ffi: fix buggy bitfield allocation.

* ffi.c (make_ffi_type_struct): When there is no room in the
current bitfield, two mistakes are made. When bit_offs is
reset to zero in this case, the dependent variable bits_alloc
that was calculated from it (bits allocated to current unit)
must also be reset. The subsequent shift depends on it.
Secondly, when we establish the memb[i].offs field, that
must come from offs, not from unit_offs, because unit_offs
is always the base offset of the existing cell (which doesn't
have room for the new bitfield in this case); the main offset
variable offs is what gets gets adjusted to the cell which has
room for the new bitfield.

1 files changed, 2 insertions, 2 deletions

diff --git a/ffi.c b/ffi.c
index beef8d1e..8776aad4 100644
--- a/ffi.c
+++ b/ffi.c
@@ -2796,7 +2796,7 @@ static val make_ffi_type_struct(val syntax, val lisp_type,
 
       if (bits > room) {
         offs = unit_offs + size;
-        bit_offs = 0;
+        bit_offs = bits_alloc = 0;
       }
 
       if (bits_alloc == 0) {
@@ -2804,7 +2804,7 @@ static val make_ffi_type_struct(val syntax, val lisp_type,
           most_align = mtft->align;
       }
 
-      memb[i].offs = unit_offs;
+      memb[i].offs = offs;
 
 #if HAVE_LITTLE_ENDIAN
       mtft->shift = bits_alloc;