i#58 MacOS: drwrap stack alignment

Preserve stack alignment inside drwrap's replace_native_xfer asm routine,
as the callouts it makes can end up going to the dyld resolver and crashing
if not aligned.

SVN-Revision: 2540

ext/drwrap/drwrap_asm.asm

@@ -1,5 +1,5 @@
 /* **********************************************************
- * Copyright (c) 2012-2013 Google, Inc.  All rights reserved.
+ * Copyright (c) 2012-2014 Google, Inc.  All rights reserved.
  * ********************************************************** */
 
 /*
@@ -65,12 +65,18 @@ GLOBAL_LABEL(FUNCNAME:)
          *
          * XXX: what about xmm0 return reg?
          */
+#ifdef MACOS
+        push     0 /* maintain 16-byte alignment for call */
+#endif
         push     REG_XAX
         push     REG_XDX
         CALLC0(GLOBAL_REF(replace_native_xfer_stack_adjust))
         mov      ecx, eax
         pop      REG_XDX
         pop      REG_XAX
+#ifdef MACOS
+        lea      REG_XSP, [ ARG_SZ + REG_XSP ]
+#endif
         /* DrMem i#1217: zero out these slots as they can contain retaddrs, which
          * messes up high-performance callstack stack scans.  This is beyond TOS,
          * but these are writes so it's signal-safe.
@@ -82,16 +88,37 @@ GLOBAL_LABEL(FUNCNAME:)
         sub      REG_XSP, REG_XCX
         /* make space for app retaddr */
         push     REG_XAX
- 
-        /* put app retaddr into the slot we made above the 2 pushes */
+
         push     REG_XAX
         push     REG_XDX
+
+#ifdef MACOS
+        /* We have to align the stack for our calls: o/w dyld lazy resolution
+         * crashes there.  Current alignment could be anything so we save a ptr
+         * and mask off esp.
+         */
+        push     REG_XBX
+        mov      REG_XBX, REG_XSP
+        and      REG_XSP, -16 /* align to 16 */
+#endif
+
+        /* put app retaddr into the slot we made above the 2 pushes */
         CALLC0(GLOBAL_REF(replace_native_xfer_app_retaddr))
+#ifdef MACOS
+        mov      PTRSZ [3 * ARG_SZ + REG_XBX], REG_XAX
+#else
         mov      PTRSZ [2 * ARG_SZ + REG_XSP], REG_XAX
+#endif
 
         /* now get our target */
         CALLC0(GLOBAL_REF(replace_native_xfer_target))
         mov      REG_XCX, REG_XAX
+
+#ifdef MACOS
+        mov      REG_XSP, REG_XBX
+        pop      REG_XBX
+#endif
+
         pop      REG_XDX
         pop      REG_XAX
         /* DrMem i#1217: zero out these slots as they can contain retaddrs, which