print warning when dlopen fails

If the file exists but could not be loaded, print the dlerror().
Often it is a missing symbol.

Signed-off-by: Jan Engelhardt <jengelh@computergmbh.de>

diff --git a/xtables.c b/xtables.c
index 0a2fdb1df03f6f4be7754e4f2e33279fdab3534d..673ba763a4f50e31d3fa8e7c78241dbe93369c17 100644 (file)
--- a/xtables.c
+++ b/xtables.c
@@ -307,6 +307,9 @@ void parse_interface(const char *arg, char *vianame, unsigned char *mask)
 struct xtables_match *find_match(const char *name, enum xt_tryload tryload,
                                 struct xtables_rule_match **matches)
 {
+#ifndef NO_SHARED_LIBS
+       struct stat sb;
+#endif
        struct xtables_match *ptr;
        const char *icmp6 = "icmp6";
 
@@ -347,12 +350,16 @@ struct xtables_match *find_match(const char *name, enum xt_tryload tryload,
                        /* Found library.  If it didn't register itself,
                           maybe they specified target as match. */
                        ptr = find_match(name, DONT_LOAD, NULL);
+               else if (stat(path, &sb) == 0)
+                       fprintf(stderr, "%s: %s\n", path, dlerror());
 
                if (ptr == NULL) {
                        sprintf(path, "%s/%s%s.so", lib_dir, afinfo.libprefix,
                                name);
                        if (dlopen(path, RTLD_NOW) != NULL)
                                ptr = find_match(name, DONT_LOAD, NULL);
+                       else if (stat(path, &sb) == 0)
+                               fprintf(stderr, "%s: %s\n", path, dlerror());
                }
 
                if (ptr == NULL && tryload == LOAD_MUST_SUCCEED)
@@ -395,6 +402,9 @@ struct xtables_match *find_match(const char *name, enum xt_tryload tryload,
 
 struct xtables_target *find_target(const char *name, enum xt_tryload tryload)
 {
+#ifndef NO_SHARED_LIBS
+       struct stat sb;
+#endif
        struct xtables_target *ptr;
 
        /* Standard target? */
@@ -420,12 +430,16 @@ struct xtables_target *find_target(const char *name, enum xt_tryload tryload)
                        /* Found library.  If it didn't register itself,
                           maybe they specified match as a target. */
                        ptr = find_target(name, DONT_LOAD);
+               else if (stat(path, &sb) == 0)
+                       fprintf(stderr, "%s: %s\n", path, dlerror());
 
                if (ptr == NULL) {
                        sprintf(path, "%s/%s%s.so", lib_dir, afinfo.libprefix,
                                name);
                        if (dlopen(path, RTLD_NOW) != NULL)
                                ptr = find_target(name, DONT_LOAD);
+                       else if (stat(path, &sb) == 0)
+                               fprintf(stderr, "%s: %s\n", path, dlerror());
                }
                if (ptr == NULL && tryload == LOAD_MUST_SUCCEED)
                        exit_error(PARAMETER_PROBLEM,