ACPI: tables: Add __nonstring annotations for unterminated strings

When a character array without a terminating NUL character has a static
initializer, GCC 15's -Wunterminated-string-initialization will only
warn if the array lacks the "nonstring" attribute[1]. Mark the 4-byte
ACPI identifier arrays with __nonstring (and the new __nonstring_array)
to correctly identify the char arrays as "not C strings" and thereby
eliminate the many warnings like this:

In file included from include/acpi/actbl.h:371,
                 from include/acpi/acpi.h:26,
                 from include/linux/acpi.h:26,
                 from drivers/acpi/tables.c:19:
include/acpi/actbl1.h:30:33: warning: initializer-string for array of 'char' truncates NUL terminator but destination lacks 'nonstring' attribute (5 chars into 4 available) [-Wunterminated-string-initialization]
   30 | #define ACPI_SIG_BERT           "BERT"  /* Boot Error Record Table */
      |                                 ^~~~~~
drivers/acpi/tables.c:400:9: note: in expansion of macro 'ACPI_SIG_BERT'
  400 |         ACPI_SIG_BERT, ACPI_SIG_BGRT, ACPI_SIG_CPEP, ACPI_SIG_ECDT,
      |         ^~~~~~~~~~~~~

Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117178 [1]
Signed-off-by: Kees Cook <kees@kernel.org>
---
Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Len Brown <lenb@kernel.org>
Cc: Robert Moore <robert.moore@intel.com>
Cc: linux-acpi@vger.kernel.org
Cc: acpica-devel@lists.linux.dev
---
 drivers/acpi/tables.c | 2 +-
 include/acpi/actbl.h  | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

On Wed, Apr 16, 2025 at 1:20 AM Kees Cook <kees@kernel.org> wrote:
>
> When a character array without a terminating NUL character has a static
> initializer, GCC 15's -Wunterminated-string-initialization will only
> warn if the array lacks the "nonstring" attribute[1]. Mark the 4-byte
> ACPI identifier arrays with __nonstring (and the new __nonstring_array)
> to correctly identify the char arrays as "not C strings" and thereby
> eliminate the many warnings like this:
>
> In file included from include/acpi/actbl.h:371,
>                  from include/acpi/acpi.h:26,
>                  from include/linux/acpi.h:26,
>                  from drivers/acpi/tables.c:19:
> include/acpi/actbl1.h:30:33: warning: initializer-string for array of 'char' truncates NUL terminator but destination lacks 'nonstring' attribute (5 chars into 4 available) [-Wunterminated-string-initialization]
>    30 | #define ACPI_SIG_BERT           "BERT"  /* Boot Error Record Table */
>       |                                 ^~~~~~
> drivers/acpi/tables.c:400:9: note: in expansion of macro 'ACPI_SIG_BERT'
>   400 |         ACPI_SIG_BERT, ACPI_SIG_BGRT, ACPI_SIG_CPEP, ACPI_SIG_ECDT,
>       |         ^~~~~~~~~~~~~
>
> Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117178 [1]
> Signed-off-by: Kees Cook <kees@kernel.org>
> ---
> Cc: "Rafael J. Wysocki" <rafael@kernel.org>
> Cc: Len Brown <lenb@kernel.org>
> Cc: Robert Moore <robert.moore@intel.com>
> Cc: linux-acpi@vger.kernel.org
> Cc: acpica-devel@lists.linux.dev
> ---
>  drivers/acpi/tables.c | 2 +-
>  include/acpi/actbl.h  | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/acpi/tables.c b/drivers/acpi/tables.c
> index 2295abbecd14..0a9ade7117bd 100644
> --- a/drivers/acpi/tables.c
> +++ b/drivers/acpi/tables.c
> @@ -396,7 +396,7 @@ static u8 __init acpi_table_checksum(u8 *buffer, u32 length)
>  }
>
>  /* All but ACPI_SIG_RSDP and ACPI_SIG_FACS: */
> -static const char table_sigs[][ACPI_NAMESEG_SIZE] __initconst = {
> +static const char table_sigs[][ACPI_NAMESEG_SIZE] __nonstring_array __initconst = {
>         ACPI_SIG_BERT, ACPI_SIG_BGRT, ACPI_SIG_CPEP, ACPI_SIG_ECDT,
>         ACPI_SIG_EINJ, ACPI_SIG_ERST, ACPI_SIG_HEST, ACPI_SIG_MADT,
>         ACPI_SIG_MSCT, ACPI_SIG_SBST, ACPI_SIG_SLIT, ACPI_SIG_SRAT,
> diff --git a/include/acpi/actbl.h b/include/acpi/actbl.h
> index 451f6276da49..2fc89704be17 100644
> --- a/include/acpi/actbl.h
> +++ b/include/acpi/actbl.h
> @@ -66,7 +66,7 @@
>   ******************************************************************************/
>
>  struct acpi_table_header {
> -       char signature[ACPI_NAMESEG_SIZE];      /* ASCII table signature */
> +       char signature[ACPI_NAMESEG_SIZE] __nonstring;  /* ASCII table signature */
>         u32 length;             /* Length of table in bytes, including this header */
>         u8 revision;            /* ACPI Specification minor version number */
>         u8 checksum;            /* To make sum of entire table == 0 */
> --

Applied as 6.16 material.

I've rebased it on top of

https://web.git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=9d7a0577c9db35c4cc52db90bc415ea248446472

so basically the hunk in actbl.h is gone.  Please see

https://web.git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm.git/commit/?h=bleeding-edge&id=18eb45b67544b995a8a6f48a72b816fd75776f52

Thanks!