Re: Program-assigned thread names on Windows

[LRN <lrn1986@gmail.com>]

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On 23.07.2016 19:39, John Baldwin wrote:
> On Saturday, July 23, 2016 12:25:15 PM LRN wrote:
>> The attached patch adds thread naming support on Windows.
>>
>> This works as documented[1] on MSDN - by catching a specific
>> exception that the program throws.
>>
>> Setting thread name this way is supported by glib[2] and winpthreads[3]
>> at least, as well as any program developed with MS toolchain (because
>> WinDbg supported this for a long time).
>>
>> [1] https://msdn.microsoft.com/en-us/library/xcb2z8hs.aspx
>> [2] https://git.gnome.org/browse/glib/commit/glib
>> /gthread-win32.c?id=e118856430a798bbc529691ad235fd0b0684439d
>> [3] https://sourceforge.net/p/mingw-w64/mingw-w64/ci
>> /0d95c795b44b76e1b60dfc119fd93cfd0cb35816/
> 
> Does this leak 'thread_name' if the first character is '\0'?
> 
> +         thread_name = NULL;
> +         if (!target_read_string ((CORE_ADDR) thread_name_target, &thread_name, 1024, 0)
> +             || !thread_name || !*thread_name)
> +           /* nothing to do */;
> +         else
> +           {
> +             xfree (named_thread->name);
> +             named_thread->name = thread_name;
> +           }
> +         result = 2;
> 
> Maybe restructure as:
> 
>     if (target_read_string (...))
>       {
>         if (thread_name && thread_name[0] != '\0')
>           {
>             xfree (named_thread->name);
>             named_thread->name = thread_name;
>           }
>         else
>           xfree (thread_name);
>       }
> 

You're right, it can leak. Fixed patch attached.

That said, handle_output_debug_string() does the same thing (and, judging
by the "nothing to do" comment, i've copied this call from there back when
i made wrote this code).

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From 83320cdb4dc349ffefd777bfcbef0848bc661c8b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=D0=A0=D1=83=D1=81=D0=BB=D0=B0=D0=BD=20=D0=98=D0=B6=D0=B1?=
 =?UTF-8?q?=D1=83=D0=BB=D0=B0=D1=82=D0=BE=D0=B2?= <lrn1986@gmail.com>
Date: Sun, 26 Jun 2016 11:14:49 +0000
Subject: [PATCH 1/3] Support settings thread name (MS-Windows)

This is done by catching an exception number 0x406D1388
(it has no documented name), which is thrown by the program.
The exception record contains an ID of a thread and a name to
give it.

This requires rolling back some changes in handle_exception(),
which now again returns more than two distinct values. The code
2 means that gdb should just continue, without returning
thread ID up the stack (which will result in further handling
of the exception, which is not what we want).
---
 gdb/windows-nat.c | 60 ++++++++++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 55 insertions(+), 5 deletions(-)

diff --git a/gdb/windows-nat.c b/gdb/windows-nat.c
index 3f67486..458790b 100644
--- a/gdb/windows-nat.c
+++ b/gdb/windows-nat.c
@@ -174,6 +174,9 @@ static int debug_registers_used;
 static int windows_initialization_done;
 #define DR6_CLEAR_VALUE 0xffff0ff0
 
+#define WINDOWS_THREADNAME_EXCEPTION 0x406D1388
+#define WINDOWS_THREADNAME_EXCEPTION_S "0x406D1388"
+
 /* The string sent by cygwin when it processes a signal.
    FIXME: This should be in a cygwin include file.  */
 #ifndef _CYGWIN_SIGNAL_STRING
@@ -1035,6 +1038,7 @@ static int
 handle_exception (struct target_waitstatus *ourstatus)
 {
   DWORD code = current_event.u.Exception.ExceptionRecord.ExceptionCode;
+  int result = 1;
 
   ourstatus->kind = TARGET_WAITKIND_STOPPED;
 
@@ -1140,6 +1144,43 @@ handle_exception (struct target_waitstatus *ourstatus)
       DEBUG_EXCEPTION_SIMPLE ("EXCEPTION_NONCONTINUABLE_EXCEPTION");
       ourstatus->value.sig = GDB_SIGNAL_ILL;
       break;
+    case WINDOWS_THREADNAME_EXCEPTION:
+      DEBUG_EXCEPTION_SIMPLE (WINDOWS_THREADNAME_EXCEPTION_S);
+      ourstatus->value.sig = GDB_SIGNAL_TRAP;
+      if (current_event.u.Exception.ExceptionRecord.NumberParameters == 4)
+	{
+	  DWORD named_thread_id;
+	  ptid_t named_thread_ptid;
+	  struct thread_info *named_thread;
+	  uintptr_t thread_name_target;
+	  char *thread_name;
+
+	  named_thread_id = (DWORD) current_event.u.Exception.ExceptionRecord.ExceptionInformation[2];
+	  thread_name_target = (uintptr_t) current_event.u.Exception.ExceptionRecord.ExceptionInformation[1];
+
+	  if (named_thread_id == (DWORD) -1)
+	    named_thread_id = current_event.dwThreadId;
+
+	  named_thread_ptid = ptid_build (current_event.dwProcessId, 0, named_thread_id),
+	  named_thread = find_thread_ptid (named_thread_ptid);
+
+	  thread_name = NULL;
+	  if (target_read_string ((CORE_ADDR) thread_name_target, &thread_name, 1024, 0))
+	    {
+	      if (thread_name != NULL && thread_name[0] != '\0')
+		{
+		  xfree (named_thread->name);
+		  named_thread->name = thread_name;
+		}
+	      else if (thread_name != NULL)
+		{
+		  /* nothing to do */;
+		  xfree (thread_name);
+		}
+	    }
+	  result = 2;
+	}
+      break;
     default:
       /* Treat unhandled first chance exceptions specially.  */
       if (current_event.u.Exception.dwFirstChance)
@@ -1153,7 +1194,7 @@ handle_exception (struct target_waitstatus *ourstatus)
     }
   exception_count++;
   last_sig = ourstatus->value.sig;
-  return 1;
+  return result;
 }
 
 /* Resume thread specified by ID, or all artificially suspended
@@ -1510,10 +1551,19 @@ get_windows_debug_event (struct target_ops *ops,
 		     "EXCEPTION_DEBUG_EVENT"));
       if (saw_create != 1)
 	break;
-      if (handle_exception (ourstatus))
-	thread_id = current_event.dwThreadId;
-      else
-	continue_status = DBG_EXCEPTION_NOT_HANDLED;
+      switch (handle_exception (ourstatus))
+	{
+	case 0:
+	default:
+	  continue_status = DBG_EXCEPTION_NOT_HANDLED;
+	  break;
+	case 1:
+	  thread_id = current_event.dwThreadId;
+	  break;
+	case 2:
+	  continue_status = DBG_CONTINUE;
+	  break;
+	}
       break;
 
     case OUTPUT_DEBUG_STRING_EVENT:	/* Message from the kernel.  */
-- 
2.4.0


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