gdb: Add a find method for RegisterDescriptorIterator

Adds a new method 'find' to the gdb.RegisterDescriptorIterator class,
this allows gdb.RegisterDescriptor objects to be looked up directly by
register name rather than having to iterate over all registers.

This will be of use for a later commit.

I've documented the new function in the manual, but I don't think a
NEWS entry is required here, as, since the last release, the whole
register descriptor mechanism is new, and is already mentioned in the
NEWS file.

gdb/ChangeLog:

	* python/py-registers.c: Add 'user-regs.h' include.
	(register_descriptor_iter_find): New function.
	(register_descriptor_iterator_object_methods): New static global
	methods array.
	(register_descriptor_iterator_object_type): Add pointer to methods
	array.

gdb/testsuite/ChangeLog:

	* gdb.python/py-arch-reg-names.exp: Add additional tests.

gdb/doc/ChangeLog:

	* python.texi (Registers In Python): Document new find function.

gdb/ChangeLog

@@ -1,3 +1,12 @@
+2020-07-28  Andrew Burgess  <andrew.burgess@embecosm.com>
+
+	* python/py-registers.c: Add 'user-regs.h' include.
+	(register_descriptor_iter_find): New function.
+	(register_descriptor_iterator_object_methods): New static global
+	methods array.
+	(register_descriptor_iterator_object_type): Add pointer to methods
+	array.
+
 2020-07-27  John Baldwin  <jhb@FreeBSD.org>
 
 	* fbsd-nat.h: Include <osreldate.h>.  Define USE_SIGTRAP_SIGINFO

gdb/doc/ChangeLog

@@ -1,3 +1,7 @@
+2020-07-28  Andrew Burgess  <andrew.burgess@embecosm.com>
+
+	* python.texi (Registers In Python): Document new find function.
+
 2020-07-22  Kevin Buettner  <kevinb@redhat.com>
 
 	* gdb.texinfo (Maintenance Commands): Add documentation for

gdb/doc/python.texi

@@ -5755,6 +5755,15 @@ A @code{gdb.RegisterDescriptor} has the following read-only properties:
 The name of this register.
 @end defvar
 
+It is also possible to lookup a register descriptor based on its name
+using the following @code{gdb.RegisterDescriptorIterator} function:
+
+@defun RegisterDescriptorIterator.find (@var{name})
+Takes @var{name} as an argument, which must be a string, and returns a
+@code{gdb.RegisterDescriptor} for the register with that name, or
+@code{None} if there is no register with that name.
+@end defun
+
 Python code can also request from a @code{gdb.Architecture}
 information about the set of register groups available on a given
 architecture

gdb/python/py-registers.c

@@ -23,6 +23,7 @@
 #include "disasm.h"
 #include "reggroups.h"
 #include "python-internal.h"
+#include "user-regs.h"
 #include <unordered_map>
 
 /* Token to access per-gdbarch data related to register descriptors.  */
@@ -337,6 +338,38 @@ gdbpy_register_descriptor_iter_next (PyObject *self)
   while (true);
 }
 
+/* Implement:
+
+   gdb.RegisterDescriptorIterator.find (self, name) -> gdb.RegisterDescriptor
+
+   Look up a descriptor for register with NAME.  If no matching register is
+   found then return None.  */
+
+static PyObject *
+register_descriptor_iter_find (PyObject *self, PyObject *args, PyObject *kw)
+{
+  static const char *keywords[] = { "name", NULL };
+  const char *register_name = NULL;
+
+  register_descriptor_iterator_object *iter_obj
+    = (register_descriptor_iterator_object *) self;
+  struct gdbarch *gdbarch = iter_obj->gdbarch;
+
+  if (!gdb_PyArg_ParseTupleAndKeywords (args, kw, "s", keywords,
+					&register_name))
+    return NULL;
+
+  if (register_name != NULL && *register_name != '\0')
+    {
+      int regnum = user_reg_map_name_to_regnum (gdbarch, register_name,
+						strlen (register_name));
+      if (regnum >= 0)
+	return gdbpy_get_register_descriptor (gdbarch, regnum).release ();
+    }
+
+  Py_RETURN_NONE;
+}
+
 /* Initializes the new Python classes from this file in the gdb module.  */
 
 int
@@ -377,6 +410,15 @@ gdbpy_initialize_registers ()
 	   (PyObject *) &register_descriptor_iterator_object_type));
 }
 
+static PyMethodDef register_descriptor_iterator_object_methods [] = {
+  { "find", (PyCFunction) register_descriptor_iter_find,
+    METH_VARARGS | METH_KEYWORDS,
+    "registers (name) -> gdb.RegisterDescriptor.\n\
+Return a register descriptor for the register NAME, or None if no register\n\
+with that name exists in this iterator." },
+  {NULL}  /* Sentinel */
+};
+
 PyTypeObject register_descriptor_iterator_object_type = {
   PyVarObject_HEAD_INIT (NULL, 0)
   "gdb.RegisterDescriptorIterator",	  	/*tp_name*/
@@ -405,7 +447,7 @@ PyTypeObject register_descriptor_iterator_object_type = {
   0,				  /*tp_weaklistoffset */
   gdbpy_register_descriptor_iter,	  /*tp_iter */
   gdbpy_register_descriptor_iter_next,  /*tp_iternext */
-  0				  /*tp_methods */
+  register_descriptor_iterator_object_methods		/*tp_methods */
 };
 
 static gdb_PyGetSetDef gdbpy_register_descriptor_getset[] = {

gdb/testsuite/ChangeLog

@@ -1,3 +1,7 @@
+2020-07-28  Andrew Burgess  <andrew.burgess@embecosm.com>
+
+	* gdb.python/py-arch-reg-names.exp: Add additional tests.
+
 2020-07-25  Andrew Burgess  <andrew.burgess@embecosm.com>
 
 	PR fortran/23051

gdb/testsuite/gdb.python/py-arch-reg-names.exp

@@ -104,3 +104,18 @@ gdb_py_test_silent_cmd \
 	 "    raise gdb.GdbError (\"miss-matched objects\")" \
 	 "\004" ] \
     "check names and objects match" 1
+
+# Ensure that the '.find' method on the iterator returns the same
+# Python object as we got from the iterator's list of descriptors.
+gdb_py_test_silent_cmd \
+    [multi_line \
+	 "python" \
+	 "def check_regs (arch, regs):" \
+	 "   for r in (regs):" \
+	 "     if (arch.registers ().find (r.name) != r):" \
+	 "       raise gdb.GdbError (\"object miss-match\")" \
+	 "end" ] \
+    "build check_obj function" 0
+gdb_py_test_silent_cmd \
+    "python check_regs (arch, arch.registers (\"general\"))" \
+    "ensure find gets expected descriptors" 1