From: Linus Torvalds <torvalds@linux-foundation.org>
To: Dan Carpenter <dan.carpenter@linaro.org>
Cc: linux-sparse@vger.kernel.org,
Ricardo Ribalda <ribalda@chromium.org>,
Kees Cook <kees@kernel.org>,
linux-media@vger.kernel.org
Subject: Re: [PATCH] builtin: implement __builtin_strlen() for constants
Date: Wed, 15 Oct 2025 08:13:51 -0700 [thread overview]
Message-ID: <CAHk-=wgKcf_dP0_7yTqL+JKc03mhFgqFHkN7jXLUrOy=WjWZUA@mail.gmail.com> (raw)
In-Reply-To: <aO-cvXncl7dbnP_J@stanley.mountain>
On Wed, 15 Oct 2025 at 06:09, Dan Carpenter <dan.carpenter@linaro.org> wrote:
>
> People are adding compile time asserts to check whether strings are
> the expected length. In GCC and Clang strlen("foo") is expanded at
> compile time so this works, but in Sparse it triggers a "bad constant
> expression" warning. Implement expand_strlen() to handle string
> literals.
Ack.
Except it's not quite right.
Try this:
int i(void)
{
return __builtin_strlen("hello\0hi");
}
and you'll see that it returns 8, even though the correct string length is 5.
So you should add a
#include <string.h>
at the top, and do something like
- expr->value = arg->string->length - 1;
+ expr->value = strlen(arg->string->data);
in there instead, because constant strings can have embedded NUL characters.
Linus
next prev parent reply other threads:[~2025-10-15 15:14 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-10-15 13:08 [PATCH] builtin: implement __builtin_strlen() for constants Dan Carpenter
2025-10-15 15:13 ` Linus Torvalds [this message]
2025-10-16 8:29 ` Dan Carpenter
2025-10-16 12:05 ` Chris Li
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