On Sun, Aug 5, 2018 at 3:38 AM, Joe Perches <j...@perches.com> wrote:
> 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.
Ah, good catch! The test was added in the v1->v2 meantime. Will do, thanks!
By the way, the file is a mess... Some other tests go inside the big
"#if GCC_VERSION >= 40000", others go at the end. We should clean it
up and sort it. I might just do it...
Cheers,
Miguel
>
>> +#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 */
