[FREELDR] Add the relocator caller on realmode code (#8439)

CORE-19882

boot/freeldr/freeldr/arch/realmode/amd64.S

@@ -29,15 +29,18 @@ Startup:
     mov byte ptr ds:[BSS_BootPartition], dh
 
     /* Setup a real mode stack */
-    mov sp, word ptr ds:[stack16]
+    mov sp, STACK16ADDR
+
+    /* Enable A20 address line */
+    call EnableA20
+
+    /* Relocate FreeLdr if necessary */
+    call RelocateFreeLdr
 
     /* Output first status */
     mov si, offset Msg_Starting
     call writestr
 
-    /* Enable A20 address line */
-    call EnableA20
-
     /* Check the CPU */
     call CheckFor64BitSupport
     test al, al
@@ -361,12 +364,13 @@ CallbackTable:
     .word PnpBiosGetDeviceNode
     .word PnpBiosGetDockStationInformation
 
-    /* 16-bit stack pointer */
+    /* 16-bit stack pointer (the code must change it to the current stack pointer later) */
 stack16:
-    .word STACK16ADDR
+    .word 0
 
 
 #include "int386.inc"
+#include "relocator.inc"
 #include "helpers.inc"
 #include "pxe.inc"
 #include "pnp.inc"

boot/freeldr/freeldr/arch/realmode/i386.S

@@ -25,11 +25,18 @@ RealModeEntryPoint:
     mov ss, ax
 
     /* Setup the stack */
-    mov sp, word ptr ds:[stack16]
+    mov sp, STACK16ADDR
 
     /* Enable A20 address line */
     call EnableA20
 
+    /* Relocate FreeLdr if necessary */
+    call RelocateFreeLdr
+
+    /* Output first status */
+    mov si, offset Msg_Starting
+    call writestr
+
     /* Save real mode entry point in shared memory */
     mov dword ptr ds:[BSS_RealModeEntry], offset switch_to_real16
 
@@ -54,6 +61,8 @@ RealModeEntryPoint:
 
     jmp exit_to_protected
 
+Msg_Starting:
+    .ascii "Starting FreeLoader...", CR, LF, NUL
 
 /* This is the entry point from protected mode */
 switch_to_real16:
@@ -143,9 +152,9 @@ CallbackTable:
     .word PnpBiosGetDockStationInformation
 
 
-    /* 16-bit stack pointer */
+    /* 16-bit stack pointer (the code must change it to the current stack pointer later) */
 stack16:
-    .word    STACK16ADDR
+    .word 0
 
 
 .align 4    /* force 4-byte alignment */
@@ -191,6 +200,7 @@ rmode_idtptr:
     .long 0             /* Base Address */
 
 #include "int386.inc"
+#include "relocator.inc"
 #if defined(SARCH_PC98)
 #include "helpers_pc98.inc"
 #else