On Thu, Jun 16, 2022 at 09:37:32PM +0200, Vit Kabele wrote:
> When the compiler warns about padding struct to alignment boundary, it
> now also informs the user about the size of the alignment that needs to
> be added to get rid of the warning.
>
> This removes the need of using pahole or similar tools, or manually
> determining the padding size.
Thanks for the patch, it looks reasonable, with the formatting fixed.
It would be nice to have a testcase, at least something like
struct S {
__UINT64_TYPE__ i;
char c;
};
The problem is what value to check for, on 32-bit arches the padding is
probably 3 bytes large and on 64-bit arches probably 7 bytes. So I think
you could use __attribute__((aligned (8))) and then it's always 7.
> Tested on x86_64-pc-linux-gnu.
>
> gcc/ChangeLog:
>
> * stor-layout.cc (finalize_record_size): Improve warning message
Missing '.' at the end.
>
> Signed-off-by: Vit Kabele <vit.kab...@sysgo.com>
> ---
> gcc/stor-layout.cc | 9 ++++++++-
> 1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/gcc/stor-layout.cc b/gcc/stor-layout.cc
> index 765f22f68b9..57ddb001780 100644
> --- a/gcc/stor-layout.cc
> +++ b/gcc/stor-layout.cc
> @@ -1781,7 +1781,14 @@ finalize_record_size (record_layout_info rli)
> && simple_cst_equal (unpadded_size, TYPE_SIZE (rli->t)) == 0
> && input_location != BUILTINS_LOCATION
> && !TYPE_ARTIFICIAL (rli->t))
> - warning (OPT_Wpadded, "padding struct size to alignment boundary");
> + {
> + tree padding_size
> + = size_binop (MINUS_EXPR,
> + TYPE_SIZE_UNIT (rli->t), unpadded_size_unit);
> + warning (OPT_Wpadded,
> + "padding struct size to alignment boundary with %E bytes",
> + padding_size);
> + }
>
> if (warn_packed && TREE_CODE (rli->t) == RECORD_TYPE
> && TYPE_PACKED (rli->t) && ! rli->packed_maybe_necessary
> --
> 2.30.2
>
Marek
