wrap _tlv_atexit and __cxa_thread_atexit

`__cxa_thread_atexit` exists in
    MacPorts provided libc++ on 10.6 and earlier
    libSystem.B.dylib on 10.8 and later
    MacPorts provided libstdc++

`_tlv_atexit` exists in libSystem.B.dylib on 10.7 and later

Upstream Clang uses `_tlv_atexit` on all Darwin systems.
MacPorts Clang uses `_tlv_atexit` on 10.6 and earlier.

When MACOSX_DEPLOYMENT_TARGET is set, allow legacy-support library
to find the appropriate atexit function at runtime so the binary
can run on systems other than then one it was built on.

See macports/macports-ports#14514

include/MacportsLegacySupport.h

@@ -166,4 +166,7 @@
 /* copyfile and its associated functions have gained functionality over the years */
 #define __MP_LEGACY_SUPPORT_COPYFILE_WRAP__ (__APPLE__ && __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ < 1060)
 
+/* _tlv_atexit and __cxa_thread_atexit */
+#define __MP_LEGACY_SUPPORT_ATEXIT_WRAP__  (__APPLE__ && __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ < 1070)
+
 #endif /* _MACPORTS_LEGACYSUPPORTDEFS_H_ */

src/add_symbols.c

@@ -29,3 +29,13 @@ extern const char pthread_setname_np_tmp5 __asm("$ld$add$os10.5$_pthread_setname
 /* extern const char copyfile_state_get_tmp4 __asm("$ld$add$os10.4$_copyfile_state_get"); __attribute__((visibility("default"))) const char copyfile_state_get_tmp4 = 0; */
 extern const char copyfile_state_get_tmp5 __asm("$ld$add$os10.5$_copyfile_state_get"); __attribute__((visibility("default"))) const char copyfile_state_get_tmp5 = 0;
 #endif
+
+#if !(__MP_LEGACY_SUPPORT_ATEXIT_WRAP__)
+extern const char _tlv_atexit_tmp4 __asm("$ld$add$os10.4$__tlv_atexit"); __attribute__((visibility("default"))) const char _tlv_atexit_tmp4 = 0;
+extern const char _tlv_atexit_tmp5 __asm("$ld$add$os10.5$__tlv_atexit"); __attribute__((visibility("default"))) const char _tlv_atexit_tmp5 = 0;
+extern const char _tlv_atexit_tmp6 __asm("$ld$add$os10.6$__tlv_atexit"); __attribute__((visibility("default"))) const char _tlv_atexit_tmp6 = 0;
+
+extern const char __cxa_thread_atexit_tmp4 __asm("$ld$add$os10.4$___cxa_thread_atexit"); __attribute__((visibility("default"))) const char __cxa_thread_atexit_tmp4 = 0;
+extern const char __cxa_thread_atexit_tmp5 __asm("$ld$add$os10.5$___cxa_thread_atexit"); __attribute__((visibility("default"))) const char __cxa_thread_atexit_tmp5 = 0;
+extern const char __cxa_thread_atexit_tmp6 __asm("$ld$add$os10.6$___cxa_thread_atexit"); __attribute__((visibility("default"))) const char __cxa_thread_atexit_tmp6 = 0;
+#endif

src/macports_legacy_atexit.c

@@ -0,0 +1,82 @@
+/*
+ * Copyright (c) 2022
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+/* MP support header */
+#include "MacportsLegacySupport.h"
+
+/* _tlv_atexit wrap */
+#if __MP_LEGACY_SUPPORT_ATEXIT_WRAP__
+
+#include <stdlib.h>
+#include <dlfcn.h>
+
+/* signature from https://opensource.apple.com/source/dyld/dyld-852.2/src/threadLocalVariables.c.auto.html */
+void _tlv_atexit(void (*func)(void*), void* objAddr) {
+    void (*real__tlv_atexit)(void (*func)(void*), void* objAddr);
+    int (*real___cxa_thread_atexit)(void (*dtor)(void*), void* obj, void* dso_symbol);
+
+    real__tlv_atexit = dlsym(RTLD_NEXT, "_tlv_atexit");
+    if (real__tlv_atexit != NULL) {
+        /* _tlv_atexit exists in libSystem.B.dylib on 10.7 and later */
+        real__tlv_atexit(func, objAddr);
+	return;
+    }
+
+    real___cxa_thread_atexit = dlsym(RTLD_DEFAULT, "__cxa_thread_atexit");
+    if (real___cxa_thread_atexit != NULL) {
+        /* __cxa_thread_atexit exists in
+               MacPorts provided libc++ on 10.6 and earlier
+               libSystem.B.dylib on 10.8 and later
+               MacPorts provided libstdc++
+
+           in all cases, third parameter (dso_handle) seems to be ignored
+        */
+	real___cxa_thread_atexit(func, objAddr, NULL);
+	return;
+    }
+
+    exit(EXIT_FAILURE);
+}
+
+/* signature from https://github.com/llvm-mirror/libcxxabi/blob/master/src/cxa_thread_atexit.cpp */
+int __cxa_thread_atexit(void (*dtor)(void*), void* obj, void* dso_symbol) {
+    void (*real__tlv_atexit)(void (*func)(void*), void* objAddr);
+    int (*real___cxa_thread_atexit)(void (*dtor)(void*), void* obj, void* dso_symbol);
+
+    real___cxa_thread_atexit = dlsym(RTLD_NEXT, "__cxa_thread_atexit");
+    if (real___cxa_thread_atexit != NULL) {
+        /* __cxa_thread_atexit exists in
+               MacPorts provided libc++ on 10.6 and earlier
+               libSystem.B.dylib on 10.8 and later
+               MacPorts provided libstdc++
+	*/
+        return real___cxa_thread_atexit(dtor, obj, dso_symbol);
+    }
+
+   real__tlv_atexit = dlsym(RTLD_DEFAULT, "_tlv_atexit");
+    if (real__tlv_atexit != NULL) {
+        /* _tlv_atexit exists in libSystem.B.dylib on 10.7 and later
+
+           it seems to be common practice to ignore dso_symbol
+        */
+        real__tlv_atexit(dtor, obj);
+	return 0;
+    }
+
+    exit(EXIT_FAILURE);
+}
+
+#endif /*__MP_LEGACY_SUPPORT_ATEXIT_WRAP__*/