Building modules gives error: "invalid output constraint '=@cce' in asm"

[Konstantin Belousov]

On Tue, Jun 16, 2020 at 12:29:14PM +0530, Rajesh Kumar wrote:
> Hi,
> 
> I am trying to build my module with freebsd current branch.  But I am
> facing compilation issue with header files as below.  I have built and
> installed the freebsd current branch and booted to that kernel before
> building my module. So, not sure what is going wrong.
> 
> *In file included from
> /root//freebsd_current/sys/sys/systm.h:44:./machine/atomic.h:230:1: error:
> invalid output constraint '=@cce' in
> asmATOMIC_CMPSET(char);^./machine/atomic.h:205:4: note: expanded from macro
> 'ATOMIC_CMPSET'        : "=@cce" (res),                /* 0 */         \*
> 
> Am I missing something?

Your compiler is too old.
You must either build on current, use buildworld/buildkernel method.