Re: issue with _Static_assert and __builtin()s

On Wed, Jan 07, 2026 at 07:41:45PM +0000, Ben Dooks wrote:
> So I am looking at why the Linux kernel's check for nul characters
> in strings is causing errors out of sparse.
> 
> EG:
> drivers/md/dm.c:3813:1: error: bad constant expression
> drivers/md/dm.c:3814:1: error: bad constant expression
> drivers/md/dm.c:3816:1: error: bad constant expression
> drivers/md/dm.c:3817:1: error: bad constant expression
> 
> I've tracked it down to the sizeof(str) - 1 == __builtin_strlen(str)
> failing to be a good constant expression...
> 
> This is an example of the assert which isn't working:
> 
> _Static_assert(sizeof("moo") - 1 == __builtin_strlen("moo"), "nul!");
> 
> This does at least get past w/o warnings
> _Static_assert(__builtin_types_compatible_p(int, int), "doh!");
> 
> I've had a go at updating builtin.c to deal with __builtin_strlen()
> for a string constant (attached) but that's just changing the
> output to "error: bad integer constant expression" so not sure
> what I've missed here.
> 

Al has a fix for that.
https://git.kernel.org/pub/scm/linux/kernel/git/viro/sparse.git/commit/?id=2634e39bf02697a18fece057208150362c985992

regards,
dan carpenter