Common build error to examples withh IDF v4.0

[Hazeline2018]

Hi, I'm new to ESP32 chip so I started with the example projects included. However, I tried all 3 examples "camera_web_server", "detection_with_command_line" and "recognition_with_command_line", they all seem to have same build error:

c:/users/tianhao/.espressif/tools/xtensa-esp32-elf/esp-2019r2-8.2.0/xtensa-esp32 -elf/bin/../lib/gcc/xtensa-esp32-elf/8.2.0/../../../../xtensa-esp32-elf/bin/ld.e xe: C:/Users/Tianhao/.espressif/esp-who/components/esp-face/lib\libfr.a(mfn.c.ob j): in function dl_lib_calloc': /home/gongxiaochao/code/esp/esp_temp/dl_lib/components/dl_lib/dl_lib_matrix3d.h: 85: undefined reference to dl_matrix3dqq_conv_1x1_with_bias' collect2.exe: error: ld returned 1 exit status ninja: build stopped: subcommand failed. ninja failed with exit code 1

How to solve this problem? I have read that this esp-who project was built with older IDF version. But I'll need the detection and all other functions so I'll have to use the latest v4.0. Please help! Thanks!

[holubcsongor]

Since they are not working on any fix in my opinion (no reaction to issues, just angry noises), the only option is to use the old Make and MSYS combo, it works with idf 4 as well.