From 9a478aa4d47541237be89814ebe03b62b5394203 Mon Sep 17 00:00:00 2001
From: Elaina Claus <elaina.claus@chtm.me>
Date: Fri, 5 Sep 2025 16:28:01 -0400
Subject: [PATCH] added another __REFLAT variant

---
 include/cdecl16.inc    | 29 +++++++++++++++++++++++++++--
 src/stage2/stage2.nasm |  4 ++--
 2 files changed, 29 insertions(+), 4 deletions(-)

diff --git a/include/cdecl16.inc b/include/cdecl16.inc
index 99fd44f..da585ec 100644
--- a/include/cdecl16.inc
+++ b/include/cdecl16.inc
@@ -69,6 +69,7 @@
 %endmacro
 %endif
 
+; set ds and es segments back to the base of the loader
 %ifnmacro __TINY_DS_ES
 %macro __TINY_DS_ES 0
     mov ax, __STAGE2_SEGMENT
@@ -77,6 +78,7 @@
 %endmacro
 %endif
 
+; for copying between locations in high memory
 %ifnmacro __REFLAT_DS_ES
 %macro __REFLAT_DS_ES 0
     cli                                   ; no interrupts   
@@ -88,8 +90,31 @@
     jmp short $+2                         ; i-cache flush
 
     mov ax, 0x10                          ; select descriptor 2
-    mov ds, ax                            ; 10h = 0001_0000b
-    mov es, ax                            ; es to big data
+    mov ds, ax
+    mov es, ax               
+
+    mov eax, cr0
+    and eax, ~1                           ; toggle bit 1 of cr0
+    mov cr0, eax                          ; back to realmode
+    jmp short $+2                         ; i-cache flush
+    sti
+
+%endmacro
+%endif
+
+; for copying from low memory to high memory (ds on a real segment, es in flat mode)
+%ifnmacro __REFLAT_ES
+%macro __REFLAT_ES 0
+    cli                                   ; no interrupts   
+    lgdt [((__STAGE2_SEGMENT << 4) + unreal_gdt_info)]                 ; load unreal gdt
+
+    mov eax, cr0                          
+    or eax, 1                             ; set pmode bit
+    mov cr0, eax                          ; switch to pmode
+    jmp short $+2                         ; i-cache flush
+
+    mov ax, 0x10                          ; select descriptor 2
+    mov es, ax                            
 
     mov eax, cr0
     and eax, ~1                           ; toggle bit 1 of cr0
diff --git a/src/stage2/stage2.nasm b/src/stage2/stage2.nasm
index 1af2838..1b87fac 100755
--- a/src/stage2/stage2.nasm
+++ b/src/stage2/stage2.nasm
@@ -224,9 +224,9 @@ EnterUnrealMode:
     jmp 0x0000:EnterUnrealMode.endp
 .endp:
     sti                                   ; re-enable interupts
-    
+
     ; set ds, es to the STAGE2_SEGMENT, for our model (generally) ds == es == cs
-    ; fs, gs & ss are all still huge data model, and the macro "__REFLAT_DS_ES" exists
+    ; fs, gs & ss are all still huge data model, and the macro(s) "__REFLAT_xxx" exists
     ; to easily access data outside of 64KiB boundries using ds/es addressing
     __TINY_DS_ES