Re: [PATCH] builtin: implement __builtin_strlen() for constants

On Wed, 15 Oct 2025 at 06:09, Dan Carpenter <[email protected]> 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