[RFC] Extend gdb.Breakpoint to allow setting a breakpoint at the current execution address

[Siva Chandra <sivachandra@google.com>]

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Hi all,

I didn't find a way to set a breakpoint at the current execution
address through the existing Python API.  The attached patch 'extends'
gdb.Breakpoint to allow this.  Probably 'extend' is not the right
word, but what this patch does is to allow the SPEC argument of the
gdb.Breakpoint constructor to be 'None' or "" or white space space
string.  When SPEC takes one of these values, a breakpoint is set at
the current execution address.  Though this is not valid for a
watchpoint, the existing error mechanism will handle this correctly.

2012-04-27  Siva Chandra Reddy  <sivachandra@google.com>

        * breakpoint.c (parse_breakpoint_sals, watch_command_1): Treat
        argument with all white space to be equivalent to NULL argument.
        * python/py-breakpoint.c (bppy_init): Make the 'spec' argument
        optional and allow it to take the value 'None'.

doc/
2012-04-27  Siva Chandra Reddy  <sivachandra@google.com>

        * gdb.texinfo (Breakpoints In Python): Document that 'spec'
        argument, of the constructor of gdb.Breakpoint when setting
        breakpoints, is optional and can also be all white space or None
        when used.

testsuite/
2012-04-27  Siva Chandra Reddy  <sivachandra@google.com>

        * gdb.python/py-breakpoint.exp: Test setting breakpoints at the
        current execution address using different values for the 'spec'
        argument of the constructor of gdb.Breakpoint.

Thanks,
Siva Chandra

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Index: breakpoint.c
===================================================================
RCS file: /cvs/src/src/gdb/breakpoint.c,v
retrieving revision 1.668
diff -u -p -r1.668 breakpoint.c
--- breakpoint.c	24 Apr 2012 14:33:12 -0000	1.668
+++ breakpoint.c	27 Apr 2012 07:55:09 -0000
@@ -8528,7 +8528,7 @@ parse_breakpoint_sals (char **address,
 
   /* If no arg given, or if first arg is 'if ', use the default
      breakpoint.  */
-  if ((*address) == NULL
+  if ((*address) == NULL || (*skip_spaces (*address)) == '\0'
       || (strncmp ((*address), "if", 2) == 0 && isspace ((*address)[2])))
     {
       /* The last displayed codepoint, if it's valid, is our default breakpoint
@@ -10054,7 +10054,7 @@ watch_command_1 (char *arg, int accessfl
   struct watchpoint *w;
 
   /* Make sure that we actually have parameters to parse.  */
-  if (arg != NULL && arg[0] != '\0')
+  if (arg != NULL && (*skip_spaces (arg)) != '\0')
     {
       char *value_start;
 
Index: doc/gdb.texinfo
===================================================================
RCS file: /cvs/src/src/gdb/doc/gdb.texinfo,v
retrieving revision 1.950
diff -u -p -r1.950 gdb.texinfo
--- doc/gdb.texinfo	25 Apr 2012 16:13:17 -0000	1.950
+++ doc/gdb.texinfo	27 Apr 2012 07:55:14 -0000
@@ -24981,12 +24981,16 @@ Return the symbol table's source absolut
 Python code can manipulate breakpoints via the @code{gdb.Breakpoint}
 class.
 
-@defun Breakpoint.__init__ (spec @r{[}, type @r{[}, wp_class @r{[},internal@r{]]]})
+@defun Breakpoint.__init__ (@r{[}spec @r{[}, type @r{[}, wp_class @r{[},internal@r{]]]]})
 Create a new breakpoint.  @var{spec} is a string naming the
 location of the breakpoint, or an expression that defines a
 watchpoint.  The contents can be any location recognized by the
 @code{break} command, or in the case of a watchpoint, by the @code{watch}
-command.  The optional @var{type} denotes the breakpoint to create
+command.  For a breakpoint, omitting  or setting @var{spec} to all white
+space sets a breakpoint at the current execution address of the selected
+stack frame.  For a watchpoint, @var{spec} should not be omitted and
+should be a valid expression in the current context of the program being
+debugged.  The optional @var{type} denotes the breakpoint to create
 from the types defined later in this chapter.  This argument can be
 either: @code{gdb.BP_BREAKPOINT} or @code{gdb.BP_WATCHPOINT}.  @var{type}
 defaults to @code{gdb.BP_BREAKPOINT}.  The optional @var{internal} argument
Index: python/py-breakpoint.c
===================================================================
RCS file: /cvs/src/src/gdb/python/py-breakpoint.c,v
retrieving revision 1.33
diff -u -p -r1.33 py-breakpoint.c
--- python/py-breakpoint.c	13 Mar 2012 13:30:42 -0000	1.33
+++ python/py-breakpoint.c	27 Apr 2012 07:55:14 -0000
@@ -590,14 +590,14 @@ static int
 bppy_init (PyObject *self, PyObject *args, PyObject *kwargs)
 {
   static char *keywords[] = { "spec", "type", "wp_class", "internal", NULL };
-  const char *spec;
+  const char *spec = NULL;
   int type = bp_breakpoint;
   int access_type = hw_write;
   PyObject *internal = NULL;
   int internal_bp = 0;
   volatile struct gdb_exception except;
 
-  if (! PyArg_ParseTupleAndKeywords (args, kwargs, "s|iiO", keywords,
+  if (! PyArg_ParseTupleAndKeywords (args, kwargs, "|ziiO", keywords,
 				     &spec, &type, &access_type, &internal))
     return -1;
 
@@ -614,8 +614,13 @@ bppy_init (PyObject *self, PyObject *arg
   
   TRY_CATCH (except, RETURN_MASK_ALL)
     {
-      char *copy = xstrdup (spec);
-      struct cleanup *cleanup = make_cleanup (xfree, copy);
+      char *copy = NULL;
+      struct cleanup *cleanup;
+
+      if (spec)
+        copy = xstrdup (spec);
+
+      cleanup = make_cleanup (xfree, copy);
 
       switch (type)
 	{
Index: testsuite/gdb.python/py-breakpoint.exp
===================================================================
RCS file: /cvs/src/src/gdb/testsuite/gdb.python/py-breakpoint.exp,v
retrieving revision 1.14
diff -u -p -r1.14 py-breakpoint.exp
--- testsuite/gdb.python/py-breakpoint.exp	16 Jan 2012 16:21:52 -0000	1.14
+++ testsuite/gdb.python/py-breakpoint.exp	27 Apr 2012 07:55:14 -0000
@@ -79,6 +79,14 @@ gdb_test "python print blist\[0\].number
 gdb_test "python print blist\[1\].number" "2" "Check breakpoint number"
 gdb_test "python print blist\[2\].number" "3" "Check breakpoint number"
 
+# Test setting breakpoint at the current execution address.
+gdb_py_test_silent_cmd "python blist_len = len(gdb.breakpoints())" "Get the number of breakpoints in the list" 0
+gdb_py_test_silent_cmd "python gdb.Breakpoint()" "Check breakpoint set at current execution address with spec omitted" 0
+gdb_py_test_silent_cmd "python gdb.Breakpoint(spec=\"\")" "Check breakpoint set at current execution address with NUL spec" 0
+gdb_py_test_silent_cmd "python gdb.Breakpoint(spec=\"  \")" "Check breakpoint set at current execution address with white space spec" 0
+gdb_py_test_silent_cmd "python gdb.Breakpoint(spec=None)" "Check breakpoint set at current execution address with spec None" 0
+gdb_test "python print len(gdb.breakpoints()) == 4 + blist_len" "True" "Check addition of breakpoints"
+
 # Start with a fresh gdb.
 clean_restart ${testfile}