On Mon, May 14, 2018 at 04:20:23PM +0100, Mark Rutland wrote: > > @@ -10499,6 +10523,9 @@ SYSCALL_DEFINE5(perf_event_open, > > goto err_cred; > > } > > > > + if (in_compat_syscall()) > > + event->event_caps |= PERF_EV_CAP_COMPAT; > > + > > After a native perf_event_open, you could pass the fd (or exec) to > another task that was compat (or vice-versa), so this wouldn't work in > that case (crazy as it may be). > > I don't have a better suggestion at present, though.
As discussed on IRC, we could trigger off of the buffer size; if the buffer is <4G the &= UINT_MAX is harmless, if the buffer is larger, you have to be using a 64bit thingy anyway. Flipping the overflow functions around on attach/detach to buffers is a little more dodgy, but could be done I suppose.
