ffi: bugfix: transition between bitfield cell sizes.

* ffi.c (make_ffi_type_struct): When a bitfield is declared for
a type whose alignment is different from that of the previous
member, then we start the new bitfield on a fresh alignment.
As usual, if the previous member is a bitfield which left a
partially filled byte, we skip to the next byte and then do the
alignment. This seems to match GCC behavior.

1 files changed, 10 insertions, 0 deletions

diff --git a/ffi.c b/ffi.c
index 364fa25a..5db3df87 100644
--- a/ffi.c
+++ b/ffi.c
@@ -3462,6 +3462,7 @@ static val make_ffi_type_struct(val syntax, val lisp_type,
                 cobj(coerce(mem_t *, tft), ffi_type_cls, &ffi_type_struct_ops));
   ucnum offs = 0;
   ucnum most_align = 1;
+  ucnum prev_align = 1;
   int need_out_handler = 0;
   int bit_offs = 0;
   const unsigned bits_int = 8 * sizeof(int);
@@ -3527,6 +3528,13 @@ static val make_ffi_type_struct(val syntax, val lisp_type,
     setcheck(obj, slot);
     setcheck(obj, type);
 
+    if (mtft->bitfield && align != prev_align) {
+      if (bit_offs)
+        offs++;
+      offs = (offs + almask) & ~almask;
+      bit_offs = 0;
+    }
+
     if (mtft->bitfield) {
       ucnum bits_type = 8 * size;
       ucnum bits = mtft->nelem;
@@ -3593,6 +3601,8 @@ static val make_ffi_type_struct(val syntax, val lisp_type,
         most_align = align;
     }
 
+    prev_align = align;
+
     need_out_handler = need_out_handler || mtft->out != 0;
 
     if (mtft->by_value_in)