On Fri, Mar 22, 2024 at 05:31:31PM +0100, Robin Jarry wrote:
> In some cases, the node context data is used to store two pointers
> because the data is larger than the reserved 16 bytes. Having to define
> intermediate structures just to be able to cast is tedious. Add two
> pointers that take the same space than ctx.
>
> Signed-off-by: Robin Jarry <rja...@redhat.com>
> ---
>
> Notes:
> v2:
>
> * Added __extension__ (not sure where it is needed, I don't have access
> to windows).
i can answer this!
windows toolchains will only require __extension__ qualification on use
of statement expressions, so msvc won't require any use of __extension__
in this patch.
as a general rule of thumb __extension__ is something you may choose to
use for any gcc compiled code that is an extension to standard C and you
intend to use the -pedantic flag (i.e. -std=c11 && -pedantic used together)
i've commented inline below.
> * It still fails the header check for C++. It seems not possible to align
> an unnamed union...
> Tyler, do you have an idea about how to fix that?
yes, see below what i suspect you want.
> * Added static_assert to ensure the anonymous union is not larger than
> RTE_NODE_CTX_SZ.
>
> lib/graph/rte_graph_worker_common.h | 12 +++++++++++-
> 1 file changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/lib/graph/rte_graph_worker_common.h
> b/lib/graph/rte_graph_worker_common.h
> index 36d864e2c14e..a60c2bc3f0c3 100644
> --- a/lib/graph/rte_graph_worker_common.h
> +++ b/lib/graph/rte_graph_worker_common.h
> @@ -112,7 +112,14 @@ struct __rte_cache_aligned rte_node {
> };
> /* Fast path area */
> #define RTE_NODE_CTX_SZ 16
> - alignas(RTE_CACHE_LINE_SIZE) uint8_t ctx[RTE_NODE_CTX_SZ]; /**< Node
> Context. */
> + __extension__ alignas(RTE_CACHE_LINE_SIZE) union {
__extension__ should not be on the anonymous union (since they are standard
C11).
anonymous union declaration is actually a type with no name and then a data
field of that type so __rte_aligned is most likely what you want, since
you're using RTE_CACHE_LINE_SIZE we can use __rte_cache_aligned.
union __rte_cache_aligned {
... your union fields ...
};
and i think checkpatches still gives a warning unrelated to alignment
for this but it can be safely ignored. it's the warning about alignment
that we care about and should be fixed.
> + uint8_t ctx[RTE_NODE_CTX_SZ];
> + /* Convenience aliases to store pointers without complex
> casting. */
> + __extension__ struct {
this is correct/recommended since anonymous structs aren't standard,
with the __extension__ -pedantic won't emit a warning (our intention).
> + void *ctx_ptr;
> + void *ctx_ptr2;
> + };
> + }; /**< Node Context. */
> uint16_t size; /**< Total number of objects available. */
> uint16_t idx; /**< Number of objects used. */
> rte_graph_off_t off; /**< Offset of node in the graph reel. */
> @@ -130,6 +137,9 @@ struct __rte_cache_aligned rte_node {
> alignas(RTE_CACHE_LINE_MIN_SIZE) struct rte_node *nodes[]; /**< Next
> nodes. */
> };
>
> +static_assert(offsetof(struct rte_node, size) - offsetof(struct rte_node,
> ctx) == RTE_NODE_CTX_SZ,
> + "The node context anonymous union cannot be larger than
> RTE_NODE_CTX_SZ");
> +
you should include directly include <stddef.h> in this file for use of offsetof.
you should include directly include <assert.h> in this file for use of the
static_assert.
hope this helps!
ty
> /**
> * @internal
> *
> --
> 2.44.0
