Don't generate 2^64 byte padding fields on unions

The --explicit-padding flag would make bindgen try to add tail padding
to rust unions, by adding up the size of all the union fields and
subtracting from the size of the union as given by clang. The total size
of a union's fields is always larger than the union, so the subtraction
underflowed and bindgen produced padding fields larger than addressable
RAM.

1 files changed, 5 insertions, 0 deletions

diff --git a/src/codegen/struct_layout.rs b/src/codegen/struct_layout.rs
index b49fab41..657be0b4 100644
--- a/src/codegen/struct_layout.rs
+++ b/src/codegen/struct_layout.rs
@@ -279,6 +279,11 @@ impl<'a> StructLayoutTracker<'a> {
             return None;
         }
 
+        // Padding doesn't make sense for rust unions.
+        if self.is_rust_union {
+            return None;
+        }
+
         if self.latest_offset == comp_layout.size {
             // This struct does not contain tail padding.
             return None;