From f808a0fbde62245f01a551cc19c4802b25d50174 Mon Sep 17 00:00:00 2001
From: MerryMage <MerryMage@users.noreply.github.com>
Date: Wed, 7 Feb 2018 12:24:42 +0000
Subject: [PATCH] devirtualize: Devirtualize Itanium ABI MFPs at runtime

---
 src/backend_x64/devirtualize.h | 33 +++++++++++++++++++++++++++++++--
 1 file changed, 31 insertions(+), 2 deletions(-)

diff --git a/src/backend_x64/devirtualize.h b/src/backend_x64/devirtualize.h
index e7714f11..4636884a 100644
--- a/src/backend_x64/devirtualize.h
+++ b/src/backend_x64/devirtualize.h
@@ -6,9 +6,12 @@
 
 #pragma once
 
+#include <cstring>
 #include <memory>
 
 #include "backend_x64/callback.h"
+#include "common/assert.h"
+#include "common/cast_util.h"
 #include "common/common_types.h"
 #include "common/mp.h"
 
@@ -30,11 +33,37 @@ struct ThunkBuilder<R(C::*)(Args...), mfp> {
 } // namespace impl
 
 template <typename FunctionType, FunctionType mfp>
-ArgCallback Devirtualize(mp::class_type_t<FunctionType>* this_) {
+ArgCallback DevirtualizeGeneric(mp::class_type_t<FunctionType>* this_) {
     return ArgCallback{&impl::ThunkBuilder<FunctionType, mfp>::Thunk, reinterpret_cast<u64>(this_)};
 }
 
-#define DEVIRT(this_, mfp) Dynarmic::BackendX64::Devirtualize<decltype(mfp), mfp>(this_)
+template <typename FunctionType, FunctionType mfp>
+ArgCallback DevirtualizeItanium(mp::class_type_t<FunctionType>* this_) {
+    struct MemberFunctionPointer {
+        /// For a non-virtual function, this is a simple function pointer.
+        /// For a virtual function, it is (1 + virtual table offset in bytes).
+        u64 ptr;
+        /// The required adjustment to `this`, prior to the call.
+        u64 adj;
+    } mfp_struct = Common::BitCast<MemberFunctionPointer>(mfp);
+
+    static_assert(sizeof(MemberFunctionPointer) == 16);
+    static_assert(sizeof(MemberFunctionPointer) == sizeof(mfp));
+
+    u64 fn_ptr = mfp_struct.ptr;
+    u64 this_ptr = reinterpret_cast<u64>(this_) + mfp_struct.adj;
+    if (mfp_struct.ptr & 1) {
+        u64 vtable = Common::BitCastPointee<u64>(this_ptr);
+        fn_ptr = Common::BitCastPointee<u64>(vtable + fn_ptr - 1);
+    }
+    return ArgCallback{fn_ptr, this_ptr};
+}
+
+#if defined(__APPLE__) || defined(linux) || defined(__linux) || defined(__linux__)
+#define DEVIRT(this_, mfp) Dynarmic::BackendX64::DevirtualizeItanium<decltype(mfp), mfp>(this_)
+#else
+#define DEVIRT(this_, mfp) Dynarmic::BackendX64::DevirtualizeGeneric<decltype(mfp), mfp>(this_)
+#endif
 
 } // namespace BackendX64
 } // namespace Dynarmic