From a53534acd20d855b3df3a66d6ec742d1660a717c Mon Sep 17 00:00:00 2001
From: Elaina Claus <elaina.claus@chtm.me>
Date: Fri, 5 Sep 2025 10:33:42 -0400
Subject: [PATCH] clear the carry flag before calling BIOS functions

---
 include/BIOS/func/E820_memory_map.nasm | 1 +
 include/BIOS/func/a20enable.nasm       | 2 ++
 include/BIOS/func/ext_read.nasm        | 1 +
 src/mbr/mbr.nasm                       | 2 ++
 4 files changed, 6 insertions(+)

diff --git a/include/BIOS/func/E820_memory_map.nasm b/include/BIOS/func/E820_memory_map.nasm
index 0a7dba9..31bffd7 100644
--- a/include/BIOS/func/E820_memory_map.nasm
+++ b/include/BIOS/func/E820_memory_map.nasm
@@ -53,6 +53,7 @@ GetMemoryMap:
 .loop_L1:
     mov eax, 0x0000E820                     ; select 0xE820 function
     mov edx, 0x534D4150                     ; 'SMAP' magic
+    clc                                     ; clear carry
     int 0x15
     jc GetMemoryMap.error
     cmp eax, 0x534D4150
diff --git a/include/BIOS/func/a20enable.nasm b/include/BIOS/func/a20enable.nasm
index c4b94ea..d0015bb 100644
--- a/include/BIOS/func/a20enable.nasm
+++ b/include/BIOS/func/a20enable.nasm
@@ -105,6 +105,7 @@ EnableA20:
     je EnableA20.endp         ; A20 is already enabled
 
     mov ax, 0x2403
+    clc                             ; clear carry
     int 0x15
     jc EnableA20.do_fallback_a20    ; carry = error...not supported?
     cmp ah, 0
@@ -121,6 +122,7 @@ EnableA20:
     ERROR STAGE2_A20_FAILED
 .do_bios_a20:
     mov ax, 0x2401
+    clc                             ; clear carry
     int 0x15
     jmp EnableA20.a20_check
 .do_fast_a20:
diff --git a/include/BIOS/func/ext_read.nasm b/include/BIOS/func/ext_read.nasm
index 94b23ba..8b0ef11 100644
--- a/include/BIOS/func/ext_read.nasm
+++ b/include/BIOS/func/ext_read.nasm
@@ -111,6 +111,7 @@ read_disk_raw:
     mov ah, 0x42                ; call #
     mov dl, byte [bp + 14]      ; drive #             
 
+    clc                         ; clear carry
     int 0x13
     jnc .endf
 
diff --git a/src/mbr/mbr.nasm b/src/mbr/mbr.nasm
index 3e81ada..9c6ff08 100755
--- a/src/mbr/mbr.nasm
+++ b/src/mbr/mbr.nasm
@@ -96,6 +96,8 @@ main:
         mov ah, 0x41
         mov bx, 0x55AA
         mov dl, 0x80
+        
+        clc
         int 0x13
         jnc main.find_active
         ERROR MBR_ERROR_NO_INT32E                         ; no extended function support