bpf, libbpf: Add type match support

This patch adds support for the proposed type match relation to
relo_core where it is shared between userspace and kernel. It plumbs
through both kernel-side and libbpf-side support.

The matching relation is defined as follows (copy from source):
- modifiers and typedefs are stripped (and, hence, effectively ignored)
- generally speaking types need to be of same kind (struct vs. struct, union
  vs. union, etc.)
  - exceptions are struct/union behind a pointer which could also match a
    forward declaration of a struct or union, respectively, and enum vs.
    enum64 (see below)
Then, depending on type:
- integers:
  - match if size and signedness match
- arrays & pointers:
  - target types are recursively matched
- structs & unions:
  - local members need to exist in target with the same name
  - for each member we recursively check match unless it is already behind a
    pointer, in which case we only check matching names and compatible kind
- enums:
  - local variants have to have a match in target by symbolic name (but not
    numeric value)
  - size has to match (but enum may match enum64 and vice versa)
- function pointers:
  - number and position of arguments in local type has to match target
  - for each argument and the return value we recursively check match

Signed-off-by: Daniel Müller <deso@posteo.net>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20220628160127.607834-5-deso@posteo.net

1 files changed, 9 insertions, 0 deletions

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 8d3c7ab8af46..4f2408a4df08 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -7443,6 +7443,15 @@ int bpf_core_types_are_compat(const struct btf *local_btf, __u32 local_id,
 					   MAX_TYPES_ARE_COMPAT_DEPTH);
 }
 
+#define MAX_TYPES_MATCH_DEPTH 2
+
+int bpf_core_types_match(const struct btf *local_btf, u32 local_id,
+			 const struct btf *targ_btf, u32 targ_id)
+{
+	return __bpf_core_types_match(local_btf, local_id, targ_btf, targ_id, false,
+				      MAX_TYPES_MATCH_DEPTH);
+}
+
 static bool bpf_core_is_flavor_sep(const char *s)
 {
 	/* check X___Y name pattern, where X and Y are not underscores */