diff --git a/xpcom/reflect/xptcall/src/md/unix/Makefile.in b/xpcom/reflect/xptcall/src/md/unix/Makefile.in
index a43d2d70aed..93c5d7c360a 100644
--- a/xpcom/reflect/xptcall/src/md/unix/Makefile.in
+++ b/xpcom/reflect/xptcall/src/md/unix/Makefile.in
@@ -64,12 +64,21 @@ include $(topsrcdir)/config/config.mk
 #
 # Lots of Unixish x86 flavors
 #
-ifneq (,$(filter FreeBSD NetBSD OpenBSD BSD_OS Darwin,$(OS_ARCH)))
+
+ifeq (Darwin,$(OS_ARCH))
+ifeq (86,$(findstring 86,$(OS_TEST)))
+ifeq (x86_64,$(OS_TEST))
+CPPSRCS		:= xptcinvoke_x86_64_unix.cpp xptcstubs_x86_64_darwin.cpp
+else
+DEFINES		+= -DKEEP_STACK_16_BYTE_ALIGNED
+CPPSRCS		:= xptcinvoke_unixish_x86.cpp xptcstubs_unixish_x86.cpp
+endif
+endif
+endif
+
+ifneq (,$(filter FreeBSD NetBSD OpenBSD BSD_OS,$(OS_ARCH)))
 ifeq (86,$(findstring 86,$(OS_TEST)))
 CPPSRCS		:= xptcinvoke_unixish_x86.cpp xptcstubs_unixish_x86.cpp
-ifeq (Darwin,$(OS_ARCH))
-DEFINES		+= -DKEEP_STACK_16_BYTE_ALIGNED
-endif
 endif
 endif
 #
@@ -79,7 +88,7 @@ endif
 ifneq (,$(filter Linux GNU_%,$(OS_ARCH)))
 # Linux/x86-64
 ifeq (x86_64,$(OS_TEST))
-CPPSRCS		:= xptcinvoke_x86_64_linux.cpp xptcstubs_x86_64_linux.cpp
+CPPSRCS		:= xptcinvoke_x86_64_unix.cpp xptcstubs_x86_64_linux.cpp
 else
 ifeq (86,$(findstring 86,$(OS_TEST)))
 CPPSRCS		:= xptcinvoke_gcc_x86_unix.cpp xptcstubs_gcc_x86_unix.cpp
diff --git a/xpcom/reflect/xptcall/src/md/unix/xptcinvoke_x86_64_linux.cpp b/xpcom/reflect/xptcall/src/md/unix/xptcinvoke_x86_64_unix.cpp
similarity index 100%
rename from xpcom/reflect/xptcall/src/md/unix/xptcinvoke_x86_64_linux.cpp
rename to xpcom/reflect/xptcall/src/md/unix/xptcinvoke_x86_64_unix.cpp
diff --git a/xpcom/reflect/xptcall/src/md/unix/xptcstubs_x86_64_darwin.cpp b/xpcom/reflect/xptcall/src/md/unix/xptcstubs_x86_64_darwin.cpp
new file mode 100644
index 00000000000..d3f5dac632c
--- /dev/null
+++ b/xpcom/reflect/xptcall/src/md/unix/xptcstubs_x86_64_darwin.cpp
@@ -0,0 +1,225 @@
+/* -*- Mode: C; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ *
+ * ***** BEGIN LICENSE BLOCK *****
+ * Version: MPL 1.1/GPL 2.0/LGPL 2.1
+ *
+ * The contents of this file are subject to the Mozilla Public License Version
+ * 1.1 (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ * http://www.mozilla.org/MPL/
+ *
+ * Software distributed under the License is distributed on an "AS IS" basis,
+ * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
+ * for the specific language governing rights and limitations under the
+ * License.
+ *
+ * The Original Code is mozilla.org Code.
+ *
+ * The Initial Developer of the Original Code is
+ * Netscape Communications Corporation.
+ * Portions created by the Initial Developer are Copyright (C) 1999
+ * the Initial Developer. All Rights Reserved.
+ *
+ * Contributor(s):
+ *
+ * Alternatively, the contents of this file may be used under the terms of
+ * either of the GNU General Public License Version 2 or later (the "GPL"),
+ * or the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
+ * in which case the provisions of the GPL or the LGPL are applicable instead
+ * of those above. If you wish to allow use of your version of this file only
+ * under the terms of either the GPL or the LGPL, and not to allow others to
+ * use your version of this file under the terms of the MPL, indicate your
+ * decision by deleting the provisions above and replace them with the notice
+ * and other provisions required by the GPL or the LGPL. If you do not delete
+ * the provisions above, a recipient may use your version of this file under
+ * the terms of any one of the MPL, the GPL or the LGPL.
+ *
+ * ***** END LICENSE BLOCK ***** */
+
+// Implement shared vtbl methods.
+
+// Keep this in sync with the linux version.
+
+#include "xptcprivate.h"
+#include "xptiprivate.h"
+
+// The Darwin/x86-64 ABI passes the first 6 integer parameters and the
+// first 8 floating point parameters in registers (rdi, rsi, rdx, rcx,
+// r8, r9 and xmm0-xmm7), no stack space is allocated for these by the
+// caller.  The rest of the parameters are passed in the callers stack
+// area.
+
+const PRUint32 PARAM_BUFFER_COUNT   = 16;
+const PRUint32 GPR_COUNT            = 6;
+const PRUint32 FPR_COUNT            = 8;
+
+// PrepareAndDispatch() is called by SharedStub() and calls the actual method.
+//
+// - 'args[]' contains the arguments passed on stack
+// - 'gpregs[]' contains the arguments passed in integer registers
+// - 'fpregs[]' contains the arguments passed in floating point registers
+// 
+// The parameters are mapped into an array of type 'nsXPTCMiniVariant'
+// and then the method gets called.
+
+extern "C" nsresult
+PrepareAndDispatch(nsXPTCStubBase * self, PRUint32 methodIndex,
+                   PRUint64 * args, PRUint64 * gpregs, double *fpregs)
+{
+    nsXPTCMiniVariant paramBuffer[PARAM_BUFFER_COUNT];
+    nsXPTCMiniVariant* dispatchParams = NULL;
+    const nsXPTMethodInfo* info;
+    PRUint32 paramCount;
+    PRUint32 i;
+    nsresult result = NS_ERROR_FAILURE;
+
+    NS_ASSERTION(self,"no self");
+
+    self->mEntry->GetMethodInfo(PRUint16(methodIndex), &info);
+    NS_ASSERTION(info,"no method info");
+    if (!info)
+        return NS_ERROR_UNEXPECTED;
+
+    paramCount = info->GetParamCount();
+
+    // setup variant array pointer
+    if (paramCount > PARAM_BUFFER_COUNT)
+        dispatchParams = new nsXPTCMiniVariant[paramCount];
+    else
+        dispatchParams = paramBuffer;
+
+    NS_ASSERTION(dispatchParams,"no place for params");
+    if (!dispatchParams)
+        return NS_ERROR_OUT_OF_MEMORY;
+
+    PRUint64* ap = args;
+    PRUint32 nr_gpr = 1;    // skip one GPR register for 'that'
+    PRUint32 nr_fpr = 0;
+    PRUint64 value;
+
+    for (i = 0; i < paramCount; i++) {
+        const nsXPTParamInfo& param = info->GetParam(i);
+        const nsXPTType& type = param.GetType();
+        nsXPTCMiniVariant* dp = &dispatchParams[i];
+	
+        if (!param.IsOut() && type == nsXPTType::T_DOUBLE) {
+            if (nr_fpr < FPR_COUNT)
+                dp->val.d = fpregs[nr_fpr++];
+            else
+                dp->val.d = *(double*) ap++;
+            continue;
+        }
+        else if (!param.IsOut() && type == nsXPTType::T_FLOAT) {
+            if (nr_fpr < FPR_COUNT)
+                // The value in %xmm register is already prepared to
+                // be retrieved as a float. Therefore, we pass the
+                // value verbatim, as a double without conversion.
+                dp->val.d = *(double*) ap++;
+            else
+                dp->val.f = *(float*) ap++;
+            continue;
+        }
+        else {
+            if (nr_gpr < GPR_COUNT)
+                value = gpregs[nr_gpr++];
+            else
+                value = *ap++;
+        }
+
+        if (param.IsOut() || !type.IsArithmetic()) {
+            dp->val.p = (void*) value;
+            continue;
+        }
+
+        switch (type) {
+        case nsXPTType::T_I8:      dp->val.i8  = (PRInt8)   value; break;
+        case nsXPTType::T_I16:     dp->val.i16 = (PRInt16)  value; break;
+        case nsXPTType::T_I32:     dp->val.i32 = (PRInt32)  value; break;
+        case nsXPTType::T_I64:     dp->val.i64 = (PRInt64)  value; break;
+        case nsXPTType::T_U8:      dp->val.u8  = (PRUint8)  value; break;
+        case nsXPTType::T_U16:     dp->val.u16 = (PRUint16) value; break;
+        case nsXPTType::T_U32:     dp->val.u32 = (PRUint32) value; break;
+        case nsXPTType::T_U64:     dp->val.u64 = (PRUint64) value; break;
+        case nsXPTType::T_BOOL:    dp->val.b   = (PRBool)   value; break;
+        case nsXPTType::T_CHAR:    dp->val.c   = (char)     value; break;
+        case nsXPTType::T_WCHAR:   dp->val.wc  = (wchar_t)  value; break;
+
+        default:
+            NS_ASSERTION(0, "bad type");
+            break;
+        }
+    }
+
+    result = self->mOuter->CallMethod((PRUint16) methodIndex, info, dispatchParams);
+
+    if (dispatchParams != paramBuffer)
+        delete [] dispatchParams;
+
+    return result;
+}
+
+// Darwin/x86-64 uses gcc >= 4.2
+#if defined(__GXX_ABI_VERSION) && __GXX_ABI_VERSION >= 1002
+#define STUB_ENTRY(n) \
+asm(".section	\".text\",regular\n\t" \
+    ".align	2\n\t" \
+    ".if	" #n " < 10\n\t" \
+    ".globl	__ZN14nsXPTCStubBase5Stub" #n "Ev\n\t" \
+    "__ZN14nsXPTCStubBase5Stub" #n "Ev:\n\t" \
+    ".elseif	" #n " < 100\n\t" \
+    ".globl	__ZN14nsXPTCStubBase6Stub" #n "Ev\n\t" \
+    "__ZN14nsXPTCStubBase6Stub" #n "Ev:\n\t" \
+    ".elseif    " #n " < 1000\n\t" \
+    ".globl     __ZN14nsXPTCStubBase7Stub" #n "Ev\n\t" \
+    "__ZN14nsXPTCStubBase7Stub" #n "Ev:\n\t" \
+    ".else\n\t" \
+    ".err	\"stub number " #n " >= 1000 not yet supported\"\n\t" \
+    ".endif\n\t" \
+    "movl	$" #n ", %eax\n\t" \
+    "jmp	SharedStub\n\t");
+
+// static nsresult SharedStub(PRUint32 methodIndex)
+asm(".section   \".text\",regular\n\t"
+    ".align     2\n\t"
+    "SharedStub:\n\t"
+    // make room for gpregs (48), fpregs (64)
+    "pushq      %rbp\n\t"
+    "movq       %rsp,%rbp\n\t"
+    "subq       $112,%rsp\n\t"
+    // save GP registers
+    "movq       %rdi,-112(%rbp)\n\t"
+    "movq       %rsi,-104(%rbp)\n\t"
+    "movq       %rdx, -96(%rbp)\n\t"
+    "movq       %rcx, -88(%rbp)\n\t"
+    "movq       %r8 , -80(%rbp)\n\t"
+    "movq       %r9 , -72(%rbp)\n\t"
+    "leaq       -112(%rbp),%rcx\n\t"
+    // save FP registers
+    "movsd      %xmm0,-64(%rbp)\n\t"
+    "movsd      %xmm1,-56(%rbp)\n\t"
+    "movsd      %xmm2,-48(%rbp)\n\t"
+    "movsd      %xmm3,-40(%rbp)\n\t"
+    "movsd      %xmm4,-32(%rbp)\n\t"
+    "movsd      %xmm5,-24(%rbp)\n\t"
+    "movsd      %xmm6,-16(%rbp)\n\t"
+    "movsd      %xmm7, -8(%rbp)\n\t"
+    "leaq       -64(%rbp),%r8\n\t"
+    // rdi has the 'self' pointer already
+    "movl       %eax,%esi\n\t"
+    "leaq       16(%rbp),%rdx\n\t"
+    "call       _PrepareAndDispatch\n\t"
+    "leave\n\t"
+    "ret\n\t");
+
+#define SENTINEL_ENTRY(n) \
+nsresult nsXPTCStubBase::Sentinel##n() \
+{ \
+    NS_ASSERTION(0,"nsXPTCStubBase::Sentinel called"); \
+    return NS_ERROR_NOT_IMPLEMENTED; \
+}
+
+#include "xptcstubsdef.inc"
+
+#else
+#error "Unsupported compiler. Use gcc >= 4.2 for Darwin/x86-64."
+#endif /* __GNUC__ */
diff --git a/xpcom/reflect/xptcall/src/md/unix/xptcstubs_x86_64_linux.cpp b/xpcom/reflect/xptcall/src/md/unix/xptcstubs_x86_64_linux.cpp
index 2b055068e81..699113af0c6 100644
--- a/xpcom/reflect/xptcall/src/md/unix/xptcstubs_x86_64_linux.cpp
+++ b/xpcom/reflect/xptcall/src/md/unix/xptcstubs_x86_64_linux.cpp
@@ -38,6 +38,8 @@
 
 // Implement shared vtbl methods.
 
+// Keep this in sync with the darwin version.
+
 #include "xptcprivate.h"
 #include "xptiprivate.h"