| Message ID | 20180920172301.21868-13-miguel.ojeda.sandonis@gmail.com (mailing list archive) |
|---|---|
| State | Not Applicable, archived |
| Headers | show |
| Series | Compiler Attributes | expand |
On Thu, Sep 20, 2018 at 10:23 AM Miguel Ojeda <miguel.ojeda.sandonis@gmail.com> 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@gmail.com> > --- > 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@google.com>
On Thu, Sep 20, 2018 at 10:22 AM, Miguel Ojeda <miguel.ojeda.sandonis@gmail.com> 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@gmail.com> Reviewed-by: Kees Cook <keescook@chromium.org> -Kees
On Thu, Sep 20, 2018 at 10:08 PM Kees Cook <keescook@chromium.org> wrote: > > Reviewed-by: Kees Cook <keescook@chromium.org> > Done! Thanks! Cheers, Miguel
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
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@gmail.com> --- include/linux/compiler_attributes.h | 14 ++++++++++++++ 1 file changed, 14 insertions(+)