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
