1 files changed, 105 insertions, 0 deletions
diff --git a/stdlib/errno-printer.py b/stdlib/errno-printer.py
new file mode 100644
index 0000000000..aa09c78235
--- /dev/null
+++ b/stdlib/errno-printer.py
@@ -0,0 +1,105 @@
+# Pretty printer for errno.
+# Copyright (C) 2016-2017 Free Software Foundation, Inc.
+# This file is part of the GNU C Library.
+#
+# The GNU C Library is free software; you can redistribute it and/or
+# modify it under the terms of the GNU Lesser General Public
+# License as published by the Free Software Foundation; either
+# version 2.1 of the License, or (at your option) any later version.
+#
+# The GNU C Library is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+# Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public
+# License along with the GNU C Library; if not, see
+# <http://www.gnu.org/licenses/>.
+
+"""This file contains the gdb pretty printers for the following types:
+
+    * __error_t (the type of 'errno')
+    * error_t   (cast any 'int' to 'error_t' to print it like an errno value)
+
+You can check which printers are registered and enabled by issuing the
+'info pretty-printer' gdb command.  Printers should trigger automatically when
+trying to print a variable of one of the types mentioned above.
+"""
+
+
+import gdb
+import gdb.printing
+import errno_constants
+
+
+def make_errno_reverse_mapping():
+    """Construct a reverse mapping from errno values to symbolic names.
+       The result is a dictionary indexed by integers, not a list,
+       because errno values are not necessarily contiguous.
+    """
+
+    # Certain errno symbols are allowed to have the same numeric value.
+    # If they do, one of them (whichever one is in POSIX, or if both or
+    # neither are, the shortest) is selected as the preferred name.
+    # This map goes from non-preferred name(s) to preferred name.
+    permitted_collisions = {
+        "EDEADLOCK":   "EDEADLK",
+        "EOPNOTSUPP":  "ENOTSUP",
+        "EWOULDBLOCK": "EAGAIN",
+    }
+
+    errno_names = { 0: "Success" }
+    for name in dir(errno_constants):
+        if name[0] == 'E':
+            number = getattr(errno_constants, name)
+            other = errno_names.get(number)
+            if other is None:
+                errno_names[number] = name
+            else:
+                p1 = permitted_collisions.get(name)
+                p2 = permitted_collisions.get(other)
+                if p1 is not None and p1 == other:
+                    pass # the value in errno_names is already what we want
+                elif p2 is not None and p2 == name:
+                    errno_names[number] = name
+                else:
+                    raise RuntimeError(
+                        "errno value collision: {} = {}, {}"
+                        .format(number, name, errno_names[number]))
+
+    return errno_names
+
+
+errno_names = make_errno_reverse_mapping()
+
+
+class ErrnoPrinter(object):
+    """Pretty printer for errno values."""
+
+    def __init__(self, val):
+        self._val = int(val)
+
+    def to_string(self):
+        """gdb API function.
+
+        This is called from gdb when we try to print an error_t.
+        """
+        if self._val in errno_names:
+            return "{:d} ({})".format(self._val, errno_names[self._val])
+        else:
+            return "{:d}".format(self._val)
+
+
+def register(objfile):
+    """Register pretty printers for the current objfile."""
+
+    printer = gdb.printing.RegexpCollectionPrettyPrinter("glibc-errno")
+    printer.add_printer('error_t', r'^(?:__)?error_t', ErrnoPrinter)
+
+    if objfile == None:
+        objfile = gdb
+
+    gdb.printing.register_pretty_printer(objfile, printer)
+
+
+register(gdb.current_objfile())