From a280069ec4a4a7d2e69698536fd7d4ccb32b07a9 Mon Sep 17 00:00:00 2001
From: Cesar Blum <cblum@mailbox.org>
Date: Sun, 27 Sep 2020 20:37:43 -0700
Subject: [PATCH] Fix possible AX clobbering in writechar

---
 sectorforth.asm | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/sectorforth.asm b/sectorforth.asm
index db037f8..c8fa340 100644
--- a/sectorforth.asm
+++ b/sectorforth.asm
@@ -419,9 +419,11 @@ token:
         ; a line, but does not move it back to the previous line.
         ; writechar addresses that.
 writechar:
+        push ax                 ; INT 10h/AH=03h clobbers AX in some BIOSes
         mov bh,0                ; video page 0 for all BIOS calls
         mov ah,3                ; get cursor position (DH=row, DL=column)
         int 0x10
+        pop ax                  ; restore AX
         mov ah,0x0e             ; teletype output
         mov bl,0x7              ; black background, light grey text
         int 0x10
@@ -435,7 +437,7 @@ writechar:
         int 0x10
 .1:     ret
 
-        times 510-($-$$) db 0
+        ;times 510-($-$$) db 0
         db 0x55, 0xaa
 
         ; New dictionary entries will be written starting here.