On Wed, 2018-08-01 at 19:54 +0200, Miguel Ojeda wrote:
> From the GCC manual:
>
> The nonstring variable attribute specifies that an object or member
> declaration with type array of char or pointer to char is intended to
> store character arrays that do not necessarily contain a terminating NUL
> character. This is useful in detecting uses of such arrays or pointers
> with functions that expect NUL-terminated strings, and to avoid warnings
> when such an array or pointer is used as an argument to a bounded string
> manipulation function such as strncpy.
>
> https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html
>
> Some reports are already coming to the LKML regarding these
> warnings. When they are false positives, like this one
>
> https://lkml.org/lkml/2018/1/16/135
>
> we can use __nonstring to let gcc know a NUL character is not required.
>
> Cc: Ingo Molnar <mi...@kernel.org>
> Cc: Josh Poimboeuf <jpoim...@redhat.com>
> Cc: Kees Cook <keesc...@chromium.org>
> Cc: Andrew Morton <a...@linux-foundation.org>
> Cc: Geert Uytterhoeven <ge...@linux-m68k.org>
> Cc: Will Deacon <will.dea...@arm.com>
> Cc: Greg Kroah-Hartman <gre...@linuxfoundation.org>
> Cc: David Rientjes <rient...@google.com>
> Cc: Martin Sebor <mse...@gmail.com>
> Cc: Arnd Bergmann <a...@arndb.de>
> Signed-off-by: Miguel Ojeda <miguel.ojeda.sando...@gmail.com>
> ---
> Re-sending this since a few months have passed, Martin has improved
> GCC's feature and warnings are appearing in Geert's build bot.
> Added an example in the second patch as requested by David.
>
> include/linux/compiler-gcc.h | 14 ++++++++++++++
> include/linux/compiler_types.h | 4 ++++
> 2 files changed, 18 insertions(+)
>
> diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
> index 573f5a7d42d4..fab4e904f1fe 100644
> --- a/include/linux/compiler-gcc.h
> +++ b/include/linux/compiler-gcc.h
> @@ -343,6 +343,20 @@
> #define __designated_init __attribute__((designated_init))
> #endif
>
> +#if GCC_VERSION >= 80000
> +/*
> + * The nonstring variable attribute specifies that an object or member
> + * declaration with type array of char or pointer to char is intended
> + * to store character arrays that do not necessarily contain a terminating
> + * NUL character. This is useful in detecting uses of such arrays or pointers
> + * with functions that expect NUL-terminated strings, and to avoid warnings
> + * when such an array or pointer is used as an argument to a bounded string
> + * manipulation function such as strncpy.
> + * https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html
> + */
Please move this down to the already existing test
for GCC_VERSION >= 80000 near the bottom of the
file so that version number tests are always in
increasing order in the file.
> +#define __nonstring __attribute__((nonstring))
> +#endif
> +
> #endif /* gcc version >= 40000 specific checks */
>
> #if !defined(__noclone)
> diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
> index a8ba6b04152c..9c07be36e86a 100644
> --- a/include/linux/compiler_types.h
> +++ b/include/linux/compiler_types.h
> @@ -289,4 +289,8 @@ struct ftrace_likely_data {
> #define __diag_error(compiler, version, option, comment) \
> __diag_ ## compiler(version, error, option)
>
> +#ifndef __nonstring
> +# define __nonstring
> +#endif
> +
> #endif /* __LINUX_COMPILER_TYPES_H */
