[WRAPPER] Make libresolv symbols runtime-resolved (res_*/dn_expand)

[yzewei]

Encountered Error: Symbol res_search not found when running the zaber_motion Python project (specifically while loading zaber-motion-core-linux-amd64.so).

The binary explicitly links against res_search, but on the host system (LoongArch64 with newer glibc), libresolv only exports __res_search. This PR adds a GO2 mapping to redirect the guest res_search to the host __res_search.

Reproduction

a minimal C program to reproduce the issue.

test_resolv.c:

#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <arpa/inet.h>
#include <arpa/nameser.h>
#include <resolv.h>
#include <netinet/in.h>
#include <dlfcn.h>

#define TEST_START(name) printf("[-] Testing %s... ", name)
#define TEST_PASS() printf("PASS\n")
#define TEST_FAIL(msg) printf("FAIL: %s\n", msg)

typedef int (*b64_ntop_t)(unsigned char const *src, size_t srclength, char *target, size_t targsize);
typedef int (*b64_pton_t)(char const *src, unsigned char *target, size_t targsize);
typedef int (*dn_comp_t)(const char *src, unsigned char *dst, int dstsiz, unsigned char **dnptrs, unsigned char **lastdnptr);

void* load_hidden_sym(void* handle, const char* name) {
    void* sym = dlsym(handle, name);
    if (!sym) {
        printf("(Skip: symbol '%s' not found via dlsym) ", name);
        return NULL;
    }
    return sym;
}

void test_base64(void* lib_handle) {
    TEST_START("__b64_ntop / __b64_pton");
    
    b64_ntop_t my_b64_ntop = (b64_ntop_t)load_hidden_sym(lib_handle, "__b64_ntop");
    b64_pton_t my_b64_pton = (b64_pton_t)load_hidden_sym(lib_handle, "__b64_pton");

    if (!my_b64_ntop || !my_b64_pton) {
        printf("SKIPPED (Internal symbols missing)\n");
        return;
    }

    unsigned char src[] = "Box64";
    char encoded[64];
    unsigned char decoded[64];

    int len = my_b64_ntop(src, sizeof(src)-1, encoded, sizeof(encoded));
    if (len < 0) { TEST_FAIL("ntop failed"); return; }
    
    if (strstr(encoded, "Qm94NjQ=") == NULL) { TEST_FAIL("ntop output mismatch"); printf("   Got: %s\n", encoded); return; }

    int len2 = my_b64_pton(encoded, decoded, sizeof(decoded));
    if (len2 < 0) { TEST_FAIL("pton failed"); return; }
    decoded[len2] = '\0';
    
    if (strcmp((char*)decoded, "Box64") != 0) { TEST_FAIL("pton output mismatch"); return; }

    TEST_PASS();
}

void test_dn_comp_expand(void* lib_handle) {
    TEST_START("__dn_comp / dn_expand");
    
    dn_comp_t my_dn_comp = (dn_comp_t)load_hidden_sym(lib_handle, "__dn_comp");
    if (!my_dn_comp) {
        printf("SKIPPED (__dn_comp missing)\n");
        return;
    }

    unsigned char packet[128];
    int len = my_dn_comp("www.google.com", packet, sizeof(packet), NULL, NULL);
    if (len < 0) { TEST_FAIL("__dn_comp failed"); return; }

    char expanded[256];
    int res = dn_expand(packet, packet + len, packet, expanded, sizeof(expanded));
    
    if (res < 0) { TEST_FAIL("dn_expand failed"); return; }
    if (strcmp(expanded, "www.google.com") != 0) { 
        TEST_FAIL("Expansion mismatch"); 
        printf("   Got: %s\n", expanded);
        return; 
    }
    TEST_PASS();
}

void test_ns_get_put() {
    TEST_START("ns_put16 / ns_get16");
    unsigned char buf[16];
    
    ns_put16(12345, buf);
    unsigned int val = ns_get16(buf);
    
    if (val != 12345) {
        TEST_FAIL("Value mismatch");
        printf("   Expected 12345, got %u\n", val);
        return;
    }
    TEST_PASS();
}

void test_res_mkquery() {
    TEST_START("res_mkquery");
    unsigned char buf[4096];
    
    int len = res_mkquery(ns_o_query, "example.com", C_IN, T_A, NULL, 0, NULL, buf, sizeof(buf));
    
    if (len < 0) { TEST_FAIL("Returned < 0"); return; }
    TEST_PASS();
}

void test_res_query() {
    TEST_START("res_query (Checking symbol map)");
    unsigned char answer[4096];
    
    int len = res_query("google.com", C_IN, T_A, answer, sizeof(answer));
    
    if (len < 0) {
        printf("PASS (Network/Query fail is fine, symbol found)\n");
    } else {
        TEST_PASS();
    }
}

void test_res_search() {
    TEST_START("res_search (Your PR fix)");
    unsigned char answer[4096];
    
    int len = res_search("google.com", C_IN, T_A, answer, sizeof(answer));
    
    if (len < 0) {
        printf("PASS (Network/Query fail is fine, symbol found)\n");
    } else {
        TEST_PASS();
    }
}

void test_inet_net() {
    TEST_START("inet_net_pton");
    char *ip_str = "192.168.1.1";
    unsigned char buf[4];
    
    int bits = inet_net_pton(AF_INET, ip_str, buf, sizeof(buf));
    if (bits == -1) { TEST_FAIL("inet_net_pton failed"); } 
    else { TEST_PASS(); }
}

int main() {
    printf("=== Box64 libresolv Comprehensive Test (v2) ===\n");
    
    if (res_init() != 0) {
        printf("FATAL: res_init failed.\n");
        return 1;
    }

    void* handle = dlopen("libresolv.so.2", RTLD_LAZY);
    if (!handle) {
        handle = dlopen("libresolv.so", RTLD_LAZY);
    }
    if (!handle) {
        printf("Warning: Could not dlopen libresolv, skipping hidden symbol tests.\n");
    }

    test_base64(handle);
    test_ns_get_put();
    test_dn_comp_expand(handle);
    test_inet_net();
    test_res_mkquery();
    test_res_query();
    test_res_search();

    if (handle) dlclose(handle);
    printf("=== End of Tests ===\n");
    return 0;
}

Before Fix (Error):

[BOX64] Error: PltResolver: Symbol  res_search(optver 2: res_search@GLIBC_2.34) not found, cannot apply R_X86_64_JUMP_SLOT 0x100004000 in /home/yzw/python-trans/box_test/test_resolv_x64 (local_maplib=(nil), global maplib=0x3a762480, deepbind=0)
 return 0x100002038[function: (nil)]
 return 

After Fix (Success):

 test_resolv_x64
[BOX64] Adding /usr/gnemul/latx-i386/lib/i386-linux-gnu/libresolv.so.2 to the libs
[BOX64] Box64 loongarch64 v0.4.1 024b1837 with Dynarec built on Jan  8 2026 15:57:13
[BOX64] Dynarec for LoongArch with extension LSX LASX LBT_X86
[BOX64] Running on Loongson-3A5000LL with 4 cores, pagesize: 16384
[BOX64] Will use hardware counter measured at 2.3 GHz
[BOX64] Didn't detect 48bits of address space, considering it's 39bits
[BOX64] Adding /usr/gnemul/latx-i386/lib/i386-linux-gnu/libresolv.so.2 to the libs
[BOX64] Counted 63 Env var
[BOX64] Library search path: 
[BOX64] Binary search path: ./:bin/:/root/.cargo/bin/:/usr/local/python3.11/bin/:/usr/local/python3.6/bin/:/usr/local/jdk-11.0.9/bin/:/usr/local/jdk-11.0.9/bin/jar/:/home/yzw/bin/go//bin/:/usr/local/bin/:/usr/lib/golang-1.19/bin/:/usr/local/jdk-11.0.19/bin/:/usr/local/jdk-11.0.19/jre/bin/:/usr/share/Modules/bin/:/usr/local/sbin/:/usr/local/bin/:/usr/sbin/:/usr/bin/
[BOX64] Looking for ../../box_test/test_resolv_full
[BOX64] Adding /usr/gnemul/latx-i386/lib/i386-linux-gnu/libresolv.so.2 to the libs
[BOX64] Adding /usr/gnemul/latx-i386/lib/i386-linux-gnu/libresolv.so.2 to the libs
[BOX64] Dynarec for LoongArch with extension LSX LASX LBT_X86
[BOX64] Running on Loongson-3A5000LL with 4 cores, pagesize: 16384
[BOX64] Will use hardware counter measured at 2.3 GHz
[BOX64] BOX64ENV: Variables overridden:
	BOX64_ADDLIBS=/usr/gnemul/latx-i386/lib/i386-linux-gnu/libresolv.so.2
	BOX64_LOG=1
[BOX64] Rename process to "test_resolv_full"
[BOX64] BOX64, Adding /usr/gnemul/latx-i386/lib/i386-linux-gnu/libresolv.so.2 to needed libs of /home/yzw/python-trans/box_test/test_resolv_full
[BOX64] BOX64, Adding /usr/gnemul/latx-i386/lib/i386-linux-gnu/libresolv.so.2 to needed libs of /home/yzw/python-trans/box_test/test_resolv_full
[BOX64] BOX64, Adding /usr/gnemul/latx-i386/lib/i386-linux-gnu/libresolv.so.2 to needed libs of /home/yzw/python-trans/box_test/test_resolv_full
[BOX64] BOX64, Adding /usr/gnemul/latx-i386/lib/i386-linux-gnu/libresolv.so.2 to needed libs of /home/yzw/python-trans/box_test/test_resolv_full
[BOX64] Using native(wrapped) libresolv.so.2
[BOX64] Using native(wrapped) libc.so.6
[BOX64] Using native(wrapped) ld-linux-x86-64.so.2
[BOX64] Using native(wrapped) libpthread.so.0
[BOX64] Using native(wrapped) libdl.so.2
[BOX64] Using native(wrapped) libutil.so.1
[BOX64] Using native(wrapped) librt.so.1
[BOX64] Using native(wrapped) libbsd.so.0
=== Box64 libresolv Comprehensive Test (v2) ===
[-] Testing __b64_ntop / __b64_pton... PASS
[-] Testing ns_put16 / ns_get16... PASS
[-] Testing __dn_comp / dn_expand... PASS
[-] Testing inet_net_pton... PASS
[-] Testing res_mkquery... PASS
[-] Testing res_query (Checking symbol map)... PASS
[-] Testing res_search (Your PR fix)... PASS
=== End of Tests ===

[yzewei]

PTAL!

[ksco]

I don't think this is the proper way to address this, the old code is there for a reason.

So from what I can tell, on some systems, there is no res_search, and on some others, there is no __res_search. We can change the code to:

GOM(res_search, iFEpiipi)
GOM(__res_search, iFEpiipi)

And probe the available symbol using dlsym in my_res_search and my___res_search.

[yzewei]

I don't think this is the proper way to address this, the old code is there for a reason.

So from what I can tell, on some systems, there is no res_search, and on some others, there is no __res_search. We can change the code to:

GOM(res_search, iFEpiipi)
GOM(__res_search, iFEpiipi)

And probe the available symbol using dlsym in my_res_search and my___res_search.

Hi,

I understand your point and agree with the approach. Before proceeding with dlsym to probe the availability of res_search and __res_search, I think it would be useful to first examine how many other function interfaces within the resolv library might be problematic in this context.

[ksco]

Yeah, there are some similar ones indeed. Could use the same approach, sounds good.

[yzewei]

Thanks! @ksco

[xiangzhai]

Thanks!