Re: [Qemu-devel] [PATCH v3 27/34] target-arm: emulate LL/SC using cmpxchg helpers

[Richard Henderson]

On 10/20/2016 10:51 AM, Pranith Kumar wrote:
> > Added back
> >
> > /* Load/Store exclusive instructions are implemented by remembering
> >    the value/address loaded, and seeing if these are the same
> >    when the store is performed.  This should be sufficient to implement
> >    the architecturally mandated semantics, and avoids having to monitor
> >    regular stores.  The compare vs the remembered value is done during
> >    the cmpxchg operation, but we must compare the addresses manually.  */
>
> FYI, I do not see this in your v7 series.

I do.  It's in patch 28:

 /* Load/Store exclusive instructions are implemented by remembering
    the value/address loaded, and seeing if these are the same
-   when the store is performed. This should be sufficient to implement
+   when the store is performed.  This should be sufficient to implement
    the architecturally mandated semantics, and avoids having to monitor
-   regular stores.
-
-   In system emulation mode only one CPU will be running at once, so
-   this sequence is effectively atomic.  In user emulation mode we
-   throw an exception and handle the atomic operation elsewhere.  */
+   regular stores.  The compare vs the remembered value is done during
+   the cmpxchg operation, but we must compare the addresses manually.  */


r~