Re: [dpdk-dev] [PATCH v1] devtools: update abi ignore for cryptodev

[Thomas Monjalon <thomas@monjalon.net>]

Question to an expert, Dodji,

We have this structure:

struct rte_cryptodev {
	lot of fields...
	uint8_t attached : 1;
} __rte_cache_aligned;

Because of the cache alignment, there is enough padding in the struct
(no matter the size of the cache line) for adding two more pointers:

struct rte_cryptodev {
	lot of fields...
	uint8_t attached : 1;
	struct rte_cryptodev_cb_rcu *enq_cbs;
	struct rte_cryptodev_cb_rcu *deq_cbs;
} __rte_cache_aligned;

We checked manually that the ABI is still compatible.
Then I've added (quickly) a libabigail exception rule:

[suppress_type]
	name = rte_cryptodev
	has_data_member_inserted_between = {0, 1023}

Now we want to improve this rule to restrict the offsets
to the padding at the end of the struct only,
so we keep forbidding changes in existing fields,
and forbidding additions further the current struct size.
Is this new rule good?

	has_data_member_inserted_between = {offset_after(attached), end}

Do you confirm that the keyword "end" means the old reference size?

What else do we need to check for adding a new field in a padding?

Thank you


20/01/2021 15:25, Ray Kinsella:
> Update the ignore entry for crytodev to use named fields instead of
> bit positions.
> 
> Fixes: 1c3ffb9559
> 
> Signed-off-by: Ray Kinsella <mdr@ashroe.eu>
> ---
>  devtools/libabigail.abignore | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/devtools/libabigail.abignore b/devtools/libabigail.abignore
> index 1dc84fa74b..1f17fbed58 100644
> --- a/devtools/libabigail.abignore
> +++ b/devtools/libabigail.abignore
> @@ -15,4 +15,4 @@
>  ; Ignore fields inserted in cacheline boundary of rte_cryptodev
>  [suppress_type]
>          name = rte_cryptodev
> -        has_data_member_inserted_between = {0, 1023}
> +        has_data_member_inserted_between = {offset_after(attached), end}