RPI3, error: invalid operand in inline asm: 'rev16 ${0:w}, ${1:w}'

[John F Carr]

> On Mar 30, 2019, at 11:23 , bob prohaska <fbsd at www.zefox.net> wrote:
> 
> In a recent attempt to compile www/chromium on an RPI3 running r345516
> compilation stopped with repeated reports of 
> 
> /usr/include/machine/endian.h:89:19: error: invalid operand in inline asm: 'rev16 ${0:w}, ${1:w}'
> 
> Chromium compiled on the same host a couple of months ago, but the 
> executable failed on a runtime library error. Now attempts to upgrade
> stop during compilation. Ports are presently at revision 496949.
> 
> Thanks for reading, and any guidance.
> 
> bob prohaska

The swap function at that line in sys/arm64/include/endian.h doesn't look right to me.  I think it should read

  __asm("rev16 %w0, %w1\n" : "=r" (ret) : "r" (w));

instead of

    __asm __volatile("rev16 %w0, %w1\n" : "=&r" (ret), "+r" (v));

Two changes: (1) it doesn't need to be volatile because it has no side effects and (2) the constraints and lack of explicit input operand are wrong.  The other swap functions should have similar changes.