...arduino15/packages/esp8266/tools/xtensa-lx106-elf-gcc/3.1.0-gcc10.3-e5f9fec/bin/../lib/gcc/xtensa-lx106-elf/10.3.0/../../../../xtensa-lx106-elf/bin/ld.exe: ...arduino\cores\1039af5ffd3b6359b7b042879fbaf35f\core.a(core_esp8266_main.cpp.o): in function `__loop_end':
...Arduino15\packages\esp8266\hardware\esp8266\3.1.2\cores\esp8266/core_esp8266_main.cpp:245: undefined reference to `setup'
...arduino15/packages/esp8266/tools/xtensa-lx106-elf-gcc/3.1.0-gcc10.3-e5f9fec/bin/../lib/gcc/xtensa-lx106-elf/10.3.0/../../../../xtensa-lx106-elf/bin/ld.exe: ...arduino\cores\1039af5ffd3b6359b7b042879fbaf35f\core.a(core_esp8266_main.cpp.o):(.text._ZL12loop_wrapperv+0xc): undefined reference to `loop'
...arduino15/packages/esp8266/tools/xtensa-lx106-elf-gcc/3.1.0-gcc10.3-e5f9fec/bin/../lib/gcc/xtensa-lx106-elf/10.3.0/../../../../xtensa-lx106-elf/bin/ld.exe: ...arduino\cores\1039af5ffd3b6359b7b042879fbaf35f\core.a(core_esp8266_main.cpp.o): in function `_ZL12loop_wrapperv':
...Arduino15\packages\esp8266\hardware\esp8266\3.1.2\cores\esp8266/core_esp8266_main.cpp:250: undefined reference to `setup'
...arduino15/packages/esp8266/tools/xtensa-lx106-elf-gcc/3.1.0-gcc10.3-e5f9fec/bin/../lib/gcc/xtensa-lx106-elf/10.3.0/../../../../xtensa-lx106-elf/bin/ld.exe: ...Arduino15\packages\esp8266\hardware\esp8266\3.1.2\cores\esp8266/core_esp8266_main.cpp:253: undefined reference to `loop'
collect2.exe: error: ld returned 1 exit status

exit status 1

Compilation error: exit status 1