vm: context switching needs to scrub the return address

basis/cpu/x86/32/bootstrap.factor

@@ -252,6 +252,10 @@ IN: bootstrap.x86
 
 ! Contexts
 : jit-switch-context ( reg -- )
+    ! Dummy return address -- it never gets returned to but it
+    ! must point to inside the current code block
+    ESP -4 [+] HEX: ffffffff MOV rc-absolute-cell rt-this jit-rel
+
     ! Save ds, rs registers
     jit-load-vm
     jit-save-context

basis/cpu/x86/64/bootstrap.factor

@@ -228,6 +228,11 @@ IN: bootstrap.x86
 
 ! Contexts
 : jit-switch-context ( reg -- )
+    ! Dummy return address -- it never gets returned to but it
+    ! must point to inside the current code block
+    R11 0 [RIP+] LEA
+    RSP -8 [+] R11 MOV
+
     ! Save ds, rs registers
     jit-save-context
 

vm/callstack.cpp

@@ -138,6 +138,11 @@ cell factor_vm::frame_scan(stack_frame *frame)
 	}
 }
 
+cell factor_vm::frame_offset(stack_frame *frame)
+{
+	return (cell)FRAME_RETURN_ADDRESS(frame,this) - (cell)frame_code(frame)->entry_point();
+}
+
 struct stack_frame_accumulator {
 	factor_vm *parent;
 	growable_array frames;

vm/gc.cpp

@@ -210,7 +210,8 @@ struct call_frame_scrubber {
 		const code_block *compiled = parent->frame_code(frame);
 		gc_info *info = compiled->block_gc_info();
 
-		u32 return_address = (cell)FRAME_RETURN_ADDRESS(frame,parent) - (cell)compiled->entry_point();
+		cell return_address = parent->frame_offset(frame);
+		assert(return_address < compiled->size());
 		int index = info->return_address_index(return_address);
 
 		if(index != -1)

vm/gc_info.cpp

@@ -3,7 +3,7 @@
 namespace factor
 {
 
-int gc_info::return_address_index(u32 return_address)
+int gc_info::return_address_index(cell return_address)
 {
 	u32 *return_address_array = return_addresses();
 

vm/gc_info.hpp

@@ -45,7 +45,7 @@ struct gc_info {
 			+ index * gc_root_count;
 	}
 
-	int return_address_index(u32 return_address);
+	int return_address_index(cell return_address);
 };
 
 }

vm/slot_visitor.hpp

@@ -286,8 +286,8 @@ struct call_frame_slot_visitor {
 	{
 		const code_block *compiled = visitor->fixup.translate_code(parent->frame_code(frame));
 		gc_info *info = compiled->block_gc_info();
-
-		u32 return_address = (cell)FRAME_RETURN_ADDRESS(frame,parent) - (cell)compiled->entry_point();
+		cell return_address = parent->frame_offset(frame);
+		assert(return_address < compiled->size());
 		int index = info->return_address_index(return_address);
 
 		if(index != -1)

vm/vm.hpp

@@ -596,6 +596,7 @@ struct factor_vm
 	cell frame_executing_quot(stack_frame *frame);
 	stack_frame *frame_successor(stack_frame *frame);
 	cell frame_scan(stack_frame *frame);
+	cell frame_offset(stack_frame *frame);
 	void primitive_callstack_to_array();
 	stack_frame *innermost_stack_frame(callstack *stack);
 	void primitive_innermost_stack_frame_executing();