From 8f530849fdef3e0dfba2ef9efed993dc91d3ff73 Mon Sep 17 00:00:00 2001
From: theraven <theraven@72102866-910b-0410-8b05-ffd578937521>
Date: Sun, 29 May 2011 13:53:15 +0000
Subject: [PATCH] When assigning a pointer to an object that is allocated on
 the stack to the heap, send a -copy message.  This lets you cast blocks to id
 and then assign them to ivars without anything breaking.  Apple's 'solution'
 to this is to segfault, which is not particularly elegant.  This code is also
 quite an ugly hack (it just checks whether the object is allocated within a
 couple of pages of the current stack frame), so I might remove it before
 release.

---
 gc_boehm.c | 36 ++++++++++++++++++++++++++++++++++--
 1 file changed, 34 insertions(+), 2 deletions(-)

diff --git a/gc_boehm.c b/gc_boehm.c
index c6d8b19..392e662 100644
--- a/gc_boehm.c
+++ b/gc_boehm.c
@@ -23,6 +23,7 @@ static dispatch_queue_t finalizer_queue;
  */
 static BOOL finalizeThreaded;
 
+struct objc_slot* objc_get_slot(Class cls, SEL selector);
 
 /*
  * Citing boehm-gc's README.linux:
@@ -151,23 +152,45 @@ BOOL objc_atomicCompareAndSwapInstanceVariableBarrier(id predicate, id replaceme
 	return objc_atomicCompareAndSwapPtr(predicate, replacement, objectLocation);
 }
 
+SEL copy;
+
+static inline id copy_to_heap(id val)
+{
+	if ((0 == val) || ((1 & (intptr_t)val) == 1) || (0 == val->isa)) { return val; }
+	struct objc_object a;
+	if (((&a - 2048) < val) && ((&a + 2048) > val))
+	{
+		struct objc_slot *slot = objc_msg_lookup_sender(&val, copy, nil);
+		if (NULL != slot)
+		{
+			val = slot->method(val, copy);
+		}
+	}
+	return val;
+}
 
 id objc_assign_strongCast(id val, id *ptr)
 {
+	val = copy_to_heap(val);
 	*ptr = val;
 	return val;
 }
 
 id objc_assign_global(id val, id *ptr)
 {
+	val = copy_to_heap(val);
 	//fprintf(stderr, "Storign %p in global %p\n", val, ptr);
-	GC_add_roots(ptr, ptr+1);
+	if (isGCEnabled)
+	{
+		GC_add_roots(ptr, ptr+1);
+	}
 	*ptr = val;
 	return val;
 }
 
 id objc_assign_ivar(id val, id dest, ptrdiff_t offset)
 {
+	val = copy_to_heap(val);
 	*(id*)((char*)dest+offset) = val;
 	return val;
 }
@@ -195,11 +218,20 @@ static void *readWeakLocked(void *ptr)
 
 id objc_read_weak(id *location)
 {
+	if (!isGCEnabled)
+	{
+		return *location;
+	}
 	return GC_call_with_alloc_lock(readWeakLocked, location);
 }
 
 id objc_assign_weak(id value, id *location)
 {
+	if (!isGCEnabled)
+	{
+		*location = value;
+		return value;
+	}
 	// Temporarily zero this pointer and get the old value
 	id old = __sync_swap(location, 0);
 	if (0 != old)
@@ -229,7 +261,6 @@ static SEL cxx_destruct;
 
 Class zombie_class;
 
-struct objc_slot* objc_get_slot(Class cls, SEL selector);
 
 static void runFinalize(void *addr, void *context)
 {
@@ -526,6 +557,7 @@ static void init(void)
 	GC_clear_roots();
 	finalize = sel_registerName("finalize");
 	cxx_destruct = sel_registerName(".cxx_destruct");
+	copy = sel_registerName("copy");
 	GC_finalizer_notifier = runFinalizers;
 }