gdbserver/windows: Ignore DLL load/unload events during child initialization.

This GDBserver patch mirrors a change made in GDB wich aims at
simplifying DLL handling during the inferior initialization
(process creation during the "run", or during an "attach").
Instead of processing each DLL load event, which is sometimes
incomplete, we ignore these events until the inferior has completed
its startup phase, and then just iterate over all DLLs via
EnumProcessModules.

As a side-effect, it fixes a small bug where win32_ensure_ntdll_loaded
was missing a 0x1000 offset in the DLL base address. This problem
should only be visible on the 64bit version of Windows 8.1, since
this is the only platform where win32_ensure_ntdll_loaded is actually
needed.

gdb/gdbserver/ChangeLog:

	* win32-low.c (win32_add_all_dlls): Renames
	win32_ensure_ntdll_loaded.  Rewrite function documentation.
	Adjust implementation to always load all DLLs.
	Add 0x1000 offset to DLL base address when calling
	win32_add_one_solib.
	(child_initialization_done): New static global.
	(do_initial_child_stuff): Set child_initialization_done to
	zero during child initialization, and 1 after.  Replace call
	to win32_ensure_ntdll_loaded by call to win32_add_all_dlls.
	Add comment.
	(match_dll_by_basename, dll_is_loaded_by_basename): Delete.
	(handle_unload_dll): Add function documentation.
	(get_child_debug_event): Ignore load and unload DLL events
	during child initialization.

2 files changed, 61 insertions, 46 deletions

diff --git a/gdb/gdbserver/ChangeLog b/gdb/gdbserver/ChangeLog
index 21c73b2..1111aae 100644
--- a/gdb/gdbserver/ChangeLog
+++ b/gdb/gdbserver/ChangeLog
@@ -1,3 +1,20 @@
+2014-02-26  Joel Brobecker  <brobecker@adacore.com>
+
+	* win32-low.c (win32_add_all_dlls): Renames
+	win32_ensure_ntdll_loaded.  Rewrite function documentation.
+	Adjust implementation to always load all DLLs.
+	Add 0x1000 offset to DLL base address when calling
+	win32_add_one_solib.
+	(child_initialization_done): New static global.
+	(do_initial_child_stuff): Set child_initialization_done to
+	zero during child initialization, and 1 after.  Replace call
+	to win32_ensure_ntdll_loaded by call to win32_add_all_dlls.
+	Add comment.
+	(match_dll_by_basename, dll_is_loaded_by_basename): Delete.
+	(handle_unload_dll): Add function documentation.
+	(get_child_debug_event): Ignore load and unload DLL events
+	during child initialization.
+
 2014-02-20  Doug Evans  <dje@google.com>
 
 	Remove global all_lwps.
diff --git a/gdb/gdbserver/win32-low.c b/gdb/gdbserver/win32-low.c
index e84306d..74ac83f 100644
--- a/gdb/gdbserver/win32-low.c
+++ b/gdb/gdbserver/win32-low.c
@@ -106,7 +106,7 @@ static ptid_t win32_wait (ptid_t ptid, struct target_waitstatus *ourstatus,
 			  int options);
 static void win32_resume (struct thread_resume *resume_info, size_t n);
 #ifndef _WIN32_WCE
-static void win32_ensure_ntdll_loaded (void);
+static void win32_add_all_dlls (void);
 #endif
 
 /* Get the thread ID from the current selected inferior (the current
@@ -324,6 +324,10 @@ child_init_thread_list (void)
   for_each_inferior (&all_threads, delete_thread_info);
 }
 
+/* Zero during the child initialization phase, and nonzero otherwise.  */
+
+static int child_initialization_done = 0;
+
 static void
 do_initial_child_stuff (HANDLE proch, DWORD pid, int attached)
 {
@@ -343,6 +347,7 @@ do_initial_child_stuff (HANDLE proch, DWORD pid, int attached)
   proc = add_process (pid, attached);
   proc->tdesc = win32_tdesc;
   child_init_thread_list ();
+  child_initialization_done = 0;
 
   if (the_low_target.initial_stuff != NULL)
     (*the_low_target.initial_stuff) ();
@@ -376,8 +381,25 @@ do_initial_child_stuff (HANDLE proch, DWORD pid, int attached)
     }
 
 #ifndef _WIN32_WCE
-  win32_ensure_ntdll_loaded ();
+  /* Now that the inferior has been started and all DLLs have been mapped,
+     we can iterate over all DLLs and load them in.
+
+     We avoid doing it any earlier because, on certain versions of Windows,
+     LOAD_DLL_DEBUG_EVENTs are sometimes not complete.  In particular,
+     we have seen on Windows 8.1 that the ntdll.dll load event does not
+     include the DLL name, preventing us from creating an associated SO.
+     A possible explanation is that ntdll.dll might be mapped before
+     the SO info gets created by the Windows system -- ntdll.dll is
+     the first DLL to be reported via LOAD_DLL_DEBUG_EVENT and other DLLs
+     do not seem to suffer from that problem.
+
+     Rather than try to work around this sort of issue, it is much
+     simpler to just ignore DLL load/unload events during the startup
+     phase, and then process them all in one batch now.  */
+  win32_add_all_dlls ();
 #endif
+
+  child_initialization_done = 1;
 }
 
 /* Resume all artificially suspended threads if we are continuing
@@ -1143,42 +1165,11 @@ failed:
 
 #ifndef _WIN32_WCE
 
-/* Helper routine for dll_is_loaded_by_basename.
-   Return non-zero if the basename in ARG matches the DLL in INF.  */
-
-static int
-match_dll_by_basename (struct inferior_list_entry *inf, void *arg)
-{
-  struct dll_info *iter = (void *) inf;
-  const char *basename = arg;
-
-  return strcasecmp (lbasename (iter->name), basename) == 0;
-}
-
-/* Return non-zero if the DLL specified by BASENAME is loaded.  */
-
-static int
-dll_is_loaded_by_basename (const char *basename)
-{
-  return find_inferior (&all_dlls, match_dll_by_basename,
-			(void *) basename) != NULL;
-}
-
-/* On certain versions of Windows, the information about ntdll.dll
-   is not available yet at the time we get the LOAD_DLL_DEBUG_EVENT,
-   thus preventing us from reporting this DLL as an SO. This has been
-   witnessed on Windows 8.1, for instance.  A possible explanation
-   is that ntdll.dll might be mapped before the SO info gets created
-   by the Windows system -- ntdll.dll is the first DLL to be reported
-   via LOAD_DLL_DEBUG_EVENT and other DLLs do not seem to suffer from
-   that problem.
-
-   If we indeed are missing ntdll.dll, this function tries to recover
-   from this issue, after the fact.  Do nothing if we encounter any
-   issue trying to locate that DLL.  */
+/* Iterate over all DLLs currently mapped by our inferior, and
+   add them to our list of solibs.  */
 
 static void
-win32_ensure_ntdll_loaded (void)
+win32_add_all_dlls (void)
 {
   size_t i;
   HMODULE dh_buf[1];
@@ -1186,9 +1177,6 @@ win32_ensure_ntdll_loaded (void)
   DWORD cbNeeded;
   BOOL ok;
 
-  if (dll_is_loaded_by_basename ("ntdll.dll"))
-    return;
-
   if (!load_psapi ())
     return;
 
@@ -1212,7 +1200,7 @@ win32_ensure_ntdll_loaded (void)
   if (!ok)
     return;
 
-  for (i = 0; i < ((size_t) cbNeeded / sizeof (HMODULE)); i++)
+  for (i = 1; i < ((size_t) cbNeeded / sizeof (HMODULE)); i++)
     {
       MODULEINFO mi;
       char dll_name[MAX_PATH];
@@ -1227,12 +1215,11 @@ win32_ensure_ntdll_loaded (void)
 					 dll_name,
 					 MAX_PATH) == 0)
 	continue;
-      if (strcasecmp (lbasename (dll_name), "ntdll.dll") == 0)
-	{
-	  win32_add_one_solib (dll_name,
-			       (CORE_ADDR) (uintptr_t) mi.lpBaseOfDll);
-	  return;
-	}
+      /* The symbols in a dll are offset by 0x1000, which is the
+	 offset from 0 of the first byte in an image - because
+	 of the file header and the section alignment. */
+      win32_add_one_solib (dll_name,
+			   (CORE_ADDR) (uintptr_t) mi.lpBaseOfDll + 0x1000);
     }
 }
 #endif
@@ -1361,6 +1348,13 @@ handle_load_dll (void)
   win32_add_one_solib (dll_name, load_addr);
 }
 
+/* Handle a DLL unload event.
+
+   This function assumes that this event did not occur during inferior
+   initialization, where their event info may be incomplete (see
+   do_initial_child_stuff and win32_add_one_solib for more info
+   on how we handle DLL loading during that phase).  */
+
 static void
 handle_unload_dll (void)
 {
@@ -1675,6 +1669,8 @@ get_child_debug_event (struct target_waitstatus *ourstatus)
 		(unsigned) current_event.dwProcessId,
 		(unsigned) current_event.dwThreadId));
       CloseHandle (current_event.u.LoadDll.hFile);
+      if (! child_initialization_done)
+	break;
       handle_load_dll ();
 
       ourstatus->kind = TARGET_WAITKIND_LOADED;
@@ -1686,6 +1682,8 @@ get_child_debug_event (struct target_waitstatus *ourstatus)
 		"for pid=%u tid=%x\n",
 		(unsigned) current_event.dwProcessId,
 		(unsigned) current_event.dwThreadId));
+      if (! child_initialization_done)
+	break;
       handle_unload_dll ();
       ourstatus->kind = TARGET_WAITKIND_LOADED;
       ourstatus->value.sig = GDB_SIGNAL_TRAP;