* 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.

1 files changed, 21 insertions, 0 deletions

diff --git a/winsup/cygwin/dlfcn.cc b/winsup/cygwin/dlfcn.cc
index a9e3295da..bc95e221c 100644
--- a/winsup/cygwin/dlfcn.cc
+++ b/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 ();
 	}