On Fri, 07 Feb 2025 09:55:00 +0100 Rasmus Villemoes <[email protected]> wrote:
> On Thu, Feb 06 2025, Kees Cook <[email protected]> wrote: > > > In preparation for adding stricter type checking to the str/mem*() > > helpers, provide a way to check that a variable is a character array > > via __must_be_char_array(). > > > > Signed-off-by: Kees Cook <[email protected]> > > --- > > include/linux/compiler.h | 8 +++++++- > > 1 file changed, 7 insertions(+), 1 deletion(-) > > > > diff --git a/include/linux/compiler.h b/include/linux/compiler.h > > index 7af999a131cb..a577fe0b1f8a 100644 > > --- a/include/linux/compiler.h > > +++ b/include/linux/compiler.h > > @@ -221,7 +221,13 @@ void ftrace_likely_update(struct ftrace_likely_data > > *f, int val, > > #endif /* __CHECKER__ */ > > > > /* &a[0] degrades to a pointer: a different type from an array */ > > -#define __must_be_array(a) __BUILD_BUG_ON_ZERO_MSG(__same_type((a), > > &(a)[0]), "must be array") > > +#define __is_array(a) (!__same_type((a), &(a)[0])) > > +#define __must_be_array(a) __BUILD_BUG_ON_ZERO_MSG(!__is_array(a), \ > > + "must be array") > > + > > +#define __is_char_array(a) (__is_array(a) && sizeof((a)[0]) == 1) > > +#define __must_be_char_array(a) > > __BUILD_BUG_ON_ZERO_MSG(!__is_char_array(a), \ > > + "must be byte array") > > > > It's probably unlikely to ever encounter an array of _Bool or array of > structs-with-a-single-char-member in the wild, but it does seem a bit > odd to base the test on sizeof(). Why not add a > > __is_character_type(t) (__same_type(t, char) || > __same_type(t, signed char) || > __same_type(t, unsigned char) ) > > helper and write the test using __is_character_type((a)[0])? > > Or if you really mean that it must be an array of char, not any of the > three "character types", simply replace the sizeof() by > __same_type(a[0], char) I'm not sure it matters enough to slow down the compilation by that much cpp bloat. David
