stage2: pad out (non-packed) struct fields when lowering to bytes

* pad out (non-packed) struct fields when lowering to bytes to be
  saved in the binary - prior to this change, fields would be
  saved at non-aligned addresses leading to wrong accesses
* add a matching test case to `behavior/struct.zig` tests
* fix offset to field calculation in `struct_field_ptr` on `x86_64`

1 files changed, 33 insertions, 0 deletions

diff --git a/test/behavior/struct.zig b/test/behavior/struct.zig
index e25f862e41..c470279aad 100644
--- a/test/behavior/struct.zig
+++ b/test/behavior/struct.zig
@@ -18,6 +18,39 @@ test "top level fields" {
     try expect(@as(i32, 1235) == instance.top_level_field);
 }
 
+const StructWithFields = struct {
+    a: u8,
+    b: u32,
+    c: u64,
+    d: u32,
+
+    fn first(self: *const StructWithFields) u8 {
+        return self.a;
+    }
+
+    fn second(self: *const StructWithFields) u32 {
+        return self.b;
+    }
+
+    fn third(self: *const StructWithFields) u64 {
+        return self.c;
+    }
+
+    fn fourth(self: *const StructWithFields) u32 {
+        return self.d;
+    }
+};
+
+test "non-packed struct has fields padded out to the required alignment" {
+    if (builtin.zig_backend == .stage2_arm) return error.SkipZigTest;
+
+    const foo = StructWithFields{ .a = 5, .b = 1, .c = 10, .d = 2 };
+    try expect(foo.first() == 5);
+    try expect(foo.second() == 1);
+    try expect(foo.third() == 10);
+    try expect(foo.fourth() == 2);
+}
+
 const StructWithNoFields = struct {
     fn add(a: i32, b: i32) i32 {
         return a + b;