[binutils-gdb] gdb/windows-nat.c: Get rid of main_thread_id global

[binutils-gdb] gdb/windows-nat.c: Get rid of main_thread_id global

[Joel Brobecker]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=ab4ee6147eb2e8fafd1fb96c945029c789182d3b

commit ab4ee6147eb2e8fafd1fb96c945029c789182d3b
Author: Joel Brobecker <brobecker@adacore.com>
Date:   Tue Apr 30 16:00:19 2019 -0500

    gdb/windows-nat.c: Get rid of main_thread_id global
    
    This global is meant to point to the "main" thread of execution of
    the program we are debugging. It is set when attaching to a process
    or when receiving a CREATE_PROCESS_DEBUG_EVENT event. The theory at
    the time was that this was also going to be the thread receiving
    the EXIT_PROCESS_DEBUG_EVENT event.
    
    Unfortunately, we have discovered since then that this is actually
    not guaranteed. What this means in practice is that there is moderate
    risk that main_thread_id refers to a thread which no longer exists.
    
    This global is used in 3 situations:
      - OUTPUT_DEBUG_STRING_EVENT
      - LOAD_DLL_DEBUG_EVENT
      - UNLOAD_DLL_DEBUG_EVENT
    
    It's not clear why we would need to use the main_thread_id in those cases
    instead of using the thread ID provided by the kernel events itself.
    So this patch implements this approach, which then allows us to delete
    the main_thread_id global.
    
    gdb/testsuite:
    
    	* windows-nat.c (main_thread_id): Delete.
    	(handle_output_debug_string): Replace main_thread_id by
    	current_event.dwThreadId.
    	(fake_create_process): Likewise.
    	(get_windows_debug_event) <CREATE_PROCESS_DEBUG_EVENT>:
    	Do not set main_thread_id.
    	<LOAD_DLL_DEBUG_EVENT>: Replace main_thread_id by
    	current_event.dwThreadId.
    	<UNLOAD_DLL_DEBUG_EVENT>: Likewise.

Diff:
---
 gdb/ChangeLog     | 12 ++++++++++++
 gdb/windows-nat.c | 11 ++++-------
 2 files changed, 16 insertions(+), 7 deletions(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 1b4b83d..126343c 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,17 @@
 2019-04-30  Joel Brobecker  <brobecker@adacore.com>
 
+	* windows-nat.c (main_thread_id): Delete.
+	(handle_output_debug_string): Replace main_thread_id by
+	current_event.dwThreadId.
+	(fake_create_process): Likewise.
+	(get_windows_debug_event) <CREATE_PROCESS_DEBUG_EVENT>:
+	Do not set main_thread_id.
+	<LOAD_DLL_DEBUG_EVENT>: Replace main_thread_id by
+	current_event.dwThreadId.
+	<UNLOAD_DLL_DEBUG_EVENT>: Likewise.
+
+2019-04-30  Joel Brobecker  <brobecker@adacore.com>
+
 	* windows-nat.c (get_windows_debug_event) <EXIT_PROCESS_DEBUG_EVENT>:
 	Use current_event.dwThreadId instead of main_thread_id.
 
diff --git a/gdb/windows-nat.c b/gdb/windows-nat.c
index 9f3242c..ae4e3d5 100644
--- a/gdb/windows-nat.c
+++ b/gdb/windows-nat.c
@@ -237,7 +237,6 @@ static DEBUG_EVENT current_event;	/* The current debug event from
 					   WaitForDebugEvent */
 static HANDLE current_process_handle;	/* Currently executing process */
 static windows_thread_info *current_thread;	/* Info on currently selected thread */
-static DWORD main_thread_id;		/* Thread ID of the main thread */
 
 /* Counts of things.  */
 static int exception_count = 0;
@@ -1030,7 +1029,7 @@ handle_output_debug_string (struct target_waitstatus *ourstatus)
 	  ourstatus->kind = TARGET_WAITKIND_STOPPED;
 	  retval = strtoul (p, &p, 0);
 	  if (!retval)
-	    retval = main_thread_id;
+	    retval = current_event.dwThreadId;
 	  else if ((x = (LPCVOID) (uintptr_t) strtoull (p, NULL, 0))
 		   && ReadProcessMemory (current_process_handle, x,
 					 &saved_context,
@@ -1406,14 +1405,13 @@ fake_create_process (void)
        (unsigned) GetLastError ());
       /*  We can not debug anything in that case.  */
     }
-  main_thread_id = current_event.dwThreadId;
   current_thread
     = windows_add_thread (ptid_t (current_event.dwProcessId, 0,
 				  current_event.dwThreadId),
 			  current_event.u.CreateThread.hThread,
 			  current_event.u.CreateThread.lpThreadLocalBase,
 			  true /* main_thread_p */);
-  return main_thread_id;
+  return current_event.dwThreadId;
 }
 
 void
@@ -1611,7 +1609,6 @@ get_windows_debug_event (struct target_ops *ops,
 	break;
 
       current_process_handle = current_event.u.CreateProcessInfo.hProcess;
-      main_thread_id = current_event.dwThreadId;
       /* Add the main thread.  */
       th = windows_add_thread
         (ptid_t (current_event.dwProcessId, 0,
@@ -1656,7 +1653,7 @@ get_windows_debug_event (struct target_ops *ops,
       catch_errors (handle_load_dll);
       ourstatus->kind = TARGET_WAITKIND_LOADED;
       ourstatus->value.integer = 0;
-      thread_id = main_thread_id;
+      thread_id = current_event.dwThreadId;
       break;
 
     case UNLOAD_DLL_DEBUG_EVENT:
@@ -1669,7 +1666,7 @@ get_windows_debug_event (struct target_ops *ops,
       catch_errors (handle_unload_dll);
       ourstatus->kind = TARGET_WAITKIND_LOADED;
       ourstatus->value.integer = 0;
-      thread_id = main_thread_id;
+      thread_id = current_event.dwThreadId;
       break;
 
     case EXCEPTION_DEBUG_EVENT: