On shared object unload, in __cxa_finalize, call and clear all installed

atexit and __cxa_atexit handlers that are either installed by unloaded
dso, or points to the functions provided by the dso.

Use _rtld_addr_phdr to locate segment information from the address of
private variable belonging to the dso, supplied by crtstuff.c. Provide
utility function __elf_phdr_match_addr to do the match of address against
dso executable segment.

Call back into libthr from __cxa_finalize using weak
__pthread_cxa_finalize symbol to remove any atfork handler which
function points into unloaded object.

The rtld needs private __pthread_cxa_finalize symbol to not require
resolution of the weak undefined symbol at initialization time. This
cannot work, since rtld is relocated before sym_zero is set up.

Idea by:	kan
Reviewed by:	kan (previous version)
MFC after:	3 weeks

2 files changed, 25 insertions, 0 deletions

diff --git a/lib/libthr/thread/thr_fork.c b/lib/libthr/thread/thr_fork.c
index 529f38f..b1c221e 100644
--- a/lib/libthr/thread/thr_fork.c
+++ b/lib/libthr/thread/thr_fork.c
@@ -59,6 +59,7 @@
 
 #include "namespace.h"
 #include <errno.h>
+#include <link.h>
 #include <string.h>
 #include <stdlib.h>
 #include <unistd.h>
@@ -94,6 +95,27 @@ _pthread_atfork(void (*prepare)(void), void (*parent)(void),
 	return (0);
 }
 
+void
+__pthread_cxa_finalize(struct dl_phdr_info *phdr_info)
+{
+	struct pthread *curthread;
+	struct pthread_atfork *af, *af1;
+
+	_thr_check_init();
+
+	curthread = _get_curthread();
+	THR_UMUTEX_LOCK(curthread, &_thr_atfork_lock);
+	TAILQ_FOREACH_SAFE(af, &_thr_atfork_list, qe, af1) {
+		if (__elf_phdr_match_addr(phdr_info, af->prepare) ||
+		    __elf_phdr_match_addr(phdr_info, af->parent) ||
+		    __elf_phdr_match_addr(phdr_info, af->child)) {
+			TAILQ_REMOVE(&_thr_atfork_list, af, qe);
+			free(af);
+		}
+	}
+	THR_UMUTEX_UNLOCK(curthread, &_thr_atfork_lock);
+}
+
 __weak_reference(_fork, fork);
 
 pid_t _fork(void);
diff --git a/lib/libthr/thread/thr_private.h b/lib/libthr/thread/thr_private.h
index 465f725..f0c3aa0 100644
--- a/lib/libthr/thread/thr_private.h
+++ b/lib/libthr/thread/thr_private.h
@@ -740,6 +740,9 @@ _thr_check_init(void)
 		_libpthread_init(NULL);
 }
 
+struct dl_phdr_info;
+void __pthread_cxa_finalize(struct dl_phdr_info *phdr_info);
+
 __END_DECLS
 
 #endif  /* !_THR_PRIVATE_H */