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

1 files changed, 20 insertions, 3 deletions

diff --git a/lib/libc/stdlib/atexit.c b/lib/libc/stdlib/atexit.c
index a7a9a32..97cf234 100644
--- a/lib/libc/stdlib/atexit.c
+++ b/lib/libc/stdlib/atexit.c
@@ -37,6 +37,7 @@ static char sccsid[] = "@(#)atexit.c	8.2 (Berkeley) 7/3/94";
 __FBSDID("$FreeBSD$");
 
 #include "namespace.h"
+#include <link.h>
 #include <stddef.h>
 #include <stdlib.h>
 #include <unistd.h>
@@ -147,6 +148,9 @@ __cxa_atexit(void (*func)(void *), void *arg, void *dso)
 	return (error);
 }
 
+#pragma weak __pthread_cxa_finalize
+void __pthread_cxa_finalize(const struct dl_phdr_info *);
+
 /*
  * Call all handlers registered with __cxa_atexit for the shared
  * object owning 'dso'.  Note: if 'dso' is NULL, then all remaining
@@ -155,18 +159,28 @@ __cxa_atexit(void (*func)(void *), void *arg, void *dso)
 void
 __cxa_finalize(void *dso)
 {
+	struct dl_phdr_info phdr_info;
 	struct atexit *p;
 	struct atexit_fn fn;
-	int n;
+	int n, has_phdr;
+
+	if (dso != NULL)
+		has_phdr = _rtld_addr_phdr(dso, &phdr_info);
+	else
+		has_phdr = 0;
 
 	_MUTEX_LOCK(&atexit_mutex);
 	for (p = __atexit; p; p = p->next) {
 		for (n = p->ind; --n >= 0;) {
 			if (p->fns[n].fn_type == ATEXIT_FN_EMPTY)
 				continue; /* already been called */
-			if (dso != NULL && dso != p->fns[n].fn_dso)
-				continue; /* wrong DSO */
 			fn = p->fns[n];
+			if (dso != NULL && dso != fn.fn_dso) {
+				/* wrong DSO ? */
+				if (!has_phdr || !__elf_phdr_match_addr(
+				    &phdr_info, fn.fn_ptr.cxa_func))
+					continue;
+			}
 			/*
 			  Mark entry to indicate that this particular handler
 			  has already been called.
@@ -185,4 +199,7 @@ __cxa_finalize(void *dso)
 	_MUTEX_UNLOCK(&atexit_mutex);
 	if (dso == NULL)
 		_MUTEX_DESTROY(&atexit_mutex);
+
+	if (&__pthread_cxa_finalize != NULL)
+		__pthread_cxa_finalize(&phdr_info);
 }