On Mon, Aug 27, 2018 at 6:34 AM H. Peter Anvin <hpa at zytor.com> wrote: > > On 08/27/18 06:11, Peter Zijlstra wrote: > > On Mon, Aug 27, 2018 at 05:26:53AM -0700, H. Peter Anvin wrote: > > > >> _THIS_IP_, however, is completely ill-defined, other than being an > >> address *somewhere* in the same global function (not even necessarily > >> the same function if the function is static!) As my experiment show, in > >> many (nearly) cases gcc will hoist the address all the way to the top of > >> the function, at least for the current generic implementation. > > > > It seems to have mostly worked so far... did anything change? > > > > Most likely because the major architectures contain a arch-specific > assembly implementation. The generic implementation used in some places > is completely broken, as my experiments show. > > >> For the case where _THIS_IP_ is passed to an out-of-line function in all > >> cases, it is extra pointless because all it does is increase the > >> footprint of every caller: _RET_IP_ is inherently passed to the function > >> anyway, and with tailcall protection it will uniquely identify a callsite. > > > > So I think we can convert many of the lockdep _THIS_IP_ calls to > > _RET_IP_ on the other side, with a wee bit of care. > > > > A little something like so perhaps... > > I don't have time to look at this right now (I'm on sabbatical, and I'm > dealing with personal legal stuff right at the moment), but I think it > is the right direction. > > -hpa Linus, Can this patch please be merged? Then we can polish off Peter's change to lockdep to not even use _THIS_IP_. -- Thanks, ~Nick Desaulniers
