gdb/python: implement Python find_exec_by_build_id hook

Implement extension_language_ops::find_objfile_from_buildid within
GDB's Python API.  Doing this allows users to write Python extensions
that can help locate missing objfiles when GDB opens a core file.  A
handler might perform some project- or site-specific actions to find a
missing objfile.  Or might provide some project- or site-specific
advice to the user on how they can obtain the missing objfile.

The implementation is very similar to the approach taken in:

  commit 8f6c452b5a4e50fbb55ff1d13328b392ad1fd416
  Date:   Sun Oct 15 22:48:42 2023 +0100

      gdb: implement missing debug handler hook for Python

The following new commands are added as commands implemented in
Python, this is similar to how the Python missing debug and unwinder
commands are implemented:

  info missing-objfile-handlers
  enable missing-objfile-handler LOCUS HANDLER
  disable missing-objfile-handler LOCUS HANDLER

To make use of this extension hook a user will create missing objfile
handler objects, and registers these handlers with GDB.  When GDB
opens a core file and encounters a missing objfile each handler is
called in turn until one is able to help.  Here is a minimal handler
that does nothing useful:

  import gdb
  import gdb.missing_objfile

  class MyFirstHandler(gdb.missing_objfile.MissingObjfileHandler):
      def __init__(self):
          super().__init__("my_first_handler")

      def __call__(self, pspace, build_id, filename):
          # This handler does nothing useful.
          return None

  gdb.missing_objfile.register_handler(None, MyFirstHandler())

Returning None from the __call__ method tells GDB that this handler
was unable to find the missing objfile, and GDB should ask any other
registered handlers.

Possible return values from a handler:

  - None: This means the handler couldn't help.  GDB will call other
          registered handlers to see if they can help instead.

  - False: The handler has done all it can, but the objfile couldn't
            be found.  GDB will not call any other handlers, and will
	    continue without the objfile.

  - True: The handler has installed the objfile into a location where
          GDB would normally expect to find it.  GDB should repeat its
	  normal lookup process and the objfile should now be found.

  - A string: The handler can return a filename, which is the missing
              objfile.  GDB will load this file.

Handlers can be registered globally, or per program space.  GDB checks
the handlers for the current program space first, and then all of the
global handles.  The first handler that returns a value that is not
None, has "handled" the missing objfile, at which point GDB continues.

The implementation of this feature is mostly straight forward.  I have
reworked some of the missing debug file related code so that it can be
shared with this feature.  E.g. gdb/python/lib/gdb/missing_files.py is
mostly content moved from gdb/python/lib/gdb/missing_debug.py, but
updated to be more generic.  Now gdb/python/lib/gdb/missing_debug.py
and the new file gdb/python/lib/gdb/missing_objfile.py both call into
the missing_files.py file.

For gdb/python/lib/gdb/command/missing_files.py this is even more
extreme, gdb/python/lib/gdb/command/missing_debug.py is completely
gone now and gdb/python/lib/gdb/command/missing_files.py provides all
of the new commands in a generic way.

I have made one change to the existing Python API, I renamed the
attribute Progspace.missing_debug_handlers to
Progspace.missing_file_handlers.  I don't see this as too
problematic.  This attribute was only used to implement the missing
debug feature and was never documented beyond the fact that it
existed.  There was no reason for users to be touching this attribute.

Reviewed-By: Eli Zaretskii <eliz@gnu.org>

7 files changed, 581 insertions, 230 deletions

diff --git a/gdb/python/lib/gdb/__init__.py b/gdb/python/lib/gdb/__init__.py
index 6c3e241..146a963 100644
--- a/gdb/python/lib/gdb/__init__.py
+++ b/gdb/python/lib/gdb/__init__.py
@@ -87,8 +87,9 @@ xmethods = []
 frame_filters = {}
 # Initial frame unwinders.
 frame_unwinders = []
-# Initial missing debug handlers.
-missing_debug_handlers = []
+# The missing file handlers.  Each item is a tuple with the form
+# (TYPE, HANDLER) where TYPE is a string either 'debug' or 'objfile'.
+missing_file_handlers = []
 
 
 def _execute_unwinders(pending_frame):
@@ -271,6 +272,61 @@ class Thread(threading.Thread):
             super().start()
 
 
+def _filter_missing_file_handlers(handlers, handler_type):
+    """Each list of missing file handlers is a list of tuples, the first
+    item in the tuple is a string either 'debug' or 'objfile' to
+    indicate what type of handler it is.  The second item in the tuple
+    is the actual handler object.
+
+    This function takes HANDLER_TYPE which is a string, either 'debug'
+    or 'objfile' and HANDLERS, a list of tuples.  The function returns
+    an iterable over all of the handler objects (extracted from the
+    tuples) which match HANDLER_TYPE.
+    """
+
+    return map(lambda t: t[1], filter(lambda t: t[0] == handler_type, handlers))
+
+
+def _handle_missing_files(pspace, handler_type, cb):
+    """Helper for _handle_missing_debuginfo and _handle_missing_objfile.
+
+    Arguments:
+        pspace: The gdb.Progspace in which we're operating.  Used to
+            lookup program space specific handlers.
+        handler_type: A string, either 'debug' or 'objfile', this is the
+            type of handler we're looking for.
+        cb: A callback which takes a handler and returns the result of
+            calling the handler.
+
+    Returns:
+        None: No suitable file could be found.
+        False: A handler has decided that the requested file cannot be
+                found, and no further searching should be done.
+        True: The file has been found and installed in a location
+                where GDB would normally look for it.  GDB should
+                repeat its lookup process, the file should now be in
+                place.
+        A string: This is the filename of where the missing file can
+                be found.
+    """
+
+    for handler in _filter_missing_file_handlers(
+        pspace.missing_file_handlers, handler_type
+    ):
+        if handler.enabled:
+            result = cb(handler)
+            if result is not None:
+                return result
+
+    for handler in _filter_missing_file_handlers(missing_file_handlers, handler_type):
+        if handler.enabled:
+            result = cb(handler)
+            if result is not None:
+                return result
+
+    return None
+
+
 def _handle_missing_debuginfo(objfile):
     """Internal function called from GDB to execute missing debug
     handlers.
@@ -293,18 +349,46 @@ def _handle_missing_debuginfo(objfile):
         A string: This is the filename of a file containing the
                   required debug information.
     """
+
     pspace = objfile.progspace
 
-    for handler in pspace.missing_debug_handlers:
-        if handler.enabled:
-            result = handler(objfile)
-            if result is not None:
-                return result
+    return _handle_missing_files(pspace, "debug", lambda h: h(objfile))
 
-    for handler in missing_debug_handlers:
-        if handler.enabled:
-            result = handler(objfile)
-            if result is not None:
-                return result
 
-    return None
+def _handle_missing_objfile(pspace, buildid, filename):
+    """Internal function called from GDB to execute missing objfile
+    handlers.
+
+    Run each of the currently registered, and enabled missing objfile
+    handler objects for the gdb.Progspace passed in as an argument,
+    and then from the global list.  Stop after the first handler that
+    returns a result other than None.
+
+    Arguments:
+        pspace: A gdb.Progspace for which the missing objfile handlers
+                should be run.  This is the program space in which an
+                objfile was found to be missing.
+        buildid: A string containing the build-id we're looking for.
+        filename: The filename of the file GDB tried to find but
+                  couldn't.  This is not where the file should be
+                  placed if found, in fact, this file might already
+                  exist on disk but have the wrong build-id.  This is
+                  mostly provided in order to be used in messages to
+                  the user.
+
+    Returns:
+        None: No objfile could be found for this build-id.
+        False: A handler has done all it can with for this build-id,
+               but no objfile could be found.
+        True: An objfile might have been installed by a handler, GDB
+              should check again.  The only place GDB checks is within
+              the .build-id sub-directory within the
+              debug-file-directory.  If the required file was not
+              installed there then GDB will not find it.
+        A string: This is the filename of a file containing the
+                  missing objfile.
+    """
+
+    return _handle_missing_files(
+        pspace, "objfile", lambda h: h(pspace, buildid, filename)
+    )
diff --git a/gdb/python/lib/gdb/command/missing_debug.py b/gdb/python/lib/gdb/command/missing_files.py
index 313b88c..463853b 100644
--- a/gdb/python/lib/gdb/command/missing_debug.py
+++ b/gdb/python/lib/gdb/command/missing_files.py
@@ -1,4 +1,4 @@
-# Missing debug related commands.
+# Missing debug and objfile related commands.
 #
 # Copyright 2023-2024 Free Software Foundation, Inc.
 #
@@ -21,7 +21,7 @@ import gdb
 
 
 def validate_regexp(exp, idstring):
-    """Compile exp into a compiler regular expression object.
+    """Compile exp into a compiled regular expression object.
 
     Arguments:
         exp: The string to compile into a re.Pattern object.
@@ -33,14 +33,15 @@ def validate_regexp(exp, idstring):
     Raises:
         SyntaxError: If exp is an invalid regexp.
     """
+
     try:
         return re.compile(exp)
     except SyntaxError:
         raise SyntaxError("Invalid %s regexp: %s." % (idstring, exp))
 
 
-def parse_missing_debug_command_args(arg):
-    """Internal utility to parse missing debug handler command argv.
+def parse_missing_file_command_args(arg):
+    """Internal utility to parse missing file handler command argv.
 
     Arguments:
         arg: The arguments to the command. The format is:
@@ -52,6 +53,7 @@ def parse_missing_debug_command_args(arg):
     Raises:
         SyntaxError: an error processing ARG
     """
+
     argv = gdb.string_to_argv(arg)
     argc = len(argv)
     if argc > 2:
@@ -68,10 +70,10 @@ def parse_missing_debug_command_args(arg):
     )
 
 
-class InfoMissingDebugHanders(gdb.Command):
-    """GDB command to list missing debug handlers.
+class InfoMissingFileHandlers(gdb.Command):
+    """GDB command to list missing HTYPE handlers.
 
-    Usage: info missing-debug-handlers [LOCUS-REGEXP [NAME-REGEXP]]
+    Usage: info missing-HTYPE-handlers [LOCUS-REGEXP [NAME-REGEXP]]
 
     LOCUS-REGEXP is a regular expression matching the location of the
     handler.  If it is omitted, all registered handlers from all
@@ -79,38 +81,47 @@ class InfoMissingDebugHanders(gdb.Command):
     the handlers from the current progspace, or a regular expression
     matching filenames of progspaces.
 
-    NAME-REGEXP is a regular expression to filter missing debug
+    NAME-REGEXP is a regular expression to filter missing HTYPE
     handler names.  If this omitted for a specified locus, then all
     registered handlers in the locus are listed.
     """
 
-    def __init__(self):
-        super().__init__("info missing-debug-handlers", gdb.COMMAND_FILES)
+    def __init__(self, handler_type):
+        # Update the doc string before calling the parent constructor,
+        # replacing the string 'HTYPE' with the value of HANDLER_TYPE.
+        # The parent constructor will grab a copy of this string to
+        # use as the commands help text.
+        self.__doc__ = self.__doc__.replace("HTYPE", handler_type)
+        super().__init__(
+            "info missing-" + handler_type + "-handlers", gdb.COMMAND_FILES
+        )
+        self.handler_type = handler_type
 
     def list_handlers(self, title, handlers, name_re):
-        """Lists the missing debug handlers whose name matches regexp.
+        """Lists the missing file handlers whose name matches regexp.
 
         Arguments:
             title: The line to print before the list.
-            handlers: The list of the missing debug handlers.
+            handlers: The list of the missing file handlers.
             name_re: handler name filter.
         """
+
         if not handlers:
             return
         print(title)
-        for handler in handlers:
+        for handler in gdb._filter_missing_file_handlers(handlers, self.handler_type):
             if name_re.match(handler.name):
                 print(
                     "  %s%s" % (handler.name, "" if handler.enabled else " [disabled]")
                 )
 
     def invoke(self, arg, from_tty):
-        locus_re, name_re = parse_missing_debug_command_args(arg)
+        locus_re, name_re = parse_missing_file_command_args(arg)
 
         if locus_re.match("progspace") and locus_re.pattern != "":
             cp = gdb.current_progspace()
             self.list_handlers(
-                "Progspace %s:" % cp.filename, cp.missing_debug_handlers, name_re
+                "Progspace %s:" % cp.filename, cp.missing_file_handlers, name_re
             )
 
         for progspace in gdb.progspaces():
@@ -125,58 +136,71 @@ class InfoMissingDebugHanders(gdb.Command):
                     msg = "Progspace %s:" % filename
                 self.list_handlers(
                     msg,
-                    progspace.missing_debug_handlers,
+                    progspace.missing_file_handlers,
                     name_re,
                 )
 
         # Print global handlers last, as these are invoked last.
         if locus_re.match("global"):
-            self.list_handlers("Global:", gdb.missing_debug_handlers, name_re)
+            self.list_handlers("Global:", gdb.missing_file_handlers, name_re)
 
 
-def do_enable_handler1(handlers, name_re, flag):
-    """Enable/disable missing debug handlers whose names match given regex.
+def do_enable_handler1(handlers, name_re, flag, handler_type):
+    """Enable/disable missing file handlers whose names match given regex.
 
     Arguments:
-        handlers: The list of missing debug handlers.
+        handlers: The list of missing file handlers.
         name_re: Handler name filter.
         flag: A boolean indicating if we should enable or disable.
+        handler_type: A string, either 'debug' or 'objfile', use to control
+            which handlers are modified.
 
     Returns:
         The number of handlers affected.
     """
+
     total = 0
-    for handler in handlers:
+    for handler in gdb._filter_missing_file_handlers(handlers, handler_type):
         if name_re.match(handler.name) and handler.enabled != flag:
             handler.enabled = flag
             total += 1
     return total
 
 
-def do_enable_handler(arg, flag):
-    """Enable or disable missing debug handlers."""
-    (locus_re, name_re) = parse_missing_debug_command_args(arg)
+def do_enable_handler(arg, flag, handler_type):
+    """Enable or disable missing file handlers."""
+
+    (locus_re, name_re) = parse_missing_file_command_args(arg)
     total = 0
     if locus_re.match("global"):
-        total += do_enable_handler1(gdb.missing_debug_handlers, name_re, flag)
+        total += do_enable_handler1(
+            gdb.missing_file_handlers, name_re, flag, handler_type
+        )
     if locus_re.match("progspace") and locus_re.pattern != "":
         total += do_enable_handler1(
-            gdb.current_progspace().missing_debug_handlers, name_re, flag
+            gdb.current_progspace().missing_file_handlers, name_re, flag, handler_type
         )
     for progspace in gdb.progspaces():
         filename = progspace.filename or ""
         if locus_re.match(filename):
-            total += do_enable_handler1(progspace.missing_debug_handlers, name_re, flag)
+            total += do_enable_handler1(
+                progspace.missing_file_handlers, name_re, flag, handler_type
+            )
     print(
-        "%d missing debug handler%s %s"
-        % (total, "" if total == 1 else "s", "enabled" if flag else "disabled")
+        "%d missing %s handler%s %s"
+        % (
+            total,
+            handler_type,
+            "" if total == 1 else "s",
+            "enabled" if flag else "disabled",
+        )
     )
 
 
-class EnableMissingDebugHandler(gdb.Command):
-    """GDB command to enable missing debug handlers.
+class EnableMissingFileHandler(gdb.Command):
+    """GDB command to enable missing HTYPE handlers.
 
-    Usage: enable missing-debug-handler [LOCUS-REGEXP [NAME-REGEXP]]
+    Usage: enable missing-HTYPE-handler [LOCUS-REGEXP [NAME-REGEXP]]
 
     LOCUS-REGEXP is a regular expression specifying the handlers to
     enable.  It can be 'global', 'progspace' for the current
@@ -187,18 +211,26 @@ class EnableMissingDebugHandler(gdb.Command):
     in the locus are affected.
     """
 
-    def __init__(self):
-        super().__init__("enable missing-debug-handler", gdb.COMMAND_FILES)
+    def __init__(self, handler_type):
+        # Update the doc string before calling the parent constructor,
+        # replacing the string 'HTYPE' with the value of HANDLER_TYPE.
+        # The parent constructor will grab a copy of this string to
+        # use as the commands help text.
+        self.__doc__ = self.__doc__.replace("HTYPE", handler_type)
+        super().__init__(
+            "enable missing-" + handler_type + "-handler", gdb.COMMAND_FILES
+        )
+        self.handler_type = handler_type
 
     def invoke(self, arg, from_tty):
         """GDB calls this to perform the command."""
-        do_enable_handler(arg, True)
+        do_enable_handler(arg, True, self.handler_type)
 
 
-class DisableMissingDebugHandler(gdb.Command):
-    """GDB command to disable missing debug handlers.
+class DisableMissingFileHandler(gdb.Command):
+    """GDB command to disable missing HTYPE handlers.
 
-    Usage: disable missing-debug-handler [LOCUS-REGEXP [NAME-REGEXP]]
+    Usage: disable missing-HTYPE-handler [LOCUS-REGEXP [NAME-REGEXP]]
 
     LOCUS-REGEXP is a regular expression specifying the handlers to
     enable.  It can be 'global', 'progspace' for the current
@@ -209,19 +241,28 @@ class DisableMissingDebugHandler(gdb.Command):
     in the locus are affected.
     """
 
-    def __init__(self):
-        super().__init__("disable missing-debug-handler", gdb.COMMAND_FILES)
+    def __init__(self, handler_type):
+        # Update the doc string before calling the parent constructor,
+        # replacing the string 'HTYPE' with the value of HANDLER_TYPE.
+        # The parent constructor will grab a copy of this string to
+        # use as the commands help text.
+        self.__doc__ = self.__doc__.replace("HTYPE", handler_type)
+        super().__init__(
+            "disable missing-" + handler_type + "-handler", gdb.COMMAND_FILES
+        )
+        self.handler_type = handler_type
 
     def invoke(self, arg, from_tty):
         """GDB calls this to perform the command."""
-        do_enable_handler(arg, False)
+        do_enable_handler(arg, False, self.handler_type)
 
 
-def register_missing_debug_handler_commands():
-    """Installs the missing debug handler commands."""
-    InfoMissingDebugHanders()
-    EnableMissingDebugHandler()
-    DisableMissingDebugHandler()
+def register_missing_file_handler_commands():
+    """Installs the missing file handler commands."""
+    for handler_type in ["debug", "objfile"]:
+        InfoMissingFileHandlers(handler_type)
+        EnableMissingFileHandler(handler_type)
+        DisableMissingFileHandler(handler_type)
 
 
-register_missing_debug_handler_commands()
+register_missing_file_handler_commands()
diff --git a/gdb/python/lib/gdb/missing_debug.py b/gdb/python/lib/gdb/missing_debug.py
index 7ccc4fe..2c2ceba 100644
--- a/gdb/python/lib/gdb/missing_debug.py
+++ b/gdb/python/lib/gdb/missing_debug.py
@@ -17,72 +17,11 @@
 MissingDebugHandler base class, and register_handler function.
 """
 
-import sys
-
 import gdb
+from gdb.missing_files import MissingFileHandler
 
-if sys.version_info >= (3, 7):
-    # Functions str.isascii() and str.isalnum are available starting Python
-    # 3.7.
-    def isascii(ch):
-        return ch.isascii()
-
-    def isalnum(ch):
-        return ch.isalnum()
-
-else:
-    # Older version of Python doesn't have str.isascii() and
-    # str.isalnum() so provide our own.
-    #
-    # We could import isalnum() and isascii() from the curses library,
-    # but that adds an extra dependency.  Given these functions are
-    # both small and trivial lets implement them here.
-    #
-    # These definitions are based on those in the curses library, but
-    # simplified as we know C will always be a single character 'str'.
-
-    def isdigit(c):
-        return 48 <= ord(c) <= 57
-
-    def islower(c):
-        return 97 <= ord(c) <= 122
-
-    def isupper(c):
-        return 65 <= ord(c) <= 90
-
-    def isalpha(c):
-        return isupper(c) or islower(c)
-
-    def isalnum(c):
-        return isalpha(c) or isdigit(c)
-
-    def isascii(c):
-        return 0 <= ord(c) <= 127
 
-
-def _validate_name(name):
-    """Validate a missing debug handler name string.
-
-    If name is valid as a missing debug handler name, then this
-    function does nothing.  If name is not valid then an exception is
-    raised.
-
-    Arguments:
-        name: A string, the name of a missing debug handler.
-
-    Returns:
-        Nothing.
-
-    Raises:
-        ValueError: If name is invalid as a missing debug handler
-                    name.
-    """
-    for ch in name:
-        if not isascii(ch) or not (isalnum(ch) or ch in "_-"):
-            raise ValueError("invalid character '%s' in handler name: %s" % (ch, name))
-
-
-class MissingDebugHandler(object):
+class MissingDebugHandler(MissingFileHandler):
     """Base class for missing debug handlers written in Python.
 
     A missing debug handler has a single method __call__ along with
@@ -93,41 +32,8 @@ class MissingDebugHandler(object):
         enabled: When true this handler is enabled.
     """
 
-    def __init__(self, name):
-        """Constructor.
-
-        Args:
-            name: An identifying name for this handler.
-
-        Raises:
-            TypeError: name is not a string.
-            ValueError: name contains invalid characters.
-        """
-
-        if not isinstance(name, str):
-            raise TypeError("incorrect type for name: %s" % type(name))
-
-        _validate_name(name)
-
-        self._name = name
-        self._enabled = True
-
-    @property
-    def name(self):
-        return self._name
-
-    @property
-    def enabled(self):
-        return self._enabled
-
-    @enabled.setter
-    def enabled(self, value):
-        if not isinstance(value, bool):
-            raise TypeError("incorrect type for enabled attribute: %s" % type(value))
-        self._enabled = value
-
     def __call__(self, objfile):
-        """GDB handle missing debug information for an objfile.
+        """Handle missing debug information for an objfile.
 
         Arguments:
             objfile: A gdb.Objfile for which GDB could not find any
@@ -148,62 +54,5 @@ class MissingDebugHandler(object):
 
 
 def register_handler(locus, handler, replace=False):
-    """Register handler in given locus.
-
-    The handler is prepended to the locus's missing debug handlers
-    list. The name of handler should be unique (or replace must be
-    True).
-
-    Arguments:
-        locus: Either a progspace, or None (in which case the unwinder
-               is registered globally).
-        handler: An object of a gdb.MissingDebugHandler subclass.
-
-        replace: If True, replaces existing handler with the same name
-                 within locus.  Otherwise, raises RuntimeException if
-                 unwinder with the same name already exists.
-
-    Returns:
-        Nothing.
-
-    Raises:
-        RuntimeError: The name of handler is not unique.
-        TypeError: Bad locus type.
-        AttributeError: Required attributes of handler are missing.
-    """
-
-    if locus is None:
-        if gdb.parameter("verbose"):
-            gdb.write("Registering global %s handler ...\n" % handler.name)
-        locus = gdb
-    elif isinstance(locus, gdb.Progspace):
-        if gdb.parameter("verbose"):
-            gdb.write(
-                "Registering %s handler for %s ...\n" % (handler.name, locus.filename)
-            )
-    else:
-        raise TypeError("locus should be gdb.Progspace or None")
-
-    # Some sanity checks on HANDLER.  Calling getattr will raise an
-    # exception if the attribute doesn't exist, which is what we want.
-    # These checks are not exhaustive; we don't check the attributes
-    # have the correct types, or the method has the correct signature,
-    # but this should catch some basic mistakes.
-    getattr(handler, "name")
-    getattr(handler, "enabled")
-    call_method = getattr(handler, "__call__")
-    if not callable(call_method):
-        raise AttributeError(
-            "'%s' object's '__call__' attribute is not callable"
-            % type(handler).__name__
-        )
-
-    i = 0
-    for needle in locus.missing_debug_handlers:
-        if needle.name == handler.name:
-            if replace:
-                del locus.missing_debug_handlers[i]
-            else:
-                raise RuntimeError("Handler %s already exists." % handler.name)
-        i += 1
-    locus.missing_debug_handlers.insert(0, handler)
+    """See gdb.missing_files.register_handler."""
+    gdb.missing_files.register_handler("debug", locus, handler, replace)
diff --git a/gdb/python/lib/gdb/missing_files.py b/gdb/python/lib/gdb/missing_files.py
new file mode 100644
index 0000000..5f2df88c
--- /dev/null
+++ b/gdb/python/lib/gdb/missing_files.py
@@ -0,0 +1,204 @@
+# Copyright (C) 2023-2024 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program 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 General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+"""
+MissingFileHandler base class, and support functions used by the
+missing_debug.py and missing_objfile.py modules.
+"""
+
+import sys
+
+import gdb
+
+if sys.version_info >= (3, 7):
+    # Functions str.isascii() and str.isalnum are available starting Python
+    # 3.7.
+    def isascii(ch):
+        return ch.isascii()
+
+    def isalnum(ch):
+        return ch.isalnum()
+
+else:
+    # Older version of Python doesn't have str.isascii() and
+    # str.isalnum() so provide our own.
+    #
+    # We could import isalnum() and isascii() from the curses library,
+    # but that adds an extra dependency.  Given these functions are
+    # both small and trivial lets implement them here.
+    #
+    # These definitions are based on those in the curses library, but
+    # simplified as we know C will always be a single character 'str'.
+
+    def isdigit(c):
+        return 48 <= ord(c) <= 57
+
+    def islower(c):
+        return 97 <= ord(c) <= 122
+
+    def isupper(c):
+        return 65 <= ord(c) <= 90
+
+    def isalpha(c):
+        return isupper(c) or islower(c)
+
+    def isalnum(c):
+        return isalpha(c) or isdigit(c)
+
+    def isascii(c):
+        return 0 <= ord(c) <= 127
+
+
+def _validate_name(name):
+    """Validate a missing file handler name string.
+
+    If name is valid as a missing file handler name, then this
+    function does nothing.  If name is not valid then an exception is
+    raised.
+
+    Arguments:
+        name: A string, the name of a missing file handler.
+
+    Returns:
+        Nothing.
+
+    Raises:
+        ValueError: If name is invalid as a missing file handler
+                    name.
+    """
+
+    for ch in name:
+        if not isascii(ch) or not (isalnum(ch) or ch in "_-"):
+            raise ValueError("invalid character '%s' in handler name: %s" % (ch, name))
+
+
+class MissingFileHandler(object):
+    """Base class for missing file handlers written in Python.
+
+    A missing file handler has a single method __call__ along with the
+    read/write attribute enabled, and a read-only attribute name.  The
+    attributes are provided by this class while the __call__ method is
+    provided by a sub-class.  Each sub-classes __call__ method will
+    have a different signature.
+
+    Attributes:
+        name: Read-only attribute, the name of this handler.
+        enabled: When true this handler is enabled.
+    """
+
+    def __init__(self, name):
+        """Constructor.
+
+        Args:
+            name: An identifying name for this handler.
+
+        Raises:
+            TypeError: name is not a string.
+            ValueError: name contains invalid characters.
+        """
+
+        if not isinstance(name, str):
+            raise TypeError("incorrect type for name: %s" % type(name))
+
+        _validate_name(name)
+
+        self._name = name
+        self._enabled = True
+
+    @property
+    def name(self):
+        return self._name
+
+    @property
+    def enabled(self):
+        return self._enabled
+
+    @enabled.setter
+    def enabled(self, value):
+        if not isinstance(value, bool):
+            raise TypeError("incorrect type for enabled attribute: %s" % type(value))
+        self._enabled = value
+
+
+def register_handler(handler_type, locus, handler, replace=False):
+    """Register handler in given locus.
+
+    The handler is prepended to the locus's missing file handlers
+    list. The name of handler should be unique (or replace must be
+    True), and the name must pass the _validate_name check.
+
+    Arguments:
+        handler_type: A string, either 'debug' or 'objfile' indicating the
+            type of handler to be registered.
+        locus: Either a progspace, or None (in which case the unwinder
+               is registered globally).
+        handler: An object used as a missing file handler.  Usually a
+            sub-class of MissingFileHandler.
+        replace: If True, replaces existing handler with the same name
+                 within locus.  Otherwise, raises RuntimeException if
+                 unwinder with the same name already exists.
+
+    Returns:
+        Nothing.
+
+    Raises:
+        RuntimeError: The name of handler is not unique.
+        TypeError: Bad locus type.
+        AttributeError: Required attributes of handler are missing.
+        ValueError: If the name of the handler is invalid, or if
+            handler_type is neither 'debug' or 'objfile'.
+    """
+
+    if handler_type != "debug" and handler_type != "objfile":
+        raise ValueError("handler_type must be 'debug' or 'objfile'")
+
+    if locus is None:
+        if gdb.parameter("verbose"):
+            gdb.write("Registering global %s handler ...\n" % handler.name)
+        locus = gdb
+    elif isinstance(locus, gdb.Progspace):
+        if gdb.parameter("verbose"):
+            gdb.write(
+                "Registering %s handler for %s ...\n" % (handler.name, locus.filename)
+            )
+    else:
+        raise TypeError("locus should be gdb.Progspace or None")
+
+    # Some sanity checks on HANDLER.  Calling getattr will raise an
+    # exception if the attribute doesn't exist, which is what we want.
+    # These checks are not exhaustive; we don't check the attributes
+    # have the correct types, or the method has the correct signature,
+    # but this should catch some basic mistakes.
+    name = getattr(handler, "name")
+    _validate_name(name)
+
+    getattr(handler, "enabled")
+
+    call_method = getattr(handler, "__call__")
+    if not callable(call_method):
+        raise AttributeError(
+            "'%s' object's '__call__' attribute is not callable"
+            % type(handler).__name__
+        )
+
+    i = 0
+    for needle in locus.missing_file_handlers:
+        if needle[0] == handler_type and needle[1].name == handler.name:
+            if replace:
+                del locus.missing_file_handlers[i]
+            else:
+                raise RuntimeError("Handler %s already exists." % handler.name)
+        i += 1
+    locus.missing_file_handlers.insert(0, (handler_type, handler))
diff --git a/gdb/python/lib/gdb/missing_objfile.py b/gdb/python/lib/gdb/missing_objfile.py
new file mode 100644
index 0000000..ace0e13
--- /dev/null
+++ b/gdb/python/lib/gdb/missing_objfile.py
@@ -0,0 +1,67 @@
+# Copyright (C) 2024 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program 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 General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+"""
+MissingObjfileHandler base class, and register_handler function.
+"""
+
+import gdb
+from gdb.missing_files import MissingFileHandler
+
+
+class MissingObjfileHandler(MissingFileHandler):
+    """Base class for missing objfile handlers written in Python.
+
+    A missing objfile handler has a single method __call__ along with
+    the read/write attribute enabled, and a read-only attribute name.
+
+    Attributes:
+        name: Read-only attribute, the name of this handler.
+        enabled: When true this handler is enabled.
+    """
+
+    def __call__(self, buildid, filename):
+        """Handle a missing objfile when GDB can knows the build-id.
+
+        Arguments:
+
+            buildid: A string containing the build-id for the objfile
+                GDB is searching for.
+            filename: A string containing the name of the file GDB is
+                searching for.  This is provided only for the purpose
+                of creating diagnostic messages.  If the file is found
+                it does not have to be placed here, and this file
+                might already exist but GDB has determined it is not
+                suitable for use, e.g. if the build-id doesn't match.
+
+        Returns:
+
+            True: GDB should try again to locate the missing objfile,
+                the handler may have installed the missing file.
+            False: GDB should move on without the objfile.  The
+                handler has determined that this objfile is not
+                available.
+            A string: GDB should load the file at the given path; it
+                contains the requested objfile.
+            None: This handler can't help with this objfile.  GDB
+                should try any other registered handlers.
+
+        """
+        raise NotImplementedError("MissingObjfileHandler.__call__()")
+
+
+def register_handler(locus, handler, replace=False):
+    """See gdb.missing_files.register_handler."""
+    gdb.missing_files.register_handler("objfile", locus, handler, replace)
diff --git a/gdb/python/py-progspace.c b/gdb/python/py-progspace.c
index aa1e713..bb44aa4 100644
--- a/gdb/python/py-progspace.c
+++ b/gdb/python/py-progspace.c
@@ -55,8 +55,8 @@ struct pspace_object
   /* The debug method list.  */
   PyObject *xmethods;
 
-  /* The missing debug handler list.  */
-  PyObject *missing_debug_handlers;
+  /* The missing file handler list.  */
+  PyObject *missing_file_handlers;
 };
 
 extern PyTypeObject pspace_object_type
@@ -166,7 +166,7 @@ pspy_dealloc (PyObject *self)
   Py_XDECREF (ps_self->frame_unwinders);
   Py_XDECREF (ps_self->type_printers);
   Py_XDECREF (ps_self->xmethods);
-  Py_XDECREF (ps_self->missing_debug_handlers);
+  Py_XDECREF (ps_self->missing_file_handlers);
   Py_TYPE (self)->tp_free (self);
 }
 
@@ -202,8 +202,8 @@ pspy_initialize (pspace_object *self)
   if (self->xmethods == NULL)
     return 0;
 
-  self->missing_debug_handlers = PyList_New (0);
-  if (self->missing_debug_handlers == nullptr)
+  self->missing_file_handlers = PyList_New (0);
+  if (self->missing_file_handlers == nullptr)
     return 0;
 
   return 1;
@@ -349,18 +349,18 @@ pspy_get_xmethods (PyObject *o, void *ignore)
 /* Return the list of missing debug handlers for this program space.  */
 
 static PyObject *
-pspy_get_missing_debug_handlers (PyObject *o, void *ignore)
+pspy_get_missing_file_handlers (PyObject *o, void *ignore)
 {
   pspace_object *self = (pspace_object *) o;
 
-  Py_INCREF (self->missing_debug_handlers);
-  return self->missing_debug_handlers;
+  Py_INCREF (self->missing_file_handlers);
+  return self->missing_file_handlers;
 }
 
 /* Set this program space's list of missing debug handlers to HANDLERS.  */
 
 static int
-pspy_set_missing_debug_handlers (PyObject *o, PyObject *handlers,
+pspy_set_missing_file_handlers (PyObject *o, PyObject *handlers,
 				 void *ignore)
 {
   pspace_object *self = (pspace_object *) o;
@@ -380,9 +380,9 @@ pspy_set_missing_debug_handlers (PyObject *o, PyObject *handlers,
     }
 
   /* Take care in case the LHS and RHS are related somehow.  */
-  gdbpy_ref<> tmp (self->missing_debug_handlers);
+  gdbpy_ref<> tmp (self->missing_file_handlers);
   Py_INCREF (handlers);
-  self->missing_debug_handlers = handlers;
+  self->missing_file_handlers = handlers;
 
   return 0;
 }
@@ -778,8 +778,8 @@ static gdb_PyGetSetDef pspace_getset[] =
     "Type printers.", NULL },
   { "xmethods", pspy_get_xmethods, NULL,
     "Debug methods.", NULL },
-  { "missing_debug_handlers", pspy_get_missing_debug_handlers,
-    pspy_set_missing_debug_handlers, "Missing debug handlers.", NULL },
+  { "missing_file_handlers", pspy_get_missing_file_handlers,
+    pspy_set_missing_file_handlers, "Missing file handlers.", NULL },
   { NULL }
 };
 
diff --git a/gdb/python/python.c b/gdb/python/python.c
index cceb7aa..b0de48d 100644
--- a/gdb/python/python.c
+++ b/gdb/python/python.c
@@ -35,6 +35,7 @@
 #include "location.h"
 #include "run-on-main-thread.h"
 #include "observable.h"
+#include "build-id.h"
 
 #if GDB_SELF_TEST
 #include "gdbsupport/selftest.h"
@@ -130,6 +131,9 @@ static std::optional<std::string> gdbpy_colorize_disasm
 (const std::string &content, gdbarch *gdbarch);
 static ext_lang_missing_file_result gdbpy_handle_missing_debuginfo
   (const struct extension_language_defn *extlang, struct objfile *objfile);
+static ext_lang_missing_file_result gdbpy_find_objfile_from_buildid
+  (const struct extension_language_defn *extlang, program_space *pspace,
+   const struct bfd_build_id *build_id, const char *missing_filename);
 
 /* The interface between gdb proper and loading of python scripts.  */
 
@@ -179,7 +183,8 @@ static const struct extension_language_ops python_extension_ops =
 
   gdbpy_print_insn,
 
-  gdbpy_handle_missing_debuginfo
+  gdbpy_handle_missing_debuginfo,
+  gdbpy_find_objfile_from_buildid
 };
 
 #endif /* HAVE_PYTHON */
@@ -1829,6 +1834,107 @@ gdbpy_handle_missing_debuginfo (const struct extension_language_defn *extlang,
   return ext_lang_missing_file_result (std::string (filename.get ()));
 }
 
+/* Implement the find_objfile_from_buildid hook for Python.  PSPACE is the
+   program space in which GDB is trying to find an objfile, BUILD_ID is the
+   build-id for the missing objfile, and EXPECTED_FILENAME is a non-NULL
+   string which can be used (if needed) in messages to the user, and
+   represents the file GDB is looking for.  */
+
+static ext_lang_missing_file_result
+gdbpy_find_objfile_from_buildid (const struct extension_language_defn *extlang,
+				 program_space *pspace,
+				 const struct bfd_build_id *build_id,
+				 const char *missing_filename)
+{
+  gdb_assert (pspace != nullptr);
+  gdb_assert (build_id != nullptr);
+  gdb_assert (missing_filename != nullptr);
+
+  /* Early exit if Python is not initialised.  */
+  if (!gdb_python_initialized || gdb_python_module == nullptr)
+    return {};
+
+  gdbpy_enter enter_py;
+
+  /* Convert BUILD_ID into a Python object.  */
+  std::string hex_form = bin2hex (build_id->data, build_id->size);
+  gdbpy_ref<> pyo_buildid = host_string_to_python_string (hex_form.c_str ());
+  if (pyo_buildid == nullptr)
+    {
+      gdbpy_print_stack ();
+      return {};
+    }
+
+  /* Convert MISSING_FILENAME to a Python object.  */
+  gdbpy_ref<> pyo_filename = host_string_to_python_string (missing_filename);
+  if (pyo_filename == nullptr)
+    {
+      gdbpy_print_stack ();
+      return {};
+    }
+
+  /* Convert PSPACE to a Python object.  */
+  gdbpy_ref<> pyo_pspace = pspace_to_pspace_object (pspace);
+  if (pyo_pspace == nullptr)
+    {
+      gdbpy_print_stack ();
+      return {};
+    }
+
+  /* Lookup the helper function within the GDB module.  */
+  gdbpy_ref<> pyo_handler
+    (PyObject_GetAttrString (gdb_python_module, "_handle_missing_objfile"));
+  if (pyo_handler == nullptr)
+    {
+      gdbpy_print_stack ();
+      return {};
+    }
+
+  /* Call the function, passing in the Python objfile object.  */
+  gdbpy_ref<> pyo_execute_ret
+    (PyObject_CallFunctionObjArgs (pyo_handler.get (), pyo_pspace.get (),
+				   pyo_buildid.get (), pyo_filename.get (),
+				   nullptr));
+  if (pyo_execute_ret == nullptr)
+    {
+      /* If the handler is cancelled due to a Ctrl-C, then propagate
+	 the Ctrl-C as a GDB exception instead of swallowing it.  */
+      gdbpy_print_stack_or_quit ();
+      return {};
+    }
+
+  /* Parse the result, and convert it back to the C++ object.  */
+  if (pyo_execute_ret == Py_None)
+    return {};
+
+  if (PyBool_Check (pyo_execute_ret.get ()))
+    {
+      /* We know the value is a bool, so it must be either Py_True or
+	 Py_False.  Anything else would not get past the above check.  */
+      bool try_again = pyo_execute_ret.get () == Py_True;
+      return ext_lang_missing_file_result (try_again);
+    }
+
+  if (!gdbpy_is_string (pyo_execute_ret.get ()))
+    {
+      PyErr_SetString (PyExc_ValueError,
+		       "return value from _find_objfile_by_buildid should "
+		       "be None, a bool, or a str");
+      gdbpy_print_stack ();
+      return {};
+    }
+
+  gdb::unique_xmalloc_ptr<char> filename
+    = python_string_to_host_string (pyo_execute_ret.get ());
+  if (filename == nullptr)
+    {
+      gdbpy_print_stack ();
+      return {};
+    }
+
+  return ext_lang_missing_file_result (std::string (filename.get ()));
+}
+
 /* Compute the list of active python type printers and store them in
    EXT_PRINTERS->py_type_printers.  The product of this function is used by
    gdbpy_apply_type_printers, and freed by gdbpy_free_type_printers.