Implement dlsym(RTLD_NEXT, symbol).

3 files changed, 42 insertions, 8 deletions

diff --git a/lib/csu/i386/crt0.c b/lib/csu/i386/crt0.c
index 5f7e4ab..4d217fb 100644
--- a/lib/csu/i386/crt0.c
+++ b/lib/csu/i386/crt0.c
@@ -27,7 +27,7 @@
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  *
- *	$Id$
+ *	$Id: crt0.c,v 1.29 1997/02/22 14:57:44 peter Exp $
  */
 
 #include <sys/param.h>
@@ -94,6 +94,8 @@ static char		empty[1];
 char			*__progname = empty;
 char			**environ;
 
+static int		ldso_version;
+
 extern	unsigned char	etext;
 extern	unsigned char	eprol asm ("eprol");
 extern			start() asm("start");
@@ -194,7 +196,6 @@ __do_dynamic_link ()
 	struct exec	hdr;
 	char		*ldso;
 	int		(*entry)();
-	int		ret;
 
 #ifdef DEBUG
 	/* Provision for alternate ld.so - security risk! */
@@ -254,14 +255,14 @@ __do_dynamic_link ()
 	crt.crt_ldentry = NULL;
 
 	entry = (int (*)())(crt.crt_ba + sizeof hdr);
-	ret = (*entry)(CRT_VERSION_BSD_4, &crt);
+	ldso_version = (*entry)(CRT_VERSION_BSD_4, &crt);
 	ld_entry = crt.crt_ldentry;
-	if (ret == -1 && ld_entry == NULL) {
+	if (ldso_version == -1 && ld_entry == NULL) {
 		/* if version 4 not recognised, try version 3 */
-		ret = (*entry)(CRT_VERSION_BSD_3, &crt);
+		ldso_version = (*entry)(CRT_VERSION_BSD_3, &crt);
 		ld_entry = _DYNAMIC.d_entry;
 	}
-	if (ret == -1) {
+	if (ldso_version == -1) {
 		_PUTMSG("ld.so failed");
 		if (ld_entry != NULL) {
 			char *msg = (ld_entry->dlerror)();
@@ -277,7 +278,7 @@ __do_dynamic_link ()
 	}
 
 
-	if (ret >= LDSO_VERSION_HAS_DLEXIT)
+	if (ldso_version >= LDSO_VERSION_HAS_DLEXIT)
 		atexit(ld_entry->dlexit);
 
 	return;
@@ -316,7 +317,11 @@ char	*name;
 	if (ld_entry == NULL)
 		return NULL;
 
-	return (ld_entry->dlsym)(fd, name);
+	if (ldso_version >= LDSO_VERSION_HAS_DLSYM3) {
+		void *retaddr = *(&fd - 1);  /* XXX - ABI/machine dependent */
+		return (ld_entry->dlsym3)(fd, name, retaddr);
+	} else
+		return (ld_entry->dlsym)(fd, name);
 }
 
 
diff --git a/lib/csu/i386/dlfcn.h b/lib/csu/i386/dlfcn.h
index feadf90..b6817fe 100644
--- a/lib/csu/i386/dlfcn.h
+++ b/lib/csu/i386/dlfcn.h
@@ -43,6 +43,13 @@
 #define RTLD_LAZY	1	/* Bind function calls lazily */
 #define RTLD_NOW	2	/* Bind function calls immediately */
 
+/*
+ * Special handle argument for dlsym().  It causes the search for the
+ * symbol to begin in the next shared object after the one containing
+ * the caller.
+ */
+#define RTLD_NEXT	((void *) -1)
+
 __BEGIN_DECLS
 void *dlopen __P((char *, int));
 void *dlsym __P((void *, char *));
diff --git a/lib/csu/i386/dlopen.3 b/lib/csu/i386/dlopen.3
index 82651c6..efd59be 100644
--- a/lib/csu/i386/dlopen.3
+++ b/lib/csu/i386/dlopen.3
@@ -152,6 +152,28 @@ returns a null pointer if the symbol cannot be found, and sets an error
 condition which may be queried with
 .Fn dlerror .
 .Pp
+If
+.Fn dlsym
+is called with the special
+.Fa handle
+.Dv RTLD_NEXT ,
+then the search for the symbol is limited to the shared objects
+which were loaded after the one issuing the call to
+.Fn dlsym .
+Thus, if the function is called from the main program, all
+the shared libraries are searched.
+If it is called from a shared library, all subsequent shared
+libraries are searched.
+.Dv RTLD_NEXT
+is useful for implementing wrappers around library functions.
+For example, a wrapper function
+.Fn getpid
+could access the
+.Dq real
+.Fn getpid
+with
+.Li dlsym(RTLD_NEXT, \&"_getpid\&") .
+.Pp
 .Fn dlerror
 returns a null-terminated character string describing the last error that
 occurred during a call to