* cxx.cc (default_cygwin_cxx_malloc): Enhance commenting.

* dll_init.cc (dll_dllcrt0_1): Likewise.
	* dlfcn.cc (dlopen): Prevent dlopen()'d DLL from installing any
	cxx malloc overrides.
	* include/cygwin/cygwin_dll.h (__dynamically_loaded): New variable.
	* lib/_cygwin_crt0_common.cc (_cygwin_crt0_common): Check it and only
	install cxx malloc overrides when statically loaded.  Extend comments.

winsup/cygwin/ChangeLog

@@ -1,3 +1,14 @@
+2009-08-13  Corinna Vinschen  <corinna@vinschen.de>
+	    Dave Korn <dave.korn.cygwin@googlemail.com>
+
+	* cxx.cc (default_cygwin_cxx_malloc): Enhance commenting.
+	* dll_init.cc (dll_dllcrt0_1): Likewise.
+	* dlfcn.cc (dlopen): Prevent dlopen()'d DLL from installing any
+	cxx malloc overrides.
+	* include/cygwin/cygwin_dll.h (__dynamically_loaded): New variable.
+	* lib/_cygwin_crt0_common.cc (_cygwin_crt0_common): Check it and only
+	install cxx malloc overrides when statically loaded.  Extend comments.
+
 2009-08-12  Corinna Vinschen  <corinna@vinschen.de>
 
 	* fhandler_socket.cc (fhandler_socket::accept): Always use local

winsup/cygwin/cxx.cc

@@ -87,7 +87,10 @@ __cxa_guard_release ()
 }
 
 /* These routines are made available as last-resort fallbacks
-   for the application.  Should not be used in practice.  */
+   for the application.  Should not be used in practice; the
+   entries in this struct get overwritten by each DLL as it
+   is loaded, and libstdc++ will override the whole lot first
+   thing of all.   */
 
 struct per_process_cxx_malloc default_cygwin_cxx_malloc =
 {

winsup/cygwin/dlfcn.cc

@@ -93,7 +93,28 @@ dlopen (const char *name, int)
 	  wchar_t *path = tp.w_get ();
 
 	  pc.get_wide_win32_path (path);
+
+	  /* Workaround for broken DLLs built against Cygwin versions 1.7.0-49
+	     up to 1.7.0-57.  They override the cxx_malloc pointer in their
+	     DLL initialization code even if loaded dynamically.  This is a
+	     no-no since a later dlclose lets cxx_malloc point into nirvana.
+	     The below kludge "fixes" that by reverting the original cxx_malloc
+	     pointer after LoadLibrary.  This implies that their overrides
+	     won't be applied; that's OK.  All overrides should be present at
+	     final link time, as Windows doesn't allow undefined references;
+	     it would actually be wrong for a dlopen'd DLL to opportunistically
+	     override functions in a way that wasn't known then.  We're not
+	     going to try and reproduce the full ELF dynamic loader here!  */
+
+	  /* Store original cxx_malloc pointer. */
+	  struct per_process_cxx_malloc *tmp_malloc;
+	  tmp_malloc = __cygwin_user_data.cxx_malloc;
+
 	  ret = (void *) LoadLibraryW (path);
+
+	  /* Restore original cxx_malloc pointer. */
+	  __cygwin_user_data.cxx_malloc = tmp_malloc;
+
 	  if (ret == NULL)
 	    __seterrno ();
 	}

winsup/cygwin/dll_init.cc

@@ -328,6 +328,26 @@ dll_dllcrt0_1 (VOID *x)
 
   bool linked = !in_forkee && !cygwin_finished_initializing;
 
+  /* Broken DLLs built against Cygwin versions 1.7.0-49 up to 1.7.0-57
+     override the cxx_malloc pointer in their DLL initialization code,
+     when loaded either statically or dynamically.  Because this leaves
+     a stale pointer into demapped memory space if the DLL is unloaded
+     by a call to dlclose, we prevent this happening for dynamically
+     loaded DLLS in dlopen by saving and restoring cxx_malloc around
+     the call to LoadLibrary, which invokes the DLL's startup sequence.
+     Modern DLLs won't even attempt to override the pointer when loaded
+     statically, but will write their overrides directly into the
+     struct it points to.  With all modern DLLs, this will remain the
+     default_cygwin_cxx_malloc struct in cxx.cc, but if any broken DLLs
+     are in the mix they will have overridden the pointer and subsequent
+     overrides will go into their embedded cxx_malloc structs.  This is
+     almost certainly not a problem as they can never be unloaded, but
+     if we ever did want to do anything about it, we could check here to
+     see if the pointer had been altered in the early parts of the DLL's
+     startup, and if so copy back the new overrides and reset it here.
+     However, that's just a note for the record; at the moment, we can't
+     see any need to worry about this happening.  */
+
   /* Partially initialize Cygwin guts for non-cygwin apps. */
   if (dynamically_loaded && user_data->magic_biscuit == 0)
     dll_crt0 (p);

winsup/cygwin/include/cygwin/cygwin_dll.h

@@ -33,6 +33,7 @@ CDECL_END								      \
 static HINSTANCE storedHandle;						      \
 static DWORD storedReason;						      \
 static void* storedPtr;							      \
+int __dynamically_loaded;						      \
 									      \
 static int __dllMain (int a, char **b, char **c)			      \
 {									      \
@@ -53,6 +54,7 @@ int WINAPI _cygwin_dll_entry (HINSTANCE h, DWORD reason, void *ptr)	      \
       storedHandle = h;							      \
       storedReason = reason;						      \
       storedPtr = ptr;							      \
+      __dynamically_loaded = (ptr == NULL);				      \
       dll_index = cygwin_attach_dll (h, &__dllMain);			      \
       if (dll_index == (DWORD) -1)					      \
 	ret = 0;							      \

winsup/cygwin/lib/_cygwin_crt0_common.cc

@@ -40,6 +40,9 @@ extern WEAK void operator delete[](void *p, const std::nothrow_t &nt) throw()
 /* Avoid an info message from linker when linking applications.  */
 extern __declspec(dllimport) struct _reent *_impure_ptr;
 
+/* Initialised in _cygwin_dll_entry. */
+extern int __dynamically_loaded;
+
 #undef environ
 
 extern "C"
@@ -70,11 +73,13 @@ _cygwin_crt0_common (MainFunc f, per_process *u)
   per_process *newu = (per_process *) cygwin_internal (CW_USER_DATA);
   int uwasnull;
 
+  /* u is non-NULL if we are in a DLL, and NULL in the main exe.
+     newu is the Cygwin DLL's internal per_process and never NULL.  */
   if (u != NULL)
     uwasnull = 0;	/* Caller allocated space for per_process structure.  */
   else
     {
-      u = newu;	/* Using DLL built-in per_process.  */
+      u = newu;		/* Using DLL built-in per_process.  */
       uwasnull = 1;	/* Remember for later.  */
     }
 
@@ -114,8 +119,10 @@ _cygwin_crt0_common (MainFunc f, per_process *u)
   u->realloc = &realloc;
   u->calloc = &calloc;
 
-  /* Likewise for the C++ memory operators - if any.  */
-  if (newu && newu->cxx_malloc)
+  /* Likewise for the C++ memory operators, if any, but not if we
+     were dlopen()'d, as we might get dlclose()'d and that would
+     leave stale function pointers behind.    */
+  if (newu && newu->cxx_malloc && !__dynamically_loaded)
     {
       /* Inherit what we don't override.  */
 #define CONDITIONALLY_OVERRIDE(MEMBER) \
@@ -129,12 +136,10 @@ _cygwin_crt0_common (MainFunc f, per_process *u)
       CONDITIONALLY_OVERRIDE(oper_new___nt);
       CONDITIONALLY_OVERRIDE(oper_delete_nt);
       CONDITIONALLY_OVERRIDE(oper_delete___nt);
+      /* Now update the resulting set into the global redirectors.  */
+      *newu->cxx_malloc = __cygwin_cxx_malloc;
     }
 
-  /* Now update the resulting set into the global redirectors.  */
-  if (newu)
-    newu->cxx_malloc = &__cygwin_cxx_malloc;
-
   /* Setup the module handle so fork can get the path name.  */
   u->hmodule = GetModuleHandle (0);