libbpf: Turn btf_dedup_opts into OPTS-based struct

btf__dedup() and struct btf_dedup_opts were added before we figured out
OPTS mechanism. As such, btf_dedup_opts is non-extensible without
breaking an ABI and potentially crashing user application.

Unfortunately, btf__dedup() and btf_dedup_opts are short and succinct
names that would be great to preserve and use going forward. So we use
___libbpf_override() macro approach, used previously for bpf_prog_load()
API, to define a new btf__dedup() variant that accepts only struct btf *
and struct btf_dedup_opts * arguments, and rename the old btf__dedup()
implementation into btf__dedup_deprecated(). This keeps both source and
binary compatibility with old and new applications.

The biggest problem was struct btf_dedup_opts, which wasn't OPTS-based,
and as such doesn't have `size_t sz;` as a first field. But btf__dedup()
is a pretty rarely used API and I believe that the only currently known
users (besides selftests) are libbpf's own bpf_linker and pahole.
Neither use case actually uses options and just passes NULL. So instead
of doing extra hacks, just rewrite struct btf_dedup_opts into OPTS-based
one, move btf_ext argument into those opts (only bpf_linker needs to
dedup btf_ext, so it's not a typical thing to specify), and drop never
used `dont_resolve_fwds` option (it was never used anywhere, AFAIK, it
makes BTF dedup much less useful and efficient).

Just in case, for old implementation, btf__dedup_deprecated(), detect
non-NULL options and error out with helpful message, to help users
migrate, if there are any user playing with btf__dedup().

The last remaining piece is dedup_table_size, which is another
anachronism from very early days of BTF dedup. Since then it has been
reduced to the only valid value, 1, to request forced hash collisions.
This is only used during testing. So instead introduce a bool flag to
force collisions explicitly.

This patch also adapts selftests to new btf__dedup() and btf_dedup_opts
use to avoid selftests breakage.

  [0] Closes: https://github.com/libbpf/libbpf/issues/281

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20211111053624.190580-4-andrii@kernel.org

1 files changed, 27 insertions, 19 deletions

diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
index 7e4c5586bd87..fcec27622e7a 100644
--- a/tools/lib/bpf/btf.c
+++ b/tools/lib/bpf/btf.c
@@ -2846,8 +2846,7 @@ __u32 btf_ext__line_info_rec_size(const struct btf_ext *btf_ext)
 
 struct btf_dedup;
 
-static struct btf_dedup *btf_dedup_new(struct btf *btf, struct btf_ext *btf_ext,
-				       const struct btf_dedup_opts *opts);
+static struct btf_dedup *btf_dedup_new(struct btf *btf, const struct btf_dedup_opts *opts);
 static void btf_dedup_free(struct btf_dedup *d);
 static int btf_dedup_prep(struct btf_dedup *d);
 static int btf_dedup_strings(struct btf_dedup *d);
@@ -2994,12 +2993,17 @@ static int btf_dedup_remap_types(struct btf_dedup *d);
  * deduplicating structs/unions is described in greater details in comments for
  * `btf_dedup_is_equiv` function.
  */
-int btf__dedup(struct btf *btf, struct btf_ext *btf_ext,
-	       const struct btf_dedup_opts *opts)
+
+DEFAULT_VERSION(btf__dedup_v0_6_0, btf__dedup, LIBBPF_0.6.0)
+int btf__dedup_v0_6_0(struct btf *btf, const struct btf_dedup_opts *opts)
 {
-	struct btf_dedup *d = btf_dedup_new(btf, btf_ext, opts);
+	struct btf_dedup *d;
 	int err;
 
+	if (!OPTS_VALID(opts, btf_dedup_opts))
+		return libbpf_err(-EINVAL);
+
+	d = btf_dedup_new(btf, opts);
 	if (IS_ERR(d)) {
 		pr_debug("btf_dedup_new failed: %ld", PTR_ERR(d));
 		return libbpf_err(-EINVAL);
@@ -3051,6 +3055,19 @@ done:
 	return libbpf_err(err);
 }
 
+COMPAT_VERSION(bpf__dedup_deprecated, btf__dedup, LIBBPF_0.0.2)
+int btf__dedup_deprecated(struct btf *btf, struct btf_ext *btf_ext, const void *unused_opts)
+{
+	LIBBPF_OPTS(btf_dedup_opts, opts, .btf_ext = btf_ext);
+
+	if (unused_opts) {
+		pr_warn("please use new version of btf__dedup() that supports options\n");
+		return libbpf_err(-ENOTSUP);
+	}
+
+	return btf__dedup(btf, &opts);
+}
+
 #define BTF_UNPROCESSED_ID ((__u32)-1)
 #define BTF_IN_PROGRESS_ID ((__u32)-2)
 
@@ -3163,8 +3180,7 @@ static bool btf_dedup_equal_fn(const void *k1, const void *k2, void *ctx)
 	return k1 == k2;
 }
 
-static struct btf_dedup *btf_dedup_new(struct btf *btf, struct btf_ext *btf_ext,
-				       const struct btf_dedup_opts *opts)
+static struct btf_dedup *btf_dedup_new(struct btf *btf, const struct btf_dedup_opts *opts)
 {
 	struct btf_dedup *d = calloc(1, sizeof(struct btf_dedup));
 	hashmap_hash_fn hash_fn = btf_dedup_identity_hash_fn;
@@ -3173,13 +3189,11 @@ static struct btf_dedup *btf_dedup_new(struct btf *btf, struct btf_ext *btf_ext,
 	if (!d)
 		return ERR_PTR(-ENOMEM);
 
-	d->opts.dont_resolve_fwds = opts && opts->dont_resolve_fwds;
-	/* dedup_table_size is now used only to force collisions in tests */
-	if (opts && opts->dedup_table_size == 1)
+	if (OPTS_GET(opts, force_collisions, false))
 		hash_fn = btf_dedup_collision_hash_fn;
 
 	d->btf = btf;
-	d->btf_ext = btf_ext;
+	d->btf_ext = OPTS_GET(opts, btf_ext, NULL);
 
 	d->dedup_table = hashmap__new(hash_fn, btf_dedup_equal_fn, NULL);
 	if (IS_ERR(d->dedup_table)) {
@@ -3708,8 +3722,6 @@ static int btf_dedup_prim_type(struct btf_dedup *d, __u32 type_id)
 				new_id = cand_id;
 				break;
 			}
-			if (d->opts.dont_resolve_fwds)
-				continue;
 			if (btf_compat_enum(t, cand)) {
 				if (btf_is_enum_fwd(t)) {
 					/* resolve fwd to full enum */
@@ -3952,8 +3964,7 @@ static int btf_dedup_is_equiv(struct btf_dedup *d, __u32 cand_id,
 		return 0;
 
 	/* FWD <--> STRUCT/UNION equivalence check, if enabled */
-	if (!d->opts.dont_resolve_fwds
-	    && (cand_kind == BTF_KIND_FWD || canon_kind == BTF_KIND_FWD)
+	if ((cand_kind == BTF_KIND_FWD || canon_kind == BTF_KIND_FWD)
 	    && cand_kind != canon_kind) {
 		__u16 real_kind;
 		__u16 fwd_kind;
@@ -3979,10 +3990,7 @@ static int btf_dedup_is_equiv(struct btf_dedup *d, __u32 cand_id,
 		return btf_equal_int_tag(cand_type, canon_type);
 
 	case BTF_KIND_ENUM:
-		if (d->opts.dont_resolve_fwds)
-			return btf_equal_enum(cand_type, canon_type);
-		else
-			return btf_compat_enum(cand_type, canon_type);
+		return btf_compat_enum(cand_type, canon_type);
 
 	case BTF_KIND_FWD:
 	case BTF_KIND_FLOAT: