On Mon, May 29, 2023 at 04:50:45PM +0200, Miguel Ojeda wrote:

Kees: what is the current stance on `[static N]` parameters? Something like:

    const char *kallsyms_lookup(unsigned long addr,
                                unsigned long *symbolsize,
                                unsigned long *offset,
    -                           char **modname, char *namebuf);
    +                           char **modname, char namebuf[static KSYM_NAME_LEN]);

makes the compiler complain about cases like these (even if trivial):

    arch/powerpc/xmon/xmon.c:1711:10: error: array argument is too small;
        contains 128 elements, callee requires at least 512
[-Werror,-Warray-bounds]
            name = kallsyms_lookup(pc, &size, &offset, NULL, tmpstr);
                 ^                                           ~~~~~~
    ./include/linux/kallsyms.h:86:29: note: callee declares array
parameter as static here
            char **modname, char namebuf[static KSYM_NAME_LEN]);
                                 ^      ~~~~~~~~~~~~~~~~~~~~~~

Wouldn't that be a good thing? (I.e. complain about the size mismatch?)

But I only see 2 files in the kernel using `[static N]` (from 2020 and
2021). Should something else be used instead (e.g. `__counted_by`),
even if constexpr-sized?.

Yeah, it seems pretty uncommon. I'd say traditionally arrays aren't
based too often, rather structs containing them.

But ultimately, yeah, everything could gain __counted_by and friends in
the future.

-- 
Kees Cook