[PATCH] gdb/readline: fix extra 'quit' message problem

[PATCH] gdb/readline: fix extra 'quit' message problem

[Andrew Burgess]

After these two commits:

  commit 4fb7bc4b147fd30b781ea2dad533956d0362295a
  Date:   Mon Mar 7 13:49:21 2022 +0000

      readline: back-port changes needed to properly detect EOF

  commit 91395d97d905c31ac38513e4aaedecb3b25e818f
  Date:   Tue Feb 15 17:28:03 2022 +0000

      gdb: handle bracketed-paste-mode and EOF correctly

It was observed that, if a previous command is selected at the
readline prompt using the up arrow key, then when the command is
accepted (by pressing return) an unexpected 'quit' message will be
printed by GDB.  Here's an example session:

  (gdb) p 123
  $1 = 123
  (gdb) p 123
  quit
  $2 = 123
  (gdb)

In this session the section 'p 123' was entered not by typing 'p 123',
but by pressing the up arrow key to select the previous command.  It
is important that the up arrow key is used, typing Ctrl-p will not
trigger the bug.

The problem here appears to be readline's EOF detection when handling
multi-character input sequences.  I have raised this issue on the
readline mailing list here:

  https://lists.gnu.org/archive/html/bug-readline/2022-04/msg00012.html

This patch includes a test for this issue as well as a proposed
readline patch (that is included in the thread linked above).  I don't
know if the above patch will be accepted into readline, or if there
will be some alternative fix for upstream readline.

My proposal for now is to wait a couple of days and see if there's a
quick turn around on this issue in upstream readline.  If there is
then I'll update this patch inline with upstream readline and merge
it.

If there's not a quick resolution in upstream readline, then I propose
to merge this patch which will resolve the immediate issue we see in
gdb master, then we can wait for readline to fix the issue properly,
hopefully that will be done in time for the 8.2 readline release.

If this problem isn't fixed in readline 8.2 then we may have to back
out the 91395d97d90 commit (mentioned above) as that's the one that is
responsible for printing the unexpected "quit" message.
---
 gdb/testsuite/gdb.base/readline.exp | 10 ++++++++++
 readline/readline/callback.c        |  2 +-
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/gdb/testsuite/gdb.base/readline.exp b/gdb/testsuite/gdb.base/readline.exp
index 4d770336eb6..caf3b4acb62 100644
--- a/gdb/testsuite/gdb.base/readline.exp
+++ b/gdb/testsuite/gdb.base/readline.exp
@@ -183,6 +183,16 @@ save_vars { env(TERM) } {
 	    }
 	}
 
+	# Use the up arrow to select a previous command.  Check that
+	# no unexpected output is added between the previously
+	# selected command, and the output of that command.
+	gdb_test "print 123" "\\\$\[0-9\]* = 123"
+	gdb_test_multiple "\033\[A" "use up arrow" {
+	    -re -wrap "print 123\r\n\\\$\[0-9\]* = 123" {
+		pass $gdb_test_name
+	    }
+	}
+
 	# Now repeat the first test with a history file that fills the entire
 	# history list.
 
diff --git a/readline/readline/callback.c b/readline/readline/callback.c
index 58b84d2e2ad..0f51a5e4f0f 100644
--- a/readline/readline/callback.c
+++ b/readline/readline/callback.c
@@ -271,7 +271,7 @@ rl_callback_read_char (void)
 	}
 
       /* Make sure application hooks can see whether we saw EOF. */
-      if (rl_eof_found = eof)
+      if (rl_eof_found = (rl_done && eof))
 	RL_SETSTATE(RL_STATE_EOF);
 
       if (rl_done)
-- 
2.25.4

Re: [PATCH] gdb/readline: fix extra 'quit' message problem

[Andrew Burgess]

There's been some feedback on the readline list.  I've updated the patch
accordingly.

My current plan is to wait until next week (hopefully the fix will be
merged to readline by then) before merging this patch.

Thanks,
Andrew

---

commit f84f51dd190c090c65af4a89123d9be87bd09aa7
Author: Andrew Burgess <aburgess@redhat.com>
Date:   Tue Apr 26 15:08:02 2022 +0100

    gdb/readline: fix extra 'quit' message problem
    
    After these two commits:
    
      commit 4fb7bc4b147fd30b781ea2dad533956d0362295a
      Date:   Mon Mar 7 13:49:21 2022 +0000
    
          readline: back-port changes needed to properly detect EOF
    
      commit 91395d97d905c31ac38513e4aaedecb3b25e818f
      Date:   Tue Feb 15 17:28:03 2022 +0000
    
          gdb: handle bracketed-paste-mode and EOF correctly
    
    It was observed that, if a previous command is selected at the
    readline prompt using the up arrow key, then when the command is
    accepted (by pressing return) an unexpected 'quit' message will be
    printed by GDB.  Here's an example session:
    
      (gdb) p 123
      $1 = 123
      (gdb) p 123
      quit
      $2 = 123
      (gdb)
    
    In this session the second 'p 123' was entered not by typing 'p 123',
    but by pressing the up arrow key to select the previous command.  It
    is important that the up arrow key is used, typing Ctrl-p will not
    trigger the bug.
    
    The problem here appears to be readline's EOF detection when handling
    multi-character input sequences.  I have raised this issue on the
    readline mailing list here:
    
      https://lists.gnu.org/archive/html/bug-readline/2022-04/msg00012.html
    
    a solution has been proposed here:
    
      https://lists.gnu.org/archive/html/bug-readline/2022-04/msg00016.html
    
    This patch includes a test for this issue as well as the proposed
    readline patch.  Hopefully the above patch (or something equivalent)
    will be make it into the readline 8.2 release.
    
    If the above fix (or something equivalent) does make it into readline
    8.2 then we can back-port the fix (or just merge 8.2 into our tree).
    However, if 8.2 is released without this fix then we may need to
    consider backing out commit 91395d97d90 as that is the one responsible
    for the extra "quit" message.
    
    I'm going to sit on this patch for a few more days, hopefully the
    above fix will be merged into readline in that time, in which case
    I'll merge this patch.

diff --git a/gdb/testsuite/gdb.base/readline.exp b/gdb/testsuite/gdb.base/readline.exp
index 4d770336eb6..caf3b4acb62 100644
--- a/gdb/testsuite/gdb.base/readline.exp
+++ b/gdb/testsuite/gdb.base/readline.exp
@@ -183,6 +183,16 @@ save_vars { env(TERM) } {
 	    }
 	}
 
+	# Use the up arrow to select a previous command.  Check that
+	# no unexpected output is added between the previously
+	# selected command, and the output of that command.
+	gdb_test "print 123" "\\\$\[0-9\]* = 123"
+	gdb_test_multiple "\033\[A" "use up arrow" {
+	    -re -wrap "print 123\r\n\\\$\[0-9\]* = 123" {
+		pass $gdb_test_name
+	    }
+	}
+
 	# Now repeat the first test with a history file that fills the entire
 	# history list.
 
diff --git a/readline/readline/callback.c b/readline/readline/callback.c
index 58b84d2e2ad..93f23d97bc2 100644
--- a/readline/readline/callback.c
+++ b/readline/readline/callback.c
@@ -271,8 +271,11 @@ rl_callback_read_char (void)
 	}
 
       /* Make sure application hooks can see whether we saw EOF. */
-      if (rl_eof_found = eof)
-	RL_SETSTATE(RL_STATE_EOF);
+      if (eof > 0)
+	{
+	  rl_eof_found = eof;
+	  RL_SETSTATE(RL_STATE_EOF);
+	}
 
       if (rl_done)
 	{

Re: [PATCH] gdb/readline: fix extra 'quit' message problem

[Andrew Burgess]

The fix for the EOF detection has now been merged into upstream
readline.  I've pushed the patch below that includes a test for this
issue and a back-port of the upstream fix.

Thanks,
Andrew

---

commit 8f3babfaf8ea582bed93fd6abcde7bfc96d3a8dd
Author: Andrew Burgess <aburgess@redhat.com>
Date:   Tue Apr 26 15:08:02 2022 +0100

    gdb/readline: fix extra 'quit' message problem
    
    After these two commits:
    
      commit 4fb7bc4b147fd30b781ea2dad533956d0362295a
      Date:   Mon Mar 7 13:49:21 2022 +0000
    
          readline: back-port changes needed to properly detect EOF
    
      commit 91395d97d905c31ac38513e4aaedecb3b25e818f
      Date:   Tue Feb 15 17:28:03 2022 +0000
    
          gdb: handle bracketed-paste-mode and EOF correctly
    
    It was observed that, if a previous command is selected at the
    readline prompt using the up arrow key, then when the command is
    accepted (by pressing return) an unexpected 'quit' message will be
    printed by GDB.  Here's an example session:
    
      (gdb) p 123
      $1 = 123
      (gdb) p 123
      quit
      $2 = 123
      (gdb)
    
    In this session the second 'p 123' was entered not by typing 'p 123',
    but by pressing the up arrow key to select the previous command.  It
    is important that the up arrow key is used, typing Ctrl-p will not
    trigger the bug.
    
    The problem here appears to be readline's EOF detection when handling
    multi-character input sequences.  I have raised this issue on the
    readline mailing list here:
    
      https://lists.gnu.org/archive/html/bug-readline/2022-04/msg00012.html
    
    a solution has been proposed here:
    
      https://lists.gnu.org/archive/html/bug-readline/2022-04/msg00016.html
    
    This patch includes a test for this issue as well as a back-port of
    (the important bits of) readline commit:
    
      commit 2ef9cec8c48ab1ae3a16b1874a49bd1f58eaaca1
      Date:   Wed May 4 11:18:04 2022 -0400
    
          fix for setting RL_STATE_EOF in callback mode
    
    That commit also includes some updates to the readline documentation
    and tests that I have not included in this commit.
    
    With this commit in place the unexpected 'quit' messages are resolved.

diff --git a/gdb/testsuite/gdb.base/readline.exp b/gdb/testsuite/gdb.base/readline.exp
index 4d770336eb6..caf3b4acb62 100644
--- a/gdb/testsuite/gdb.base/readline.exp
+++ b/gdb/testsuite/gdb.base/readline.exp
@@ -183,6 +183,16 @@ save_vars { env(TERM) } {
 	    }
 	}
 
+	# Use the up arrow to select a previous command.  Check that
+	# no unexpected output is added between the previously
+	# selected command, and the output of that command.
+	gdb_test "print 123" "\\\$\[0-9\]* = 123"
+	gdb_test_multiple "\033\[A" "use up arrow" {
+	    -re -wrap "print 123\r\n\\\$\[0-9\]* = 123" {
+		pass $gdb_test_name
+	    }
+	}
+
 	# Now repeat the first test with a history file that fills the entire
 	# history list.
 
diff --git a/readline/readline/callback.c b/readline/readline/callback.c
index 58b84d2e2ad..93f23d97bc2 100644
--- a/readline/readline/callback.c
+++ b/readline/readline/callback.c
@@ -271,8 +271,11 @@ rl_callback_read_char (void)
 	}
 
       /* Make sure application hooks can see whether we saw EOF. */
-      if (rl_eof_found = eof)
-	RL_SETSTATE(RL_STATE_EOF);
+      if (eof > 0)
+	{
+	  rl_eof_found = eof;
+	  RL_SETSTATE(RL_STATE_EOF);
+	}
 
       if (rl_done)
 	{