On Thu, Sep 20, 2018 at 10:23 AM Miguel Ojeda <miguel.ojeda.sandonis@xxxxxxxxx> wrote: > > From the GCC manual: > > nonstring > > The nonstring variable attribute specifies that an object or member > declaration with type array of char, signed char, or unsigned char, > or pointer to such a type is intended to store character arrays that > do not necessarily contain a terminating NUL. 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 > > This attribute can be used for documentation purposes (i.e. replacing > comments), but it is most helpful when the following warnings are enabled: > > -Wstringop-overflow > > Warn for calls to string manipulation functions such as memcpy and > strcpy that are determined to overflow the destination buffer. > > [...] > > -Wstringop-truncation > > Warn for calls to bounded string manipulation functions such as > strncat, strncpy, and stpncpy that may either truncate the copied > string or leave the destination unchanged. > > [...] > > In situations where a character array is intended to store a sequence > of bytes with no terminating NUL such an array may be annotated with > attribute nonstring to avoid this warning. Such arrays, however, > are not suitable arguments to functions that expect NUL-terminated > strings. To help detect accidental misuses of such arrays GCC issues > warnings unless it can prove that the use is safe. > > https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html > > Signed-off-by: Miguel Ojeda <miguel.ojeda.sandonis@xxxxxxxxx> > --- > include/linux/compiler_attributes.h | 14 ++++++++++++++ > 1 file changed, 14 insertions(+) > > diff --git a/include/linux/compiler_attributes.h b/include/linux/compiler_attributes.h > index f0f9fc398440..6b28c1b7310c 100644 > --- a/include/linux/compiler_attributes.h > +++ b/include/linux/compiler_attributes.h > @@ -34,6 +34,7 @@ > # define __GCC4_has_attribute___externally_visible__ 1 > # define __GCC4_has_attribute___noclone__ 1 > # define __GCC4_has_attribute___optimize__ 1 > +# define __GCC4_has_attribute___nonstring__ 0 > # define __GCC4_has_attribute___no_sanitize_address__ (__GNUC_MINOR__ >= 8) > #endif > > @@ -181,6 +182,19 @@ > */ > #define noinline __attribute__((__noinline__)) > > +/* > + * Optional: only supported since gcc >= 8 > + * Optional: not supported by clang > + * Optional: not supported by icc > + * > + * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-nonstring-variable-attribute > + */ > +#if __has_attribute(__nonstring__) > +# define __nonstring __attribute__((__nonstring__)) > +#else > +# define __nonstring > +#endif > + > /* > * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-noreturn-function-attribute > * clang: https://clang.llvm.org/docs/AttributeReference.html#noreturn > -- > 2.17.1 > Reviewed-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> -- Thanks, ~Nick Desaulniers
