libbpf: Hashmap interface update to allow both long and void* keys/values

An update for libbpf's hashmap interface from void* -> void* to a
polymorphic one, allowing both long and void* keys and values.

This simplifies many use cases in libbpf as hashmaps there are mostly
integer to integer.

Perf copies hashmap implementation from libbpf and has to be
updated as well.

Changes to libbpf, selftests/bpf and perf are packed as a single
commit to avoid compilation issues with any future bisect.

Polymorphic interface is acheived by hiding hashmap interface
functions behind auxiliary macros that take care of necessary
type casts, for example:

    #define hashmap_cast_ptr(p)						\
	({								\
		_Static_assert((p) == NULL || sizeof(*(p)) == sizeof(long),\
			       #p " pointee should be a long-sized integer or a pointer"); \
		(long *)(p);						\
	})

    bool hashmap_find(const struct hashmap *map, long key, long *value);

    #define hashmap__find(map, key, value) \
		hashmap_find((map), (long)(key), hashmap_cast_ptr(value))

- hashmap__find macro casts key and value parameters to long
  and long* respectively
- hashmap_cast_ptr ensures that value pointer points to a memory
  of appropriate size.

This hack was suggested by Andrii Nakryiko in [1].
This is a follow up for [2].

[1] https://lore.kernel.org/bpf/CAEf4BzZ8KFneEJxFAaNCCFPGqp20hSpS2aCj76uRk3-qZUH5xg@mail.gmail.com/
[2] https://lore.kernel.org/bpf/af1facf9-7bc8-8a3d-0db4-7b3f333589a2@meta.com/T/#m65b28f1d6d969fcd318b556db6a3ad499a42607d

Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20221109142611.879983-2-eddyz87@gmail.com

1 files changed, 7 insertions, 12 deletions

diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c
index cf8b4e525c88..01bb8d8f5568 100644
--- a/tools/bpf/bpftool/gen.c
+++ b/tools/bpf/bpftool/gen.c
@@ -1660,21 +1660,16 @@ struct btfgen_info {
 	struct btf *marked_btf; /* btf structure used to mark used types */
 };
 
-static size_t btfgen_hash_fn(const void *key, void *ctx)
+static size_t btfgen_hash_fn(long key, void *ctx)
 {
-	return (size_t)key;
+	return key;
 }
 
-static bool btfgen_equal_fn(const void *k1, const void *k2, void *ctx)
+static bool btfgen_equal_fn(long k1, long k2, void *ctx)
 {
 	return k1 == k2;
 }
 
-static void *u32_as_hash_key(__u32 x)
-{
-	return (void *)(uintptr_t)x;
-}
-
 static void btfgen_free_info(struct btfgen_info *info)
 {
 	if (!info)
@@ -2086,18 +2081,18 @@ static int btfgen_record_obj(struct btfgen_info *info, const char *obj_path)
 			struct bpf_core_spec specs_scratch[3] = {};
 			struct bpf_core_relo_res targ_res = {};
 			struct bpf_core_cand_list *cands = NULL;
-			const void *type_key = u32_as_hash_key(relo->type_id);
 			const char *sec_name = btf__name_by_offset(btf, sec->sec_name_off);
 
 			if (relo->kind != BPF_CORE_TYPE_ID_LOCAL &&
-			    !hashmap__find(cand_cache, type_key, (void **)&cands)) {
+			    !hashmap__find(cand_cache, relo->type_id, &cands)) {
 				cands = btfgen_find_cands(btf, info->src_btf, relo->type_id);
 				if (!cands) {
 					err = -errno;
 					goto out;
 				}
 
-				err = hashmap__set(cand_cache, type_key, cands, NULL, NULL);
+				err = hashmap__set(cand_cache, relo->type_id, cands,
+						   NULL, NULL);
 				if (err)
 					goto out;
 			}
@@ -2120,7 +2115,7 @@ out:
 
 	if (!IS_ERR_OR_NULL(cand_cache)) {
 		hashmap__for_each_entry(cand_cache, entry, i) {
-			bpf_core_free_cands(entry->value);
+			bpf_core_free_cands(entry->pvalue);
 		}
 		hashmap__free(cand_cache);
 	}