undefined reference to `app_main'

[zhn1021256354]

PS E:\esp32\sdk\app\source> idf.py build
Executing action: all (aliases: build)
Running ninja in directory e:\esp32\sdk\app\source\build
Executing "ninja all"...
[1/5] Performing build step for 'bootloader'
ninja: no work to do.
[2/3] Linking CXX executable source.elf
FAILED: source.elf
cmd.exe /C "cd . && E:\esp32\sdk\.espressif\tools\xtensa-esp32-elf\esp-2021r1-8.4.0\xtensa-esp32-elf\bin\xtensa-esp32-elf-g++.exe -mlongcalls -Wno-frame-address @CMakeFiles\source.elf.rsp -o source.elf && cd ."
e:/esp32/sdk/.espressif/tools/xtensa-esp32-elf/esp-2021r1-8.4.0/xtensa-esp32-elf/bin/../lib/gcc/xtensa-esp32-elf/8.4.0/../../../../xtensa-esp32-elf/bin/ld.exe: esp-idf/freertos/libfreertos.a(port_common.c.obj):(.literal.main_task+0x14): undefined reference to `app_main'
e:/esp32/sdk/.espressif/tools/xtensa-esp32-elf/esp-2021r1-8.4.0/xtensa-esp32-elf/bin/../lib/gcc/xtensa-esp32-elf/8.4.0/../../../../xtensa-esp32-elf/bin/ld.exe: esp-idf/freertos/libfreertos.a(port_common.c.obj): in function `main_task':
E:/esp32/sdk/esp-idf/components/freertos/port/port_common.c:129: undefined reference to `app_main'
collect2.exe: error: ld returned 1 exit status
ninja: build stopped: subcommand failed.
ninja failed with exit code 1



但是我的app_main（）函数是可以找到的，怎么破？？？？？

[abansal22]

Seems like you want are trying to compile as cpp file.
for that you put the declaration as
extern void app_main()

[smkaranam]

I have the exact same issue and I am not using CPP file.

c:/espressif/tools/xtensa-esp32-elf/esp-2021r2-patch2-8.4.0/xtensa-esp32-elf/bin/../lib/gcc/xtensa-esp32-elf/8.4.0/../../../../xtensa-esp32-elf/bin/ld.exe: esp-idf/freertos/libfreertos.a(port_common.c.obj): in function `main_task':
C:/Espressif/frameworks/esp-idf-v4.4/components/freertos/port/port_common.c:125: undefined reference to `app_main'
collect2.exe: error: ld returned 1 exit status
ninja: build stopped: subcommand failed.
ninja failed with exit code 1

Any pointers? Thank you.

[ESP_Sprite]

Do you have a source file which defines an app_main() function? And if so, is your CMakeLists.txt configured to compile it?

[abansal22]

I have the exact same issue and I am not using CPP file.

c:/espressif/tools/xtensa-esp32-elf/esp-2021r2-patch2-8.4.0/xtensa-esp32-elf/bin/../lib/gcc/xtensa-esp32-elf/8.4.0/../../../../xtensa-esp32-elf/bin/ld.exe: esp-idf/freertos/libfreertos.a(port_common.c.obj): in function `main_task':
C:/Espressif/frameworks/esp-idf-v4.4/components/freertos/port/port_common.c:125: undefined reference to `app_main'
collect2.exe: error: ld returned 1 exit status
ninja: build stopped: subcommand failed.
ninja failed with exit code 1

Any pointers? Thank you.

did you try to compile the hello world example present in the example folder in esp-idf directory?

[kyo4229]

Check the CMakeLists.txt file of the source code directory ,add it into compile.

# This file was automatically generated for projects
# without default 'CMakeLists.txt' file.
#FILE(GLOB_RECURSE app_sources ${CMAKE_SOURCE_DIR}/src/*.*)
#idf_component_register(SRCS ${app_sources})
idf_component_register(SRCS "main.c"
INCLUDE_DIRS "")

[kyo4229]

Check the \esp-idf\tools\cmake\project.cmake file, it define the component directory of CMakeLists.txt.
if(EXISTS "${CMAKE_CURRENT_LIST_DIR}/main")
__project_component_dir("${CMAKE_CURRENT_LIST_DIR}/main")
endif()

So if the app_main function directory is not this main directory, need to modify the project.cmake file.

[dana2048]

This happens when main.c (or similar) is not listed as a component in project_description.json

To fix this run:
idf.py reconfigure

https://docs.espressif.com/projects/esp ... ystem.html

[Zyx106]

I noticed that on newer esp-idf versions, the reference to 'app_main' only works when the main folder of the project is named "main".
Had it already twice, I think both times with an esp32S3. Lost a lot of time but now I have already changed it in all my projects, even some examples have folder names like "src" where the main.cpp is, the fix for me was to change it to "main".

[Vinay Janewad]

Hi. I am also facing the same issue. I am trying to integrate Matter protocol with an existing IDF project using ESP Matter SDK and ESP32-S3 chip. I am using ESP IDF v5.2.1. @Zyx106 can you please share your CMakeLists file? Thank you.