问带有C共享库的ffi Node.js中未定义的符号- libmodbus

EN

#include <modbus.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>

extern int read(void);

int main(void)
{
        int i=0;
        printf("starte\n");
        i = read();
        return i;
}

extern int read(void)
{
        modbus_t *ctx;
        uint16_t tab_reg[32];
        int anzahl = 1;
        int rc;

        ctx = modbus_new_tcp("10.69.69.103",502);
        modbus_set_slave(ctx, 180);

        if(modbus_connect(ctx) == -1)
        {
                modbus_free(ctx);
                return -1;
        }

        rc = modbus_read_input_registers(ctx, 100, anzahl, tab_reg);

        if (rc == -1)
        {
                modbus_free(ctx);
                return -1;
        }

        printf("Reg: %d\n", tab_reg[0]);
        return tab_reg[0];
}

gcc -c -Wall -Werror -fPIC modtest.c -I/usr/local/include/modbus/ -L/usr/lib/ -lmodbus

gcc -shared -o libmodtest.so modtest.o

var ffi = require('ffi');

var libmod = ffi.Library('libmodtest', {
        'read': ['int', [ 'void'] ]

});


var cb = libmod.read();
console.log(cb);

/home/frala/tmp/node_modules/ffi/lib/dynamic_library.js:74
    throw new Error('Dynamic Linking Error: ' + err)
          ^
Error: Dynamic Linking Error: /usr/lib/libmodtest.so: undefined symbol: modbus_connect
    at new DynamicLibrary (/home/frala/tmp/node_modules/ffi/lib/dynamic_library.js:74:11)
    at Object.Library (/home/frala/tmp/node_modules/ffi/lib/library.js:45:12)
    at Object.<anonymous> (/home/frala/tmp/test/modtest.js:4:18)
    at Module._compile (module.js:456:26)
    at Object.Module._extensions..js (module.js:474:10)
    at Module.load (module.js:356:32)
    at Function.Module._load (module.js:312:12)
    at Function.Module.runMain (module.js:497:10)
    at startup (node.js:119:16)
    at node.js:906:3

000006a8 T main
         U modbus_connect
         U modbus_free
         U modbus_new_tcp
         U modbus_read_input_registers
         U modbus_set_slave
         U printf@@GLIBC_2.4
         U puts@@GLIBC_2.4
000006d0 T read
00000608 t register_tm_clones
0000904c d __TMC_END__