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[binutils-gdb] Fix PR 21218: GDB dumps core when escaping newline in multi-line command


https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=6e5d74e74756fafe59e8198c4cc462cf7c57e12c

commit 6e5d74e74756fafe59e8198c4cc462cf7c57e12c
Author: Pedro Alves <palves@redhat.com>
Date:   Wed Mar 8 11:41:35 2017 +0000

    Fix PR 21218: GDB dumps core when escaping newline in multi-line command
    
    With commit 3b12939dfc2399 ("Replace the sync_execution global with a
    new enum prompt_state tristate"), GDB started aborting if you try
    splitting an input line with a continuation char (backslash) while in
    a multi-line command:
    
     (gdb) commands
     Type commands for breakpoint(s) 1, one per line.
     End with a line saying just "end".
     >print \
    
     (gdb) 1      # note "(gdb)" incorrectly printed here.
     >end
    
     readline: readline_callback_read_char() called with no handler!
     $
    
    That abort is actually a symptom of an old problem introduced when
    gdb_readline_wrapper was rewritten to use asynchronous readline, back
    in 2007.  Note how the "(gdb)" prompt is printed above in the "(gdb)
    1" line.  Clearly it shouldn't be there, but it already was before the
    commit mentioned above.  Fixing that also fixes the readline abort
    shown above.
    
    The problem starts when command_line_input passes a NULL prompt to
    gdb_readline_wrapper when it finds previous incomplete input due to a
    backslash, trying to fetch more input without printing another ">"
    secondary prompt.  That itself should not be a problem, because
    passing NULL to gdb_readline_wrapper has the same meaning as passing a
    pointer to empty string, since gdb_readline_wrapper exposes the same
    interface as 'readline(char *)'.  However, gdb_readline_wrapper passes
    the prompt argument directly to display_gdb_prompt, and for the
    latter, a NULL prompt argument has a different meaning - it requests
    printing the primary prompt.
    
    Before commit 782a7b8ef9c096 (which rewrote gdb_readline_wrapper to
    use asynchronous readline), GDB behaved like this:
    
     (gdb) commands
     [....]
     >print \
     1
     >end
     (gdb)
    
    The above is what this commit restores GDB back to.
    
    New test included.
    
    gdb/ChangeLog:
    2017-03-08  Pedro Alves  <palves@redhat.com>
    
    	PR cli/21218
    	* top.c (gdb_readline_wrapper): Avoid passing NULL to
    	display_gdb_prompt.
    	(command_line_input): Add comment.
    
    gdb/testsuite/ChangeLog:
    2017-03-08  Pedro Alves  <palves@redhat.com>
    	    Jan Kratochvil  <jan.kratochvil@redhat.com>
    
    	PR cli/21218
    	* gdb.base/commands.exp (backslash_in_multi_line_command_test):
    	New proc.
    	(top level): Call it.

Diff:
---
 gdb/ChangeLog                       |  7 +++++++
 gdb/testsuite/ChangeLog             |  8 ++++++++
 gdb/testsuite/gdb.base/commands.exp | 29 +++++++++++++++++++++++++++++
 gdb/top.c                           | 10 ++++++++--
 4 files changed, 52 insertions(+), 2 deletions(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 432cdcc..92847f7 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,12 @@
 2017-03-08  Pedro Alves  <palves@redhat.com>
 
+	PR cli/21218
+	* top.c (gdb_readline_wrapper): Avoid passing NULL to
+	display_gdb_prompt.
+	(command_line_input): Add comment.
+
+2017-03-08  Pedro Alves  <palves@redhat.com>
+
 	PR tui/21216
 	* tui/tui-file.c (tui_file::write): New.
 	* tui/tui-file.h (tui_file): Override "write".
diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index 0654bef..d7b603b 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,4 +1,12 @@
 2017-03-08  Pedro Alves  <palves@redhat.com>
+	    Jan Kratochvil  <jan.kratochvil@redhat.com>
+
+	PR cli/21218
+	* gdb.base/commands.exp (backslash_in_multi_line_command_test):
+	New proc.
+	(top level): Call it.
+
+2017-03-08  Pedro Alves  <palves@redhat.com>
 
 	PR tui/21216
 	* gdb.tui/tui-nl-filtered-output.exp: New file.
diff --git a/gdb/testsuite/gdb.base/commands.exp b/gdb/testsuite/gdb.base/commands.exp
index 9ad70f5..6d3c398 100644
--- a/gdb/testsuite/gdb.base/commands.exp
+++ b/gdb/testsuite/gdb.base/commands.exp
@@ -1003,6 +1003,34 @@ proc_with_prefix redefine_backtrace_test {} {
     gdb_test "bt" "hibob" "execute bt command"
 }
 
+# Test an input line split with a continuation character (backslash)
+# while entering a multi-line command (in a secondary prompt).
+
+proc_with_prefix backslash_in_multi_line_command_test {} {
+    gdb_breakpoint "main"
+
+    gdb_test_multiple "commands" "commands" {
+	-re "End with a line saying just \"end\"\\.\r\n>$" {
+	    pass "commands"
+	}
+    }
+
+    set test "input line split with backslash"
+    send_gdb "print \\\nargc\n"
+    gdb_test_multiple "" $test {
+	-re "^print \\\\\r\nargc\r\n>$" {
+	    pass $test
+	}
+    }
+
+    gdb_test_no_output "end"
+
+    # Input any command, just to be sure the readline state is sane.
+    # In PR 21218, this would trigger the infamous:
+    # readline: readline_callback_read_char() called with no handler!
+    gdb_test "print 1" "" "run command"
+}
+
 gdbvar_simple_if_test
 gdbvar_simple_while_test
 gdbvar_complex_if_while_test
@@ -1027,5 +1055,6 @@ recursive_source_test
 if_commands_test
 error_clears_commands_left
 redefine_hook_test
+backslash_in_multi_line_command_test
 # This one should come last, as it redefines "backtrace".
 redefine_backtrace_test
diff --git a/gdb/top.c b/gdb/top.c
index 6bf9d8c..295b680 100644
--- a/gdb/top.c
+++ b/gdb/top.c
@@ -1030,8 +1030,11 @@ gdb_readline_wrapper (const char *prompt)
   if (cleanup->target_is_async_orig)
     target_async (0);
 
-  /* Display our prompt and prevent double prompt display.  */
-  display_gdb_prompt (prompt);
+  /* Display our prompt and prevent double prompt display.  Don't pass
+     down a NULL prompt, since that has special meaning for
+     display_gdb_prompt -- it indicates a request to print the primary
+     prompt, while we want a secondary prompt here.  */
+  display_gdb_prompt (prompt != NULL ? prompt : "");
   if (ui->command_editing)
     rl_already_prompted = 1;
 
@@ -1307,6 +1310,9 @@ command_line_input (const char *prompt_arg, int repeat, char *annotation_suffix)
       if (cmd != NULL)
 	break;
 
+      /* Got partial input.  I.e., got a line that ends with a
+	 continuation character (backslash).  Suppress printing the
+	 prompt again.  */
       prompt = NULL;
     }


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