Re: [Valgrind-developers] Atomic ppc instructions versus Imbe_BusLock / Imbe_BusUnlock

[Julian S. <js...@ac...>]

> What is your opinion about the patch below ? This patch allows
> Helgrind and DRD to recognize stwcx instructions as atomic: if stwcx
> performs a store, bus lock and bus unlock events are passed to
> Valgrind tools around the actual store.

>           /* Success?  Do the (32bit) store */
> +         stmt( IRStmt_MBE(Imbe_BusLock) );
>           storeBE( mkexpr(EA), mkSzNarrow32(ty, mkexpr(rS)) );
> +         stmt( IRStmt_MBE(Imbe_BusUnlock) );

Well, I see that it would cause drd to not complain about stwcx 
accesses, by causing it to ignore them:

    case Ist_Store:
      if (instrument && ! bus_locked)
      {
        instrument_store(bb, [...]

Problem is this really just uses Imbe_Bus{Lock,Unlock} as markers
around stores which you want to ignore.  They are however intended
to state that an imaginary lock is held (on an x86 machine) for
the duration of a read-modify-write instruction, and I don't want to
re-use them for a different purpose.  So I've added Imbe_SnoopedStoreBegin
and Imbe_SnoopedStoreEnd for that purpose instead.  (r1857, r8316).

J