On Mon, Feb 20, 2012 at 07:27:48PM +0100, Uros Bizjak wrote:
> IIUC the documentation, the fallback label is a parameter to xbegin
> insn, but the insn itself doesn't jump anywhere - it just records the
> parameter as a fallback address. However, there is no guarantee that
> the fallback code is exactly at (pc)+6, so we have to use asm labels
> here.
6 bytes is the length of the xbegin instruction, so xbegin .+6
says that it has the fallback address at the immediately next insn
after xbegin. Which is the _xbegin () semantics.
One would use it as
if (_xbegin () != 0xffffffff)
{
fallback_txn_aborted;
}
else
{
txn_code;
_xend ();
}
Jakub
