arch/x86/boot/pm.c

go_to_protected_mode

go_to_protected_mode is the last function being called from main().

The last statement in go_to_protected_mode() is:

protected_mode_jump(boot_params.hdr.code32_start, (u32)&boot_params + (ds() << 4));

For code32_start, see arch/x86/boot/header.S.