rtadvd segfaults when run with the -d flag in my environment. It seems to be caused by sections like the following in rtadvd.c:

        /* O flag */
        if ((nra->nd_ra_flags_reserved & ND_RA_FLAG_OTHER) !=
            rai->rai_otherflg) {
                syslog(LOG_NOTICE,
                    "O flag inconsistent on %s:"
                    " %s from %s, %s from us",
                    ifi->ifi_ifname, on_off[!rai->rai_otherflg],
                    inet_ntop(AF_INET6, &from->sin6_addr, ntopbuf,
                        sizeof(ntopbuf)), on_off[rai->rai_otherflg]);
                inconsistent++;
        }

where rai->rai_otherflg in this case is 0x40 but handled as a bool. Here's a diff that fixes it for my case as well as other similarly-handled flags:

--- config.c.orig	2025-12-04 16:54:44.000000000 +0000
+++ config.c	2026-06-11 11:59:51.691932000 +0100
@@ -443,8 +443,8 @@
 	} else
 		MAYHAVE(val, "raflags", 0);
 
-	rai->rai_managedflg = val & ND_RA_FLAG_MANAGED;
-	rai->rai_otherflg = val & ND_RA_FLAG_OTHER;
+	rai->rai_managedflg = !!(val & ND_RA_FLAG_MANAGED);
+	rai->rai_otherflg = !!(val & ND_RA_FLAG_OTHER);
 #ifndef ND_RA_FLAG_RTPREF_MASK
 #define ND_RA_FLAG_RTPREF_MASK	0x18 /* 00011000 */
 #define ND_RA_FLAG_RTPREF_RSV	0x10 /* 00010000 */
@@ -456,7 +456,7 @@
 		goto getconfig_free_rai;
 	}
 #ifdef DRAFT_IETF_6MAN_IPV6ONLY_FLAG
-	rai->rai_ipv6onlyflg = val & ND_RA_FLAG_IPV6_ONLY;
+	rai->rai_ipv6onlyflg = !!(val & ND_RA_FLAG_IPV6_ONLY);
 #endif
 
 	MAYHAVE(val, "rltime", rai->rai_maxinterval * 3);