On Thu, May 16, 2024 at 10:44:05AM +0200, Hernan Ponce de Leon wrote: > On 5/16/2024 10:31 AM, Jonas Oberhauser wrote: > > > > > > Am 5/16/2024 um 3:43 AM schrieb Alan Stern: > > > Hernan and Jonas: > > > > > > Can you explain more fully the changes you want to make to herd7 and/or > > > the LKMM? The goal is to make the memory barriers currently implicit in > > > RMW operations explicit, but I couldn't understand how you propose to do > > > this. > > > > > > Are you going to change herd7 somehow, and if so, how? It seems like > > > you should want to provide sufficient information so that the .bell > > > and .cat files can implement the appropriate memory barriers associated > > > with each RMW operation. What additional information is needed? And > > > how (explained in English, not by quoting source code) will the .bell > > > and .cat files make use of this information? > > > > > > Alan > > > > > > I don't know whether herd7 needs to be changed. Probably, herd7 does the > > following: > > - if a tag called Mb appears on an rmw instruction (by instruction I > > mean things like xchg(), atomic_inc_return_relaxed()), replace it with > > one of those things: > > * full mb ; once (the rmw) ; full mb, if a value returning > > (successful) rmw > > * once (the rmw) otherwise > > - everything else gets translated 1:1 into some internal representation > > This is my understanding from reading the source code of CSem.ml in herd7's > repo. > > Also, this is exactly what dartagnan is currently doing. > > > > > What I'm proposing is: > > 1. remove this transpilation step, > > 2. and instead allow the Mb tag to actually appear on RMW instructions > > 3. change the cat file to explicitly define the behavior of the Mb tag > > on RMW instructions > > These are the exact 3 things I changed in dartagnan for testing what Jonas > proposed. > > I am not sure if further changes are needed for herd7. Okay, good. This answers the first part of what I asked. What about the second part? That is, how will the changes to the .def, .bell, and .cat files achieve your goals? Alan
