Search notes:

arch/x86/boot/compressed/head_64.S

The main goal of head_64.S is to prepare and enter long mode.

efi64_stub_entry

efi64_stub_entry was called in 64-bit linux from efi_pe_entry in earlier releases of Linux.

efi64_stub_entry was compiled if CONFIG_EFI_STUB as enabled.

Additionally, if CONFIG_EFI_HANDOVER_PROTOCOL was enabled, this symbol was positioned at 0x390.

See also

arch/x86/kernel/head_64.S

arch/x86/boot/compressed/head_32.S

Links

Linux Inside: Kernel booting process. Part 4.