ffi: reproduce odd GNU C behavior for aligned bitfields.

We've already taken care of imitating the situation that GNU
C allows __attribute__((aligned(n))) to weaken the alignment
of a bitfield, contrary to it being documented that align only
strengthens alignment. Even a value of n == 1 is meaningful
in that it can cause the bitfield to start allocating from
a new byte.

This patch corrects a newly discovered nuance: when a bitfield
is attributed with a weaker alignment than its underlying
type (e.g. uint32_t field marked with 2 byte alignment),
the original type's alignment is still in effect for calculating
the alignment of the structure, and the padding.

* ffi.c (struct txr_ffi_type): New member oalign, for keeping
track of the type's original alignment, prior to adjustment.
(make_ffi_type_struct): For a named bitfield, take the oalign
value into account when determining the most strict member
alignment.
(ffi_type_compile): When marking a type as aligned, the
we remember the original alignment in atft->oalign.

* tests/017/bitfields.tl: New test case, struct s16.

* txr.1: Documented.

0 files changed, 0 insertions, 0 deletions