undefined reference to `NeuralNetwork::Layer::BackProp...

[GiorgosXou]

Compiling FeedForward_Individual_MNIST_PROGMEM.ino with Espressif's core results to (const issue ofcourse and):

Linking everything together...
/home/xou/.arduino15/packages/esp32/tools/riscv32-esp-elf-gcc/esp-2021r2-patch5-8.4.0/bin/riscv32-esp-elf-g++ -Wl,--Map=/tmp/arduino_build_227969/FeedForward_Individual_MNIST_PROGMEM.ino.map -L/home/xou/.arduino15/packages/esp32/hardware/esp32/2.0.11/tools/sdk/esp32c3/lib -L/home/xou/.arduino15/packages/esp32/hardware/esp32/2.0.11/tools/sdk/esp32c3/ld -L/home/xou/.arduino15/packages/esp32/hardware/esp32/2.0.11/tools/sdk/esp32c3/qio_qspi -T memory.ld -T sections.ld -T esp32c3.rom.ld -T esp32c3.rom.api.ld -T esp32c3.rom.libgcc.ld -T esp32c3.rom.newlib.ld -T esp32c3.rom.version.ld -T esp32c3.rom.newlib-time.ld -T esp32c3.rom.eco3.ld -T esp32c3.peripherals.ld -nostartfiles -march=rv32imc --specs=nosys.specs -Wl,--cref -Wl,--gc-sections -fno-rtti -fno-lto -Wl,--wrap=esp_log_write -Wl,--wrap=esp_log_writev -Wl,--wrap=log_printf -u _Z5setupv -u _Z4loopv -u esp_app_desc -u pthread_include_pthread_impl -u pthread_include_pthread_cond_impl -u pthread_include_pthread_local_storage_impl -u pthread_include_pthread_rwlock_impl -u include_esp_phy_override -u start_app -u __ubsan_include -u __assert_func -u vfs_include_syscalls_impl -Wl,--undefined=uxTopUsedPriority -u app_main -u newlib_include_heap_impl -u newlib_include_syscalls_impl -u newlib_include_pthread_impl -u newlib_include_assert_impl -u __cxa_guard_dummy -DESP32 -DCORE_DEBUG_LEVEL=0 -DARDUINO_USB_MODE=1 -DARDUINO_USB_CDC_ON_BOOT=0 -Wl,--start-group /tmp/arduino_build_227969/sketch/FeedForward_Individual_MNIST_PROGMEM.ino.cpp.o /tmp/arduino_cache_865625/core/core_8656a7c07f9f6a1e2f397413729e10b2.a -lesp_ringbuf -lefuse -lesp_ipc -ldriver -lesp_pm -lmbedtls -lapp_update -lbootloader_support -lspi_flash -lnvs_flash -lpthread -lesp_gdbstub -lespcoredump -lesp_phy -lesp_system -lesp_rom -lhal -lvfs -lesp_eth -ltcpip_adapter -lesp_netif -lesp_event -lwpa_supplicant -lesp_wifi -lconsole -llwip -llog -lheap -lsoc -lesp_hw_support -lriscv -lesp_common -lesp_timer -lfreertos -lnewlib -lcxx -lapp_trace -lasio -lbt -lcbor -lunity -lcmock -lcoap -lnghttp -lesp-tls -lesp_adc_cal -lesp_hid -ltcp_transport -lesp_http_client -lesp_http_server -lesp_https_ota -lesp_https_server -lesp_lcd -lprotobuf-c -lprotocomm -lmdns -lesp_local_ctrl -lsdmmc -lesp_serial_slave_link -lesp_websocket_client -lexpat -lwear_levelling -lfatfs -lfreemodbus -ljsmn -ljson -llibsodium -lmqtt -lopenssl -lspiffs -lwifi_provisioning -lrmaker_common -lesp_diagnostics -lrtc_store -lesp_insights -ljson_parser -ljson_generator -lesp_schedule -lespressif__esp_secure_cert_mgr -lesp_rainmaker -lgpio_button -lqrcode -lws2812_led -lesp32-camera -lesp_littlefs -lespressif__esp-dsp -lfb_gfx -lasio -lcmock -lunity -lcoap -lesp_lcd -lesp_websocket_client -lexpat -lfreemodbus -ljsmn -llibsodium -lesp_adc_cal -lesp_hid -lfatfs -lwear_levelling -lopenssl -lspiffs -lesp_insights -lcbor -lesp_diagnostics -lrtc_store -lesp_rainmaker -lesp_local_ctrl -lesp_https_server -lwifi_provisioning -lprotocomm -lbt -lbtdm_app -lprotobuf-c -lmdns -ljson -ljson_parser -ljson_generator -lesp_schedule -lespressif__esp_secure_cert_mgr -lqrcode -lrmaker_common -lmqtt -lcat_face_detect -lhuman_face_detect -lcolor_detect -lmfn -ldl -lesp_ringbuf -lefuse -lesp_ipc -ldriver -lesp_pm -lmbedtls -lapp_update -lbootloader_support -lspi_flash -lnvs_flash -lpthread -lesp_gdbstub -lespcoredump -lesp_phy -lesp_system -lesp_rom -lhal -lvfs -lesp_eth -ltcpip_adapter -lesp_netif -lesp_event -lwpa_supplicant -lesp_wifi -lconsole -llwip -llog -lheap -lsoc -lesp_hw_support -lriscv -lesp_common -lesp_timer -lfreertos -lnewlib -lcxx -lapp_trace -lnghttp -lesp-tls -ltcp_transport -lesp_http_client -lesp_http_server -lesp_https_ota -lsdmmc -lesp_serial_slave_link -lmbedtls_2 -lmbedcrypto -lmbedx509 -lcoexist -lcore -lespnow -lmesh -lnet80211 -lpp -lsmartconfig -lwapi -lesp_ringbuf -lefuse -lesp_ipc -ldriver -lesp_pm -lmbedtls -lapp_update -lbootloader_support -lspi_flash -lnvs_flash -lpthread -lesp_gdbstub -lespcoredump -lesp_phy -lesp_system -lesp_rom -lhal -lvfs -lesp_eth -ltcpip_adapter -lesp_netif -lesp_event -lwpa_supplicant -lesp_wifi -lconsole -llwip -llog -lheap -lsoc -lesp_hw_support -lriscv -lesp_common -lesp_timer -lfreertos -lnewlib -lcxx -lapp_trace -lnghttp -lesp-tls -ltcp_transport -lesp_http_client -lesp_http_server -lesp_https_ota -lsdmmc -lesp_serial_slave_link -lmbedtls_2 -lmbedcrypto -lmbedx509 -lcoexist -lcore -lespnow -lmesh -lnet80211 -lpp -lsmartconfig -lwapi -lesp_ringbuf -lefuse -lesp_ipc -ldriver -lesp_pm -lmbedtls -lapp_update -lbootloader_support -lspi_flash -lnvs_flash -lpthread -lesp_gdbstub -lespcoredump -lesp_phy -lesp_system -lesp_rom -lhal -lvfs -lesp_eth -ltcpip_adapter -lesp_netif -lesp_event -lwpa_supplicant -lesp_wifi -lconsole -llwip -llog -lheap -lsoc -lesp_hw_support -lriscv -lesp_common -lesp_timer -lfreertos -lnewlib -lcxx -lapp_trace -lnghttp -lesp-tls -ltcp_transport -lesp_http_client -lesp_http_server -lesp_https_ota -lsdmmc -lesp_serial_slave_link -lmbedtls_2 -lmbedcrypto -lmbedx509 -lcoexist -lcore -lespnow -lmesh -lnet80211 -lpp -lsmartconfig -lwapi -lesp_ringbuf -lefuse -lesp_ipc -ldriver -lesp_pm -lmbedtls -lapp_update -lbootloader_support -lspi_flash -lnvs_flash -lpthread -lesp_gdbstub -lespcoredump -lesp_phy -lesp_system -lesp_rom -lhal -lvfs -lesp_eth -ltcpip_adapter -lesp_netif -lesp_event -lwpa_supplicant -lesp_wifi -lconsole -llwip -llog -lheap -lsoc -lesp_hw_support -lriscv -lesp_common -lesp_timer -lfreertos -lnewlib -lcxx -lapp_trace -lnghttp -lesp-tls -ltcp_transport -lesp_http_client -lesp_http_server -lesp_https_ota -lsdmmc -lesp_serial_slave_link -lmbedtls_2 -lmbedcrypto -lmbedx509 -lcoexist -lcore -lespnow -lmesh -lnet80211 -lpp -lsmartconfig -lwapi -lesp_ringbuf -lefuse -lesp_ipc -ldriver -lesp_pm -lmbedtls -lapp_update -lbootloader_support -lspi_flash -lnvs_flash -lpthread -lesp_gdbstub -lespcoredump -lesp_phy -lesp_system -lesp_rom -lhal -lvfs -lesp_eth -ltcpip_adapter -lesp_netif -lesp_event -lwpa_supplicant -lesp_wifi -lconsole -llwip -llog -lheap -lsoc -lesp_hw_support -lriscv -lesp_common -lesp_timer -lfreertos -lnewlib -lcxx -lapp_trace -lnghttp -lesp-tls -ltcp_transport -lesp_http_client -lesp_http_server -lesp_https_ota -lsdmmc -lesp_serial_slave_link -lmbedtls_2 -lmbedcrypto -lmbedx509 -lcoexist -lcore -lespnow -lmesh -lnet80211 -lpp -lsmartconfig -lwapi -lesp_ringbuf -lefuse -lesp_ipc -ldriver -lesp_pm -lmbedtls -lapp_update -lbootloader_support -lspi_flash -lnvs_flash -lpthread -lesp_gdbstub -lespcoredump -lesp_phy -lesp_system -lesp_rom -lhal -lvfs -lesp_eth -ltcpip_adapter -lesp_netif -lesp_event -lwpa_supplicant -lesp_wifi -lconsole -llwip -llog -lheap -lsoc -lesp_hw_support -lriscv -lesp_common -lesp_timer -lfreertos -lnewlib -lcxx -lapp_trace -lnghttp -lesp-tls -ltcp_transport -lesp_http_client -lesp_http_server -lesp_https_ota -lsdmmc -lesp_serial_slave_link -lmbedtls_2 -lmbedcrypto -lmbedx509 -lcoexist -lcore -lespnow -lmesh -lnet80211 -lpp -lsmartconfig -lwapi -lphy -lbtbb -lesp_phy -lphy -lbtbb -lesp_phy -lphy -lbtbb -lm -lnewlib -lstdc++ -lpthread -lgcc -lcxx -lapp_trace -lgcov -lapp_trace -lgcov -lc -Wl,--end-group -Wl,-EL -o /tmp/arduino_build_227969/FeedForward_Individual_MNIST_PROGMEM.ino.elf
/home/xou/.arduino15/packages/esp32/tools/riscv32-esp-elf-gcc/esp-2021r2-patch5-8.4.0/bin/../lib/gcc/riscv32-esp-elf/8.4.0/../../../../riscv32-esp-elf/bin/ld: /tmp/arduino_build_227969/sketch/FeedForward_Individual_MNIST_PROGMEM.ino.cpp.o: in function `NeuralNetwork::BackProp(float const*)':
/home/xou/Arduino/libraries/NeuralNetwork/src/NeuralNetwork.h:819: undefined reference to `NeuralNetwork::Layer::BackPropOutput(float const*, float const*)'
/home/xou/.arduino15/packages/esp32/tools/riscv32-esp-elf-gcc/esp-2021r2-patch5-8.4.0/bin/../lib/gcc/riscv32-esp-elf/8.4.0/../../../../riscv32-esp-elf/bin/ld: /home/xou/Arduino/libraries/NeuralNetwork/src/NeuralNetwork.h:823: undefined reference to `NeuralNetwork::Layer::BackPropHidden(NeuralNetwork::Layer const*, float const*)'
/home/xou/.arduino15/packages/esp32/tools/riscv32-esp-elf-gcc/esp-2021r2-patch5-8.4.0/bin/../lib/gcc/riscv32-esp-elf/8.4.0/../../../../riscv32-esp-elf/bin/ld: /home/xou/Arduino/libraries/NeuralNetwork/src/NeuralNetwork.h:828: undefined reference to `NeuralNetwork::Layer::BackPropHidden(NeuralNetwork::Layer const*, float const*)'
collect2: error: ld returned 1 exit status
Using library NeuralNetwork at version 1.8.1 in folder: /home/xou/Arduino/libraries/NeuralNetwork 
exit status 1
Error compiling for board ESP32C3 Dev Module.

To fix this just add #if !defined(NO_BACKPROP) ... #endif to:

https://github.com/GiorgosXou/NeuralNetworks/blob/31bb95e4cefcaefb28f6b031a634ded6c7274a7d/src/NeuralNetwork.h#L352-L353

https://github.com/GiorgosXou/NeuralNetworks/blob/31bb95e4cefcaefb28f6b031a634ded6c7274a7d/src/NeuralNetwork.h#L557

https://github.com/GiorgosXou/NeuralNetworks/blob/31bb95e4cefcaefb28f6b031a634ded6c7274a7d/src/NeuralNetwork.h#L811-L835