https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53037
--- Comment #32 from Eric Botcazou <ebotcazou at gcc dot gnu.org> ---
> Sparc defines STRICT_ALIGNMENT which leads to
>
> unsigned mode_align = GET_MODE_ALIGNMENT (TYPE_MODE (type));
>
> /* Don't override a larger alignment requirement coming from a user
> alignment of one of the fields. */
> if (mode_align >= TYPE_ALIGN (type))
> {
> SET_TYPE_ALIGN (type, mode_align);
> TYPE_USER_ALIGN (type) = 0;
> }
>
> so __attribute__ ((packed)) is basically ignored on Sparc.
I don't think that's correct. Simply, on strict-alignment targets, you cannot
have an aggregate type less aligned than its scalar mode, if any; for other
targets, that's only true for scalar types. But you can have an aggregate type
with alignment 1 if it has BLKmode.
> diff --git a/gcc/stor-layout.c b/gcc/stor-layout.c
> index 3028d55773a..6dd605810ac 100644
> --- a/gcc/stor-layout.c
> +++ b/gcc/stor-layout.c
> @@ -1784,7 +1784,7 @@ finalize_type_size (tree type)
>
> /* Don't override a larger alignment requirement coming from a user
> alignment of one of the fields. */
> - if (mode_align >= TYPE_ALIGN (type))
> + if (mode_align > TYPE_ALIGN (type))
> {
> SET_TYPE_ALIGN (type, mode_align);
> TYPE_USER_ALIGN (type) = 0;
>
> works with cross compiler.
The existing code works as intended: if the alignment given by the mode is
larger than or equal to the type's alignment, then this alignment given by the
mode becomes the natural alignment and TYPE_USER_ALIGN becomes obsolete/wrong.
So I think that the absence of warning is correct on strict-alignment platforms
and that, if you want to make the tests portable, then you must use structures
whose rounded size is not a power of 2 or is larger than 128 bits, so that they
don't get a scalar mode.
