Re: [PATCH 3/3] module: Add compile-time check for embedded NUL characters

Sami Tolvanen
2025-12-11T17:51:07Z

On Fri, Dec 12, 2025 at 02:30:48AM +0900, Daniel Gomez wrote:
>
>
> On 12/12/2025 02.03, Sami Tolvanen wrote:
> > On Thu, Dec 11, 2025 at 12:28 AM Dan Carpenter <dan.carpenter@linaro.org> wrote:
> >>
> >> On Wed, Dec 10, 2025 at 02:29:45PM -0800, Luck, Tony wrote:
> >>>> diff --git a/expand.c b/expand.c
> >>>> index f14e7181..71221d35 100644
> >>>> --- a/expand.c
> >>>> +++ b/expand.c
> >>>> @@ -535,6 +535,8 @@ static int expand_compare(struct expression *expr)
> >>>> expr->taint = 0;
> >>>> return 0;
> >>>> }
> >>>> + if (left->flags & CEF_ICE && right->flags & CEF_ICE)
> >>>> + expr->flags |= CEF_SET_ICE;
> >>>> if (simplify_cmp_binop(expr, left->ctype))
> >>>> return 0;
> >>>> if (simplify_float_cmp(expr, left->ctype))
> >>
> >> I'm not an expert in the C standard, but this feels correct to me.
> >
> > It only fixes comparisons though, the problem still exists for other
> > expressions. For example, while `_Static_assert(__builtin_strlen("")
> > == 0);` works with this change,
> > `_Static_assert(!__builtin_strlen(""));` still fails. Perhaps there's
> > a better way to fix this than changing each expression expansion
> > function to handle this flag?
>
> Maybe the flag fix just needs to be applied to the evaluation? Other op
> structs do the same. But Dan's patch did not implement evaluate. E.g.:
>
> static struct symbol_op constant_p_op = {
> .evaluate = evaluate_to_int_const_expr,
> .expand = expand_constant_p
> };

Nice catch! This seems to fix the issue for me:

diff --git a/builtin.c b/builtin.c
index 9149c43d..7573abf8 100644
--- a/builtin.c
+++ b/builtin.c
@@ -616,6 +616,7 @@ static int expand_strlen(struct expression *expr, int cost)
}

static struct symbol_op strlen_op = {
+ .evaluate = evaluate_to_int_const_expr,
.expand = expand_strlen,
};

I wonder if there are any other __builtin_* functions that need this too?
Looks like __builtin_object_size doesn't have this either.

Sami