From 3748de36714958902ebaf0669e004ae4113204db Mon Sep 17 00:00:00 2001
From: "H. Peter Anvin" <hpa@zytor.com>
Date: Thu, 28 Sep 2006 11:25:20 -0700
Subject: [PATCH] Add "safeint" mode to memdisk

---
 memdisk/memdisk.asm | 48 ++++++++++++++++++++++++++++++++++++++++++++----
 memdisk/memdisk.doc |  3 +++
 memdisk/setup.c     |  9 +++++++++
 3 files changed, 56 insertions(+), 4 deletions(-)

diff --git a/memdisk/memdisk.asm b/memdisk/memdisk.asm
index 5b6afcf..7be5e25 100644
--- a/memdisk/memdisk.asm
+++ b/memdisk/memdisk.asm
@@ -6,7 +6,7 @@
 ;  A program to emulate an INT 13h disk BIOS from a "disk" in extended
 ;  memory.
 ;
-;   Copyright (C) 2001-2005  H. Peter Anvin
+;   Copyright (C) 2001-2006  H. Peter Anvin
 ;
 ;  This program is free software; you can redistribute it and/or modify
 ;  it under the terms of the GNU General Public License as published by
@@ -44,6 +44,7 @@
 
 %define CONFIG_READONLY	0x01
 %define CONFIG_RAW	0x02
+%define CONFIG_SAFEINT	0x04
 %define CONFIG_BIGRAW	0x08		; MUST be 8!
 
 		org 0h
@@ -605,7 +606,9 @@ bcopy:
 		push edx
 		push ebp
 
-		test byte [ConfigFlags],CONFIG_RAW
+		mov bx, real_int15_stub
+
+		test byte [ConfigFlags], CONFIG_RAW|CONFIG_SAFEINT
 		jz .anymode
 
 		smsw ax			; Unprivileged!
@@ -613,6 +616,33 @@ bcopy:
 		jnz .protmode
 
 .realmode:
+		test byte [ConfigFlags], CONFIG_RAW
+		jnz .raw
+
+		; We're in real mode with CONFIG_SAFEINT, invoke INT 15h
+		; directly if the vector is unchanged, otherwise invoke
+		; the *old* INT 15h vector.
+
+		push ds
+		xor ax, ax
+		mov fs,ax
+
+		cmp word [4*0x15], Int15Start
+		jne .changed
+
+		mov ax, cs
+		cmp word [4*0x15+2], ax
+		jne .changed
+
+		pop ds
+		jmp .anymode		; INT 15h unchanged, safe to execute
+
+.changed:	; INT 15h modified, execute *old* INT 15h
+		pop ds
+		mov bx, fake_int15_stub
+		jmp .anymode
+
+.raw:
 		TRACER 'r'
 		; We're in real mode, do it outselves
 
@@ -716,8 +746,7 @@ bcopy:
 		mov si,Mover
 		mov ah, 87h
 		shl cx,1	; Convert to 16-bit words
-		int 15h
-		cli		; Some BIOSes enable interrupts on INT 15h
+		call bx		; INT 15h stub
 		pop eax		; Transfer size this cycle
 		pop ecx
 		pop edi
@@ -736,6 +765,17 @@ bcopy:
 		pop eax
 		ret
 
+real_int15_stub:
+		int 15h
+		cli		; Some BIOSes enable interrupts on INT 15h
+		ret
+
+fake_int15_stub:
+		pushf
+		call far [OldInt15]
+		cli
+		ret
+
 %ifdef DEBUG_TRACERS
 debug_tracer:	pushad
 		pushfd
diff --git a/memdisk/memdisk.doc b/memdisk/memdisk.doc
index a9a43ac..fdcc259 100644
--- a/memdisk/memdisk.doc
+++ b/memdisk/memdisk.doc
@@ -86,6 +86,9 @@ d) MEMDISK normally uses the BIOS "INT 15h mover" API to access high
    bigraw	Use raw access to protected mode memory, and leave the
 		CPU in "big real" mode afterwards.
 
+   safeint	Use INT 15h access to protected memory, but invoke
+		INT 15h the way it was *before* MEMDISK was loaded.
+
 
 Some interesting things to note:
 
diff --git a/memdisk/setup.c b/memdisk/setup.c
index 76775fd..2f41a4d 100644
--- a/memdisk/setup.c
+++ b/memdisk/setup.c
@@ -85,8 +85,10 @@ struct patch_area {
   uint8_t  drivetype;
   uint8_t  drivecnt;
   uint8_t  configflags;
+
 #define CONFIG_READONLY	0x01
 #define CONFIG_RAW	0x02
+#define CONFIG_SAFEINT	0x04
 #define CONFIG_BIGRAW	0x08		/* MUST be 8! */
 
   uint16_t mystack;
@@ -586,10 +588,17 @@ uint32_t setup(syscall_t cs_syscall, void *cs_bounce)
   }
   if ( getcmditem("raw") != CMD_NOTFOUND ) {
     puts("Using raw access to high memory\n");
+    pptr->configflags &= ~CONFIG_SAFEINT|CONFIG_BIGRAW;
     pptr->configflags |= CONFIG_RAW;
   }
+  if ( getcmditem("safeint") != CMD_NOTFOUND ) {
+    puts("Using safe INT 15h access to high memory\n");
+    pptr->configflags &= ~CONFIG_RAW|CONFIG_BIGRAW;
+    pptr->configflags |= CONFIG_SAFEINT;
+  }
   if ( getcmditem("bigraw") != CMD_NOTFOUND ) {
     puts("Using raw access to high memory - assuming big real mode\n");
+    pptr->configflags &= ~CONFIG_SAFEINT;
     pptr->configflags |= CONFIG_BIGRAW|CONFIG_RAW;
   }
 
-- 
2.7.4