ntdll: Preserve rbx register when calling DLL entry point on x64.

dlls/ntdll/loader.c

@@ -264,7 +264,7 @@ void WINAPI RtlGetUnloadEventTraceEx(ULONG **size, ULONG **count, void **trace)
  * that only modifying esi leads to a crash, so use this one to backup
  * ebp while running the dll entry proc.
  */
-#ifdef __i386__
+#if defined(__i386__)
 extern BOOL call_dll_entry_point( DLLENTRYPROC proc, void *module, UINT reason, void *reserved );
 __ASM_GLOBAL_FUNC(call_dll_entry_point,
                   "pushl %ebp\n\t"
@@ -298,13 +298,36 @@ __ASM_GLOBAL_FUNC(call_dll_entry_point,
                   __ASM_CFI(".cfi_def_cfa %esp,4\n\t")
                   __ASM_CFI(".cfi_same_value %ebp\n\t")
                   "ret" )
-#else /* __i386__ */
+#elif defined(__x86_64__)
+extern BOOL CDECL call_dll_entry_point( DLLENTRYPROC proc, void *module, UINT reason, void *reserved );
+/* Some apps modify rbx in TLS entry point. */
+__ASM_GLOBAL_FUNC(call_dll_entry_point,
+                  "pushq %rbx\n\t"
+                  __ASM_SEH(".seh_pushreg %rbx\n\t")
+                  __ASM_CFI(".cfi_adjust_cfa_offset 8\n\t")
+                  __ASM_CFI(".cfi_rel_offset %rbx,0\n\t")
+                  "subq $48,%rsp\n\t"
+                  __ASM_SEH(".seh_stackalloc 48\n\t")
+                  __ASM_SEH(".seh_endprologue\n\t")
+                  __ASM_CFI(".cfi_adjust_cfa_offset 48\n\t")
+                  "mov %rcx,%r10\n\t"
+                  "mov %rdx,%rcx\n\t"
+                  "mov %r8d,%edx\n\t"
+                  "mov %r9,%r8\n\t"
+                  "call *%r10\n\t"
+                  "addq $48,%rsp\n\t"
+                  __ASM_CFI(".cfi_adjust_cfa_offset -48\n\t")
+                  "popq %rbx\n\t"
+                   __ASM_CFI(".cfi_adjust_cfa_offset -8\n\t")
+                   __ASM_CFI(".cfi_same_value %rbx\n\t")
+                  "ret" )
+#else
 static inline BOOL call_dll_entry_point( DLLENTRYPROC proc, void *module,
                                          UINT reason, void *reserved )
 {
     return proc( module, reason, reserved );
 }
-#endif /* __i386__ */
+#endif
 
 
 #if defined(__i386__) || defined(__x86_64__) || defined(__arm__) || defined(__aarch64__)