New python function gdb.lookup_objfile.

diff --git a/gdb/NEWS b/gdb/NEWS
index 6a2cb9b..93e06d4 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -28,6 +28,7 @@ 
   ** A new event "gdb.clear_objfiles" has been added, triggered when
      selecting a new file to debug.
   ** You can now add attributes to gdb.Objfile and gdb.Progspace objects.
+  ** New function gdb.lookup_objfile.
 
 * New Python-based convenience functions:
 
diff --git a/gdb/doc/python.texi b/gdb/doc/python.texi
index efd258d..b54d341 100644
--- a/gdb/doc/python.texi
+++ b/gdb/doc/python.texi
@@ -3488,6 +3488,22 @@  Return a sequence of all the objfiles current known to @value{GDBN}.
 @xref{Objfiles In Python}.
 @end defun
 
+@findex gdb.lookup_objfile
+@defun gdb.lookup_objfile (name @r{[}, by_build_id{]})
+Look up @var{name}, which is a file name, in the list of objfiles
+for the current program space (@pxref{Progspaces In Python}).
+If the objfile is not found then a Python @code{ValueError} exception
+is thrown.
+
+If @var{by_build_id} is provided and is @code{True} then @var{name}
+is the build ID of the objfile.
+This is supported only on some operating systems, notably those which use
+the ELF format for binary files and the @sc{gnu} Binutils.  For more details
+about this feature, see the description of the @option{--build-id}
+command-line option in @ref{Options, , Command Line Options, ld.info,
+The GNU Linker}.
+@end defun
+
 Each objfile is represented by an instance of the @code{gdb.Objfile}
 class.
 
diff --git a/gdb/python/py-objfile.c b/gdb/python/py-objfile.c
index 51cf47c..e78ceba 100644
--- a/gdb/python/py-objfile.c
+++ b/gdb/python/py-objfile.c
@@ -24,6 +24,7 @@ 
 #include "language.h"
 #include "build-id.h"
 #include "elf-bfd.h"
+#include "symtab.h"
 
 typedef struct
 {
@@ -380,6 +385,147 @@  objfpy_add_separate_debug_file (PyObject *self, PyObject *args, PyObject *kw)
   Py_RETURN_NONE;
 }
 
+/* Subroutine of gdbpy_lookup_objfile_by_build_id to simplify it.
+   Return non-zero if STRING is a potentially valid build id.  */
+
+static int
+objfpy_build_id_ok (const char *string)
+{
+  size_t i, n = strlen (string);
+
+  if (n % 2 != 0)
+    return 0;
+  for (i = 0; i < n; ++i)
+    {
+      if (!isxdigit (string[i]))
+	return 0;
+    }
+  return 1;
+}
+
+/* Subroutine of gdbpy_lookup_objfile_by_build_id to simplify it.
+   Returns non-zero if BUILD_ID matches STRING.
+   It is assumed that objfpy_build_id_ok (string) returns TRUE.  */
+
+static int
+objfpy_build_id_matches (const struct elf_build_id *build_id,
+			 const char *string)
+{
+  size_t i;
+
+  if (strlen (string) != 2 * build_id->size)
+    return 0;
+
+  for (i = 0; i < build_id->size; ++i)
+    {
+      char c1 = string[i * 2], c2 = string[i * 2 + 1];
+      int byte = (host_hex_value (c1) << 4) | host_hex_value (c2);
+
+      if (byte != build_id->data[i])
+	return 0;
+    }
+
+  return 1;
+}
+
+/* Subroutine of gdbpy_lookup_objfile to simplify it.
+   Look up an objfile by its file name.  */
+
+static struct objfile *
+objfpy_lookup_objfile_by_name (const char *name)
+{
+  struct objfile *objfile;
+
+  ALL_OBJFILES (objfile)
+    {
+      if ((objfile->flags & OBJF_NOT_FILENAME) != 0)
+	continue;
+      /* Don't return separate debug files.  */
+      if (objfile->separate_debug_objfile_backlink != NULL)
+	continue;
+      if (compare_filenames_for_search (objfile_name (objfile), name))
+	return objfile;
+    }
+
+  return NULL;
+}
+
+/* Subroutine of gdbpy_lookup_objfile to simplify it.
+   Look up an objfile by its build id.  */
+
+static struct objfile *
+objfpy_lookup_objfile_by_build_id (const char *build_id)
+{
+  struct objfile *objfile;
+
+  ALL_OBJFILES (objfile)
+    {
+      const struct elf_build_id *obfd_build_id;
+
+      if (objfile->obfd == NULL)
+	continue;
+      /* Don't return separate debug files.  */
+      if (objfile->separate_debug_objfile_backlink != NULL)
+	continue;
+      obfd_build_id = build_id_bfd_get (objfile->obfd);
+      if (obfd_build_id == NULL)
+	continue;
+      if (objfpy_build_id_matches (obfd_build_id, build_id))
+	return objfile;
+    }
+
+  return NULL;
+}
+
+/* Implementation of gdb.lookup_objfile.  */
+
+PyObject *
+gdbpy_lookup_objfile (PyObject *self, PyObject *args, PyObject *kw)
+{
+  static char *keywords[] = { "name", "by_build_id", NULL };
+  const char *name;
+  PyObject *by_build_id_obj = NULL;
+  int by_build_id;
+  struct objfile *objfile;
+
+  if (! PyArg_ParseTupleAndKeywords (args, kw, "s|O!", keywords,
+				     &name, &PyBool_Type, &by_build_id_obj))
+    return NULL;
+
+  by_build_id = 0;
+  if (by_build_id_obj != NULL)
+    {
+      int cmp = PyObject_IsTrue (by_build_id_obj);
+
+      if (cmp < 0)
+	return NULL;
+      by_build_id = cmp;
+    }
+
+  if (by_build_id)
+    {
+      if (!objfpy_build_id_ok (name))
+	{
+	  PyErr_SetString (PyExc_TypeError, _("Not a valid build id."));
+	  return NULL;
+	}
+      objfile = objfpy_lookup_objfile_by_build_id (name);
+    }
+  else
+    objfile = objfpy_lookup_objfile_by_name (name);
+
+  if (objfile != NULL)
+    {
+      PyObject *result = objfile_to_objfile_object (objfile);
+
+      Py_XINCREF (result);
+      return result;
+    }
+
+  PyErr_SetString (PyExc_ValueError, _("Objfile not found."));
+  return NULL;
+}
+
 
 
 /* Clear the OBJFILE pointer in an Objfile object and remove the
diff --git a/gdb/python/python-internal.h b/gdb/python/python-internal.h
index 716c0de..544fe93 100644
--- a/gdb/python/python-internal.h
+++ b/gdb/python/python-internal.h
@@ -393,6 +393,7 @@  PyObject *objfile_to_objfile_object (struct objfile *)
 PyObject *objfpy_get_printers (PyObject *, void *);
 PyObject *objfpy_get_frame_filters (PyObject *, void *);
 PyObject *objfpy_get_xmethods (PyObject *, void *);
+PyObject *gdbpy_lookup_objfile (PyObject *self, PyObject *args, PyObject *kw);
 
 PyObject *gdbarch_to_arch_object (struct gdbarch *gdbarch);
 
diff --git a/gdb/python/python.c b/gdb/python/python.c
index 1362bd2..b1d8283 100644
--- a/gdb/python/python.c
+++ b/gdb/python/python.c
@@ -1956,6 +1956,14 @@  a boolean indicating if name is a field of the current implied argument\n\
     METH_VARARGS | METH_KEYWORDS,
     "lookup_global_symbol (name [, domain]) -> symbol\n\
 Return the symbol corresponding to the given name (or None)." },
+
+  { "lookup_objfile", (PyCFunction) gdbpy_lookup_objfile,
+    METH_VARARGS | METH_KEYWORDS,
+    "lookup_objfile (name, [by_build_id]) -> objfile\n\
+Look up the specified objfile.\n\
+If by_build_id is True, the objfile is looked up by using name\n\
+as its build id." },
+
   { "block_for_pc", gdbpy_block_for_pc, METH_VARARGS,
     "Return the block containing the given pc value, or None." },
   { "solib_name", gdbpy_solib_name, METH_VARARGS,
diff --git a/gdb/testsuite/gdb.python/py-objfile.exp b/gdb/testsuite/gdb.python/py-objfile.exp
index f3a8a6c..a56bc95 100644
--- a/gdb/testsuite/gdb.python/py-objfile.exp
+++ b/gdb/testsuite/gdb.python/py-objfile.exp
@@ -32,23 +32,39 @@  if ![runto_main] then {
     return 0
 }
 
+set python_error_text "Error while executing Python code\\."
+
 gdb_py_test_silent_cmd "python sym = gdb.lookup_symbol(\"some_var\")" \
     "Find a symbol in objfile" 1
 gdb_py_test_silent_cmd "python objfile = sym\[0\].symtab.objfile" \
     "Get backing object file" 1
 
-gdb_test "python print (objfile.filename)" ".*py-objfile.*" \
+gdb_test "python print (objfile.filename)" ".*${testfile}" \
   "Get objfile file name"
 
+gdb_test "python print (gdb.lookup_objfile (\"${testfile}\").filename)" \
+    "${testfile}"
+gdb_test "python print (gdb.lookup_objfile (\"junk\"))" \
+    "Objfile not found\\.\r\n${python_error_text}"
+
 set binfile_build_id [get_build_id $binfile]
 if [string compare $binfile_build_id ""] {
     verbose -log "binfile_build_id = $binfile_build_id"
     gdb_test "python print (objfile.build_id)" "$binfile_build_id" \
     "Get objfile build id"
+    gdb_test "python print (gdb.lookup_objfile (\"$binfile_build_id\", by_build_id=True).filename)" \
+	"${testfile}"
 } else {
     unsupported "build-id is not supported by the compiler"
 }
 
+# Other lookup_objfile_by_build_id tests we can do, even if compiler doesn't
+# support them.
+gdb_test "python print (gdb.lookup_objfile (\"foo\", by_build_id=True))" \
+    "Not a valid build id\\.\r\n${python_error_text}"
+gdb_test "python print (gdb.lookup_objfile (\"1234abcdef\", by_build_id=True))" \
+    "Objfile not found\\.\r\n${python_error_text}"
+
 gdb_test "python print (objfile.progspace)" "<gdb\.Progspace object at .*>" \
   "Get objfile program space"
 gdb_test "python print (objfile.is_valid())" "True" \
@@ -93,3 +109,9 @@  gdb_test "python print (sep_objfile.owner.filename)" "${testfile}2" \
 
 gdb_test "p main" "= {int \\(\\)} $hex <main>" \
     "print main with debug info"
+
+# Separate debug files are not findable.
+if { [get_python_valueof "sep_objfile.build_id" "None"] != "None" } {
+    gdb_test "python print (gdb.lookup_objfile (sep_objfile.build_id, by_build_id=True))" \
+	"Objfile not found\\.\r\n${python_error_text}"
+}
diff --git a/gdb/testsuite/lib/gdb-python.exp b/gdb/testsuite/lib/gdb-python.exp
index d5e7928..eefff73 100644
--- a/gdb/testsuite/lib/gdb-python.exp
+++ b/gdb/testsuite/lib/gdb-python.exp
@@ -45,3 +45,24 @@  proc gdb_py_test_multiple { name args } {
     }
     return 0
 }
+
+# Return the result of python expression EXPR.
+# DEFAULT is returned if there's an error.
+# This is modelled after get_integer_valueof.
+
+proc get_python_valueof { exp default } {
+    global gdb_prompt
+
+    set test "get python valueof \"${exp}\""
+    set val ${default}
+    gdb_test_multiple "python print (\"valueof: %s\" % (${exp}))" "$test" {
+	-re "valueof: (\[^\r\n\]*)\[\r\n\]*$gdb_prompt $" {
+	    set val $expect_out(1,string)
+	    pass "$test ($val)"
+	}
+	timeout {
+	    fail "$test (timeout)"
+	}
+    }
+    return ${val}
+}