From ae24fd4e410dc8ec4f02752aa8f417eae7d405dc Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Herm=C3=A8s=20B=C3=A9lusca-Ma=C3=AFto?=
 <hermes.belusca-maito@reactos.org>
Date: Sun, 12 Oct 2014 17:23:20 +0000
Subject: [PATCH] [NTVDM] - Move the stack frame indices to where they belong
 (this is the stack layout when an interrupt is called). - In the bootstrap
 interrupt, modify the CS:IP stored in the stack instead of the current CS:IP
 of the CPU, so that we can clean up everything and the interrupt return
 correctly, instead of breaking everything... (some apps wouldn't start with
 the original code^^). This is an addendum/fix to revision 64521.

svn path=/trunk/; revision=64701
---
 reactos/subsystems/ntvdm/bios/bios32/bios32.c | 15 ++++++++++++---
 reactos/subsystems/ntvdm/cpu/callback.h       | 10 ----------
 reactos/subsystems/ntvdm/int32.h              | 15 +++++++++++++++
 3 files changed, 27 insertions(+), 13 deletions(-)

diff --git a/reactos/subsystems/ntvdm/bios/bios32/bios32.c b/reactos/subsystems/ntvdm/bios/bios32/bios32.c
index eb6f385daf5..4a14b6e2499 100644
--- a/reactos/subsystems/ntvdm/bios/bios32/bios32.c
+++ b/reactos/subsystems/ntvdm/bios/bios32/bios32.c
@@ -295,9 +295,18 @@ static VOID WINAPI BiosBootstrapLoader(LPWORD Stack)
 
     /* Load DOS */
     DosBootsectorInitialize();
-    /* Position CPU to 0000:7C00 to boot the OS */
-    setCS(0x0000);
-    setIP(0x7C00);
+
+    /*
+     * Position CPU to 0000:7C00 to boot the OS.
+     *
+     * Since we are called via the INT32 mechanism, we need to correctly set
+     * CS:IP, not by changing the current one (otherwise the interrupt could
+     * not be clean up and return properly), but by changing the CS:IP in the
+     * stack, so that when the interrupt returns, the modified CS:IP is popped
+     * off the stack and the CPU is correctly repositioned.
+     */
+    Stack[STACK_CS] = 0x0000;
+    Stack[STACK_IP] = 0x7C00;
 
     DPRINT1("<-- BiosBootstrapLoader\n");
 }
diff --git a/reactos/subsystems/ntvdm/cpu/callback.h b/reactos/subsystems/ntvdm/cpu/callback.h
index 265669f3611..8813d3b6273 100644
--- a/reactos/subsystems/ntvdm/cpu/callback.h
+++ b/reactos/subsystems/ntvdm/cpu/callback.h
@@ -29,16 +29,6 @@ typedef struct _CALLBACK16
     USHORT NextOffset;
 } CALLBACK16, *PCALLBACK16;
 
-//
-// WARNING WARNING!!
-// If you're changing the indices here, you then need to
-// also fix the BOP code in callback.c !!!!!!!!!!!!!!!!!
-//
-#define STACK_INT_NUM   0
-#define STACK_IP        1
-#define STACK_CS        2
-#define STACK_FLAGS     3
-
 /* FUNCTIONS ******************************************************************/
 
 VOID
diff --git a/reactos/subsystems/ntvdm/int32.h b/reactos/subsystems/ntvdm/int32.h
index d9dc9f8c774..552d9107a36 100644
--- a/reactos/subsystems/ntvdm/int32.h
+++ b/reactos/subsystems/ntvdm/int32.h
@@ -19,6 +19,21 @@
 /* 32-bit Interrupt Identifiers */
 #define EMULATOR_MAX_INT32_NUM  0xFF + 1
 
+
+//
+// WARNING WARNING!!
+// If you're changing the stack indices here, you then need
+// to also fix the Int16To32 handler code in int32.c !!
+//
+
+// Custom variable pushed onto the stack for INT32 interrupts
+#define STACK_INT_NUM   0
+
+// This is the standard stack layout for an interrupt
+#define STACK_IP        1
+#define STACK_CS        2
+#define STACK_FLAGS     3
+
 extern const ULONG Int16To32StubSize;
 
 /* FUNCTIONS ******************************************************************/