Re: Regression: GDB stopped on run with attached process (PR 17347) [Re: [pushed+7.8] Re: [PATCH] Fix "attach" command vs user input race

[Pedro Alves <palves@redhat.com>]

On 09/07/2014 08:28 PM, Jan Kratochvil wrote:

> Temporary breakpoint 1 at 0x8048481: file gdb/testsuite/gdb.base/attach.c, line 13.^M
> Starting program: /unsafe/home/jkratoch/hammock/20140907fedorarel21-f21/fedora-2---Type <return> to continue, or q <return> to quit---ERROR: Window too small.
> UNRESOLVED: gdb.base/attach.exp: cmdline attach run: run to main

Good catch.  I see that if one runs the test with a short enough terminal,
do_command_attach_tests fails as well.  I'm leaving that for a
separate patch.

>> +proc test_command_line_attach_run {} {
>> +    global gdb_prompt
>> +    global binfile
> 
>> +    global verbose
>> +    global GDB
>> +    global INTERNAL_GDBFLAGS
> 
> These 3 lines are unused.

Thanks, removed.


>> +	set test "run to prompt"
>> +	gdb_exit
>> +	set res [gdb_spawn_with_cmdline_opts "--pid=$testpid -ex \"start\""]
> 
> Here see the attachment.

Thanks for this.


> Missing:
> /* See top.h.  */
> 
> Unless that rule from me has been abandoned.

Added.

Here's the updated patch.  WDYT?

---------- 8< ----------
Subject: [PATCH 2/2] gdb/17347 - Regression: GDB stopped on run with attached
 process

Doing:

  gdb --pid=PID -ex run

Results in GDB getting a SIGTTIN, and thus ending stopped.  That's
usually indicative of a missing target_terminal_ours call.

E.g., from the PR:

 $ sleep 1h & p=$!; sleep 0.1; gdb -batch sleep $p -ex run
 [1] 28263
 [1]   Killed                  sleep 1h

 [2]+  Stopped                 gdb -batch sleep $p -ex run

The workaround is doing:

 gdb -ex "attach $PID" -ex "run"

instead of

 gdb [-p] $PID -ex "run"

With the former, gdb waits for the attach command to complete before
moving on to the "run" command, because the interpreter is in sync
mode at this point, within execute_command.  But for the latter,
attach_command is called directly from captured_main, and thus misses
that waiting.  IOW, "run" is running before the attach continuation
has run, before the program stops and attach completes.  The broken
terminal settings are just one symptom of that.  Any command that
queries or requires input results in the same.

The fix is to wait in catch_command_errors (which is specific to
main.c nowadays), just like we wait in execute_command.

gdb/ChangeLog:
2014-09-08  Pedro Alves  <palves@redhat.com>

	PR gdb/17347
	* main.c: Include "infrun.h".
	(catch_command_errors, catch_command_errors_const): Wait for the
	foreground command to complete.
	* top.c (maybe_wait_sync_command_done): New function, factored out
	from ...
	(maybe_wait_sync_command_done): ... here.
	* top.h (maybe_wait_sync_command_done): New declaration.

gdb/testsuite/ChangeLog:
2014-09-08  Pedro Alves  <palves@redhat.com>

	PR gdb/17347
	* lib/gdb.exp (gdb_spawn_with_cmdline_opts): New procedure.
	* gdb.base/attach.exp (test_command_line_attach_run): New
	procedure.
	(top level): Call it.
---
 gdb/main.c                        |  9 ++++++++
 gdb/testsuite/gdb.base/attach.exp | 45 +++++++++++++++++++++++++++++++++++++++
 gdb/testsuite/lib/gdb.exp         | 16 ++++++++++++++
 gdb/top.c                         | 28 +++++++++++++++---------
 gdb/top.h                         |  8 +++++++
 5 files changed, 96 insertions(+), 10 deletions(-)

diff --git a/gdb/main.c b/gdb/main.c
index 12f0146..756dd4f 100644
--- a/gdb/main.c
+++ b/gdb/main.c
@@ -45,6 +45,7 @@
 #include "filestuff.h"
 #include <signal.h>
 #include "event-top.h"
+#include "infrun.h"
 
 /* The selected interpreter.  This will be used as a set command
    variable, so it should always be malloc'ed - since
@@ -369,7 +370,11 @@ catch_command_errors (catch_command_errors_ftype *command,
 
   TRY_CATCH (e, mask)
     {
+      int was_sync = sync_execution;
+
       command (arg, from_tty);
+
+      maybe_wait_sync_command_done (was_sync);
     }
   return handle_command_errors (e);
 }
@@ -388,7 +393,11 @@ catch_command_errors_const (catch_command_errors_const_ftype *command,
 
   TRY_CATCH (e, mask)
     {
+      int was_sync = sync_execution;
+
       command (arg, from_tty);
+
+      maybe_wait_sync_command_done (was_sync);
     }
   return handle_command_errors (e);
 }
diff --git a/gdb/testsuite/gdb.base/attach.exp b/gdb/testsuite/gdb.base/attach.exp
index a20c51a..6340496 100644
--- a/gdb/testsuite/gdb.base/attach.exp
+++ b/gdb/testsuite/gdb.base/attach.exp
@@ -396,6 +396,49 @@ proc do_command_attach_tests {} {
     remote_exec build "kill -9 ${testpid}"
 }
 
+# Test ' gdb --pid PID -ex "run" '.  GDB used to have a bug where
+# "run" would run before the attach finished - PR17347.
+
+proc test_command_line_attach_run {} {
+    global gdb_prompt
+    global binfile
+
+    if ![isnative] then {
+	unsupported "commandline attach run test"
+	return 0
+    }
+
+    with_test_prefix "cmdline attach run" {
+	set testpid [spawn_wait_for_attach $binfile]
+
+	set test "run to prompt"
+	gdb_exit
+
+	set res [gdb_spawn_with_cmdline_opts \
+		     "-iex \"set height 0\" -iex \"set width 0\" --pid=$testpid -ex \"start\""]
+	if { $res != 0} {
+	    fail $test
+	    return $res
+	}
+	gdb_test_multiple "" $test {
+	    -re {Attaching to.*Start it from the beginning\? \(y or n\) } {
+		pass $test
+	    }
+	}
+
+	send_gdb "y\n"
+
+	set test "run to main"
+	gdb_test_multiple "" $test {
+	    -re "Temporary breakpoint .* main .*$gdb_prompt $" {
+		pass $test
+	    }
+	}
+
+	# Get rid of the process
+	remote_exec build "kill -9 ${testpid}"
+    }
+}
 
 # Start with a fresh gdb
 
@@ -420,4 +463,6 @@ do_call_attach_tests
 
 do_command_attach_tests
 
+test_command_line_attach_run
+
 return 0
diff --git a/gdb/testsuite/lib/gdb.exp b/gdb/testsuite/lib/gdb.exp
index ecf942e..c54ba4b 100644
--- a/gdb/testsuite/lib/gdb.exp
+++ b/gdb/testsuite/lib/gdb.exp
@@ -3334,6 +3334,22 @@ proc gdb_spawn { } {
     default_gdb_spawn
 }
 
+# Spawn GDB with CMDLINE_FLAGS appended to the GDBFLAGS global.
+
+proc gdb_spawn_with_cmdline_opts { cmdline_flags } {
+    global GDBFLAGS
+
+    set saved_gdbflags $GDBFLAGS
+
+    append GDBFLAGS $cmdline_flags
+
+    set res [gdb_spawn]
+
+    set GDBFLAGS $saved_gdbflags
+
+    return $res
+}
+
 # Start gdb running, wait for prompt, and disable the pagers.
 
 # Overridable function -- you can override this function in your
diff --git a/gdb/top.c b/gdb/top.c
index fc2b84d..d6696cd 100644
--- a/gdb/top.c
+++ b/gdb/top.c
@@ -373,6 +373,23 @@ check_frame_language_change (void)
     }
 }
 
+/* See top.h.  */
+
+void
+maybe_wait_sync_command_done (int was_sync)
+{
+  /* If the interpreter is in sync mode (we're running a user
+     command's list, running command hooks or similars), and we
+     just ran a synchronous command that started the target, wait
+     for that command to end.  */
+  if (!interpreter_async && !was_sync && sync_execution)
+    {
+      while (gdb_do_one_event () >= 0)
+	if (!sync_execution)
+	  break;
+    }
+}
+
 /* Execute the line P as a command, in the current user context.
    Pass FROM_TTY as second argument to the defining function.  */
 
@@ -459,16 +476,7 @@ execute_command (char *p, int from_tty)
       else
 	cmd_func (c, arg, from_tty);
 
-      /* If the interpreter is in sync mode (we're running a user
-	 command's list, running command hooks or similars), and we
-	 just ran a synchronous command that started the target, wait
-	 for that command to end.  */
-      if (!interpreter_async && !was_sync && sync_execution)
-	{
-	  while (gdb_do_one_event () >= 0)
-	    if (!sync_execution)
-	      break;
-	}
+      maybe_wait_sync_command_done (was_sync);
 
       /* If this command has been post-hooked, run the hook last.  */
       execute_cmd_post_hook (c);
diff --git a/gdb/top.h b/gdb/top.h
index c322c33..94f6c48 100644
--- a/gdb/top.h
+++ b/gdb/top.h
@@ -42,6 +42,14 @@ extern void quit_command (char *, int);
 extern void quit_cover (void);
 extern void execute_command (char *, int);
 
+/* If the interpreter is in sync mode (we're running a user command's
+   list, running command hooks or similars), and we just ran a
+   synchronous command that started the target, wait for that command
+   to end.  WAS_SYNC indicates whether sync_execution was set before
+   the command was run.  */
+
+extern void maybe_wait_sync_command_done (int was_sync);
+
 extern void check_frame_language_change (void);
 
 /* Prepare for execution of a command.
-- 
1.9.3