Re: [PATCH -v2 14/33] locking,m68k: Implement atomic_fetch_{add,sub,and,or,xor}()

Peter Zijlstra
2016-06-16T14:35:30Z

On Thu, Jun 16, 2016 at 02:53:09PM +0200, Andreas Schwab wrote:
> Peter Zijlstra <peterz@infradead.org> writes:

> > OK, care to elucidate? Clearly I need help reading this.
>
> grep '2.*atomic_read'

Much thanks to your detailed answer I found yet another obscure inline
asm syntax 'feature'.

So the "2" input operand actually sets the value of "=&d" (tmp), how
creative...

I would find:

#define ATOMIC_OP_RETURN(op, c_op, asm_op) \
static inline int atomic_##op##_return(int i, atomic_t *v) \
{ \
int t, tmp = atomic_read(v); \
\
__asm__ __volatile__( \
"1: movel %2,%1\n" \
" " #asm_op "l %3,%1\n" \
" casl %2,%1,%0\n" \
" jne 1b" \
: "+m" (*v), "=&d" (t), "+d" (tmp) \
: "g" (i)); \
return t; \
}

Much more obvious.

But you're right, it seems to be sorted. I'll queue a patch removing
that comment.

Thanks!