On Mon, Jun 20, 2022 at 6:50 AM Vit Kabele <vit.kab...@sysgo.com> wrote:
>
> I fixed the formatting and added the test.
>
> The test has first element 32bit so that it should work on both 32 and
> 64bit architectures, even without the aligned attribute.
>
> If there is some better way how to write the test properly formatted
> (i.e. not on a single line), please let me know.
>
> -- >8 --
> Subject: [PATCH] c: Extend the -Wpadded message with actual padding size
>
> 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.
>
> Tested on x86_64-pc-linux-gnu.
>
> gcc/ChangeLog:
>
> * stor-layout.cc (finalize_record_size): Extend warning message.
>
> gcc/testsuite/ChangeLog:
>
> * c-c++-common/Wpadded.c: New test.
>
> Signed-off-by: Vit Kabele <vit.kab...@sysgo.com>
> ---
> gcc/stor-layout.cc | 7 ++++++-
> gcc/testsuite/c-c++-common/Wpadded.c | 10 ++++++++++
> 2 files changed, 16 insertions(+), 1 deletion(-)
> create mode 100644 gcc/testsuite/c-c++-common/Wpadded.c
>
> diff --git a/gcc/stor-layout.cc b/gcc/stor-layout.cc
> index 765f22f68b9..88923c4136b 100644
> --- a/gcc/stor-layout.cc
> +++ b/gcc/stor-layout.cc
> @@ -1781,7 +1781,12 @@ 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 pad_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",
> pad_size);
> + }
>
> if (warn_packed && TREE_CODE (rli->t) == RECORD_TYPE
> && TYPE_PACKED (rli->t) && ! rli->packed_maybe_necessary
> diff --git a/gcc/testsuite/c-c++-common/Wpadded.c
> b/gcc/testsuite/c-c++-common/Wpadded.c
> new file mode 100644
> index 00000000000..e8f1044a36b
> --- /dev/null
> +++ b/gcc/testsuite/c-c++-common/Wpadded.c
> @@ -0,0 +1,10 @@
> +/* { dg-do compile } */
> +/* { dg-options "-Wpadded" } */
> +
> +/*
> + * The struct is on single line, because C++ compiler emits the -Wpadded
> + * warning at the first line of the struct, while the C compiler at the last
> + * line of the struct definition. This way the test passes on both
> + */
> +struct S { __UINT32_TYPE__ i; char c; }; /* { dg-warning "padding struct
> size to alignment boundary with 3 bytes" } */
> +
Note the testcase will fail on some targets where alignment is 1 for everything.
You most likely want the dg-warning to be like it is in gcc.dg/Wpadded.c:
/* { dg-warning "padding struct size to alignment boundary with 3
bytes" "" { target { ! default_packed } } } */
You might want the following from the same file too:
/* -fpack-struct is necessary because the warning expected requires the initial
packing to be larger than 1, which cannot be guaranteed for all targets.
We won't get a warning anyway if the target has "packed" structure
layout. */
/* { dg-options "-Wpadded -fpack-struct=8" } */
/* { dg-additional-options "-mno-ms-bitfields" { target *-*-mingw* } } */
Thanks,
Andrew Pinski
> --
> 2.30.2
