GDB 显示奇怪的堆栈跟踪

我有一个C++守护进程，它在工作几天后出现段错误。我使用调试选项编译了它（我确定我做得很好，因为我用有预谋的崩溃对其进行了测试，并且 gdb 显示了正确的堆栈跟踪），但在生产中的"真实"崩溃中，我只看到以下跟踪：

(gdb) where
#0  0x00007ffff674d5a7 in ?? () from /lib/x86_64-linux-gnu/libc.so.6
#1  0xffffffffffffffff in ?? ()
#2  0x0000000000000000 in ?? ()

什么意思？

以下源代码存在潜在问题，因为它是自守护程序变得不稳定以来唯一的新代码：

namespace Foo {
    Bar* Bar::instance = NULL;
    Bar* Bar::getInstance() {
        if (!instance)
            instance = new Bar();
        return instance;
    }
    Bar::Bar() {
        curl = curl_easy_init();
        if(CURLE_OK != curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, &data_write)
        || CURLE_OK != curl_easy_setopt(curl, CURLOPT_NOPROGRESS, 1L)
        || CURLE_OK != curl_easy_setopt(curl, CURLOPT_FOLLOWLOCATION, 1L)
        || CURLE_OK != curl_easy_setopt(curl, CURLOPT_TIMEOUT_MS, Bar::timeout)) {
            throw std::runtime_error(std::string("Can't initialize curl."));
        }
    }
    Bar::~Bar() {
        curl_easy_cleanup(curl);
    }
    std::string Bar::getByIp(const std::string &id) {
        Bar *self = getInstance();
        std::string url = "example.com";
        url.append(id); 
        std::ostringstream oss;
        if (CURLE_OK == self->curl_read(url, oss)) {
            std::string output(oss.str());
            if (output.empty())
                return NULL_OBJECT;
            TiXmlDocument xml;
            xml.Parse(output.c_str());
           if (
                xml.Error()
                || !xml.FirstChild("a")
                || !xml.FirstChild("a")->FirstChild("b")
                || !xml.FirstChild("a")->FirstChild("b")->FirstChildElement("lat")
                || !xml.FirstChild("a")->FirstChild("b")->FirstChildElement("lng")
            )
                return NULL_OBJECT;
            std::string lat = xml.FirstChild("a")->FirstChild("b")->FirstChildElement("lat")->GetText();
            std::string lng = xml.FirstChild("a")->FirstChild("b")->FirstChildElement("lng")->GetText();
            return Region::getByCoordinates(lng, lat);
        }
        return NULL_OBJECT;
    }
    size_t Bar::data_write(void* buf, size_t size, size_t nmemb, void* userp)
    {
        if(userp)
        {
            std::ostream& os = *static_cast<std::ostream*>(userp);
            std::streamsize len = size * nmemb;
            if(os.write(static_cast<char*>(buf), len))
                return len;
        }
        return 0;
    }
    CURLcode Bar::curl_read(const std::string& url, std::ostringstream& os)
    {
        CURLcode code(CURLE_FAILED_INIT);
        if(curl)
        {
            if(
                CURLE_OK == (code = curl_easy_setopt(curl, CURLOPT_FILE, &os))
                && CURLE_OK == (code = curl_easy_setopt(curl, CURLOPT_URL, url.c_str()))
            ) {
                code = curl_easy_perform(curl);
            }
        }
        return code;
    }
}