1 files changed, 33 insertions, 5 deletions
diff --git a/src/Module.zig b/src/Module.zig
index 995fdda7ea..3ae61c264f 100644
--- a/src/Module.zig
+++ b/src/Module.zig
@@ -935,13 +935,41 @@ pub const Struct = struct {
         /// If true then `default_val` is the comptime field value.
         is_comptime: bool,
 
-        /// Returns the field alignment, assuming the struct is not packed.
-        pub fn normalAlignment(field: Field, target: Target) u32 {
-            if (field.abi_align == 0) {
-                return field.ty.abiAlignment(target);
-            } else {
+        /// Returns the field alignment. If the struct is packed, returns 0.
+        pub fn alignment(
+            field: Field,
+            target: Target,
+            layout: std.builtin.Type.ContainerLayout,
+        ) u32 {
+            if (field.abi_align != 0) {
+                assert(layout != .Packed);
                 return field.abi_align;
             }
+
+            switch (layout) {
+                .Packed => return 0,
+                .Auto => {
+                    if (target.ofmt == .c) {
+                        return alignmentExtern(field, target);
+                    } else {
+                        return field.ty.abiAlignment(target);
+                    }
+                },
+                .Extern => return alignmentExtern(field, target),
+            }
+        }
+
+        pub fn alignmentExtern(field: Field, target: Target) u32 {
+            // This logic is duplicated in Type.abiAlignmentAdvanced.
+            const ty_abi_align = field.ty.abiAlignment(target);
+
+            if (field.ty.isAbiInt() and field.ty.intInfo(target).bits >= 128) {
+                // The C ABI requires 128 bit integer fields of structs
+                // to be 16-bytes aligned.
+                return @maximum(ty_abi_align, 16);
+            }
+
+            return ty_abi_align;
         }
     };