Re: [RFC] - Exposing find_pc_line through Python API

[Siva Chandra <sivachandra@google.com>]

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Eli> If I were that user, I would "feel" that the execution is at the first
Eli> line (or maybe in the prologue) of 'func', since PC is (in my mind)
Eli> unaffected by commands that walk the call stack.  And if you are
Eli> talking about the value of PC saved in the frame of the caller of
Eli> 'func', then saying that line 22 is the "actual" location is again
Eli> confusing, because execution did not yet reach that point.

Eli> So I have hard time understanding why we need the distinction.  And
Eli> since you say that the current Symtab_and_line.line gives the second
Eli> alternatives, I'm confused even more.

Eli> It's possible that I'm the only confused person here, but in that
Eli> case, at least the example should be fixed to show and explain the
Eli> distinction more clearly and unequivocally, and also in which
Eli> situations the "actual" value is useful.

The more I think about your comments, the more I feel that exposing
this 'actual' argument is not a good idea.  I am now of the opinion
that the 'notcurrent' argument to the internal function find_pc_line
caters to a internal usage which depends on much more than just what
the user feels.  Hence, I have modified the patch to remove the
'actual' argument.  The new version of the patch is attached.

2012-05-07  Siva Chandra Reddy  <sivachandra@google.com>

        Add a new function gdb.find_pc_line to the Python API.
        * NEWS (Python Scripting): Add entry about the new function.
        * python/python.c (gdbpy_find_pc_line): New function which
        implements gdb.find_pc_line.
        (GdbMethods): Add entry for the new function.

        doc/
        * gdb.texinfo (Basic Python): Add description about the function
        gdb.find_pc_line

        testsuite/
        * gdb.python/python.c: Add a new breakpoint comment.
        * gdb.python/python.exp: Add tests to test gdb.find_pc_line.

Thanks,
Siva Chandra

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Index: NEWS
===================================================================
RCS file: /cvs/src/src/gdb/NEWS,v
retrieving revision 1.514
diff -u -p -r1.514 NEWS
--- NEWS	3 May 2012 07:07:24 -0000	1.514
+++ NEWS	9 May 2012 06:23:26 -0000
@@ -43,6 +43,9 @@
      which return the global and static blocks (as gdb.Block objects),
      of the underlying symbol table, respectively.
 
+  ** New function gdb.find_pc_line which returns the gdb.Symtab_and_line
+     object associated with a PC value.
+
 * Go language support.
   GDB now supports debugging programs written in the Go programming
   language.
Index: doc/gdb.texinfo
===================================================================
RCS file: /cvs/src/src/gdb/doc/gdb.texinfo,v
retrieving revision 1.955
diff -u -p -r1.955 gdb.texinfo
--- doc/gdb.texinfo	6 May 2012 15:31:04 -0000	1.955
+++ doc/gdb.texinfo	9 May 2012 06:23:32 -0000
@@ -22392,6 +22392,12 @@ compute values, for example, it is the o
 convenience variable (@pxref{Convenience Vars}) as a @code{gdb.Value}.
 @end defun
 
+@findex gdb.find_pc_line
+@defun gdb.find_pc_line (pc)
+Return the @code{gdb.Symtab_and_line} object corresponding to the
+@var{pc} value.  @xref{Symbol Tables In Python}.
+@end defun
+
 @findex gdb.post_event
 @defun gdb.post_event (event)
 Put @var{event}, a callable object taking no arguments, into
Index: python/python.c
===================================================================
RCS file: /cvs/src/src/gdb/python/python.c,v
retrieving revision 1.86
diff -u -p -r1.86 python.c
--- python/python.c	30 Mar 2012 20:05:55 -0000	1.86
+++ python/python.c	9 May 2012 06:23:32 -0000
@@ -631,6 +631,25 @@ gdbpy_parse_and_eval (PyObject *self, Py
   return value_to_value_object (result);
 }
 
+/* Implementation of gdb.find_pc_line function.
+   Returns the gdb.Symtab_and_line object corresponding to a PC value.  */
+
+static PyObject *
+gdbpy_find_pc_line (PyObject *self, PyObject *args)
+{
+  struct symtab_and_line sal;
+  CORE_ADDR pc;
+  unsigned long long pc_llu;
+  PyObject *actual = NULL;
+
+  if (!PyArg_ParseTuple (args, GDB_PY_LLU_ARG, &pc_llu))
+    return NULL;
+
+  pc = (CORE_ADDR) pc_llu;
+  sal = find_pc_line (pc, 0);
+  return symtab_and_line_to_sal_object (sal);
+}
+
 /* Read a file as Python code.
    FILE is the file to run.  FILENAME is name of the file FILE.
    This does not throw any errors.  If an exception occurs python will print
@@ -1458,6 +1477,9 @@ gdb.Symtab_and_line objects (or None)."}
     "parse_and_eval (String) -> Value.\n\
 Parse String as an expression, evaluate it, and return the result as a Value."
   },
+  { "find_pc_line", gdbpy_find_pc_line, METH_VARARGS,
+    "find_pc_line (pc) -> Symtab_and_line.\n\
+Return the gdb.Symtab_and_line object corresponding to the pc value." },
 
   { "post_event", gdbpy_post_event, METH_VARARGS,
     "Post an event into gdb's event loop." },
Index: testsuite/gdb.python/python.c
===================================================================
RCS file: /cvs/src/src/gdb/testsuite/gdb.python/python.c,v
retrieving revision 1.4
diff -u -p -r1.4 python.c
--- testsuite/gdb.python/python.c	4 Jan 2012 08:27:49 -0000	1.4
+++ testsuite/gdb.python/python.c	9 May 2012 06:23:32 -0000
@@ -23,6 +23,6 @@ int
 main (int argc, char *argv[])
 {
   func1 ();
-  func2 ();
+  func2 ();      /* Break at func2 call site.  */
   return 0;      /* Break to end.  */
 }
Index: testsuite/gdb.python/python.exp
===================================================================
RCS file: /cvs/src/src/gdb/testsuite/gdb.python/python.exp,v
retrieving revision 1.32
diff -u -p -r1.32 python.exp
--- testsuite/gdb.python/python.exp	30 Mar 2012 19:16:52 -0000	1.32
+++ testsuite/gdb.python/python.exp	9 May 2012 06:23:32 -0000
@@ -367,3 +367,23 @@ gdb_test_multiple "python gdb.prompt_hoo
 
 gdb_py_test_silent_cmd "python gdb.prompt_hook = None" \
     "set the hook to default" 1
+
+# Start with a fresh gdb.
+clean_restart ${testfile}
+
+# The following tests require execution.
+
+if ![runto_main] then {
+    fail "Can't run to main"
+    return 0
+}
+
+runto [gdb_get_line_number "Break at func2 call site."]
+
+gdb_py_test_silent_cmd "python line = gdb.selected_frame().find_sal().line" "Get line number of func2 call site" 1
+gdb_test "python print gdb.find_pc_line(gdb.selected_frame().pc()).line == line" "True" "Test find_pc_line at func2 call site"
+
+gdb_py_test_silent_cmd "step" "Step into func2" 1
+gdb_py_test_silent_cmd "up" "Step out of func2" 1
+
+gdb_test "python print gdb.find_pc_line(gdb.selected_frame().pc()).line > line" "True" "Test find_pc_line with resume address"