CLI condition and the Python method. I renamed the method to
'stop'. Plus all the other review comments regarding the #HAVE Python
defines . I included some changes from the branch that alter how
breakpoints are initialized (the tests require those changes).

I think I got everything.

WDYT?

Cheers

Phil

--

diff --git a/gdb/breakpoint.c b/gdb/breakpoint.c
index 5bcab87..9736b12 100644
--- a/gdb/breakpoint.c
+++ b/gdb/breakpoint.c
@@ -72,6 +72,7 @@
#undef savestring

#include "mi/mi-common.h"
+#include "python/python.h"

/* Arguments to pass as context to some catch command handlers. */
#define CATCH_PERMANENT ((void *) (uintptr_t) 0)
@@ -643,6 +644,14 @@ condition_command (char *arg, int from_tty)
ALL_BREAKPOINTS (b)
if (b->number == bnum)
{
+ /* Check if this breakpoint has a Python object assigned to
+ it, and if it has a definition of the "stop"
+ method. This method and conditions entered into GDB from
+ the CLI are mutually exclusive. */
+ if (b->py_bp_object
+ && gdbpy_breakpoint_has_py_cond (b->py_bp_object))
+ error (_("Cannot set a condition where a Python 'stop' " \
+ "method has been defined in the breakpoint."));
set_breakpoint_condition (b, p, from_tty);
return;
}
@@ -4070,6 +4079,11 @@ bpstat_check_breakpoint_conditions (bpstat bs, ptid_t ptid)
int value_is_zero = 0;
struct expression *cond;

+ /* Evaluate Python breakpoints that have a "stop"
+ method implemented. */
+ if (b->py_bp_object)
+ bs->stop = gdbpy_should_stop (b->py_bp_object);
+
if (is_watchpoint (b))
cond = b->cond_exp;
else
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index a5eaa72..9ca6c09 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -23099,6 +23099,34 @@ argument defines the class of watchpoint to create, if @var{type} is
assumed to be a @var{WP_WRITE} class.
@end defmethod

+@defop Operation {gdb.Breakpoint} stop (self)
+The @code{gdb.Breakpoint} class can be sub-classed and, in
+particular, you may choose to implement the @code{stop} method.
+If this method is defined as a sub-class of @code{gdb.Breakpoint},
+it will be called when the inferior stops at any location of a
+breakpoint which instantiates that sub-class. If the method returns
+@code{True}, the inferior will be stopped at the location of the
+breakpoint, otherwise the inferior will continue.
+
+If there are multiple breakpoints at the same location with a
+@code{stop} method, each one will be called regardless of the
+return status of the previous. This ensures that all @code{stop}
+methods have a chance to execute at that location. In this scenario
+if one of the methods returns @code{True} but the others return
+@code{False}, the inferior will still be stopped.
+
+Example @code{stop} implementation:
+
+@smallexample
+class MyBreakpoint (gdb.Breakpoint):
+ def stop (self):
+ inf_val = gdb.parse_and_eval("foo")
+ if inf_val == 3:
+ return True
+ return False
+@end smallexample
+@end defop
+
The available watchpoint types represented by constants are defined in the
@code{gdb} module:

diff --git a/gdb/python/py-breakpoint.c b/gdb/python/py-breakpoint.c
index bfad002..6e5db8f 100644
--- a/gdb/python/py-breakpoint.c
+++ b/gdb/python/py-breakpoint.c
@@ -28,6 +28,8 @@
#include "observer.h"
#include "cli/cli-script.h"
#include "ada-lang.h"
+#include "arch-utils.h"
+#include "language.h"

static PyTypeObject breakpoint_object_type;

@@ -38,6 +40,9 @@ static int bppy_live;
constructor and the breakpoint-created hook function. */
static breakpoint_object *bppy_pending_object;

+/* Function that is called when a Python condition is evaluated. */
+char *stop_func = "stop";
+
struct breakpoint_object
{
PyObject_HEAD
@@ -586,10 +591,9 @@ bppy_get_ignore_count (PyObject *self, void *closure)
}

/* Python function to create a new breakpoint. */
-static PyObject *
-bppy_new (PyTypeObject *subtype, PyObject *args, PyObject *kwargs)
+static int
+bppy_init (PyObject *self, PyObject *args, PyObject *kwargs)
{
- PyObject *result;
static char *keywords[] = { "spec", "type", "wp_class", "internal", NULL };
char *spec;
int type = bp_breakpoint;
@@ -600,19 +604,16 @@ bppy_new (PyTypeObject *subtype, PyObject *args, PyObject *kwargs)

if (! PyArg_ParseTupleAndKeywords (args, kwargs, "s|iiO", keywords,
&spec, &type, &access_type, &internal))
- return NULL;
+ return -1;

if (internal)
{
internal_bp = PyObject_IsTrue (internal);
if (internal_bp == -1)
- return NULL;
+ return -1;
}

- result = subtype->tp_alloc (subtype, 0);
- if (! result)
- return NULL;
- bppy_pending_object = (breakpoint_object *) result;
+ bppy_pending_object = (breakpoint_object *) self;
bppy_pending_object->number = -1;
bppy_pending_object->bp = NULL;

@@ -649,14 +650,14 @@ bppy_new (PyTypeObject *subtype, PyObject *args, PyObject *kwargs)
}
if (except.reason < 0)
{
- subtype->tp_free (result);
- return PyErr_Format (except.reason == RETURN_QUIT
- ? PyExc_KeyboardInterrupt : PyExc_RuntimeError,
- "%s", except.message);
+ PyErr_Format (except.reason == RETURN_QUIT
+ ? PyExc_KeyboardInterrupt : PyExc_RuntimeError,
+ "%s", except.message);
+ return -1;
}

- BPPY_REQUIRE_VALID ((breakpoint_object *) result);
- return result;
+ BPPY_SET_REQUIRE_VALID ((breakpoint_object *) self);
+ return 0;
}

\f
@@ -707,6 +708,69 @@ gdbpy_breakpoints (PyObject *self, PyObject *args)
return PyList_AsTuple (list);
}

+/* Call the "stop" method (if implemented) in the breakpoint
+ class. If the method returns True, the inferior will be
+ stopped at the breakpoint. Otherwise the inferior will be
+ allowed to continue. */
+
+int
+gdbpy_should_stop (struct breakpoint_object *bp_obj)
+{
+ int stop = 1;
+
+ PyObject *py_bp = (PyObject *) bp_obj;
+ struct breakpoint *b = bp_obj->bp;
+ struct gdbarch *garch = b->gdbarch ? b->gdbarch : get_current_arch ();
+ struct cleanup *cleanup = ensure_python_env (garch, current_language);
+
+ if (PyObject_HasAttrString (py_bp, stop_func))
+ {
+ PyObject *result = PyObject_CallMethod (py_bp, stop_func, NULL);
+
+ if (result)
+ {
+ int evaluate = PyObject_IsTrue (result);
+
+ if (evaluate == -1)
+ gdbpy_print_stack ();
+
+ /* If the "stop" function returns False that means
+ the Python breakpoint wants GDB to continue. */
+ if (! evaluate)
+ stop = 0;
+
+ Py_DECREF (result);
+ }
+ else
+ gdbpy_print_stack ();
+ }
+ do_cleanups (cleanup);
+
+ return stop;
+}
+
+/* Checks if the "stop" method exists in this breakpoint.
+ Used by condition_command to ensure mutual exclusion of breakpoint
+ conditions. */
+
+int
+gdbpy_breakpoint_has_py_cond (struct breakpoint_object *bp_obj)
+{
+ int has_func = 0;
+ PyObject *py_bp = (PyObject *) bp_obj;
+ struct gdbarch *garch = bp_obj->bp->gdbarch ? bp_obj->bp->gdbarch :
+ get_current_arch ();
+ struct cleanup *cleanup = ensure_python_env (garch, current_language);
+
+ if (py_bp == NULL)
+ return 0;
+
+ has_func = PyObject_HasAttrString (py_bp, stop_func);
+ do_cleanups (cleanup);
+
+ return has_func;
+}
+
\f

/* Event callback functions. */
@@ -793,7 +857,6 @@ gdbpy_initialize_breakpoints (void)
{
int i;

- breakpoint_object_type.tp_new = bppy_new;
if (PyType_Ready (&breakpoint_object_type) < 0)
return;

@@ -828,6 +891,36 @@ gdbpy_initialize_breakpoints (void)

\f

+/* Helper function that overrides this Python object's
+ PyObject_GenericSetAttr to allow extra validation of the attribute
+ being set. */
+static int
+local_setattro (PyObject *self, PyObject *name, PyObject *v)
+{
+ breakpoint_object *obj = (breakpoint_object *) self;
+ char *attr = python_string_to_host_string (name);
+
+ if (attr == NULL)
+ return -1;
+
+ /* If the attribute trying to be set is the "stop" method,
+ but we already have a condition set in the CLI, disallow this
+ operation. */
+ if (strcmp (attr, stop_func) == 0 && obj->bp->cond_string)
+ {
+ xfree (attr);
+ PyErr_SetString (PyExc_RuntimeError,
+ _("Cannot set 'stop' method. There is an " \
+ "existing GDB condition attached to the " \
+ "breakpoint."));
+ return -1;
+ }
+
+ xfree (attr);
+
+ return PyObject_GenericSetAttr ((PyObject *)self, name, v);
+}
+
static PyGetSetDef breakpoint_object_getset[] = {
{ "enabled", bppy_get_enabled, bppy_set_enabled,
"Boolean telling whether the breakpoint is enabled.", NULL },
@@ -897,9 +990,9 @@ static PyTypeObject breakpoint_object_type =
0, /*tp_call*/
0, /*tp_str*/
0, /*tp_getattro*/
- 0, /*tp_setattro*/
+ (setattrofunc)local_setattro, /*tp_setattro */
0, /*tp_as_buffer*/
- Py_TPFLAGS_DEFAULT, /*tp_flags*/
+ Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE, /*tp_flags*/
"GDB breakpoint object", /* tp_doc */
0, /* tp_traverse */
0, /* tp_clear */
@@ -909,5 +1002,13 @@ static PyTypeObject breakpoint_object_type =
0, /* tp_iternext */
breakpoint_object_methods, /* tp_methods */
0, /* tp_members */
- breakpoint_object_getset /* tp_getset */
+ breakpoint_object_getset, /* tp_getset */
+ 0, /* tp_base */
+ 0, /* tp_dict */
+ 0, /* tp_descr_get */
+ 0, /* tp_descr_set */
+ 0, /* tp_dictoffset */
+ bppy_init, /* tp_init */
+ 0, /* tp_alloc */
+ PyType_GenericNew /* tp_new */
};
diff --git a/gdb/python/python.c b/gdb/python/python.c
index 3b10d8c..2d7213a 100644
--- a/gdb/python/python.c
+++ b/gdb/python/python.c
@@ -30,6 +30,7 @@
#include "exceptions.h"
#include "event-loop.h"
#include "serial.h"
+#include "python.h"

#include <ctype.h>

@@ -864,6 +864,22 @@ source_python_script (FILE *stream, const char *file)
_("Python scripting is not supported in this copy of GDB."));
}

+int
+gdbpy_should_stop (struct breakpoint_object *bp_obj)
+{
+ internal_error (__FILE__, __LINE__,
+ _("gdbpy_should_stop called when Python scripting is " \
+ "not supported."));
+}
+
+int
+gdbpy_breakpoint_has_py_cond (struct breakpoint_object *bp_obj)
+{
+ internal_error (__FILE__, __LINE__,
+ _("gdbpy_breakpoint_has_py_cond called when Python " \
+ "scripting is not supported."));
+}
+
#endif /* HAVE_PYTHON */

\f
diff --git a/gdb/python/python.h b/gdb/python/python.h
index 58d97fc..ce0eb35 100644
--- a/gdb/python/python.h
+++ b/gdb/python/python.h
@@ -22,6 +22,8 @@

#include "value.h"

+struct breakpoint_object;
+
extern int gdbpy_global_auto_load;

extern void finish_python_initialization (void);
@@ -41,4 +43,8 @@ void preserve_python_values (struct objfile *objfile, htab_t copied_types);

void load_auto_scripts_for_objfile (struct objfile *objfile);

+int gdbpy_should_stop (struct breakpoint_object *bp_obj);
+
+int gdbpy_breakpoint_has_py_cond (struct breakpoint_object *bp_obj);
+
#endif /* GDB_PYTHON_H */
diff --git a/gdb/testsuite/gdb.python/py-breakpoint.exp b/gdb/testsuite/gdb.python/py-breakpoint.exp
index 8f58181..f0a83f1 100644
--- a/gdb/testsuite/gdb.python/py-breakpoint.exp
+++ b/gdb/testsuite/gdb.python/py-breakpoint.exp
@@ -195,3 +195,101 @@ gdb_py_test_silent_cmd "python wp1 = gdb.Breakpoint (\"result\", type=gdb.BP_WA
gdb_test "info breakpoints" "No breakpoints or watchpoints.*" "Check info breakpoints does not show invisible breakpoints"
gdb_test "maint info breakpoints" ".*watchpoint.*result.*" "Check maint info breakpoints shows invisible breakpoints"
gdb_test "continue" ".*\[Ww\]atchpoint.*result.*Old value = 0.*New value = 25.*" "Test watchpoint write"
+
+# Breakpoints that have an evaluation function.
+
+# Start with a fresh gdb.
+clean_restart ${testfile}
+
+if ![runto_main] then {
+ fail "Cannot run to main."
+ return 0
+}
+delete_breakpoints
+
+gdb_py_test_multiple "Sub-class a breakpoint" \
+ "python" "" \
+ "class bp_eval (gdb.Breakpoint):" "" \
+ " inf_i = 0" "" \
+ " count = 0" "" \
+ " def stop (self):" "" \
+ " self.count = self.count + 1" "" \
+ " self.inf_i = gdb.parse_and_eval(\"i\")" "" \
+ " if self.inf_i == 3:" "" \
+ " return True" "" \
+ " return False" "" \
+ "end" ""
+
+gdb_py_test_multiple "Sub-class a second breakpoint" \
+ "python" "" \
+ "class bp_also_eval (gdb.Breakpoint):" "" \
+ " count = 0" "" \
+ " def stop (self):" "" \
+ " self.count = self.count + 1" "" \
+ " if self.count == 9:" "" \
+ " return True" "" \
+ " return False" "" \
+ "end" ""
+
+gdb_py_test_multiple "Sub-class a third breakpoint" \
+ "python" "" \
+ "class basic (gdb.Breakpoint):" "" \
+ " count = 0" "" \
+ "end" ""
+
+set bp_location2 [gdb_get_line_number "Break at multiply."]
+set end_location [gdb_get_line_number "Break at end."]
+gdb_py_test_silent_cmd "python eval_bp1 = bp_eval(\"$bp_location2\")" "Set breakpoint" 0
+gdb_py_test_silent_cmd "python also_eval_bp1 = bp_also_eval(\"$bp_location2\")" "Set breakpoint" 0
+gdb_py_test_silent_cmd "python never_eval_bp1 = bp_also_eval(\"$end_location\")" "Set breakpoint" 0
+gdb_continue_to_breakpoint "Break at multiply." ".*/$srcfile:$bp_location2.*"
+gdb_test "print i" "3" "Check inferior value matches python accounting"
+gdb_test "python print eval_bp1.inf_i" "3" "Check python accounting matches inferior"
+gdb_test "python print also_eval_bp1.count" "4" \
+ "Check non firing same-location breakpoint eval function was also called at each stop."
+gdb_test "python print eval_bp1.count" "4" \
+ "Check non firing same-location breakpoint eval function was also called at each stop."
+
+delete_breakpoints
+set cond_bp [gdb_get_line_number "Break at multiply."]
+gdb_py_test_silent_cmd "python eval_bp1 = bp_eval(\"$cond_bp\")" "Set breakpoint" 0
+set test_cond {cond $bpnum}
+gdb_test "$test_cond \"foo==3\"" "Cannot set a condition where a Python.*" \
+ "Check you cannot add a CLI condition to a Python breakpoint that" \
+ "has defined stop"
+gdb_py_test_silent_cmd "python eval_bp2 = basic(\"$cond_bp\")" "Set breakpoint" 0
+gdb_py_test_silent_cmd "python eval_bp2.condition = \"1==1\"" "Set a condition" 0
+gdb_py_test_multiple "Construct an eval function" \
+ "python" "" \
+ "def stop_func ():" "" \
+ " return True" "" \
+ "end" ""
+
+gdb_test "python eval_bp2.stop = stop_func" \
+ "RuntimeError: Cannot set 'stop' method.*" \
+ "Assign stop function to a breakpoint that has a condition"
+
+delete_breakpoints
+gdb_breakpoint [gdb_get_line_number "Break at multiply."]
+gdb_py_test_silent_cmd "python check_eval = bp_eval(\"$bp_location2\")" "Set breakpoint" 0
+gdb_test "python print check_eval.count" "0" \
+ "Test that evaluate function has not been yet executed (ie count = 0)"
+gdb_continue_to_breakpoint "Break at multiply." ".*/$srcfile:$bp_location2.*"
+gdb_test "python print check_eval.count" "1" \
+ "Test that evaluate function is run when location also has normal bp"
+
+gdb_py_test_multiple "Sub-class a watchpoint" \
+ "python" "" \
+ "class wp_eval (gdb.Breakpoint):" "" \
+ " def stop (self):" "" \
+ " self.result = gdb.parse_and_eval(\"result\")" "" \
+ " if self.result == 788:" "" \
+ " return True" "" \
+ " return False" "" \
+ "end" ""
+
+delete_breakpoints
+gdb_py_test_silent_cmd "python wp1 = wp_eval (\"result\", type=gdb.BP_WATCHPOINT, wp_class=gdb.WP_WRITE)" "Set watchpoint" 0
+gdb_test "continue" ".*\[Ww\]atchpoint.*result.*Old value =.*New value = 788.*" "Test watchpoint write"
+gdb_test "python print never_eval_bp1.count" "0" \
+ "Check that this unrelated breakpoints eval function was never called."