[[ Bug 20411 ]] Correct call to objc_msgSend

runrevmark · runrevmark · commit 37ec97ea4f14 · 2017-09-19T08:58:53.000+01:00
Whilst 'objc_msgSend' and friends are declared as variadic, they
aren't actually variadic functions.

The objc_msgSend functions forward the call to the appropriate
message, meaning that they must be called with the prototype of the
message and not variadically.

This difference was not seen on x86 processors where the difference
between variadic and non-variadic functions is much less; on ARM
however there is a significant difference, resulting in the obj-c
FFI not working in many cases on iOS devices.
diff --git a/docs/notes/bugfix-20411.md b/docs/notes/bugfix-20411.md
@@ -0,0 +1 @@
+# Fix crash when using Obj-C FFI on iOS
diff --git a/libscript/src/script-execute.cpp b/libscript/src/script-execute.cpp
@@ -268,7 +268,7 @@ class MCScriptForeignInvocation
         /* There are different variants of objc_msgSend we need to use
          * depending on architecture and return type:
          *   struct return
-         *     all: _stret
+         *     all but arm64: _stret
          *   float return
          *     arm: no difference
          *     i386: _fpret
@@ -289,7 +289,9 @@ class MCScriptForeignInvocation
          
         ffi_cif *t_cif = (ffi_cif *)p_handler->objc.function_cif;
         void (*t_objc_msgSend)() = nullptr;
-#if defined(__ARM__)
+#if defined(__ARM64__)
+        t_objc_msgSend = (void(*)())objc_msgSend;
+#elif defined(__ARM__)
         if (t_cif->rtype->type == FFI_TYPE_STRUCT)
             t_objc_msgSend = (void(*)())objc_msgSend_stret;
         else
@@ -310,12 +312,14 @@ class MCScriptForeignInvocation
             t_objc_msgSend = (void(*)())objc_msgSend_fpret;
         else
             t_objc_msgSend = (void(*)())objc_msgSend;
+#else
+#error unknown architecture for objc_msgSend
 #endif
         /* We must use a wrapper function written in an obj-c++ source file so that
          * we can capture any obj-c exceptions. */
         extern bool MCScriptCallObjCCatchingErrors(ffi_cif*, void (*)(), void *, void **);
         return MCScriptCallObjCCatchingErrors(t_cif,
-                                              (void(*)())objc_msgSend,
+                                              t_objc_msgSend,
                                               p_result_slot_ptr,
                                               t_objc_values);
 #else
diff --git a/libscript/src/script-instance.cpp b/libscript/src/script-instance.cpp
@@ -1147,9 +1147,8 @@ __MCScriptResolveForeignFunctionBindingForObjC(MCScriptInstanceRef p_instance,
      * make. */
     if (t_valid)
     {
-        if (ffi_prep_cif_var(t_cif,
+        if (ffi_prep_cif(t_cif,
                              FFI_DEFAULT_ABI,
-                             2,
                              t_arg_count,
                              t_cif_return_type,
                              t_cif_arg_types) != FFI_OK)

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1 @@`
	`1`	`+# Fix crash when using Obj-C FFI on iOS`