Use GetThreadDescription on Windows

Windows 10 introduced SetThreadDescription and GetThreadDescription, a
simpler way to set a thread's name.  This changes gdb and gdbserver to
use this convention when it is available.

This is part of PR win32/29050.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=29050

gdb/nat/windows-nat.c

@@ -58,6 +58,10 @@ Wow64GetThreadSelectorEntry_ftype *Wow64GetThreadSelectorEntry;
 #endif
 GenerateConsoleCtrlEvent_ftype *GenerateConsoleCtrlEvent;
 
+#define GetThreadDescription dyn_GetThreadDescription
+typedef HRESULT WINAPI (GetThreadDescription_ftype) (HANDLE, PWSTR *);
+static GetThreadDescription_ftype *GetThreadDescription;
+
 /* Note that 'debug_events' must be locally defined in the relevant
    functions.  */
 #define DEBUG_EVENTS(fmt, ...) \
@@ -106,6 +110,29 @@ windows_thread_info::resume ()
   suspended = 0;
 }
 
+const char *
+windows_thread_info::thread_name ()
+{
+  if (GetThreadDescription != nullptr)
+    {
+      PWSTR value;
+      HRESULT result = GetThreadDescription (h, &value);
+      if (SUCCEEDED (result))
+	{
+	  size_t needed = wcstombs (nullptr, value, 0);
+	  if (needed != (size_t) -1)
+	    {
+	      name.reset ((char *) xmalloc (needed));
+	      if (wcstombs (name.get (), value, needed) == (size_t) -1)
+		name.reset ();
+	    }
+	  LocalFree (value);
+	}
+    }
+
+  return name.get ();
+}
+
 /* Return the name of the DLL referenced by H at ADDRESS.  UNICODE
    determines what sort of string is read from the inferior.  Returns
    the name of the DLL, or NULL on error.  If a name is returned, it
@@ -662,6 +689,7 @@ initialize_loadable ()
       GPA (hm, Wow64GetThreadSelectorEntry);
 #endif
       GPA (hm, GenerateConsoleCtrlEvent);
+      GPA (hm, GetThreadDescription);
     }
 
   /* Set variables to dummy versions of these processes if the function
@@ -718,6 +746,15 @@ initialize_loadable ()
 	OpenProcessToken = bad;
     }
 
+  /* On some versions of Windows, this function is only available in
+     KernelBase.dll, not kernel32.dll.  */
+  if (GetThreadDescription == nullptr)
+    {
+      hm = LoadLibrary (TEXT ("KernelBase.dll"));
+      if (hm)
+	GPA (hm, GetThreadDescription);
+    }
+
 #undef GPA
 
   return result;

gdb/nat/windows-nat.h

@@ -51,6 +51,11 @@ struct windows_thread_info
   /* Resume the thread if it has been suspended.  */
   void resume ();
 
+  /* Return the thread's name, or nullptr if not known.  The name is
+     stored in this thread and is guaranteed to live until at least
+     the next call.  */
+  const char *thread_name ();
+
   /* The Win32 thread identifier.  */
   DWORD tid;
 

gdb/windows-nat.c

@@ -2997,8 +2997,10 @@ windows_nat_target::get_ada_task_ptid (long lwp, ULONGEST thread)
 const char *
 windows_nat_target::thread_name (struct thread_info *thr)
 {
-  return windows_process.thread_rec (thr->ptid,
+  windows_thread_info *th
-				     DONT_INVALIDATE_CONTEXT)->name.get ();
+    = windows_process.thread_rec (thr->ptid,
+				  DONT_INVALIDATE_CONTEXT);
+  return th->thread_name ();
 }
 
 

gdbserver/win32-low.cc

@@ -1508,7 +1508,7 @@ win32_process_target::thread_name (ptid_t thread)
   windows_thread_info *th
     = windows_process.thread_rec (current_thread_ptid (),
 				  DONT_INVALIDATE_CONTEXT);
-  return th->name.get ();
+  return th->thread_name ();
 }
 
 /* The win32 target ops object.  */