Esp-idf: undefined reference to `app_main' (IDFGH-4559)

[ESP32DE]

hi guys

this

undefined reference to app_main

phenomenon comes again over me ( win 7, msys32, last esp-idf )

CC trax.o
CC eri.o
AR libxtensa-debug-module.a
LD hello-world.elf
C:/nod/11/build/esp32\libesp32.a(cpu_start.o):(.literal.main_task+0x8): undefined reference to app_main' C:/nod/11/build/esp32\libesp32.a(cpu_start.o): In functionmain_task':
C:/sdk32/esp-idf/components/esp32/cpu_start.c:267: undefined reference to `app_main'
collect2.exe: error: ld returned 1 exit status
make: * [C:/sdk32/esp-idf/make/project.mk:323: /c/nod/11/build/hello-world.elf] Fehler 1

i search just in time but find no mistake - i used the hello world example for minimal code.

best wishes
rudi ;-)

[projectgus]

Hi rudi,

Can you run the following command and copy/paste the output, please:

make V=1

Also, if you can, please run make clean and then re-run the above command and copy/paste that output separately.

[ESP32DE]

Hi Angus,
txs,
step 1:
$ make V=1
including /c/sdk32/esp-idf/components/bootloader/Makefile.projbuild...
including /c/sdk32/esp-idf/components/bootloader_support/Makefile.projbuild...
including /c/sdk32/esp-idf/components/coap/Makefile.projbuild...
including /c/sdk32/esp-idf/components/esp32/Makefile.projbuild...
including /c/sdk32/esp-idf/components/esptool_py/Makefile.projbuild...
including /c/sdk32/esp-idf/components/mbedtls/Makefile.projbuild...
including /c/sdk32/esp-idf/components/nghttp/Makefile.projbuild...
including /c/sdk32/esp-idf/components/partition_table/Makefile.projbuild...
make -C /c/sdk32/esp-idf/components/bootloader/src V=1 BUILD_DIR_BASE=/c/nod/11/build/bootloader TEST_COMPONENTS= /c/nod/11/build/bootloader/bootloader.bin
make[1]: Verzeichnis „/c/sdk32/esp-idf/components/bootloader/src“ wird betreten
including /c/sdk32/esp-idf/components/esptool_py/Makefile.projbuild...
including /c/sdk32/esp-idf/components/bootloader/Makefile.projbuild...
including /c/sdk32/esp-idf/components/bootloader_support/Makefile.projbuild...
make -C /c/nod/11/build/bootloader/bootloader_support -f /c/sdk32/esp-idf/make/component_wrapper.mk COMPONENT_MAKEFILE=/c/sdk32/esp-idf/components/bootloader_support/component.mk COMPONENT_NAME=bootloader_support build
make[2]: Verzeichnis „/c/nod/11/build/bootloader/bootloader_support“ wird betreten
make[2]: Verzeichnis „/c/nod/11/build/bootloader/bootloader_support“ wird verlassen
Target 'bootloader_support-build' responsible for '/c/nod/11/build/bootloader/bootloader_support/libbootloader_support.a'
make -C /c/nod/11/build/bootloader/log -f /c/sdk32/esp-idf/make/component_wrapper.mk COMPONENT_MAKEFILE=/c/sdk32/esp-idf/components/log/component.mk COMPONENT_NAME=log build
make[2]: Verzeichnis „/c/nod/11/build/bootloader/log“ wird betreten
make[2]: Verzeichnis „/c/nod/11/build/bootloader/log“ wird verlassen
Target 'log-build' responsible for '/c/nod/11/build/bootloader/log/liblog.a'
make -C /c/nod/11/build/bootloader/spi_flash -f /c/sdk32/esp-idf/make/component_wrapper.mk COMPONENT_MAKEFILE=/c/sdk32/esp-idf/components/spi_flash/component.mk COMPONENT_NAME=spi_flash build
make[2]: Verzeichnis „/c/nod/11/build/bootloader/spi_flash“ wird betreten
make[2]: Verzeichnis „/c/nod/11/build/bootloader/spi_flash“ wird verlassen
Target 'spi_flash-build' responsible for '/c/nod/11/build/bootloader/spi_flash/libspi_flash.a'
make -C /c/nod/11/build/bootloader/micro-ecc -f /c/sdk32/esp-idf/make/component_wrapper.mk COMPONENT_MAKEFILE=/c/sdk32/esp-idf/components/micro-ecc/component.mk COMPONENT_NAME=micro-ecc build
make[2]: Verzeichnis „/c/nod/11/build/bootloader/micro-ecc“ wird betreten
make[2]: Verzeichnis „/c/nod/11/build/bootloader/micro-ecc“ wird verlassen
Target 'micro-ecc-build' responsible for '/c/nod/11/build/bootloader/micro-ecc/libmicro-ecc.a'
make -C /c/nod/11/build/bootloader/main -f /c/sdk32/esp-idf/make/component_wrapper.mk COMPONENT_MAKEFILE=/c/sdk32/esp-idf/components/bootloader/src/main/component.mk COMPONENT_NAME=main build
make[2]: Verzeichnis „/c/nod/11/build/bootloader/main“ wird betreten
make[2]: Verzeichnis „/c/nod/11/build/bootloader/main“ wird verlassen
Target 'main-build' responsible for '/c/nod/11/build/bootloader/main/libmain.a'
make[1]: Verzeichnis „/c/sdk32/esp-idf/components/bootloader/src“ wird verlassen
make -C /c/nod/11/build/app_update -f /c/sdk32/esp-idf/make/component_wrapper.mk COMPONENT_MAKEFILE=/c/sdk32/esp-idf/components/app_update/component.mk COMPONENT_NAME=app_update build
make[1]: Verzeichnis „/c/nod/11/build/app_update“ wird betreten
make[1]: Verzeichnis „/c/nod/11/build/app_update“ wird verlassen
Target 'app_update-build' responsible for '/c/nod/11/build/app_update/libapp_update.a'
make -C /c/nod/11/build/bootloader_support -f /c/sdk32/esp-idf/make/component_wrapper.mk COMPONENT_MAKEFILE=/c/sdk32/esp-idf/components/bootloader_support/component.mk COMPONENT_NAME=bootloader_support build
make[1]: Verzeichnis „/c/nod/11/build/bootloader_support“ wird betreten
make[1]: Verzeichnis „/c/nod/11/build/bootloader_support“ wird verlassen
Target 'bootloader_support-build' responsible for '/c/nod/11/build/bootloader_support/libbootloader_support.a'
make -C /c/nod/11/build/bt -f /c/sdk32/esp-idf/make/component_wrapper.mk COMPONENT_MAKEFILE=/c/sdk32/esp-idf/components/bt/component.mk COMPONENT_NAME=bt build
make[1]: Verzeichnis „/c/nod/11/build/bt“ wird betreten
make[1]: Verzeichnis „/c/nod/11/build/bt“ wird verlassen
Target 'bt-build' responsible for '/c/nod/11/build/bt/libbt.a'
make -C /c/nod/11/build/coap -f /c/sdk32/esp-idf/make/component_wrapper.mk COMPONENT_MAKEFILE=/c/sdk32/esp-idf/components/coap/component.mk COMPONENT_NAME=coap build
make[1]: Verzeichnis „/c/nod/11/build/coap“ wird betreten
make[1]: Verzeichnis „/c/nod/11/build/coap“ wird verlassen
Target 'coap-build' responsible for '/c/nod/11/build/coap/libcoap.a'
make -C /c/nod/11/build/cxx -f /c/sdk32/esp-idf/make/component_wrapper.mk COMPONENT_MAKEFILE=/c/sdk32/esp-idf/components/cxx/component.mk COMPONENT_NAME=cxx build
make[1]: Verzeichnis „/c/nod/11/build/cxx“ wird betreten
make[1]: Verzeichnis „/c/nod/11/build/cxx“ wird verlassen
Target 'cxx-build' responsible for '/c/nod/11/build/cxx/libcxx.a'
make -C /c/nod/11/build/driver -f /c/sdk32/esp-idf/make/component_wrapper.mk COMPONENT_MAKEFILE=/c/sdk32/esp-idf/components/driver/component.mk COMPONENT_NAME=driver build
make[1]: Verzeichnis „/c/nod/11/build/driver“ wird betreten
make[1]: Verzeichnis „/c/nod/11/build/driver“ wird verlassen
Target 'driver-build' responsible for '/c/nod/11/build/driver/libdriver.a'
make -C /c/nod/11/build/esp32 -f /c/sdk32/esp-idf/make/component_wrapper.mk COMPONENT_MAKEFILE=/c/sdk32/esp-idf/components/esp32/component.mk COMPONENT_NAME=esp32 build
make[1]: Verzeichnis „/c/nod/11/build/esp32“ wird betreten
make[1]: Verzeichnis „/c/nod/11/build/esp32“ wird verlassen
Target 'esp32-build' responsible for '/c/nod/11/build/esp32/libesp32.a'
make -C /c/nod/11/build/ethernet -f /c/sdk32/esp-idf/make/component_wrapper.mk COMPONENT_MAKEFILE=/c/sdk32/esp-idf/components/ethernet/component.mk COMPONENT_NAME=ethernet build
make[1]: Verzeichnis „/c/nod/11/build/ethernet“ wird betreten
make[1]: Verzeichnis „/c/nod/11/build/ethernet“ wird verlassen
Target 'ethernet-build' responsible for '/c/nod/11/build/ethernet/libethernet.a'
make -C /c/nod/11/build/expat -f /c/sdk32/esp-idf/make/component_wrapper.mk COMPONENT_MAKEFILE=/c/sdk32/esp-idf/components/expat/component.mk COMPONENT_NAME=expat build
make[1]: Verzeichnis „/c/nod/11/build/expat“ wird betreten
make[1]: Verzeichnis „/c/nod/11/build/expat“ wird verlassen
Target 'expat-build' responsible for '/c/nod/11/build/expat/libexpat.a'
make -C /c/nod/11/build/fatfs -f /c/sdk32/esp-idf/make/component_wrapper.mk COMPONENT_MAKEFILE=/c/sdk32/esp-idf/components/fatfs/component.mk COMPONENT_NAME=fatfs build
make[1]: Verzeichnis „/c/nod/11/build/fatfs“ wird betreten
make[1]: Verzeichnis „/c/nod/11/build/fatfs“ wird verlassen
Target 'fatfs-build' responsible for '/c/nod/11/build/fatfs/libfatfs.a'
make -C /c/nod/11/build/freertos -f /c/sdk32/esp-idf/make/component_wrapper.mk COMPONENT_MAKEFILE=/c/sdk32/esp-idf/components/freertos/component.mk COMPONENT_NAME=freertos build
make[1]: Verzeichnis „/c/nod/11/build/freertos“ wird betreten
make[1]: Verzeichnis „/c/nod/11/build/freertos“ wird verlassen
Target 'freertos-build' responsible for '/c/nod/11/build/freertos/libfreertos.a'
make -C /c/nod/11/build/json -f /c/sdk32/esp-idf/make/component_wrapper.mk COMPONENT_MAKEFILE=/c/sdk32/esp-idf/components/json/component.mk COMPONENT_NAME=json build
make[1]: Verzeichnis „/c/nod/11/build/json“ wird betreten
make[1]: Verzeichnis „/c/nod/11/build/json“ wird verlassen
Target 'json-build' responsible for '/c/nod/11/build/json/libjson.a'
make -C /c/nod/11/build/log -f /c/sdk32/esp-idf/make/component_wrapper.mk COMPONENT_MAKEFILE=/c/sdk32/esp-idf/components/log/component.mk COMPONENT_NAME=log build
make[1]: Verzeichnis „/c/nod/11/build/log“ wird betreten
make[1]: Verzeichnis „/c/nod/11/build/log“ wird verlassen
Target 'log-build' responsible for '/c/nod/11/build/log/liblog.a'
make -C /c/nod/11/build/lwip -f /c/sdk32/esp-idf/make/component_wrapper.mk COMPONENT_MAKEFILE=/c/sdk32/esp-idf/components/lwip/component.mk COMPONENT_NAME=lwip build
make[1]: Verzeichnis „/c/nod/11/build/lwip“ wird betreten
make[1]: Verzeichnis „/c/nod/11/build/lwip“ wird verlassen
Target 'lwip-build' responsible for '/c/nod/11/build/lwip/liblwip.a'
make -C /c/nod/11/build/mbedtls -f /c/sdk32/esp-idf/make/component_wrapper.mk COMPONENT_MAKEFILE=/c/sdk32/esp-idf/components/mbedtls/component.mk COMPONENT_NAME=mbedtls build
make[1]: Verzeichnis „/c/nod/11/build/mbedtls“ wird betreten
make[1]: Verzeichnis „/c/nod/11/build/mbedtls“ wird verlassen
Target 'mbedtls-build' responsible for '/c/nod/11/build/mbedtls/libmbedtls.a'
make -C /c/nod/11/build/mdns -f /c/sdk32/esp-idf/make/component_wrapper.mk COMPONENT_MAKEFILE=/c/sdk32/esp-idf/components/mdns/component.mk COMPONENT_NAME=mdns build
make[1]: Verzeichnis „/c/nod/11/build/mdns“ wird betreten
make[1]: Verzeichnis „/c/nod/11/build/mdns“ wird verlassen
Target 'mdns-build' responsible for '/c/nod/11/build/mdns/libmdns.a'
make -C /c/nod/11/build/micro-ecc -f /c/sdk32/esp-idf/make/component_wrapper.mk COMPONENT_MAKEFILE=/c/sdk32/esp-idf/components/micro-ecc/component.mk COMPONENT_NAME=micro-ecc build
make[1]: Verzeichnis „/c/nod/11/build/micro-ecc“ wird betreten
make[1]: Verzeichnis „/c/nod/11/build/micro-ecc“ wird verlassen
Target 'micro-ecc-build' responsible for '/c/nod/11/build/micro-ecc/libmicro-ecc.a'
make -C /c/nod/11/build/newlib -f /c/sdk32/esp-idf/make/component_wrapper.mk COMPONENT_MAKEFILE=/c/sdk32/esp-idf/components/newlib/component.mk COMPONENT_NAME=newlib build
make[1]: Verzeichnis „/c/nod/11/build/newlib“ wird betreten
make[1]: Verzeichnis „/c/nod/11/build/newlib“ wird verlassen
Target 'newlib-build' responsible for '/c/nod/11/build/newlib/libnewlib.a'
make -C /c/nod/11/build/nghttp -f /c/sdk32/esp-idf/make/component_wrapper.mk COMPONENT_MAKEFILE=/c/sdk32/esp-idf/components/nghttp/component.mk COMPONENT_NAME=nghttp build
make[1]: Verzeichnis „/c/nod/11/build/nghttp“ wird betreten
make[1]: Verzeichnis „/c/nod/11/build/nghttp“ wird verlassen
Target 'nghttp-build' responsible for '/c/nod/11/build/nghttp/libnghttp.a'
make -C /c/nod/11/build/nvs_flash -f /c/sdk32/esp-idf/make/component_wrapper.mk COMPONENT_MAKEFILE=/c/sdk32/esp-idf/components/nvs_flash/component.mk COMPONENT_NAME=nvs_flash build
make[1]: Verzeichnis „/c/nod/11/build/nvs_flash“ wird betreten
make[1]: Verzeichnis „/c/nod/11/build/nvs_flash“ wird verlassen
Target 'nvs_flash-build' responsible for '/c/nod/11/build/nvs_flash/libnvs_flash.a'
make -C /c/nod/11/build/openssl -f /c/sdk32/esp-idf/make/component_wrapper.mk COMPONENT_MAKEFILE=/c/sdk32/esp-idf/components/openssl/component.mk COMPONENT_NAME=openssl build
make[1]: Verzeichnis „/c/nod/11/build/openssl“ wird betreten
make[1]: Verzeichnis „/c/nod/11/build/openssl“ wird verlassen
Target 'openssl-build' responsible for '/c/nod/11/build/openssl/libopenssl.a'
make -C /c/nod/11/build/sdmmc -f /c/sdk32/esp-idf/make/component_wrapper.mk COMPONENT_MAKEFILE=/c/sdk32/esp-idf/components/sdmmc/component.mk COMPONENT_NAME=sdmmc build
make[1]: Verzeichnis „/c/nod/11/build/sdmmc“ wird betreten
make[1]: Verzeichnis „/c/nod/11/build/sdmmc“ wird verlassen
Target 'sdmmc-build' responsible for '/c/nod/11/build/sdmmc/libsdmmc.a'
make -C /c/nod/11/build/spi_flash -f /c/sdk32/esp-idf/make/component_wrapper.mk COMPONENT_MAKEFILE=/c/sdk32/esp-idf/components/spi_flash/component.mk COMPONENT_NAME=spi_flash build
make[1]: Verzeichnis „/c/nod/11/build/spi_flash“ wird betreten
make[1]: Verzeichnis „/c/nod/11/build/spi_flash“ wird verlassen
Target 'spi_flash-build' responsible for '/c/nod/11/build/spi_flash/libspi_flash.a'
make -C /c/nod/11/build/tcpip_adapter -f /c/sdk32/esp-idf/make/component_wrapper.mk COMPONENT_MAKEFILE=/c/sdk32/esp-idf/components/tcpip_adapter/component.mk COMPONENT_NAME=tcpip_adapter build
make[1]: Verzeichnis „/c/nod/11/build/tcpip_adapter“ wird betreten
make[1]: Verzeichnis „/c/nod/11/build/tcpip_adapter“ wird verlassen
Target 'tcpip_adapter-build' responsible for '/c/nod/11/build/tcpip_adapter/libtcpip_adapter.a'
make -C /c/nod/11/build/ulp -f /c/sdk32/esp-idf/make/component_wrapper.mk COMPONENT_MAKEFILE=/c/sdk32/esp-idf/components/ulp/component.mk COMPONENT_NAME=ulp build
make[1]: Verzeichnis „/c/nod/11/build/ulp“ wird betreten
make[1]: Verzeichnis „/c/nod/11/build/ulp“ wird verlassen
Target 'ulp-build' responsible for '/c/nod/11/build/ulp/libulp.a'
make -C /c/nod/11/build/vfs -f /c/sdk32/esp-idf/make/component_wrapper.mk COMPONENT_MAKEFILE=/c/sdk32/esp-idf/components/vfs/component.mk COMPONENT_NAME=vfs build
make[1]: Verzeichnis „/c/nod/11/build/vfs“ wird betreten
make[1]: Verzeichnis „/c/nod/11/build/vfs“ wird verlassen
Target 'vfs-build' responsible for '/c/nod/11/build/vfs/libvfs.a'
make -C /c/nod/11/build/wpa_supplicant -f /c/sdk32/esp-idf/make/component_wrapper.mk COMPONENT_MAKEFILE=/c/sdk32/esp-idf/components/wpa_supplicant/component.mk COMPONENT_NAME=wpa_supplicant build
make[1]: Verzeichnis „/c/nod/11/build/wpa_supplicant“ wird betreten
make[1]: Verzeichnis „/c/nod/11/build/wpa_supplicant“ wird verlassen
Target 'wpa_supplicant-build' responsible for '/c/nod/11/build/wpa_supplicant/libwpa_supplicant.a'
make -C /c/nod/11/build/xtensa-debug-module -f /c/sdk32/esp-idf/make/component_wrapper.mk COMPONENT_MAKEFILE=/c/sdk32/esp-idf/components/xtensa-debug-module/component.mk COMPONENT_NAME=xtensa-debug-module build
make[1]: Verzeichnis „/c/nod/11/build/xtensa-debug-module“ wird betreten
make[1]: Verzeichnis „/c/nod/11/build/xtensa-debug-module“ wird verlassen
Target 'xtensa-debug-module-build' responsible for '/c/nod/11/build/xtensa-debug-module/libxtensa-debug-module.a'
xtensa-esp32-elf-gcc -nostdlib -L/c/nod/11/build/app_update -L/c/nod/11/build/bootloader -L/c/nod/11/build/bootloader_support -L/c/nod/11/build/bt -L/c/nod/11/build/coap -L/c/nod/11/build/cxx -L/c/nod/11/build/driver -L/c/nod/11/build/esp32 -L/c/nod/11/build/espcoredump -L/c/nod/11/build/esptool_py -L/c/nod/11/build/ethernet -L/c/nod/11/build/expat -L/c/nod/11/build/fatfs -L/c/nod/11/build/freertos -L/c/nod/11/build/idf_test -L/c/nod/11/build/json -L/c/nod/11/build/log -L/c/nod/11/build/lwip -L/c/nod/11/build/mbedtls -L/c/nod/11/build/mdns -L/c/nod/11/build/micro-ecc -L/c/nod/11/build/newlib -L/c/nod/11/build/nghttp -L/c/nod/11/build/nvs_flash -L/c/nod/11/build/openssl -L/c/nod/11/build/partition_table -L/c/nod/11/build/sdmmc -L/c/nod/11/build/spi_flash -L/c/nod/11/build/tcpip_adapter -L/c/nod/11/build/ulp -L/c/nod/11/build/vfs -L/c/nod/11/build/wpa_supplicant -L/c/nod/11/build/xtensa-debug-module -L/c/nod/11/build/main -u call_user_start_cpu0 -Wl,--gc-sections -Wl,-static -Wl,--start-group -lapp_update -lbootloader_support -lbt -lcoap -lcxx -u __cxa_guard_dummy -ldriver -lesp32 /c/sdk32/esp-idf/components/esp32/libhal.a -L/c/sdk32/esp-idf/components/esp32/lib -lcore -lrtc -lphy -lcoexist -lnet80211 -lpp -lwpa -lsmartconfig -lcoexist -lwps -lwpa2 -L /c/sdk32/esp-idf/components/esp32/ld -T esp32_out.ld -T esp32.common.ld -T esp32.rom.ld -T esp32.peripherals.ld -lethernet -lexpat -lfatfs -lfreertos -Wl,--undefined=uxTopUsedPriority -ljson -llog -llwip -lmbedtls -lmdns -lmicro-ecc /c/sdk32/esp-idf/components/newlib/lib/libc.a /c/sdk32/esp-idf/components/newlib/lib/libm.a -lnewlib -lnghttp -lnvs_flash -lopenssl -lsdmmc -lspi_flash -ltcpip_adapter -lulp -lvfs -lwpa_supplicant -lxtensa-debug-module -lgcc -lstdc++ -Wl,--end-group -Wl,-EL -o /c/nod/11/build/hello-world.elf -Wl,-Map=/c/nod/11/build/hello-world.map
C:/nod/11/build/esp32\libesp32.a(cpu_start.o):(.literal.main_task+0x8): undefined reference to app_main' C:/nod/11/build/esp32\libesp32.a(cpu_start.o): In functionmain_task':
C:/sdk32/esp-idf/components/esp32/cpu_start.c:267: undefined reference to `app_main'
collect2.exe: error: ld returned 1 exit status
make: * [C:/sdk32/esp-idf/make/project.mk:323: /c/nod/11/build/hello-world.elf] Fehler 1

[ESP32DE]

and here after make clean, the output of make V=1
( You can't comment at this time — your comment is too long (maximum is 65536 characters).

here the second as file
log2.txt

thank you!
best wishes
rudi ;-)

[ESP32DE]

Hi Angus

sry for this action.
usually i create the "empty" component.mk file in the main folder.
but in this example i have forget to cpy the empty file...
and the undefined mistake comes.

Please - can you check this:

if we have no File: component.mk
in the main, then the undefined mistake comes

if we have a File: component.mk
in the main, then compile is ok

but i think this is not ok?
the file in hello_world is empty ( only coments ) :

but if this file is missed, then undefined mistake comes for app_main()

#
# "main" pseudo-component makefile.
#
# (Uses default behaviour of compiling all source files in directory, adding 'include' to include path.)

[ESP32DE]

Hi Angus,
for reproduce this you can example use the hello world example,
rename the component.mk example to component.mk_
compile, and compiler catch with undefined reference to `app_main'.

do we need this file (component.mk) allways created, named in the project main folder?

sry again for the action! after i created this ( cpy ) compile is ok.
i had the same problem in the past, but have not reminder me,
that i have forget to create the ( component.mk ) file in the main folder.

if we allways need this file, would be nice, you can short answere,
yes - you can close this.

if this is a bug, and we do not need to create this file
how we can stop the compile error message?

thank you again for your effort!

best wishes
rudi ;-)

[Spritetm]

The existence of a component.mk is actually how esp-idf recognizes a component, and the 'main' component effectively isn't much more than just another component... but if you don't know that logic, I agree this behaviour can be puzzling. We'll discuss internally if for the main directory we want to make the existence of this file optional.

[ESP32DE]

Txs Jeroen,
yes, the logic it self how esp-idf recognizes a component is wellknowed,
the "entry" to the main folder and "missing" the ( empty ) component.mk file itself has stopped the compile. that have me let puzzled after i saw my mistake to forget to create an empty file named component.mk in the main
but ok, txs

proposal:
if file is missing - ( check for existence )
not
undefined reference to app_main'

perhabs better
"file component.mk in the main is missing"

then it is more clear to me whats wrong ( was forget )

proposal:
check existence component.mk before compile proc. start
if one is missing, give an info ...

[weshouman]

3 years after and I can't agree more with this proposal

[projectgus]

@weshouman The CMake build system we introduced in ESP-IDF V4.0 does this. If there's a directory in the component search patch with no CMakeLists.txt file (the equivalent of component.mk) then it will log a line like

-- Component directory /path/to/direcctory does not contain a CMakeLists.txt file. No component will be added