[RFC] - Exposing find_pc_line through Python API

[Siva Chandra <sivachandra@google.com>]

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Hi all,

I wanted a way to get the actual line number given a PC value using
the Python API.  The currently available Symtab_and_line.line gives
the line number which the user thinks the current execution is, but
not the actual.  Attached is a patch which adds gdb.find_pc_line
corresponding to the C function find_pc_line.

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

        Add a new function gdb.find_pc_line to the Python API.
        * python/python.c (gdbpy_find_pc_line): New function which
        implements gdb.find_pc_line.

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

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

Thanks,
Siva Chandra

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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	7 May 2012 17:55:53 -0000
@@ -22392,6 +22392,53 @@ 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 [, actual])
+Return the @code{gdb.Symtab_and_line} object corresponding to the
+@var{pc} value.  If @var{actual} is @code{True}, it returns the
+@code{gdb.Symtab_and_line} object with the actual line corresponding
+to the pc value.  Otherwise, it returns the @code{gdb.Symtab_and_line}
+object with a line which the user feels the execution is currently at.
+If @var{actual} is not specified, it defaults to @code{True}.
+@xref{Symbol Tables In Python}
+
+The difference between @var{actual} being @code{True} or @code{False}
+can be illustrated with an example.  Let a call to a function @code{func}
+be on line 20 in a C source file as
+
+@smallexample
+18  ...
+19
+20  func ();
+21
+22  return 0;
+23
+24  ...
+@end smallexample
+
+After executing @value{GDBN} commands @code{step} followed by @code{up}
+at line 20, the actual value of the @code{PC} register should correspond
+to the next code line at line 22.  However, since the function
+@code{func} has not yet been executed, the user feels that the execution
+is still at line 20 (the call site) in the caller.  Hence, invoking 
+
+@smallexample
+gdb.find_pc_line (gdb.selected_frame().pc(), True)
+@end smallexample
+
+@noindent
+will return a @code{gdb.Symtab_and_line} object corresponding to the
+actual line 22, while invoking
+
+@smallexample
+gdb.find_pc_line (gdb.selected_frame().pc(), False)
+@end smallexample
+
+@noindent
+will return a @code{gdb.Symtab_and_line} object corresponding to the
+call site line 20.
+@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	7 May 2012 17:55:54 -0000
@@ -631,6 +631,28 @@ 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;
+  PyObject *actual = NULL;
+  int notcurrent = 0;
+
+  if (!PyArg_ParseTuple (args, (GDB_PY_LLU_ARG "|O!"), &pc, &PyBool_Type,
+                         &actual))
+    return NULL;
+
+  if (actual)
+      notcurrent = !PyObject_IsTrue (actual);
+
+  sal = find_pc_line (pc, notcurrent);
+  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 +1480,14 @@ 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[, actual]) -> Symtab_and_line.\n\
+Return the gdb.Symtab_and_line object corresponding to the pc value.  If\n\
+actual is True, it returns the gdb.Symtab_and_line object with the actual\n\
+line corresponding to the pc value.  Otherwise, it returns the\n\
+gdb.Symtab_and_line object with a line which the users feels the execution\n\
+is currently at.  If actual is not specified, it defaults to True."
+  },
 
   { "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	7 May 2012 17:55:59 -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	7 May 2012 17:55:59 -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 "step" "Step into func2" 1
+gdb_py_test_silent_cmd "up" "Step out of func2" 1
+gdb_py_test_silent_cmd "python line = gdb.selected_frame().find_sal().line" "Get line number of func2 call site" 1
+
+# Test gdb.find_pc_line
+gdb_test "python print gdb.find_pc_line(gdb.selected_frame().pc(), True).line > line" "True" "Get actual line"
+gdb_test "python print gdb.find_pc_line(gdb.selected_frame().pc(), False).line == line" "True" "Get user line"