From 4365775be655f80bedaef9db5c687238efa9165e Mon Sep 17 00:00:00 2001
From: Stefan Ginsberg <stefanginsberg@gmail.com>
Date: Sat, 5 Sep 2015 15:20:27 +0000
Subject: [PATCH] - Don't have two different implementation of
 KiConvertToGuiThread, first as inlined assembly gcc and second as a function
 call (for msvc). Always use the function call to be consistent with both
 compilers.

svn path=/trunk/; revision=69032
---
 reactos/ntoskrnl/include/internal/i386/ke.h | 55 +++------------------
 reactos/ntoskrnl/ke/i386/trap.s             | 22 +++++++--
 2 files changed, 25 insertions(+), 52 deletions(-)

diff --git a/reactos/ntoskrnl/include/internal/i386/ke.h b/reactos/ntoskrnl/include/internal/i386/ke.h
index 7c9cce3ffcc..5af888b7e07 100644
--- a/reactos/ntoskrnl/include/internal/i386/ke.h
+++ b/reactos/ntoskrnl/include/internal/i386/ke.h
@@ -526,6 +526,12 @@ KiDispatchExceptionFromTrapFrame(
     IN PKTRAP_FRAME TrapFrame
 );
 
+NTSTATUS
+NTAPI
+KiConvertToGuiThread(
+    VOID
+);
+
 //
 // Global x86 only Kernel data
 //
@@ -776,55 +782,6 @@ KiCheckForApcDelivery(IN PKTRAP_FRAME TrapFrame)
     }
 }
 
-//
-// Converts a base thread to a GUI thread
-//
-#ifdef __GNUC__
-FORCEINLINE
-NTSTATUS
-KiConvertToGuiThread(VOID)
-{
-    NTSTATUS NTAPI PsConvertToGuiThread(VOID);
-    NTSTATUS Result;
-    PVOID StackFrame;
-
-    /*
-     * Converting to a GUI thread safely updates ESP in-place as well as the
-     * current Thread->TrapFrame and EBP when KeSwitchKernelStack is called.
-     *
-     * However, PsConvertToGuiThread "helpfully" restores EBP to the original
-     * caller's value, since it is considered a nonvolatile register. As such,
-     * as soon as we're back after the conversion and we try to store the result
-     * which will probably be in some stack variable (EBP-based), we'll crash as
-     * we are touching the de-allocated non-expanded stack.
-     *
-     * Thus we need a way to update our EBP before EBP is touched, and the only
-     * way to guarantee this is to do the call itself in assembly, use the EAX
-     * register to store the result, fixup EBP, and then let the C code continue
-     * on its merry way.
-     *
-     */
-    __asm__ __volatile__
-    (
-        "movl %%ebp, %1\n\t"
-        "subl %%esp, %1\n\t"
-        "call _PsConvertToGuiThread@0\n\t"
-        "addl %%esp, %1\n\t"
-        "movl %1, %%ebp"
-        : "=a"(Result), "=r"(StackFrame)
-        : "p"(PsConvertToGuiThread)
-        : "%esp", "%ecx", "%edx", "memory"
-    );
-    return Result;
-}
-#elif defined(_MSC_VER)
-NTSTATUS
-NTAPI
-KiConvertToGuiThread(VOID);
-#else
-#error Unknown Compiler
-#endif
-
 //
 // Switches from boot loader to initial kernel stack
 //
diff --git a/reactos/ntoskrnl/ke/i386/trap.s b/reactos/ntoskrnl/ke/i386/trap.s
index d8533be0f6f..538ab6e6ad2 100644
--- a/reactos/ntoskrnl/ke/i386/trap.s
+++ b/reactos/ntoskrnl/ke/i386/trap.s
@@ -177,12 +177,29 @@ KiTrapExitStub KiTrapReturn,              (KI_RESTORE_VOLATILES OR KI_RESTORE_SE
 KiTrapExitStub KiTrapReturnNoSegments,    (KI_RESTORE_VOLATILES OR KI_EXIT_IRET)
 KiTrapExitStub KiTrapReturnNoSegmentsRet8,(KI_RESTORE_VOLATILES OR KI_RESTORE_EFLAGS OR KI_EXIT_RET8)
 
-#ifdef _MSC_VER
 EXTERN _PsConvertToGuiThread@0:PROC
 
 PUBLIC _KiConvertToGuiThread@0
 _KiConvertToGuiThread@0:
-    /* Safe ebx */
+
+    /*
+     * Converting to a GUI thread safely updates ESP in-place as well as the
+     * current Thread->TrapFrame and EBP when KeSwitchKernelStack is called.
+     *
+     * However, PsConvertToGuiThread "helpfully" restores EBP to the original
+     * caller's value, since it is considered a nonvolatile register. As such,
+     * as soon as we're back after the conversion and we try to store the result
+     * which will probably be in some stack variable (EBP-based), we'll crash as
+     * we are touching the de-allocated non-expanded stack.
+     *
+     * Thus we need a way to update our EBP before EBP is touched, and the only
+     * way to guarantee this is to do the call itself in assembly, use the EAX
+     * register to store the result, fixup EBP, and then let the C code continue
+     * on its merry way.
+     *
+     */
+
+    /* Save ebx */
     push ebx
 
     /* Calculate the stack frame offset in ebx */
@@ -201,6 +218,5 @@ _KiConvertToGuiThread@0:
 
     /* return to the caller */
     ret
-#endif
 
 END