I am using uVision V5.26.2.0. You can see I only choose core and startup section at the environment and you can see I create a blank function as you can see at the jpg. When I try to build that programme I get an errors. You can see my Build Output down below. I am not sure but this might be related to linker section. I attached my linker section down below too. But for my opinion this is related to startup file.
Build Output:
Build target 'Target 1'compiling system_samd51j18a.c...compiling main.c...compiling startup_samd51j18a.c...linking...c:/program files (x86)/gnu arm embedded toolchain/10 2021.10/bin/../lib/gcc/arm-none-eabi/10.3.1/../../../../arm-none-eabi/bin/ld.exe: warning: RTE/Device/ATSAMD51J18A/samd51j18a_sram.ld contains output sections; did you forget -T?c:/program files (x86)/gnu arm embedded toolchain/10 2021.10/bin/../lib/gcc/arm-none-eabi/10.3.1/../../../../arm-none-eabi/bin/ld.exe: warning: cannot find entry symbol _start; defaulting to 20000000c:/program files (x86)/gnu arm embedded toolchain/10 2021.10/bin/../lib/gcc/arm-none-eabi/10.3.1/../../../../arm-none-eabi/bin/ld.exe: c:/program files (x86)/gnu arm embedded toolchain/10 2021.10/bin/../lib/gcc/arm-none-eabi/10.3.1/../../../../arm-none-eabi/lib\libc.a(lib_a-init.o): in function `__libc_init_array':init.c:(.text.__libc_init_array+0x44): undefined reference to `_init'collect2.exe: error: ld returned 1 exit status".\Objects\ACDC_D51.elf" - 1 Error(s), 0 Warning(s).Target not created.Build Time Elapsed: 00:00:01