ntdll: Clear the thread stack by hand instead of remapping zero pages.

dlls/ntdll/signal_arm.c

@@ -268,10 +268,7 @@ USHORT WINAPI RtlCaptureStackBackTrace( ULONG skip, ULONG count, PVOID *buffer,
  */
 __ASM_GLOBAL_FUNC( signal_start_thread,
                    "mov sp, r0\n\t"  /* context */
-                   "and r0, #~0xff0\n\t"  /* round down to page size */
-                   "bl " __ASM_NAME("virtual_clear_thread_stack") "\n\t"
                    "mov r1, #1\n\t"
-                   "mov r0, sp\n\t"
                    "b " __ASM_NAME("NtContinue") )
 
 /**********************************************************************

dlls/ntdll/signal_arm64.c

@@ -1222,9 +1222,6 @@ USHORT WINAPI RtlCaptureStackBackTrace( ULONG skip, ULONG count, PVOID *buffer,
  */
 __ASM_GLOBAL_FUNC( signal_start_thread,
                    "mov sp, x0\n\t"  /* context */
-                   "and x0, x0, #~0xfff\n\t"  /* round down to page size */
-                   "bl " __ASM_NAME("virtual_clear_thread_stack") "\n\t"
-                   "mov x0, sp\n\t"
                    "mov x1, #1\n\t"
                    "b " __ASM_NAME("NtContinue") )
 

dlls/ntdll/signal_i386.c

@@ -475,13 +475,18 @@ USHORT WINAPI RtlCaptureStackBackTrace( ULONG skip, ULONG count, PVOID *buffer,
  */
 __ASM_GLOBAL_FUNC( signal_start_thread,
                    "movl 4(%esp),%esi\n\t"   /* context */
-                   "leal -12(%esi),%eax\n\t"
-                   "movl %eax,%esp\n\t"
-                   /* clear the stack */
-                   "andl $~0xfff,%eax\n\t"  /* round down to page size */
-                   "movl %eax,(%esp)\n\t"
-                   "call " __ASM_NAME("virtual_clear_thread_stack") "\n\t"
+                   "leal -12(%esi),%ecx\n\t"
+                   /* clear the thread stack */
+                   "andl $~0xfff,%ecx\n\t"   /* round down to page size */
+                   "movl %fs:8,%edi\n\t"     /* NtCurrentTeb()->Tib.StackLimit */
+                   "addl $0x1000,%edi\n\t"
+                   "movl %edi,%esp\n\t"
+                   "subl %edi,%ecx\n\t"
+                   "xorl %eax,%eax\n\t"
+                   "shrl $2,%ecx\n\t"
+                   "rep; stosl\n\t"
                    /* switch to the initial context */
+                   "leal -12(%esi),%esp\n\t"
                    "movl $1,4(%esp)\n\t"
                    "movl %esi,(%esp)\n\t"
                    "call " __ASM_STDCALL("NtContinue", 8) )

dlls/ntdll/signal_x86_64.c

@@ -1486,13 +1486,21 @@ USHORT WINAPI RtlCaptureStackBackTrace( ULONG skip, ULONG count, PVOID *buffer,
  *           signal_start_thread
  */
 __ASM_GLOBAL_FUNC( signal_start_thread,
-                   "movq %rcx,%rbx\n\t"     /* context */
-                   "leaq -32(%rcx),%rcx\n\t"
-                   "movq %rcx,%rsp\n\t"
-                   "andq $~0xfff,%rcx\n\t"  /* round down to page size */
-                   "call " __ASM_NAME("virtual_clear_thread_stack") "\n\t"
-                   "movl $1,%edx\n\t"
+                   "movq %rcx,%rbx\n\t"        /* context */
+                   /* clear the thread stack */
+                   "andq $~0xfff,%rcx\n\t"     /* round down to page size */
+                   "movq %gs:0x30,%rax\n\t"
+                   "movq 0x10(%rax),%rdi\n\t"  /* NtCurrentTeb()->Tib.StackLimit */
+                   "addq $0x2000,%rdi\n\t"
+                   "movq %rdi,%rsp\n\t"
+                   "subq %rdi,%rcx\n\t"
+                   "xorl %eax,%eax\n\t"
+                   "shrq $3,%rcx\n\t"
+                   "rep; stosq\n\t"
+                   /* switch to the initial context */
+                   "leaq -32(%rbx),%rsp\n\t"
                    "movq %rbx,%rcx\n\t"
+                   "movl $1,%edx\n\t"
                    "call " __ASM_NAME("NtContinue") )
 
 

dlls/ntdll/virtual.c

@@ -105,18 +105,3 @@ void WINAPI RtlFreeUserStack( void *stack )
 
     NtFreeVirtualMemory( NtCurrentProcess(), &stack, &size, MEM_RELEASE );
 }
-
-
-/***********************************************************************
- *           virtual_clear_thread_stack
- *
- * Clear the stack contents before calling the main entry point, some broken apps need that.
- */
-void CDECL virtual_clear_thread_stack( void *stack_end )
-{
-    void *stack = NtCurrentTeb()->Tib.StackLimit;
-    SIZE_T size = (char *)stack_end - (char *)stack;
-
-    NtFreeVirtualMemory( GetCurrentProcess(), &stack, &size, MEM_DECOMMIT );
-    NtAllocateVirtualMemory( GetCurrentProcess(), &stack, 0, &size, MEM_COMMIT, PAGE_READWRITE );
-}