Re: Program-assigned thread names on Windows

[LRN <lrn1986@gmail.com>]

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On 10.08.2016 15:15, Pedro Alves wrote:
> On 08/10/2016 08:11 AM, LRN wrote:
>> No one seems to object.
>>
> 
> I was going to apply your patches, so I squashed them all, and
> only after did I notice the problems, so I went ahead and did
> the changes.  I also fixed a couple typos in the commit log.
> 
> Could you give this updated patch a try?  I build-tested it using
> a cross compiler, but haven't tried it out on Windows.


Curses! I've been reading your message like a set of last-minute nitpicks,
fixing things in my patch as i went along. I got to the named_thread->name
and overriding "thread name" part, then went ahead and fixed that too. Then
got to the end of the email and found out that you've done that already!
:-\ Good job, me...

Anyway, i've applied your patch. gdb compiles. threadname-setting
functionality works as expected: "thread name X" has precedence, "thread
name" (with no name) allows app-assigned name (if any) to be shown once again.

I've also applied my version of the patch. gdb also compiles.
threadname-setting functionality also works as expected. Therefore i'm
attaching my version, in case you find it useful.

I've only tested 32-bit version of gdb (hoping that none of the recent
changes touch anything architecture-dependent).

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From 34c05e6eb6e9d94700f8dc9695a214fdf6fabaea 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, though MSDN dubs it "MS_VC_EXCEPTION"
in one code example), 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 value
HANDLE_EXCEPTION_IGNORED 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 | 121 +++++++++++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 107 insertions(+), 14 deletions(-)

diff --git a/gdb/windows-nat.c b/gdb/windows-nat.c
index 3f67486..6315303 100644
--- a/gdb/windows-nat.c
+++ b/gdb/windows-nat.c
@@ -174,6 +174,18 @@ static int debug_registers_used;
 static int windows_initialization_done;
 #define DR6_CLEAR_VALUE 0xffff0ff0
 
+/* This exception has no documented name, but MSDN dubs it "MS_VC_EXCEPTION"
+   in one code example. It's thrown by a program to tell the debugger the name
+   of a thread. */
+#define MS_VC_EXCEPTION 0x406d1388
+
+typedef enum
+{
+  HANDLE_EXCEPTION_UNHANDLED = 0,
+  HANDLE_EXCEPTION_HANDLED,
+  HANDLE_EXCEPTION_IGNORED
+} handle_exception_result;
+
 /* The string sent by cygwin when it processes a signal.
    FIXME: This should be in a cygwin include file.  */
 #ifndef _CYGWIN_SIGNAL_STRING
@@ -441,6 +453,7 @@ windows_delete_thread (ptid_t ptid, DWORD exit_code)
     {
       windows_thread_info *here = th->next;
       th->next = here->next;
+      xfree (here->name);
       xfree (here);
     }
 }
@@ -1031,10 +1044,12 @@ display_selectors (char * args, int from_tty)
     host_address_to_string (\
       current_event.u.Exception.ExceptionRecord.ExceptionAddress))
 
-static int
+static handle_exception_result
 handle_exception (struct target_waitstatus *ourstatus)
 {
-  DWORD code = current_event.u.Exception.ExceptionRecord.ExceptionCode;
+  EXCEPTION_RECORD *rec = &current_event.u.Exception.ExceptionRecord;
+  DWORD code = rec->ExceptionCode;
+  handle_exception_result result = HANDLE_EXCEPTION_HANDLED;
 
   ourstatus->kind = TARGET_WAITKIND_STOPPED;
 
@@ -1057,14 +1072,13 @@ handle_exception (struct target_waitstatus *ourstatus)
 	   cygwin-specific-signal.  So, ignore SEGVs if they show up
 	   within the text segment of the DLL itself.  */
 	const char *fn;
-	CORE_ADDR addr = (CORE_ADDR) (uintptr_t)
-	  current_event.u.Exception.ExceptionRecord.ExceptionAddress;
+	CORE_ADDR addr = (CORE_ADDR) (uintptr_t) rec->ExceptionAddress;
 
 	if ((!cygwin_exceptions && (addr >= cygwin_load_start
 				    && addr < cygwin_load_end))
 	    || (find_pc_partial_function (addr, &fn, NULL, NULL)
 		&& startswith (fn, "KERNEL32!IsBad")))
-	  return 0;
+	  return HANDLE_EXCEPTION_UNHANDLED;
       }
 #endif
       break;
@@ -1140,20 +1154,64 @@ handle_exception (struct target_waitstatus *ourstatus)
       DEBUG_EXCEPTION_SIMPLE ("EXCEPTION_NONCONTINUABLE_EXCEPTION");
       ourstatus->value.sig = GDB_SIGNAL_ILL;
       break;
+    case MS_VC_EXCEPTION:
+      if (rec->NumberParameters >= 3
+          && (rec->ExceptionInformation[0] & 0xffffffff) == 0x1000)
+	{
+	  long named_thread_id;
+	  windows_thread_info *named_windows_thread;
+	  CORE_ADDR thread_name_target;
+	  char *thread_name;
+	  int thread_name_len;
+
+	  DEBUG_EXCEPTION_SIMPLE ("MS_VC_EXCEPTION");
+
+	  named_thread_id = (long) (0xffffffff & rec->ExceptionInformation[2]);
+	  thread_name_target = rec->ExceptionInformation[1];
+
+	  if (named_thread_id == (DWORD) -1)
+	    named_thread_id = current_event.dwThreadId;
+
+	  named_windows_thread = thread_rec (named_thread_id, 0);
+
+	  thread_name = NULL;
+	  thread_name_len = 0;
+
+	  if (named_windows_thread != NULL)
+	    thread_name_len = target_read_string (thread_name_target,
+					          &thread_name, 1025, 0);
+
+	  if (thread_name_len > 0 && thread_name != NULL)
+	    {
+	      thread_name[thread_name_len - 1] = '\0';
+	      if (thread_name[0] != '\0')
+		{
+		  xfree (named_windows_thread->name);
+		  named_windows_thread->name = thread_name;
+		}
+	      else
+		{
+		  xfree (thread_name);
+		}
+	    }
+	  ourstatus->value.sig = GDB_SIGNAL_TRAP;
+	  result = HANDLE_EXCEPTION_IGNORED;
+	  break;
+	}
+	/* treat improperly formed exception as unknown, fallthrough */
     default:
       /* Treat unhandled first chance exceptions specially.  */
       if (current_event.u.Exception.dwFirstChance)
-	return 0;
+	return HANDLE_EXCEPTION_UNHANDLED;
       printf_unfiltered ("gdb: unknown target exception 0x%08x at %s\n",
-	(unsigned) current_event.u.Exception.ExceptionRecord.ExceptionCode,
-	host_address_to_string (
-	  current_event.u.Exception.ExceptionRecord.ExceptionAddress));
+	(unsigned) rec->ExceptionCode,
+	host_address_to_string (rec->ExceptionAddress));
       ourstatus->value.sig = GDB_SIGNAL_UNKNOWN;
       break;
     }
   exception_count++;
   last_sig = ourstatus->value.sig;
-  return 1;
+  return result;
 }
 
 /* Resume thread specified by ID, or all artificially suspended
@@ -1510,10 +1568,19 @@ 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 HANDLE_EXCEPTION_UNHANDLED:
+	default:
+	  continue_status = DBG_EXCEPTION_NOT_HANDLED;
+	  break;
+	case HANDLE_EXCEPTION_HANDLED:
+	  thread_id = current_event.dwThreadId;
+	  break;
+	case HANDLE_EXCEPTION_IGNORED:
+	  continue_status = DBG_CONTINUE;
+	  break;
+	}
       break;
 
     case OUTPUT_DEBUG_STRING_EVENT:	/* Message from the kernel.  */
@@ -2514,6 +2581,31 @@ windows_get_ada_task_ptid (struct target_ops *self, long lwp, long thread)
   return ptid_build (ptid_get_pid (inferior_ptid), 0, lwp);
 }
 
+static const char *
+windows_get_thread_name (struct target_ops *self, struct thread_info *thr)
+{
+  struct thread_info *threadinfo;
+  windows_thread_info *windows_threadinfo;
+  DWORD id = ptid_get_tid (thr->ptid);
+  char *name;
+
+  name = NULL;
+  threadinfo = find_thread_ptid (thr->ptid);
+
+  if (threadinfo != NULL)
+    name = threadinfo->name;
+
+  if (name == NULL && id != 0)
+    {
+      windows_threadinfo = thread_rec (id, 0);
+
+      if (windows_threadinfo != NULL)
+        name = windows_threadinfo->name;
+    }
+
+  return (const char *) name;
+}
+
 static struct target_ops *
 windows_target (void)
 {
@@ -2538,6 +2630,7 @@ windows_target (void)
   t->to_pid_to_exec_file = windows_pid_to_exec_file;
   t->to_get_ada_task_ptid = windows_get_ada_task_ptid;
   t->to_get_tib_address = windows_get_tib_address;
+  t->to_thread_name = windows_get_thread_name;
 
   return t;
 }
-- 
2.4.0


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