我在ubuntu的系统中调用ncnn和opencv的库生成自己的库文件，结果发现 undefined symbol: _ZTIN4ncnn3NetE错误，
使用 readelf -Ws test.so | grep ncnn命令发现如下：

1: 0000000000000000 0 NOTYPE GLOBAL DEFAULT UND _ZN4ncnn3Mat18from_pixels_resizeEPKhiiiiiPNS_9AllocatorE 4: 0000000000000000 0 NOTYPE GLOBAL DEFAULT UND _ZN4ncnn9Extractor7extractEPKcRNS_3MatEi 5: 0000000000000000 0 NOTYPE GLOBAL DEFAULT UND _ZN4ncnn9Extractor5inputEPKcRKNS_3MatE 19: 0000000000000000 0 NOTYPE GLOBAL DEFAULT UND _ZN4ncnn9Extractor15set_num_threadsEi 46: 0000000000000000 0 NOTYPE GLOBAL DEFAULT UND _ZN4ncnn3NetD1Ev 123: 0000000000000000 0 NOTYPE GLOBAL DEFAULT UND _ZNK4ncnn3Net16create_extractorEv 142: 0000000000000000 0 NOTYPE GLOBAL DEFAULT UND _ZN4ncnn16get_current_timeEv 163: 0000000000000000 0 NOTYPE GLOBAL DEFAULT UND _ZN4ncnn3Net10load_paramEPKc 173: 0000000000000000 0 NOTYPE GLOBAL DEFAULT UND _ZN4ncnn3Net10load_modelEPKc 184: 0000000000000000 0 NOTYPE GLOBAL DEFAULT UND _ZTIN4ncnn3NetE 191: 0000000000000000 0 NOTYPE GLOBAL DEFAULT UND _ZN4ncnn9ExtractorD1Ev 237: 0000000000000000 0 NOTYPE GLOBAL DEFAULT UND _ZN4ncnn3NetC1Ev 247: 0000000000000000 0 NOTYPE GLOBAL DEFAULT UND _ZN4ncnn3Mat24substract_mean_normalizeEPKfS2_ 255: 0000000000259b80 16 OBJECT WEAK DEFAULT 20 _ZTIFiRN4ncnn3NetEE 263: 000000000003ca00 16 OBJECT WEAK DEFAULT 13 _ZTSFiRN4ncnn3NetEE 266: 000000000003c9e0 17 OBJECT WEAK DEFAULT 13 _ZTSPFiRN4ncnn3NetEE 294: 0000000000259b60 32 OBJECT WEAK DEFAULT 20 _ZTIPFiRN4ncnn3NetEE 56: 0000000000007522 33 FUNC LOCAL DEFAULT 11 _ZN4ncnnL8fastFreeEPv.26507.3112 57: 0000000000007544 124 FUNC LOCAL DEFAULT 11 _ZN4ncnn3MatC2Ev.local.21.3106 58: 00000000000075c0 26 FUNC LOCAL DEFAULT 11 _ZN4ncnn3MatD2Ev.local.17.3100 59: 00000000000076bc 238 FUNC LOCAL DEFAULT 11 [_ZN4ncnn3Mat7releaseEv.local.19.3093 ]
并且尝试使用了部分问题中的cmake -DNCNN_DISABLE_RTTI=OFF命令，问题并没有任何改变，请问这种情况是怎么造成的？