undefined symbol error when loading a module, using AWS C++ SDK, in Freeswitch

Question

I am asking this question again as the mods decided to close my question here as a duplicate, within minutes of it being asked (and also down-voted!!). Now I have gone through all 33 answers of what was thought to be an answer to my solution, but it didn't help. So I am asking again.

I am trying to build a FreeSWITCH module to add text-to-speech functionality using AWS Polly & the AWS C++ SDK. Dev environment is Debian 8, g++ 4.9.2. AWS C++ SDK is built using instructions here except that I turned off shared libs (produces .a lib files).

The AWS C++ SDK was built as recommended here (basically C++ code with C++ linkage). mod_polly.cpp is built with C++ linkage as well to produce mod_polly.so . It does refer to some C headers & functions. This was built as -

g++ -shared -o mod_polly.so -L/usr/local/lib/ -laws-cpp-sdk-polly -laws-cpp-sdk-core -fPIC -g -ggdb -std=c++11 -Wall -Werror -I/usr/src/freeswitch/src/include/ -I/usr/src/freeswitch/libs/libteletone/src/ mod_polly.cpp

Source below -

extern "C" {
#include <switch.h>
}


#include <fstream>

#define BIG_ENDIAN_SYSTEM (*(uint16_t *)"\0\xff" < 0x100)

#define REVERSE_BYTES(...) do for(size_t REVERSE_BYTES=0; REVERSE_BYTES<sizeof(__VA_ARGS__)>>1; ++REVERSE_BYTES)\
    ((unsigned char*)&(__VA_ARGS__))[REVERSE_BYTES] ^= ((unsigned char*)&(__VA_ARGS__))[sizeof(__VA_ARGS__)-1-REVERSE_BYTES],\
    ((unsigned char*)&(__VA_ARGS__))[sizeof(__VA_ARGS__)-1-REVERSE_BYTES] ^= ((unsigned char*)&(__VA_ARGS__))[REVERSE_BYTES],\
    ((unsigned char*)&(__VA_ARGS__))[REVERSE_BYTES] ^= ((unsigned char*)&(__VA_ARGS__))[sizeof(__VA_ARGS__)-1-REVERSE_BYTES];\
while(0)

#include <aws/core/Aws.h>
#include <aws/core/auth/AWSCredentials.h>
#include <aws/core/client/ClientConfiguration.h>
#include <aws/core/utils/Outcome.h>
#include <aws/polly/PollyClient.h>
#include <aws/polly/model/SynthesizeSpeechRequest.h>
#include <aws/polly/model/SynthesizeSpeechResult.h>
#include <aws/polly/model/TextType.h>
#include <aws/polly/model/LanguageCode.h>
#include <aws/polly/model/OutputFormat.h>
#include <aws/polly/model/VoiceId.h>

typedef unsigned long DWORD;    // 32-bit unsigned integer
typedef unsigned short WORD;    // 16-bit unsigned integer

struct riff                                 // Data             Bytes   Total
{
    char            chunkID[4];             // "RIFF"           4       4
    DWORD           riffSize;               // file size - 8    4       8
    char            typeID[4];              // "WAVE"           4       12
    char            formatChunkID[4];       // "fmt "           4       16
    DWORD           formatChunkSize;        // 16 bytes         4       20          
    WORD            formatTag;              //                  2       22
    WORD            noOfChannels;           //                  2       24
    DWORD           samplesPerSec;          //                  4       28
    DWORD           bytesPerSec;            //                  4       32
    WORD            blockAlign;             //                  2       34
    WORD            bitsPerSample;          //                  2       36
    char            dataChunkID[4];         // "data"           4       40
    DWORD           dataChunkSize;          // not fixed        4       44
};

static struct {
    switch_mutex_t *mutex;
    switch_thread_rwlock_t *running_rwlock;
    switch_memory_pool_t *pool;
    int running;
} process;

static struct {
    Aws::Auth::AWSCredentials *credentials;
    Aws::Client::ClientConfiguration *config;
    Aws::SDKOptions *options;
} globals;

switch_loadable_module_interface_t *MODULE_INTERFACE;

static char *supported_formats[SWITCH_MAX_CODECS] = { 0 };

/* Prototypes */

SWITCH_MODULE_LOAD_FUNCTION(mod_polly_load);
SWITCH_MODULE_SHUTDOWN_FUNCTION(mod_polly_shutdown);
SWITCH_MODULE_DEFINITION(mod_polly, mod_polly_load, mod_polly_shutdown, NULL);

// ------------------------------------------------------------------------------------------------------------------

/* Implementation */

std::ostream& operator<<(std::ostream& out, const riff& h)
{
    if BIG_ENDIAN_SYSTEM {
        struct riff hdr = std::move(h);

        REVERSE_BYTES(hdr.riffSize);
        REVERSE_BYTES(hdr.formatChunkSize);
        REVERSE_BYTES(hdr.formatTag);
        REVERSE_BYTES(hdr.noOfChannels);
        REVERSE_BYTES(hdr.samplesPerSec);
        REVERSE_BYTES(hdr.bytesPerSec);
        REVERSE_BYTES(hdr.blockAlign);
        REVERSE_BYTES(hdr.bitsPerSample);
        REVERSE_BYTES(hdr.dataChunkSize);

        return out 
            .write(hdr.chunkID, 4)
            .write((const char *)&hdr.riffSize, 4)
            .write(hdr.typeID, 4)
            .write(hdr.formatChunkID, 4)
            .write((const char *)&hdr.formatChunkSize, 4)
            .write((const char *)&hdr.formatTag, 2)
            .write((const char *)&hdr.noOfChannels, 2)
            .write((const char *)&hdr.samplesPerSec, 4)
            .write((const char *)&hdr.bytesPerSec, 4)
            .write((const char *)&hdr.blockAlign, 2)
            .write((const char *)&hdr.bitsPerSample, 2)
            .write(hdr.dataChunkID, 4)
            .write((const char *)&hdr.dataChunkSize, 4);
    } else {
        return out
            .write(h.chunkID, 4)
            .write((const char *)&h.riffSize, 4)
            .write(h.typeID, 4)
            .write(h.formatChunkID, 4)
            .write((const char *)&h.formatChunkSize, 4)
            .write((const char *)&h.formatTag, 2)
            .write((const char *)&h.noOfChannels, 2)
            .write((const char *)&h.samplesPerSec, 4)
            .write((const char *)&h.bytesPerSec, 4)
            .write((const char *)&h.blockAlign, 2)
            .write((const char *)&h.bitsPerSample, 2)
            .write(h.dataChunkID, 4)
            .write((const char *)&h.dataChunkSize, 4);
    }
}

riff init_pcm_header(std::ostream& in)
{
    // get length of file
    in.seekp(0, in.end);
    DWORD sz = in.tellp();
    in.seekp(0, in.beg);

    struct riff result = {
        {'R','I','F','F'},      // chunkID
        sz + 0x24,              // riffSize         (size of stream + 0x24) or (file size - 8)
        {'W','A','V','E'},      // typeID
        {'f','m','t',' '},      // formatChunkID
        16,                     // formatChunkSize
        1,                      // formatTag        (PCM)
        1,                      // noOfChannels     (mono)
        8000,                   // samplesPerSec    (8KHz)
        16000,                  // bytesPerSec      ((Sample Rate * BitsPerSample * Channels) / 8)
        2,                      // blockAlign       ((bits per sample * channels) / 8)
        16,                     // bitsPerSample    (multiples of 8)
        {'d','a','t','a'},      // dataChunkID
        sz                      // dataChunkSize    (sample size)   
    };

    return result;
}

struct voice_sync {
    char* session_uuid;
    Aws::IOStream *audio_stream;
    switch_size_t blockAlign;
};

typedef struct voice_sync voice_sync_t;

static switch_status_t polly_file_open(switch_file_handle_t *handle, const char *path)
{
    voice_sync_t *sync_info = (voice_sync_t*)malloc(sizeof(voice_sync_t));
    sync_info->audio_stream = new Aws::StringStream(std::ios::in | std::ios::out | std::ios::binary);

    handle->private_info = sync_info;
    handle->samplerate = 8000;
    handle->channels = 1;
    handle->pos = 0;
    handle->format = 0;
    handle->sections = 0;
    handle->seekable = 0;
    handle->speed = 0.5;

    switch_log_printf(SWITCH_CHANNEL_LOG, SWITCH_LOG_DEBUG, "submitting text [%s] to polly", path);

    Aws::Polly::PollyClient polly_client(*globals.credentials, *globals.config);
    Aws::Polly::Model::SynthesizeSpeechRequest request;

    request.SetLanguageCode(Aws::Polly::Model::LanguageCode::en_US);
    request.SetOutputFormat(Aws::Polly::Model::OutputFormat::pcm);
    request.SetSampleRate("8000");
    request.SetTextType(Aws::Polly::Model::TextType::text);  // or ssml
    request.SetVoiceId(Aws::Polly::Model::VoiceId::Matthew);
    request.SetText(path);

    if (handle->params) {
        // get the session UUID for this channel
        // note: this doesnt fire for a standard call session in the audio context; is there a way to make sure it is there?
        const char *uuid = switch_event_get_header(handle->params, "session");
        if (!zstr(uuid)) {
            sync_info->session_uuid = switch_core_strdup(handle->memory_pool, uuid);
            switch_log_printf(SWITCH_CHANNEL_UUID_LOG(sync_info->session_uuid), SWITCH_LOG_DEBUG, "Polly linked to session %s\n", sync_info->session_uuid);
        }
    }
    sync_info->audio_stream->clear();
//    sync_info->audio_stream.open(filename.c_str(), std::ios::out | std::ios::binary);

    auto outcome = polly_client.SynthesizeSpeech(request);

    // Output operation status
    if (outcome.IsSuccess()) {
        switch_log_printf(SWITCH_CHANNEL_LOG, SWITCH_LOG_DEBUG, "received audio response for %s", request.GetServiceRequestName());

        Aws::Polly::Model::SynthesizeSpeechResult& result = ((Aws::Polly::Model::SynthesizeSpeechResult&)(outcome));
        Aws::IOStream*  audio_stream = &result.GetAudioStream();

        // this is raw PCM so we need to add a wav header!
        riff header = init_pcm_header(*audio_stream);
        *sync_info->audio_stream << header;

        // tansfer audio data into stream
        *sync_info->audio_stream << audio_stream->rdbuf();
        sync_info->audio_stream->seekp(0, sync_info->audio_stream->beg);

        // update handle information about audio stream
        handle->samplerate = header.samplesPerSec;
        handle->channels = header.noOfChannels;
        handle->format = header.formatTag;
        handle->duration = header.dataChunkSize / header.bytesPerSec +1;
        handle->samples_in = header.dataChunkSize / header.blockAlign +1;

        sync_info->blockAlign = header.blockAlign;

        switch_log_printf(SWITCH_CHANNEL_LOG, SWITCH_LOG_DEBUG, "polly audio stream ready; duration: %ld secs", handle->duration);
        return SWITCH_STATUS_SUCCESS;
    }

    switch_log_printf(SWITCH_CHANNEL_LOG, SWITCH_LOG_ERROR, "something went wrong retrieving audio from polly");
    return SWITCH_STATUS_FALSE;
}

static switch_status_t polly_file_close(switch_file_handle_t *handle)
{
    switch_log_printf(SWITCH_CHANNEL_LOG, SWITCH_LOG_DEBUG, "closiing polly audio stream");

    voice_sync_t *sync_info = (voice_sync_t*)handle->private_info;

    //sync_info->audio_stream->close(); -- doesnt exist on stringstream
    delete sync_info->audio_stream;

    if (sync_info->session_uuid) {
        switch_safe_free(sync_info->session_uuid);
    }

    switch_safe_free(sync_info);
    handle->private_info = NULL;

    return SWITCH_STATUS_SUCCESS;
}

static switch_status_t polly_file_read(switch_file_handle_t *handle, void *data, size_t *len)
{
    voice_sync_t *sync_info = (voice_sync_t*)handle->private_info;
    switch_size_t bytes;

    sync_info->audio_stream->read((char *)data, *len * sync_info->blockAlign);
    if ((bytes = sync_info->audio_stream->gcount()) <= 0) {
        return SWITCH_STATUS_FALSE;
    }

    *len = bytes / sync_info->blockAlign;
    return SWITCH_STATUS_SUCCESS;
}

SWITCH_MODULE_LOAD_FUNCTION(mod_polly_load)
{
    switch_log_printf(SWITCH_CHANNEL_LOG, SWITCH_LOG_DEBUG, "Initializing polly audio interface");

    supported_formats[0] = (char*)"polly";

    /*
        switch_application_interface_t *app_interface;
        switch_api_interface_t *api_interface;
    */
    switch_file_interface_t *file_interface;

    *module_interface = switch_loadable_module_create_module_interface(pool, modname);
    file_interface = (switch_file_interface_t*)switch_loadable_module_create_interface(*module_interface, SWITCH_FILE_INTERFACE);
    file_interface->interface_name = modname;
    file_interface->extens = supported_formats;
    file_interface->file_open = polly_file_open;
    file_interface->file_close = polly_file_close;
    file_interface->file_read = polly_file_read;

    MODULE_INTERFACE = *module_interface;

    memset(&process, 0, sizeof(process));
    memset(&globals, 0, sizeof(globals));
    process.pool = pool;

    switch_thread_rwlock_create(&process.running_rwlock, pool);
    switch_mutex_init(&process.mutex, SWITCH_MUTEX_NESTED, pool);

    globals.options = new Aws::SDKOptions();
    globals.options->loggingOptions.logLevel = Aws::Utils::Logging::LogLevel::Debug;

    globals.credentials = new Aws::Auth::AWSCredentials();
    globals.credentials->SetAWSAccessKeyId("your aws key");
    globals.credentials->SetAWSSecretKey("your aws secret");

    globals.config = new Aws::Client::ClientConfiguration();
    globals.config->region = "eu-west-1";  // Ireland

    switch_log_printf(SWITCH_CHANNEL_LOG, SWITCH_LOG_DEBUG, "Initializing aws api");

    Aws::InitAPI(*globals.options);

    switch_thread_rwlock_wrlock(process.running_rwlock);
    process.running = 1;
    switch_thread_rwlock_unlock(process.running_rwlock);

    switch_log_printf(SWITCH_CHANNEL_LOG, SWITCH_LOG_DEBUG, "Ready to rock!");

    /* indicate that the module should continue to be loaded */
    return SWITCH_STATUS_SUCCESS;
}

SWITCH_MODULE_SHUTDOWN_FUNCTION(mod_polly_shutdown)
{   
    switch_log_printf(SWITCH_CHANNEL_LOG, SWITCH_LOG_DEBUG, "Shutting down polly polly audio interface");

    switch_thread_rwlock_wrlock(process.running_rwlock);
    process.running = 0;
    switch_thread_rwlock_unlock(process.running_rwlock);

    switch_log_printf(SWITCH_CHANNEL_LOG, SWITCH_LOG_DEBUG, "Closing aws api");
    Aws::ShutdownAPI(*globals.options);

    delete globals.credentials;
    delete globals.config;
    delete globals.options;

    switch_log_printf(SWITCH_CHANNEL_LOG, SWITCH_LOG_DEBUG, "Module shutdown finished");
    return SWITCH_STATUS_UNLOAD;
}

Now when i try to load this on Freeswitch , it throws an error

2019-07-31 22:00:51.918181 [CRIT] switch_loadable_module.c:1522 Error Loading module /usr/local/freeswitch/mod/mod_polly.so

/usr/local/freeswitch/mod/mod_polly.so: undefined symbol: _ZNK3Aws35AmazonSerializableWebServiceRequest7GetBodyEv

Freeswitch is C code with C++ guards in header files (extern "C" declaration).

Looking at symbols in mod_polly.so

readelf -Ws mod_polly.so | grep _ZNK3Aws35AmazonSerializableWebServiceRequest7GetBodyEv

66: 0000000000000000 0 NOTYPE GLOBAL DEFAULT UND _ZNK3Aws35AmazonSerializableWebServiceRequest7GetBodyEv

590: 0000000000000000 0 NOTYPE GLOBAL DEFAULT UND _ZNK3Aws35AmazonSerializableWebServiceRequest7GetBodyEv

Now my basic understanding of the post here tells me that the symbol is present in the so file but Freeswitch cannot find it or load it.

Now this error has very likely to do with mixing C/C++ code but looking at this and this hasn't helped me figure out how to fix it.

I do not want to build Freeswitch to load my module and I am thinking I shouldn't have to, as that renders this project un-scalable.

What am I missing here?

PS:

readelf -Ws libaws-cpp-sdk-core.a | grep AmazonSerializableWebServiceRequest7GetBodyEv

165: 0000000000000000 716 FUNC GLOBAL DEFAULT 42 _ZNK3Aws35AmazonSerializableWebServiceRequest7GetBodyEv

Symbol is defined in libaws-cpp-sdk-core.a which is part of the compilation command for mod_polly.cpp

Answer 1

@Sam V - turns out it was ordering issue while building. Change in ordering of build command to

g++ -shared -o mod_polly.so -fPIC -g -ggdb -std=c++11 -Wall -Werror -I/usr/src/freeswitch/src/include/ -I/usr/src/freeswitch/libs/libteletone/src/ mod_polly.cpp -L/usr/local/lib/ -laws-cpp-sdk-polly -laws-cpp-sdk-core

fixed the problem. Your 1st comment was the key. Thanks.