Fix entry point to always start a binary

Keep vectors table.
Do not keep boot data if not referenced.

linker/aarch64.ld

@@ -16,9 +16,10 @@ SECTIONS
     __boot_start = .;
     .text :
     {
-        KEEP(*(.text.boot))
+        KEEP(*(.text.boot.entry)) // Entry point must go first
+        *(.text.boot)
         . = ALIGN(4096);
-        KEEP(*(.data.boot))
+        *(.data.boot)
         . = ALIGN(4096); /* Here boot code ends */
         __boot_end = .; // __boot_end must be 4KiB aligned
         __ro_start = .;
@@ -27,7 +28,7 @@ SECTIONS
 
     .vectors ALIGN(2048):
     {
-        *(.vectors)
+        KEEP(*(.vectors))
     }
 
     .rodata ALIGN(4):

nucleus/src/arch/aarch64/boot.rs

@@ -179,7 +179,7 @@ fn setup_and_enter_el1_from_el3() -> ! {
 /// [here](https://leiradel.github.io/2019/01/20/Raspberry-Pi-Stubs.html).
 ///
 #[no_mangle]
-#[link_section = ".text.boot"]
+#[link_section = ".text.boot.entry"]
 pub unsafe extern "C" fn _boot_cores() -> ! {
     const CORE_0: u64 = 0;
     const CORE_MASK: u64 = 0x3;