Allow ldd(1) be used on shared libraries in addition to executables.

include/dlfcn.h

@@ -45,6 +45,7 @@
 #define RTLD_MODEMASK	0x3
 #define RTLD_GLOBAL	0x100	/* Make symbols globally available */
 #define RTLD_LOCAL	0	/* Opposite of RTLD_GLOBAL, and the default */
+#define RTLD_TRACE	0x200	/* Trace loaded objects and exit */
 
 /*
  * Special handle arguments for dlsym().

lib/libc/gen/dlopen.3

@@ -123,6 +123,13 @@ Symbols in this shared object and its DAG of needed objects will be
 available for resolving undefined references only from other objects
 in the same DAG.  This is the default, but it may be specified
 explicitly with this flag.
+.It Dv RTLD_TRACE
+When set, causes dynamic linker to exit after loading all objects
+needed by this shared object and printing a summary which includes
+the absolute pathnames of all objects, to standard output.
+With this flag
+.Fn dlopen
+will return to the caller only in the case of error.
 .El
 .Pp
 If

libexec/rtld-elf/rtld.c

@@ -107,6 +107,7 @@ static void objlist_remove_unref(Objlist *);
 static int relocate_objects(Obj_Entry *, bool);
 static void rtld_exit(void);
 static char *search_library_path(const char *, const char *);
+static const void **get_program_var_addr(const char *name);
 static void set_program_var(const char *, const void *);
 static const Elf_Sym *symlook_default(const char *, unsigned long hash,
   const Obj_Entry *refobj, const Obj_Entry **defobj_out, bool in_plt);
@@ -1556,6 +1557,11 @@ dlopen(const char *name, int mode)
     Obj_Entry **old_obj_tail;
     Obj_Entry *obj;
     Objlist initlist;
+    int result;
+
+    ld_tracing = (mode & RTLD_TRACE) == 0 ? NULL : "1";
+    if (ld_tracing != NULL)
+	environ = (char **)*get_program_var_addr("environ");
 
     objlist_init(&initlist);
 
@@ -1581,7 +1587,14 @@ dlopen(const char *name, int mode)
 	if (*old_obj_tail != NULL) {		/* We loaded something new. */
 	    assert(*old_obj_tail == obj);
 
-	    if (load_needed_objects(obj) == -1 ||
+	    result = load_needed_objects(obj);
+	    if (result != -1 && ld_tracing) {
+		trace_loaded_objects(obj);
+		wlock_release();
+		exit(0);
+	    }
+
+	    if (result == -1 ||
 	      (init_dag(obj), relocate_objects(obj, mode == RTLD_NOW)) == -1) {
 		obj->dl_refcount--;
 		unref_dag(obj);
@@ -1812,12 +1825,10 @@ r_debug_state(struct r_debug* rd, struct link_map *m)
 }
 
 /*
- * Set a pointer variable in the main program to the given value.  This
- * is used to set key variables such as "environ" before any of the
- * init functions are called.
+ * Get address of the pointer variable in the main program.
  */
-static void
-set_program_var(const char *name, const void *value)
+static const void **
+get_program_var_addr(const char *name)
 {
     const Obj_Entry *obj;
     unsigned long hash;
@@ -1830,11 +1841,26 @@ set_program_var(const char *name, const void *value)
 	    const void **addr;
 
 	    addr = (const void **)(obj->relocbase + def->st_value);
-	    dbg("\"%s\": *%p <-- %p", name, addr, value);
-	    *addr = value;
-	    break;
+	    return addr;
 	}
     }
+    return NULL;
+}
+
+/*
+ * Set a pointer variable in the main program to the given value.  This
+ * is used to set key variables such as "environ" before any of the
+ * init functions are called.
+ */
+static void
+set_program_var(const char *name, const void *value)
+{
+    const void **addr;
+
+    if ((addr = get_program_var_addr(name)) != NULL) {
+	dbg("\"%s\": *%p <-- %p", name, addr, value);
+	*addr = value;
+    }
 }
 
 /*

usr.bin/ldd/ldd.1

@@ -13,7 +13,8 @@
 .Ar program ...
 .Sh DESCRIPTION
 .Nm
-displays all shared objects that are needed to run the given program.
+displays all shared objects that are needed to run the given program or
+to load the given shared object.
 Contrary to
 .Xr nm 1 ,
 the list includes

usr.bin/ldd/ldd.c

@@ -36,6 +36,7 @@ static const char rcsid[] =
 #include <sys/wait.h>
 #include <machine/elf.h>
 #include <a.out.h>
+#include <dlfcn.h>
 #include <err.h>
 #include <fcntl.h>
 #include <stdio.h>
@@ -116,6 +117,7 @@ char	*argv[];
 		int	n;
 		int	status;
 		int	file_ok;
+		int	is_shlib;
 
 		if ((fd = open(*argv, O_RDONLY, 0)) < 0) {
 			warn("%s", *argv);
@@ -130,6 +132,7 @@ char	*argv[];
 		}
 
 		file_ok = 1;
+		is_shlib = 0;
 		if (n >= sizeof hdr.aout && !N_BADMAG(hdr.aout)) {
 			/* a.out file */
 			if ((N_GETFLAG(hdr.aout) & EX_DPMASK) != EX_DYNAMIC
@@ -167,6 +170,8 @@ char	*argv[];
 			if (!dynamic) {
 				warnx("%s: not a dynamic executable", *argv);
 				file_ok = 0;
+			} else if (hdr.elf.e_type == ET_DYN) {
+				is_shlib = 1;
 			}
 		} else {
 			warnx("%s: not a dynamic executable", *argv);
@@ -204,8 +209,13 @@ char	*argv[];
 			}
 			break;
 		case 0:
-			execl(*argv, *argv, (char *)NULL);
-			warn("%s", *argv);
+			if (is_shlib == 0) {
+				execl(*argv, *argv, (char *)NULL);
+				warn("%s", *argv);
+			} else {
+				dlopen(*argv, RTLD_TRACE);
+				warnx("%s: %s", *argv, dlerror());
+			}
 			_exit(1);
 		}
 	}