[BPF] Visit nested map array during BTF generation (#150608)

Fixes missing inner map struct type definitions [^1]. We should visit
the type of nested array of maps like we do for global maps. This patch
adds a boolean to convey the information to visitTypeEntry and
visitDerivedType that the pointee is a map definition and should be
treated as such.

It ressembles and works with commit 0d21c956a5c1 ("[BPF] Handle nested
wrapper structs in BPF map definition traversal (#144097)") which
focused on directly nested wrapper structs.

Before that patch, this ARRAY_OF_MAPS definition would lead to the BTF
information include the 'missing_type' as "FWD 'missing_type'
fwd_kind=struct":

	struct missing_type { uint64_t foo; };
	struct {
		__uint(type, BPF_MAP_TYPE_ARRAY_OF_MAPS);
		[...]
		__array(
			values, struct {
				[...]
				__type(value, struct missing_type);
			});
	} map SEC(".maps");

Which lead to errors while trying to load the map:

libbpf: map 'outer_map.inner': can't determine value size for type [N]:
-22.

To solve this issue, users had to use the struct in a dummy variable or
in a dummy function for the BTF to be generated correctly [^2].

[^1]: https://lore.kernel.org/netdev/aH_cGvgC20iD8qs9@gmail.com/T/#u
[^2]:
https://github.com/cilium/ebpf/discussions/1658#discussioncomment-12491339

---------

Signed-off-by: Mahe Tardy <mahe.tardy@gmail.com>
Co-authored-by: Eduard Zingerman <eddyz87@gmail.com>

0 files changed, 0 insertions, 0 deletions