On Mon, Sep 30, 2024 at 12:57:06PM +0200, Jonas Oberhauser wrote:
> The current macros in linux-kernel.def reference instructions such as
> __xchg{mb} or __cmpxchg{acquire}, which are invalid combinations of tags
> and instructions according to the declarations in linux-kernel.bell.
> This works with current herd7 because herd7 removes these tags anyways
> and does not actually enforce validity of combinations at all.
>
> If a future herd7 version no longer applies these hardcoded
> transformations, then all currently invalid combinations will actually
> appear on some instruction.
>
> We therefore adjust the declarations to make the resulting combinations
> valid, by adding the 'mb tag to the set of Accesses and allowing all
> Accesses to appear on all read, write, and RMW instructions.
>
> Signed-off-by: Jonas Oberhauser <jonas.oberhauser@huaweicloud.com>
Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
Regards,
Boqun
> ---
> tools/memory-model/linux-kernel.bell | 9 +++++----
> 1 file changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/tools/memory-model/linux-kernel.bell b/tools/memory-model/linux-kernel.bell
> index ce068700939c..dba6b5b6dee0 100644
> --- a/tools/memory-model/linux-kernel.bell
> +++ b/tools/memory-model/linux-kernel.bell
> @@ -16,10 +16,11 @@
> enum Accesses = 'once (*READ_ONCE,WRITE_ONCE*) ||
> 'release (*smp_store_release*) ||
> 'acquire (*smp_load_acquire*) ||
> - 'noreturn (* R of non-return RMW *)
> -instructions R[{'once,'acquire,'noreturn}]
> -instructions W[{'once,'release}]
> -instructions RMW[{'once,'acquire,'release}]
> + 'noreturn (* R of non-return RMW *) ||
> + 'mb (*xchg(),cmpxchg(),...*)
> +instructions R[Accesses]
> +instructions W[Accesses]
> +instructions RMW[Accesses]
>
> enum Barriers = 'wmb (*smp_wmb*) ||
> 'rmb (*smp_rmb*) ||
> --
> 2.34.1
>
>