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Backport upstream fix and test case for a dprintf bug (RHBZ 2022177)

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This commit is contained in:
Kevin Buettner 2021-11-10 19:13:29 -07:00
parent 1c15f132e5
commit 8fedf35634
6 changed files with 524 additions and 1 deletions
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6
_gdb.spec.Patch.include
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@ -328,3 +328,9 @@ Patch078: gdb-rhbz2012976-paper-over-fortran-lex-problems.patch
# Backport manpage update
Patch079: gdb-rhbz-853071-update-manpages.patch
# Backport fix for dprintf bug (RH BZ 2022177).
Patch080: gdb-rhbz2022177-dprintf-1.patch
# Backport test case for dprintf bug (RH BZ 2022177).
Patch081: gdb-rhbz2022177-dprintf-2.patch

2
_gdb.spec.patch.include
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@ -77,3 +77,5 @@
%patch077 -p1
%patch078 -p1
%patch079 -p1
%patch080 -p1
%patch081 -p1

2
_patch_order
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@ -77,3 +77,5 @@ gdb-rhbz1976887-field-location-kind.patch
gdb-test-for-rhbz1976887.patch
gdb-rhbz2012976-paper-over-fortran-lex-problems.patch
gdb-rhbz-853071-update-manpages.patch
gdb-rhbz2022177-dprintf-1.patch
gdb-rhbz2022177-dprintf-2.patch

315
gdb-rhbz2022177-dprintf-1.patch Normal file
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@ -0,0 +1,315 @@
From FEDORA_PATCHES Mon Sep 17 00:00:00 2001
From: Kevin Buettner <kevinb@redhat.com>
Date: Wed, 10 Nov 2021 18:52:22 -0700
Subject: gdb-rhbz2022177-dprintf-1.patch
;; Backport fix for dprintf bug (RH BZ 2022177).
Fix PR 28308 - dprintf breakpoints not working when run from script
This commit fixes Bug 28308, titled "Strange interactions with
dprintf and break/commands":
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=28308
Since creating that bug report, I've found a somewhat simpler way of
reproducing the problem. I've encapsulated it into the GDB test case
which I've created along with this bug fix. The name of the new test
is gdb.base/dprintf-execution-x-script.exp, I'll demonstrate the
problem using this test case, though for brevity, I've placed all
relevant files in the same directory and have renamed the files to all
start with 'dp-bug' instead of 'dprintf-execution-x-script'.
The script file, named dp-bug.gdb, consists of the following commands:
dprintf increment, "dprintf in increment(), vi=%d\n", vi
break inc_vi
commands
continue
end
run
Note that the final command in this script is 'run'. When 'run' is
instead issued interactively, the bug does not occur. So, let's look
at the interactive case first in order to see the correct/expected
output:
$ gdb -q -x dp-bug.gdb dp-bug
... eliding buggy output which I'll discuss later ...
(gdb) run
Starting program: /mesquite2/sourceware-git/f34-master/bld/gdb/tmp/dp-bug
vi=0
dprintf in increment(), vi=0
Breakpoint 2, inc_vi () at dprintf-execution-x-script.c:26
26 in dprintf-execution-x-script.c
vi=1
dprintf in increment(), vi=1
Breakpoint 2, inc_vi () at dprintf-execution-x-script.c:26
26 in dprintf-execution-x-script.c
vi=2
dprintf in increment(), vi=2
Breakpoint 2, inc_vi () at dprintf-execution-x-script.c:26
26 in dprintf-execution-x-script.c
vi=3
[Inferior 1 (process 1539210) exited normally]
In this run, in which 'run' was issued from the gdb prompt (instead
of at the end of the script), there are three dprintf messages along
with three 'Breakpoint 2' messages. This is the correct output.
Now let's look at the output that I snipped above; this is the output
when 'run' is issued from the script loaded via GDB's -x switch:
$ gdb -q -x dp-bug.gdb dp-bug
Reading symbols from dp-bug...
Dprintf 1 at 0x40116e: file dprintf-execution-x-script.c, line 38.
Breakpoint 2 at 0x40113a: file dprintf-execution-x-script.c, line 26.
vi=0
dprintf in increment(), vi=0
Breakpoint 2, inc_vi () at dprintf-execution-x-script.c:26
26 dprintf-execution-x-script.c: No such file or directory.
vi=1
Breakpoint 2, inc_vi () at dprintf-execution-x-script.c:26
26 in dprintf-execution-x-script.c
vi=2
Breakpoint 2, inc_vi () at dprintf-execution-x-script.c:26
26 in dprintf-execution-x-script.c
vi=3
[Inferior 1 (process 1539175) exited normally]
In the output shown above, only the first dprintf message is printed.
The 2nd and 3rd dprintf messages are missing! However, all three
'Breakpoint 2...' messages are still printed.
Why does this happen?
bpstat_do_actions_1() in gdb/breakpoint.c contains the following
comment and code near the start of the function:
/* Avoid endless recursion if a `source' command is contained
in bs->commands. */
if (executing_breakpoint_commands)
return 0;
scoped_restore save_executing
= make_scoped_restore (&executing_breakpoint_commands, 1);
Also, as described by this comment prior to the 'async' field
in 'struct ui' in top.h, the main UI starts off in sync mode
when processing command line arguments:
/* True if the UI is in async mode, false if in sync mode. If in
sync mode, a synchronous execution command (e.g, "next") does not
return until the command is finished. If in async mode, then
running a synchronous command returns right after resuming the
target. Waiting for the command's completion is later done on
the top event loop. For the main UI, this starts out disabled,
until all the explicit command line arguments (e.g., `gdb -ex
"start" -ex "next"') are processed. */
This combination of things, the state of the static global
'executing_breakpoint_commands' plus the state of the async
field in the main UI causes this behavior.
This is a backtrace after hitting the dprintf breakpoint for
the second time when doing 'run' from the script file, i.e.
non-interactively:
Thread 1 "gdb" hit Breakpoint 3, bpstat_do_actions_1 (bsp=0x7fffffffc2b8)
at /ironwood1/sourceware-git/f34-master/bld/../../worktree-master/gdb/breakpoint.c:4431
4431 if (executing_breakpoint_commands)
#0 bpstat_do_actions_1 (bsp=0x7fffffffc2b8)
at gdb/breakpoint.c:4431
#1 0x00000000004d8bc6 in dprintf_after_condition_true (bs=0x1538090)
at gdb/breakpoint.c:13048
#2 0x00000000004c5caa in bpstat_stop_status (aspace=0x116dbc0, bp_addr=0x40116e, thread=0x137f450, ws=0x7fffffffc718,
stop_chain=0x1538090) at gdb/breakpoint.c:5498
#3 0x0000000000768d98 in handle_signal_stop (ecs=0x7fffffffc6f0)
at gdb/infrun.c:6172
#4 0x00000000007678d3 in handle_inferior_event (ecs=0x7fffffffc6f0)
at gdb/infrun.c:5662
#5 0x0000000000763cd5 in fetch_inferior_event ()
at gdb/infrun.c:4060
#6 0x0000000000746d7d in inferior_event_handler (event_type=INF_REG_EVENT)
at gdb/inf-loop.c:41
#7 0x00000000007a702f in handle_target_event (error=0, client_data=0x0)
at gdb/linux-nat.c:4207
#8 0x0000000000b8cd6e in gdb_wait_for_event (block=block@entry=0)
at gdbsupport/event-loop.cc:701
#9 0x0000000000b8d032 in gdb_wait_for_event (block=0)
at gdbsupport/event-loop.cc:597
#10 gdb_do_one_event () at gdbsupport/event-loop.cc:212
#11 0x00000000009d19b6 in wait_sync_command_done ()
at gdb/top.c:528
#12 0x00000000009d1a3f in maybe_wait_sync_command_done (was_sync=0)
at gdb/top.c:545
#13 0x00000000009d2033 in execute_command (p=0x7fffffffcb18 "", from_tty=0)
at gdb/top.c:676
#14 0x0000000000560d5b in execute_control_command_1 (cmd=0x13b9bb0, from_tty=0)
at gdb/cli/cli-script.c:547
#15 0x000000000056134a in execute_control_command (cmd=0x13b9bb0, from_tty=0)
at gdb/cli/cli-script.c:717
#16 0x00000000004c3bbe in bpstat_do_actions_1 (bsp=0x137f530)
at gdb/breakpoint.c:4469
#17 0x00000000004c3d40 in bpstat_do_actions ()
at gdb/breakpoint.c:4533
#18 0x00000000006a473a in command_handler (command=0x1399ad0 "run")
at gdb/event-top.c:624
#19 0x00000000009d182e in read_command_file (stream=0x113e540)
at gdb/top.c:443
#20 0x0000000000563697 in script_from_file (stream=0x113e540, file=0x13bb0b0 "dp-bug.gdb")
at gdb/cli/cli-script.c:1642
#21 0x00000000006abd63 in source_gdb_script (extlang=0xc44e80 <extension_language_gdb>, stream=0x113e540,
file=0x13bb0b0 "dp-bug.gdb") at gdb/extension.c:188
#22 0x0000000000544400 in source_script_from_stream (stream=0x113e540, file=0x7fffffffd91a "dp-bug.gdb",
file_to_open=0x13bb0b0 "dp-bug.gdb")
at gdb/cli/cli-cmds.c:692
#23 0x0000000000544557 in source_script_with_search (file=0x7fffffffd91a "dp-bug.gdb", from_tty=1, search_path=0)
at gdb/cli/cli-cmds.c:750
#24 0x00000000005445cf in source_script (file=0x7fffffffd91a "dp-bug.gdb", from_tty=1)
at gdb/cli/cli-cmds.c:759
#25 0x00000000007cf6d9 in catch_command_errors (command=0x5445aa <source_script(char const*, int)>,
arg=0x7fffffffd91a "dp-bug.gdb", from_tty=1, do_bp_actions=false)
at gdb/main.c:523
#26 0x00000000007cf85d in execute_cmdargs (cmdarg_vec=0x7fffffffd1b0, file_type=CMDARG_FILE, cmd_type=CMDARG_COMMAND,
ret=0x7fffffffd18c) at gdb/main.c:615
#27 0x00000000007d0c8e in captured_main_1 (context=0x7fffffffd3f0)
at gdb/main.c:1322
#28 0x00000000007d0eba in captured_main (data=0x7fffffffd3f0)
at gdb/main.c:1343
#29 0x00000000007d0f25 in gdb_main (args=0x7fffffffd3f0)
at gdb/main.c:1368
#30 0x00000000004186dd in main (argc=5, argv=0x7fffffffd508)
at gdb/gdb.c:32
There are two frames for bpstat_do_actions_1(), one at frame #16 and
the other at frame #0. The one at frame #16 is processing the actions
for Breakpoint 2, which is a 'continue'. The one at frame #0 is attempting
to process the dprintf breakpoint action. However, at this point,
the value of 'executing_breakpoint_commands' is 1, forcing an early
return, i.e. prior to executing the command(s) associated with the dprintf
breakpoint.
For the sake of comparison, this is what the stack looks like when hitting
the dprintf breakpoint for the second time when issuing the 'run'
command from the GDB prompt.
Thread 1 "gdb" hit Breakpoint 3, bpstat_do_actions_1 (bsp=0x7fffffffccd8)
at /ironwood1/sourceware-git/f34-master/bld/../../worktree-master/gdb/breakpoint.c:4431
4431 if (executing_breakpoint_commands)
#0 bpstat_do_actions_1 (bsp=0x7fffffffccd8)
at gdb/breakpoint.c:4431
#1 0x00000000004d8bc6 in dprintf_after_condition_true (bs=0x16b0290)
at gdb/breakpoint.c:13048
#2 0x00000000004c5caa in bpstat_stop_status (aspace=0x116dbc0, bp_addr=0x40116e, thread=0x13f0e60, ws=0x7fffffffd138,
stop_chain=0x16b0290) at gdb/breakpoint.c:5498
#3 0x0000000000768d98 in handle_signal_stop (ecs=0x7fffffffd110)
at gdb/infrun.c:6172
#4 0x00000000007678d3 in handle_inferior_event (ecs=0x7fffffffd110)
at gdb/infrun.c:5662
#5 0x0000000000763cd5 in fetch_inferior_event ()
at gdb/infrun.c:4060
#6 0x0000000000746d7d in inferior_event_handler (event_type=INF_REG_EVENT)
at gdb/inf-loop.c:41
#7 0x00000000007a702f in handle_target_event (error=0, client_data=0x0)
at gdb/linux-nat.c:4207
#8 0x0000000000b8cd6e in gdb_wait_for_event (block=block@entry=0)
at gdbsupport/event-loop.cc:701
#9 0x0000000000b8d032 in gdb_wait_for_event (block=0)
at gdbsupport/event-loop.cc:597
#10 gdb_do_one_event () at gdbsupport/event-loop.cc:212
#11 0x00000000007cf512 in start_event_loop ()
at gdb/main.c:421
#12 0x00000000007cf631 in captured_command_loop ()
at gdb/main.c:481
#13 0x00000000007d0ebf in captured_main (data=0x7fffffffd3f0)
at gdb/main.c:1353
#14 0x00000000007d0f25 in gdb_main (args=0x7fffffffd3f0)
at gdb/main.c:1368
#15 0x00000000004186dd in main (argc=5, argv=0x7fffffffd508)
at gdb/gdb.c:32
This relatively short backtrace is due to the current UI's async field
being set to 1.
Yet another thing to be aware of regarding this problem is the
difference in the way that commands associated to dprintf breakpoints
versus regular breakpoints are handled. While they both use a command
list associated with the breakpoint, regular breakpoints will place
the commands to be run on the bpstat chain constructed in
bp_stop_status(). These commands are run later on. For dprintf
breakpoints, commands are run via the 'after_condition_true' function
pointer directly from bpstat_stop_status(). (The 'commands' field in
the bpstat is cleared in dprintf_after_condition_true(). This
prevents the dprintf commands from being run again later on when other
commands on the bpstat chain are processed.)
Another thing that I noticed is that dprintf breakpoints are the only
type of breakpoint which use 'after_condition_true'. This suggests
that one possible way of fixing this problem, that of making dprintf
breakpoints work more like regular breakpoints, probably won't work.
(I must admit, however, that my understanding of this code isn't
complete enough to say why. I'll trust that whoever implemented it
had a good reason for doing it this way.)
The comment referenced earlier regarding 'executing_breakpoint_commands'
states that the reason for checking this variable is to avoid
potential endless recursion when a 'source' command appears in
bs->commands. We know that a dprintf command is constrained to either
1) execution of a GDB printf command, 2) an inferior function call of
a printf-like function, or 3) execution of an agent-printf command.
Therefore, infinite recursion due to a 'source' command cannot happen
when executing commands upon hitting a dprintf breakpoint.
I chose to fix this problem by having dprintf_after_condition_true()
directly call execute_control_commands(). This means that it no
longer attempts to go through bpstat_do_actions_1() avoiding the
infinite recursion check for potential 'source' commands on the
command chain. I think it simplifies this code a little bit too, a
definite bonus.
Summary:
* breakpoint.c (dprintf_after_condition_true): Don't call
bpstat_do_actions_1(). Call execute_control_commands()
instead.
diff --git a/gdb/breakpoint.c b/gdb/breakpoint.c
--- a/gdb/breakpoint.c
+++ b/gdb/breakpoint.c
@@ -13043,9 +13043,6 @@ dprintf_print_recreate (struct breakpoint *tp, struct ui_file *fp)
static void
dprintf_after_condition_true (struct bpstats *bs)
{
- struct bpstats tmp_bs;
- struct bpstats *tmp_bs_p = &tmp_bs;
-
/* dprintf's never cause a stop. This wasn't set in the
check_status hook instead because that would make the dprintf's
condition not be evaluated. */
@@ -13056,14 +13053,9 @@ dprintf_after_condition_true (struct bpstats *bs)
bpstat_do_actions, if a breakpoint that causes a stop happens to
be set at same address as this dprintf, or even if running the
commands here throws. */
- tmp_bs.commands = bs->commands;
- bs->commands = NULL;
-
- bpstat_do_actions_1 (&tmp_bs_p);
-
- /* 'tmp_bs.commands' will usually be NULL by now, but
- bpstat_do_actions_1 may return early without processing the whole
- list. */
+ counted_command_line cmds = std::move (bs->commands);
+ gdb_assert (cmds != nullptr);
+ execute_control_commands (cmds.get (), 0);
}
/* The breakpoint_ops structure to be used on static tracepoints with

194
gdb-rhbz2022177-dprintf-2.patch Normal file
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@ -0,0 +1,194 @@
From FEDORA_PATCHES Mon Sep 17 00:00:00 2001
From: Kevin Buettner <kevinb@redhat.com>
Date: Wed, 10 Nov 2021 18:55:43 -0700
Subject: gdb-rhbz2022177-dprintf-2.patch
;; Backport test case for dprintf bug (RH BZ 2022177).
Test case for Bug 28308
The purpose of this test is described in the comments in
dprintf-execution-x-script.exp.
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=28308
The name of this new test was based on that of an existing test,
bp-cmds-execution-x-script.exp. I started off by copying that test,
adding to it, and then rewriting almost all of it. It's different
enough that I decided that listing the copyright year as 2021
was sufficient.
diff --git a/gdb/testsuite/gdb.base/dprintf-execution-x-script.c b/gdb/testsuite/gdb.base/dprintf-execution-x-script.c
new file mode 100644
--- /dev/null
+++ b/gdb/testsuite/gdb.base/dprintf-execution-x-script.c
@@ -0,0 +1,53 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+ Copyright 2021 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/>. */
+
+#include <stdlib.h>
+#include <stdio.h>
+
+volatile int vi = 0;
+
+void
+inc_vi ()
+{
+ vi++;
+}
+
+void
+print_vi ()
+{
+ printf ("vi=%d\n", vi);
+}
+
+void
+increment ()
+{
+ inc_vi ();
+}
+
+int
+main (int argc, char **argv)
+{
+ print_vi ();
+ increment ();
+ print_vi ();
+ increment ();
+ print_vi ();
+ increment ();
+ print_vi ();
+
+ exit (0);
+}
diff --git a/gdb/testsuite/gdb.base/dprintf-execution-x-script.exp b/gdb/testsuite/gdb.base/dprintf-execution-x-script.exp
new file mode 100644
--- /dev/null
+++ b/gdb/testsuite/gdb.base/dprintf-execution-x-script.exp
@@ -0,0 +1,85 @@
+# Copyright 2021 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/>. */
+
+# Test that commands in a GDB script file run via GDB's -x flag work
+# as expected. Specifically, the script creates a dprintf breakpoint
+# as well as a normal breakpoint that has "continue" in its command
+# list, and then does "run". Correct output from GDB is checked as
+# part of this test.
+
+# Bail out if the target can't use the 'run' command.
+if ![target_can_use_run_cmd] {
+ return 0
+}
+
+standard_testfile
+
+if {[build_executable "failed to prepare" $testfile $srcfile debug]} {
+ return -1
+}
+
+# This is the name of the GDB script to load.
+set x_file ${srcdir}/${subdir}/$testfile.gdb
+
+# Create context in which the global, GDBFLAGS, will be restored at
+# the end of the block. All commands run within the block are
+# actually run in the outer context. (This is why 'res' is available
+# outside of the save_vars block.)
+save_vars { GDBFLAGS } {
+ # Set flags with which to start GDB.
+ append GDBFLAGS " -ex \"set height unlimited\""
+ append GDBFLAGS " -x \"$x_file\""
+ append GDBFLAGS " --args \"$binfile\""
+
+ # Start GDB with above flags.
+ set res [gdb_spawn]
+}
+
+set test "load and run script with -x"
+if { $res != 0} {
+ fail $test
+ return -1
+}
+
+# The script loaded via -x contains a run command; while running, GDB
+# is expected to print three messages from dprintf breakpoints along
+# with three interspersed messages from an ordinary breakpoint (which
+# was set up with a continue command). Set up pattern D to match
+# output from hitting the dprintf breakpoint and B for the ordinary
+# breakpoint. Then set PAT to contain the entire pattern of expected
+# output from the interspersed dprintf and ordinary breakpoints along
+# with some (additional) expected output from the dprintf breakpoints,
+# i.e. 0, 1, and 2.
+set d "dprintf in increment.., vi="
+set b "Breakpoint ., inc_vi"
+set pat "${d}0.*?$b.*?${d}1.*?$b.*?${d}2.*?$b.*?"
+
+proc do_test {cmd test} {
+ gdb_test $cmd "$::pat$::inferior_exited_re normally.*" $test
+}
+
+# Check output from running script with -x
+do_test "" $test
+
+# Restart GDB and 'source' the script; this will (still) run the program
+# due to the 'run' command in the script.
+clean_restart $binfile
+do_test "source $x_file" "load and run script using source command"
+
+# This should leave us at the gdb prompt; Run program again using
+# already established breakpoints, i.e. those loaded from the
+# script. Prior to fixing PR 28308, this was the only test that
+# would pass.
+do_test "run" "run again"
diff --git a/gdb/testsuite/gdb.base/dprintf-execution-x-script.gdb b/gdb/testsuite/gdb.base/dprintf-execution-x-script.gdb
new file mode 100644
--- /dev/null
+++ b/gdb/testsuite/gdb.base/dprintf-execution-x-script.gdb
@@ -0,0 +1,21 @@
+# Copyright 2021 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/>. */
+
+dprintf increment, "dprintf in increment(), vi=%d\n", vi
+break inc_vi
+commands
+ continue
+end
+run

6
gdb.spec
View File

@ -37,7 +37,7 @@ Version: 11.1
# The release always contains a leading reserved number, start it at 1.
# `upstream' is not a part of `name' to stay fully rpm dependencies compatible for the testing.
Release: 4%{?dist}
Release: 5%{?dist}
License: GPLv3+ and GPLv3+ with exceptions and GPLv2+ and GPLv2+ with exceptions and GPL+ and LGPLv2+ and LGPLv3+ and BSD and Public Domain and GFDL
# Do not provide URL for snapshots as the file lasts there only for 2 days.
@ -1143,6 +1143,10 @@ fi
%endif
%changelog
* Wed Nov 10 2021 Kevin Buettner - 11.1-5
- Backport upstream fix and test case for a dprintf bug (RHBZ 2022177, Kevin
Buettner).
* Tue Nov 9 2021 Bruno Larsen - 11.1-4
- Backport manpage update to be closer to -help (RHBZ 853071)