Add a "fork" of musl as //fusl.

fusl/src/network/gethostbyaddr_r.c

+#define _GNU_SOURCE
+
+#include <sys/socket.h>
+#include <netdb.h>
+#include <string.h>
+#include <netinet/in.h>
+#include <errno.h>
+#include <inttypes.h>
+
+int gethostbyaddr_r(const void *a, socklen_t l, int af,
+        struct hostent *h, char *buf, size_t buflen,
+        struct hostent **res, int *err)
+{
+        union {
+                struct sockaddr_in sin;
+                struct sockaddr_in6 sin6;
+        } sa = { .sin.sin_family = af };
+        socklen_t sl = af==AF_INET6 ? sizeof sa.sin6 : sizeof sa.sin;
+        int i;
+
+        *res = 0;
+
+        /* Load address argument into sockaddr structure */
+        if (af==AF_INET6 && l==16) memcpy(&sa.sin6.sin6_addr, a, 16);
+        else if (af==AF_INET && l==4) memcpy(&sa.sin.sin_addr, a, 4);
+        else {
+                *err = NO_RECOVERY;
+                return EINVAL;
+        }
+
+        /* Align buffer and check for space for pointers and ip address */
+        i = (uintptr_t)buf & sizeof(char *)-1;
+        if (!i) i = sizeof(char *);
+        if (buflen <= 5*sizeof(char *)-i + l) return ERANGE;
+        buf += sizeof(char *)-i;
+        buflen -= 5*sizeof(char *)-i + l;
+
+        h->h_addr_list = (void *)buf;
+        buf += 2*sizeof(char *);
+        h->h_aliases = (void *)buf;
+        buf += 2*sizeof(char *);
+
+        h->h_addr_list[0] = buf;
+        memcpy(h->h_addr_list[0], a, l);
+        buf += l;
+        h->h_addr_list[1] = 0;
+        h->h_aliases[0] = buf;
+        h->h_aliases[1] = 0;
+
+        switch (getnameinfo((void *)&sa, sl, buf, buflen, 0, 0, 0)) {
+        case EAI_AGAIN:
+                *err = TRY_AGAIN;
+                return EAGAIN;
+        case EAI_OVERFLOW:
+                return ERANGE;
+        default:
+        case EAI_MEMORY:
+        case EAI_SYSTEM:
+        case EAI_FAIL:
+                *err = NO_RECOVERY;
+                return errno;
+        case 0:
+                break;
+        }
+
+        h->h_addrtype = af;
+        h->h_name = h->h_aliases[0];
+        *res = h;
+        return 0;
+}