[PATCH] Add Frame.read_register to Python API

[Sasha Smundak]

Thanks.
Here it is again:

The ability to read registers is needed to use Frame Filter API to
display the frames created by JIT compilers.

gdb/ChangeLog:

2014-08-29  Sasha Smundak  <asmundak@google.com>

	* python/py-frame.c (frapy_read_register): New function.

gdb/doc/ChangeLog

2014-08-26  Sasha Smundak  <asmundak@google.com>

	* python.texi (Frames in Python): Add read_register description.

gdb/testsuite/ChangeLog:

2014-08-26  Sasha Smundak  <asmundak@google.com>

	* gdb.python/py-frame.exp: Test Frame.read_register.
-------------- next part --------------
diff --git a/gdb/NEWS b/gdb/NEWS
index d603cf7..46c6a87 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -3,6 +3,9 @@
 
 *** Changes since GDB 7.8
 
+* Python Scripting
+  You can now access frame registers from Python scripts.
+
 * On resume, GDB now always passes the signal the program had stopped
   for to the thread the signal was sent to, even if the user changed
   threads before resuming.  Previously GDB would often (but not
diff --git a/gdb/doc/python.texi b/gdb/doc/python.texi
index 4688783..3cb6bf8 100644
--- a/gdb/doc/python.texi
+++ b/gdb/doc/python.texi
@@ -3589,6 +3589,13 @@ Return the frame's symtab and line object.
 @xref{Symbol Tables In Python}.
 @end defun
 
+@defun Frame.read_register (register)
+Return the value of @var{register} in this frame.  The @var{register}
+argument must be a string (e.g., @code{'sp'} or @code{'rax'}).
+Returns a @code{Gdb.Value} object.  Throws an exception if @var{register}
+does not exist.
+@end defun
+
 @defun Frame.read_var (variable @r{[}, block@r{]})
 Return the value of @var{variable} in this frame.  If the optional
 argument @var{block} is provided, search for the variable from that
diff --git a/gdb/python/py-frame.c b/gdb/python/py-frame.c
index 120e147..859d115 100644
--- a/gdb/python/py-frame.c
+++ b/gdb/python/py-frame.c
@@ -28,6 +28,7 @@
 #include "python-internal.h"
 #include "symfile.h"
 #include "objfiles.h"
+#include "user-regs.h"
 
 typedef struct {
   PyObject_HEAD
@@ -235,6 +236,40 @@ frapy_pc (PyObject *self, PyObject *args)
   return gdb_py_long_from_ulongest (pc);
 }
 
+/* Implementation of gdb.Frame.read_register (self, register) -> gdb.Value.
+   Returns the value of a register in this frame.  */
+
+static PyObject *
+frapy_read_register (PyObject *self, PyObject *args)
+{
+  volatile struct gdb_exception except;
+  const char *regnum_str;
+  struct value *val = NULL;
+
+  if (!PyArg_ParseTuple (args, "s", &regnum_str))
+    return NULL;
+
+  TRY_CATCH (except, RETURN_MASK_ALL)
+    {
+      struct frame_info *frame;
+      int regnum;
+
+      FRAPY_REQUIRE_VALID (self, frame);
+
+      regnum = user_reg_map_name_to_regnum (get_frame_arch (frame),
+                                            regnum_str,
+                                            strlen (regnum_str));
+      if (regnum >= 0)
+        val = value_of_register (regnum, frame);
+
+      if (val == NULL)
+        PyErr_SetString (PyExc_ValueError, _("Unknown register."));
+    }
+  GDB_PY_HANDLE_EXCEPTION (except);
+
+  return val == NULL ? NULL : value_to_value_object (val);
+}
+
 /* Implementation of gdb.Frame.block (self) -> gdb.Block.
    Returns the frame's code block.  */
 
@@ -674,6 +709,9 @@ Return the reason why it's not possible to find frames older than this." },
   { "pc", frapy_pc, METH_NOARGS,
     "pc () -> Long.\n\
 Return the frame's resume address." },
+  { "read_register", frapy_read_register, METH_VARARGS,
+    "read_register (register_name) -> gdb.Value\n\
+Return the value of the register in the frame." },
   { "block", frapy_block, METH_NOARGS,
     "block () -> gdb.Block.\n\
 Return the frame's code block." },
diff --git a/gdb/testsuite/gdb.python/py-frame.exp b/gdb/testsuite/gdb.python/py-frame.exp
index 3517824..e47f340 100644
--- a/gdb/testsuite/gdb.python/py-frame.exp
+++ b/gdb/testsuite/gdb.python/py-frame.exp
@@ -94,3 +94,20 @@ gdb_test "python print ('result = %s' % f0.read_var ('variable_which_surely_does
 gdb_test "python print ('result = %s' % f0.read_var ('a'))" " = 1" "test Frame.read_var - success"
 
 gdb_test "python print ('result = %s' % (gdb.selected_frame () == f1))" " = True" "test gdb.selected_frame"
+
+# Can read SP register.
+gdb_test "python print ('result = %s' % (gdb.selected_frame ().read_register ('sp') == gdb.parse_and_eval ('\$sp')))" \
+  " = True" \
+  "test Frame.read_register(sp)"
+
+# PC value obtained via read_register is as expected.
+gdb_test "python print ('result = %s' % (f0.read_register('pc') == f0.pc()))" \
+  " = True" \
+  "test Frame.read_register(pc)"
+
+# On x86-64, PC is in $rip register.
+if {[istarget x86_64-*]} {
+    gdb_test "python print ('result = %s' % (f0.read_register('pc') == f0.read_register('rip')))" \
+	" = True" \
+	"test Frame.read_register(rip)"
+}