From a1dd909bc416de49524618913b72edc9f9f7456f Mon Sep 17 00:00:00 2001
From: whitequark <whitequark@whitequark.org>
Date: Thu, 25 Feb 2016 01:44:05 +0000
Subject: [PATCH] Take alignment into account during attribute writeback (fixes
 #293).

---
 artiq/compiler/transforms/llvm_ir_generator.py | 8 ++++++--
 artiq/runtime/ksupport.c                       | 4 ++++
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/artiq/compiler/transforms/llvm_ir_generator.py b/artiq/compiler/transforms/llvm_ir_generator.py
index 37ad5add4..6f8e0633a 100644
--- a/artiq/compiler/transforms/llvm_ir_generator.py
+++ b/artiq/compiler/transforms/llvm_ir_generator.py
@@ -443,7 +443,7 @@ class LLVMIRGenerator:
         lldatalayout = llvm.create_target_data(self.llmodule.data_layout)
 
         llrpcattrty = self.llcontext.get_identified_type("attr_desc")
-        llrpcattrty.elements = [lli32, llptr, llptr]
+        llrpcattrty.elements = [lli32, lli32, llptr, llptr]
 
         lldescty = self.llcontext.get_identified_type("type_desc")
         lldescty.elements = [llrpcattrty.as_pointer().as_pointer(), llptr.as_pointer()]
@@ -459,7 +459,10 @@ class LLVMIRGenerator:
                 type_name = "instance.{}".format(typ.name)
 
             def llrpcattr_of_attr(name, typ):
-                size = self.llty_of_type(typ).get_abi_size(lldatalayout, context=self.llcontext)
+                size      = self.llty_of_type(typ). \
+                    get_abi_size(lldatalayout, context=self.llcontext)
+                alignment = self.llty_of_type(typ). \
+                    get_abi_alignment(lldatalayout, context=self.llcontext)
 
                 def rpc_tag_error(typ):
                     print(typ)
@@ -476,6 +479,7 @@ class LLVMIRGenerator:
                                               name="attr.{}.{}".format(type_name, name))
                 llrpcattr.initializer = ll.Constant(llrpcattrty, [
                     ll.Constant(lli32, size),
+                    ll.Constant(lli32, alignment),
                     llrpctag,
                     self.llstr_of_str(name)
                 ])
diff --git a/artiq/runtime/ksupport.c b/artiq/runtime/ksupport.c
index c8a0f24db..d5825f746 100644
--- a/artiq/runtime/ksupport.c
+++ b/artiq/runtime/ksupport.c
@@ -407,6 +407,7 @@ int recv_rpc(void *slot) {
 
 struct attr_desc {
     uint32_t size;
+    uint32_t alignment;
     const char *tag;
     const char *name;
 };
@@ -434,6 +435,9 @@ void attribute_writeback(void *utypes) {
             while(*attrs) {
                 struct attr_desc *attr = *attrs++;
 
+                if(offset % attr->alignment != 0)
+                    offset += attr->alignment - (offset % attr->alignment);
+
                 if(attr->tag) {
                     uintptr_t value = (uintptr_t)object + offset;
                     send_rpc(0, attr->tag, &object, &attr->name, value);