Implement support for dlsym() with RTLD_DEFAULT and RTLD_NEXT

dlsym() with RTLD_DEFAULT handle behaves in same way like with global handle
returned by dlopen() with NULL file name.

dlsym() with RTLD_NEXT handle search for next loaded module which provides
specified symbol. "Next" means module which in EnumProcessModules() result
after the module which called dlsym().

To get caller function of dlsym() use _ReturnAddress() intrinsic. To get
module where is caller function use the fact that HMODULE is the same value
as the module's base address.

When compiling under gcc, defines _ReturnAddress() macro via gcc's builtin
as it does not provide MSC's specific _ReturnAddress() intrinsic.

Added tests demonstrate that both RTLD_DEFAULT and RTLD_NEXT are working as
expected.

1 files changed, 55 insertions, 0 deletions

diff --git a/testdll2.c b/testdll2.c
new file mode 100644
index 0000000..910c820
--- /dev/null
+++ b/testdll2.c
@@ -0,0 +1,55 @@
+/*

+ * dlfcn-win32

+ * Copyright (c) 2007 Ramiro Polla

+ * Copyright (c) 2019 Pali Rohár <pali.rohar@gmail.com>

+ *

+ * dlfcn-win32 is free software; you can redistribute it and/or

+ * modify it under the terms of the GNU Lesser General Public

+ * License as published by the Free Software Foundation; either

+ * version 2.1 of the License, or (at your option) any later version.

+ *

+ * dlfcn-win32 is distributed in the hope that it will be useful,

+ * but WITHOUT ANY WARRANTY; without even the implied warranty of

+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

+ * Lesser General Public License for more details.

+ *

+ * You should have received a copy of the GNU Lesser General Public

+ * License along with dlfcn-win32; if not, write to the Free Software

+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA

+ */

+

+#ifdef _DEBUG

+#define _CRTDBG_MAP_ALLOC

+#include <stdlib.h>

+#include <crtdbg.h>

+#endif

+#include <stdio.h>

+

+#include "dlfcn.h"

+

+#if defined(_WIN32)

+#define EXPORT __declspec(dllexport)

+#else

+#define EXPORT

+#endif

+

+EXPORT int function2( void )

+{

+    char *error;

+    int (*function2_orig)(void);

+    printf( "Hello, world! from wrapper library\n" );

+    function2_orig = dlsym(RTLD_NEXT, "function2");

+    if (!function2_orig)

+    {

+        error = dlerror( );

+        printf( "ERROR\tCould not get symbol from RTLD_NEXT handle: %s\n",

+                error ? error : "" );

+        return 1;

+    }

+    if (function2_orig() != 0)

+    {

+        printf( "ERROR\tOriginal function from RTLD_NEXT handle did not return correct value\n" );

+        return 1;

+    }

+    return 2;

+}