From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by sourceware.org (Postfix) with ESMTPS id B095B384189E for ; Mon, 6 Jun 2022 12:46:57 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org B095B384189E Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-169-T6WLrrwANYeAQym0ZhUcBg-1; Mon, 06 Jun 2022 08:46:56 -0400 X-MC-Unique: T6WLrrwANYeAQym0ZhUcBg-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id EB86B80159B for ; Mon, 6 Jun 2022 12:46:55 +0000 (UTC) Received: from [10.97.116.36] (ovpn-116-36.gru2.redhat.com [10.97.116.36]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 4B6C92166B26 for ; Mon, 6 Jun 2022 12:46:55 +0000 (UTC) Message-ID: <4b921470-0dcd-de1e-9aa2-e1b9d5032878@redhat.com> Date: Mon, 6 Jun 2022 09:46:53 -0300 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.9.1 Subject: [PINGv4] [PATCH v2] gdb/stack.c: avoid stale pointers when printing frame arguments From: Bruno Larsen To: "gdb-patches@sourceware.org" References: <20220504191036.143360-1-blarsen@redhat.com> <75aa2fe2-9ed0-83ed-e1de-4b814849707a@redhat.com> <9e7e6dbc-4f66-7366-1e82-ec6a0fef597e@redhat.com> In-Reply-To: <9e7e6dbc-4f66-7366-1e82-ec6a0fef597e@redhat.com> X-Scanned-By: MIMEDefang 2.78 on 10.11.54.6 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Spam-Status: No, score=-11.2 required=5.0 tests=BAYES_00, BODY_8BITS, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, GIT_PATCH_0, KAM_SHORT, RCVD_IN_DNSWL_NONE, SPF_HELO_NONE, SPF_NONE, TXREP, T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org X-BeenThere: gdb-patches@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gdb-patches mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 06 Jun 2022 12:47:00 -0000 ping! Cheers! Bruno Larsen On 5/30/22 08:16, Bruno Larsen wrote: > ping > > Cheers! > Bruno Larsen > > On 5/24/22 08:25, Bruno Larsen wrote: >> ping >> >> Cheers! >> Bruno Larsen >> >> On 5/18/22 08:24, Bruno Larsen wrote: >>> ping >>> >>> Cheers! >>> Bruno Larsen >>> >>> On 5/4/22 16:10, Bruno Larsen wrote: >>>> When a pretty printer calls an inferior function by hand, the whole >>>> framestack cache has to be rebuilt for that function call. However, if >>>> this pretty printer is called when printing the arguments of a frame, >>>> there are many instances where frame_info pointers were kept and end up >>>> stale, or used after free. This could snowball into an infinite >>>> recursion and GDB crash. The problem was documented as PR python/28856. >>>> >>>> To fix this problem, we must ensure that the frame cache is up to date >>>> after printing any arguments, so we cache the frame_id of the pointer >>>> that will become stale, and reset that pointer using frame_find_by_id. >>>> >>>> This commit also adds a testcase that exercises this codepath with 7 >>>> different triggers, run, continue, step, backtrace, finish, up and down. >>>> Some of them can seem to be testing the same thing twice, but since this >>>> test relies on stale pointers, there is always a chance that GDB got lucky >>>> when testing, so better to test extra. >>>> >>>> Regression tested on x86_64, using both gcc and clang. >>>> >>>> --- >>>> Changelog: >>>> v2: >>>>   * Addressed Tom Tromey's and Andrew's comments >>>>   * Added the testcase to this patch >>>>   * Slightly changed "finish" test, to deal better with clang >>>> >>>> --- >>>>   gdb/infcall.c                                 |  13 +- >>>>   gdb/infcmd.c                                  |   5 + >>>>   gdb/mi/mi-cmd-stack.c                         |   6 + >>>>   gdb/stack.c                                   |  31 +++- >>>>   .../gdb.python/pretty-print-call-by-hand.c    |  53 +++++++ >>>>   .../gdb.python/pretty-print-call-by-hand.exp  | 136 ++++++++++++++++++ >>>>   .../gdb.python/pretty-print-call-by-hand.py   |  41 ++++++ >>>>   7 files changed, 280 insertions(+), 5 deletions(-) >>>>   create mode 100644 gdb/testsuite/gdb.python/pretty-print-call-by-hand.c >>>>   create mode 100644 gdb/testsuite/gdb.python/pretty-print-call-by-hand.exp >>>>   create mode 100644 gdb/testsuite/gdb.python/pretty-print-call-by-hand.py >>>> >>>> diff --git a/gdb/infcall.c b/gdb/infcall.c >>>> index 5365f97049c..ad31a910da5 100644 >>>> --- a/gdb/infcall.c >>>> +++ b/gdb/infcall.c >>>> @@ -738,8 +738,17 @@ call_function_by_hand (struct value *function, >>>>                  type *default_return_type, >>>>                  gdb::array_view args) >>>>   { >>>> -  return call_function_by_hand_dummy (function, default_return_type, >>>> -                      args, NULL, NULL); >>>> +  scoped_restore_selected_frame restore_frame; >>>> +  struct value *ret = call_function_by_hand_dummy (function, >>>> +                           default_return_type, >>>> +                           args, NULL, NULL); >>>> +  /* Ensure that the frame cache does not contain any frames that were >>>> +     specific to the handmade function call.  If something is leftover >>>> +     while GDB has kept a reference to a frame (for instance, when a >>>> +     stacktrace is being printed and a pretty printed called an inferior >>>> +     function), GDB could crash.  */ >>>> +  reinit_frame_cache (); >>>> +  return ret; >>>>   } >>>>   /* All this stuff with a dummy frame may seem unnecessarily complicated >>>> diff --git a/gdb/infcmd.c b/gdb/infcmd.c >>>> index e909d4d4c81..380d5f0201b 100644 >>>> --- a/gdb/infcmd.c >>>> +++ b/gdb/infcmd.c >>>> @@ -1853,6 +1853,7 @@ finish_command (const char *arg, int from_tty) >>>>        source.  */ >>>>     if (from_tty) >>>>       { >>>> +      struct frame_id id = get_frame_id (get_selected_frame (NULL)); >>>>         if (execution_direction == EXEC_REVERSE) >>>>       gdb_printf (_("Run back to call of ")); >>>>         else >>>> @@ -1866,6 +1867,10 @@ finish_command (const char *arg, int from_tty) >>>>       } >>>>         print_stack_frame (get_selected_frame (NULL), 1, LOCATION, 0); >>>> +      frame = frame_find_by_id (id); >>>> +      if (frame == nullptr) >>>> +      error (_("frames disappeared mid-printing.")); >>>> +      frame = get_prev_frame (frame); >>>>       } >>>>     if (execution_direction == EXEC_REVERSE) >>>> diff --git a/gdb/mi/mi-cmd-stack.c b/gdb/mi/mi-cmd-stack.c >>>> index 0fe204dbc66..51c6573e9be 100644 >>>> --- a/gdb/mi/mi-cmd-stack.c >>>> +++ b/gdb/mi/mi-cmd-stack.c >>>> @@ -176,10 +176,16 @@ mi_cmd_stack_list_frames (const char *command, char **argv, int argc) >>>>          i++, fi = get_prev_frame (fi)) >>>>       { >>>>         QUIT; >>>> +      /* We get the frame ID here because getting it in the for line >>>> +         could result in getting the previous's frame ID instead.  */ >>>> +      struct frame_id fid = get_frame_id (fi); >>>>         /* Print the location and the address always, even for level 0. >>>>            If args is 0, don't print the arguments.  */ >>>>         print_frame_info (user_frame_print_options, >>>>                   fi, 1, LOC_AND_ADDRESS, 0 /* args */, 0); >>>> +      fi = frame_find_by_id (fid); >>>> +      if (fi == nullptr) >>>> +        error (_("frames disappeared mid-printing.")); >>>>       } >>>>       } >>>>   } >>>> diff --git a/gdb/stack.c b/gdb/stack.c >>>> index 71d85985d18..52fc8af3cb9 100644 >>>> --- a/gdb/stack.c >>>> +++ b/gdb/stack.c >>>> @@ -364,11 +364,19 @@ print_stack_frame (struct frame_info *frame, int print_level, >>>>     try >>>>       { >>>> +      /* print_frame_info may invalidate FRAME. >>>> +         It's better to use frame_id if we want to set the current sal.  */ >>>> +      struct frame_id fid = get_frame_id (frame); >>>>         print_frame_info (user_frame_print_options, >>>>               frame, print_level, print_what, 1 /* print_args */, >>>>               set_current_sal); >>>>         if (set_current_sal) >>>> -    set_current_sal_from_frame (frame); >>>> +        { >>>> +      frame = frame_find_by_id (fid); >>>> +      if (frame == nullptr) >>>> +          error (_("frames disappeared mid-printing.")); >>>> +      set_current_sal_from_frame (frame); >>>> +    } >>>>       } >>>>     catch (const gdb_exception_error &e) >>>>       { >>>> @@ -742,6 +750,8 @@ print_frame_args (const frame_print_options &fp_opts, >>>>       = (print_names >>>>          && fp_opts.print_frame_arguments != print_frame_arguments_none); >>>> +  struct frame_id printed_frame = get_frame_id (frame); >>>> + >>>>     /* Temporarily change the selected frame to the given FRAME. >>>>        This allows routines that rely on the selected frame instead >>>>        of being given a frame as parameter to use the correct frame.  */ >>>> @@ -902,6 +912,9 @@ print_frame_args (const frame_print_options &fp_opts, >>>>           } >>>>         first = 0; >>>> +      frame = frame_find_by_id (printed_frame); >>>> +      if (frame == nullptr) >>>> +        error (_("frames disappeared mid-printing.")); >>>>       } >>>>       } >>>> @@ -1109,12 +1122,21 @@ print_frame_info (const frame_print_options &fp_opts, >>>>        to get the line containing FRAME->pc.  */ >>>>     symtab_and_line sal = find_frame_sal (frame); >>>> +  /* print_frame can invalidate frame, so cache the frame_id to rebuild >>>> +     the whole stack later, if needed.  */ >>>> +  struct frame_id frame_id = get_frame_id (frame); >>>> + >>>>     location_print = (print_what == LOCATION >>>>               || print_what == SRC_AND_LOC >>>>               || print_what == LOC_AND_ADDRESS >>>>               || print_what == SHORT_LOCATION); >>>>     if (location_print || !sal.symtab) >>>> -    print_frame (fp_opts, frame, print_level, print_what, print_args, sal); >>>> +    { >>>> +      print_frame (fp_opts, frame, print_level, print_what, print_args, sal); >>>> +      frame = frame_find_by_id (frame_id); >>>> +      if (frame == nullptr) >>>> +      error (_("frames disappeared mid-printing.")); >>>> +    } >>>>     source_print = (print_what == SRC_LINE || print_what == SRC_AND_LOC); >>>> @@ -2060,6 +2082,7 @@ backtrace_command_1 (const frame_print_options &fp_opts, >>>>         for (fi = trailing; fi && count--; fi = get_prev_frame (fi)) >>>>       { >>>>         QUIT; >>>> +      struct frame_id frame_id = get_frame_id (fi); >>>>         /* Don't use print_stack_frame; if an error() occurs it probably >>>>            means further attempts to backtrace would fail (on the other >>>> @@ -2067,9 +2090,11 @@ backtrace_command_1 (const frame_print_options &fp_opts, >>>>            the frame->prev field gets set to NULL in that case).  */ >>>>         print_frame_info (fp_opts, fi, 1, LOCATION, 1, 0); >>>> +      fi = frame_find_by_id (frame_id); >>>> +      if (fi == nullptr) >>>> +        error (_("frames disappeared mid-printing.")); >>>>         if ((flags & PRINT_LOCALS) != 0) >>>>           { >>>> -          struct frame_id frame_id = get_frame_id (fi); >>>>             print_frame_local_vars (fi, false, NULL, NULL, 1, gdb_stdout); >>>> diff --git a/gdb/testsuite/gdb.python/pretty-print-call-by-hand.c b/gdb/testsuite/gdb.python/pretty-print-call-by-hand.c >>>> new file mode 100644 >>>> index 00000000000..3be5675b096 >>>> --- /dev/null >>>> +++ b/gdb/testsuite/gdb.python/pretty-print-call-by-hand.c >>>> @@ -0,0 +1,53 @@ >>>> +/* This testcase is part of GDB, the GNU debugger. >>>> + >>>> +   Copyright 2022 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  .  */ >>>> + >>>> +struct mytype >>>> +{ >>>> +  char *x; >>>> +}; >>>> + >>>> +void >>>> +rec (int i) >>>> +{ >>>> +  if (i <= 0) >>>> +    return; >>>> +  rec (i-1); >>>> +} >>>> + >>>> +int >>>> +f () >>>> +{ >>>> +  rec (100); >>>> +  return 2; >>>> +} >>>> + >>>> +void >>>> +g (struct mytype mt, int depth) >>>> +{ >>>> +  if (depth <= 0) >>>> +    return; /* TAG: final frame */ >>>> +  g (mt, depth - 1); /* TAG: first frame */ >>>> +} >>>> + >>>> +int >>>> +main () >>>> +{ >>>> +  struct mytype mt; >>>> +  mt.x = "hello world"; >>>> +  g (mt, 10); /* TAG: outside the frame */ >>>> +  return 0; >>>> +} >>>> diff --git a/gdb/testsuite/gdb.python/pretty-print-call-by-hand.exp b/gdb/testsuite/gdb.python/pretty-print-call-by-hand.exp >>>> new file mode 100644 >>>> index 00000000000..0aeb2218f91 >>>> --- /dev/null >>>> +++ b/gdb/testsuite/gdb.python/pretty-print-call-by-hand.exp >>>> @@ -0,0 +1,136 @@ >>>> +# Copyright (C) 2022 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 . >>>> + >>>> +# This file is part of the GDB testsuite.  It tests a pretty printer that >>>> +# calls an inferior function by hand, triggering a Use-after-Free bug >>>> +# (PR gdb/28856). >>>> + >>>> +load_lib gdb-python.exp >>>> + >>>> +standard_testfile >>>> + >>>> +# gdb needs to be started here for skip_python_tests to work. >>>> +# prepare_for_testing could be used instead, but it could compile the program >>>> +# unnecessarily, so starting GDB like this is preferable. >>>> +gdb_start >>>> + >>>> +# Skip all tests if Python scripting is not enabled. >>>> +if { [skip_python_tests] } { continue } >>>> + >>>> +if { [prepare_for_testing "failed to prepare" $testfile $srcfile debug] } { >>>> +    untested "failed to compile" >>>> +    return -1 >>>> +} >>>> + >>>> +# This proc restarts GDB, makes the inferior reach the desired spot - marked >>>> +# by a comment in the .c file - and turns on the pretty printer for testing. >>>> +# Starting with a new GDB is important because the test may crash GDB.  The >>>> +# return values are here to avoid us trying to test the pretty printer if >>>> +# there was a problem getting to main. >>>> +proc start_test { breakpoint_comment } { >>>> +    global srcdir subdir testfile binfile >>>> + >>>> +    # Start with a fresh gdb. >>>> +    # This is important because the test can crash GDB. >>>> + >>>> +    clean_restart ${binfile} >>>> + >>>> +    if { ![runto_main] } then { >>>> +    untested "couldn't run to breakpoint" >>>> +    return -1 >>>> +    } >>>> + >>>> +    # Let GDB get to the return line. >>>> +    gdb_breakpoint [gdb_get_line_number ${breakpoint_comment} ${testfile}.c ] >>>> +    gdb_continue_to_breakpoint ${breakpoint_comment} ".*" >>>> + >>>> +    gdb_test_no_output "set print pretty on" "starting to pretty print" >>>> + >>>> +    set remote_python_file [gdb_remote_download host ${srcdir}/${subdir}/${testfile}.py] >>>> +    gdb_test_no_output "source ${remote_python_file}" "load python file" >>>> + >>>> +    return 0 >>>> +} >>>> + >>>> +# Start by testing the "run" command, it can't leverage start_test >>>> +with_test_prefix "run to frame" { >>>> +    if { ![runto_main] } then { >>>> +    untested "couldn't run to main" >>>> +    } >>>> + >>>> +    gdb_test_no_output "set print pretty on" "starting to pretty print" >>>> + >>>> +    set remote_python_file [gdb_remote_download host ${srcdir}/${subdir}/${testfile}.py] >>>> +    gdb_test_no_output "source ${remote_python_file}" "load python file" >>>> + >>>> +    gdb_breakpoint [gdb_get_line_number "TAG: final frame" ${testfile}.c] >>>> +    gdb_continue_to_breakpoint "TAG: final frame" ".*" >>>> +} >>>> + >>>> +# Testing the backtrace command. >>>> +with_test_prefix "frame print" { >>>> +    if { [start_test "TAG: final frame"] == 0 } { >>>> +    gdb_test "backtrace -frame-arguments all" [multi_line \ >>>> +    "#0 .*g \\(mt=mytype is .*\\, depth=0\\).*"\ >>>> +    "#1 .*g \\(mt=mytype is .*\\, depth=1\\).*"\ >>>> +    "#2 .*g \\(mt=mytype is .*\\, depth=2\\).*"\ >>>> +    "#3 .*g \\(mt=mytype is .*\\, depth=3\\).*"\ >>>> +    "#4 .*g \\(mt=mytype is .*\\, depth=4\\).*"\ >>>> +    "#5 .*g \\(mt=mytype is .*\\, depth=5\\).*"\ >>>> +    "#6 .*g \\(mt=mytype is .*\\, depth=6\\).*"\ >>>> +    "#7 .*g \\(mt=mytype is .*\\, depth=7\\).*"\ >>>> +    "#8 .*g \\(mt=mytype is .*\\, depth=8\\).*"\ >>>> +    "#9 .*g \\(mt=mytype is .*\\, depth=9\\).*"\ >>>> +    "#10 .*g \\(mt=mytype is .*\\, depth=10\\).*"\ >>>> +    "#11 .*main \\(\\).*"] \ >>>> +    "backtrace test" >>>> +    } >>>> +} >>>> +# Testing the down command. >>>> +with_test_prefix "frame movement down" { >>>> +    if { [start_test "TAG: first frame"] == 0 } { >>>> +    gdb_test "up" [multi_line "#1 .*in main \\(\\) at .*" ".*outside the frame.*"] >>>> +    gdb_test "down" [multi_line "#0\\s+g \\(mt=mytype is .*\\, depth=10\\).*" ".*first frame.*"] >>>> +    } >>>> +} >>>> + >>>> +# Testing the up command. >>>> +with_test_prefix "frame movement up" { >>>> +    if { [start_test "TAG: final frame"] == 0 } { >>>> +    gdb_test "up" [multi_line "#1 .*in g \\(mt=mytype is .*\\, depth=1\\).*" ".*first frame.*"] >>>> +    } >>>> +} >>>> + >>>> +# Testing the finish command. >>>> +with_test_prefix "frame exit through finish" { >>>> +    if { [start_test "TAG: final frame"] == 0 } { >>>> +    gdb_test "finish" [multi_line ".*.*g \\(mt=mytype is .*\\, depth=0\\).*" ".*g \\(mt=mytype is .*\\, depth=1\\).*" ".*"] >>>> +    } >>>> +} >>>> + >>>> +# Testing the step command. >>>> +with_test_prefix "frame enter through step" { >>>> +    if { [start_test "TAG: outside the frame"] == 0 } { >>>> +    gdb_test "step" [multi_line "g \\(mt=mytype is .*\\, depth=10\\).*" "41.*if \\(depth \\<= 0\\)"] >>>> +    } >>>> +} >>>> + >>>> +# Testing the continue command. >>>> +with_test_prefix "frame enter through continue" { >>>> +    if { [start_test "TAG: outside the frame"] == 0 } { >>>> +    gdb_breakpoint [gdb_get_line_number "TAG: first frame" ${testfile}.c ] >>>> +    gdb_continue_to_breakpoint "TAG: first frame" ".*TAG: first frame.*" >>>> +    } >>>> +} >>>> diff --git a/gdb/testsuite/gdb.python/pretty-print-call-by-hand.py b/gdb/testsuite/gdb.python/pretty-print-call-by-hand.py >>>> new file mode 100644 >>>> index 00000000000..f8f5df678f8 >>>> --- /dev/null >>>> +++ b/gdb/testsuite/gdb.python/pretty-print-call-by-hand.py >>>> @@ -0,0 +1,41 @@ >>>> +# Copyright (C) 2022 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 . >>>> + >>>> + >>>> +class MytypePrinter: >>>> +    """pretty print my type""" >>>> + >>>> +    def __init__(self, val): >>>> +        self.val = val >>>> + >>>> +    def to_string(self): >>>> +        calls = gdb.parse_and_eval('f()') >>>> +        return "mytype is %s" % self.val['x'] >>>> + >>>> +def ec_lookup_function(val): >>>> +    typ = val.type >>>> +    if typ.code == gdb.TYPE_CODE_REF: >>>> +        typ = typ.target() >>>> +    if str(typ) == 'struct mytype': >>>> +        return MytypePrinter(val) >>>> +    return None >>>> + >>>> +def disable_lookup_function(): >>>> +    ec_lookup_function.enabled = False >>>> + >>>> +def enable_lookup_function(): >>>> +    ec_lookup_function.enabled = True >>>> + >>>> +gdb.pretty_printers.append(ec_lookup_function)