Provide a macro to define a map along with type safe accessors

Test: atest libbpf_android_test libnetdbpf_test netd_integration_test netd_unit_test netdutils_test resolv_integration_test resolv_unit_test
Bug: 130746652
Bug: 131268436
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: Ib7a351ff876891a2296e32deebd0308ff9c7fcc8
Merged-In: Ib7a351ff876891a2296e32deebd0308ff9c7fcc8
(cherry picked from commit 6564b8eac46fc27dde807a39856386d98d2471c3)

1 files changed, 56 insertions, 4 deletions

diff --git a/progs/include/bpf_helpers.h b/progs/include/bpf_helpers.h
index 3ae4291..408a981 100644
--- a/progs/include/bpf_helpers.h
+++ b/progs/include/bpf_helpers.h
@@ -11,11 +11,63 @@
  * Helper functions called from eBPF programs written in C. These are
  * implemented in the kernel sources.
  */
+
 /* generic functions */
-static void* (*bpf_map_lookup_elem)(void* map, void* key) = (void*) BPF_FUNC_map_lookup_elem;
-static int (*bpf_map_update_elem)(void* map, void* key, void* value,
-                                  unsigned long long flags) = (void*) BPF_FUNC_map_update_elem;
-static int (*bpf_map_delete_elem)(void* map, void* key) = (void*) BPF_FUNC_map_delete_elem;
+
+/*
+ * Type-unsafe bpf map functions - avoid if possible.
+ *
+ * Using these it is possible to pass in keys/values of the wrong type/size,
+ * or, for 'unsafe_bpf_map_lookup_elem' receive into a pointer to the wrong type.
+ * You will not get a compile time failure, and for certain types of errors you
+ * might not even get a failure from the kernel's ebpf verifier during program load,
+ * instead stuff might just not work right at runtime.
+ *
+ * Instead please use:
+ *   DEFINE_BPF_MAP(foo_map, TYPE, KeyType, ValueType, num_entries)
+ * where TYPE can be something like HASH or ARRAY, and num_entries is an integer.
+ *
+ * This defines the map (hence this should not be used in a header file included
+ * from multiple locations) and provides type safe accessors:
+ *   ValueType * bpf_foo_map_lookup_elem(KeyType *)
+ *   int bpf_foo_map_update_elem(KeyType *, ValueType *, flags)
+ *   int bpf_foo_map_delete_elem(KeyType *)
+ *
+ * This will make sure that if you change the type of a map you'll get compile
+ * errors at any spots you forget to update with the new type.
+ */
+static void* (*unsafe_bpf_map_lookup_elem)(void* map, void* key) = (void*)BPF_FUNC_map_lookup_elem;
+static int (*unsafe_bpf_map_update_elem)(void* map, void* key, void* value,
+                                         unsigned long long flags) = (void*)
+        BPF_FUNC_map_update_elem;
+static int (*unsafe_bpf_map_delete_elem)(void* map, void* key) = (void*)BPF_FUNC_map_delete_elem;
+
+/* type safe macro to declare a map and related accessor functions */
+#define DEFINE_BPF_MAP_NO_ACCESSORS(the_map, TYPE, TypeOfKey, TypeOfValue, num_entries) \
+    struct bpf_map_def SEC("maps") the_map = {                                          \
+            .type = BPF_MAP_TYPE_##TYPE,                                                \
+            .key_size = sizeof(TypeOfKey),                                              \
+            .value_size = sizeof(TypeOfValue),                                          \
+            .max_entries = (num_entries),                                               \
+    };
+
+#define DEFINE_BPF_MAP(the_map, TYPE, TypeOfKey, TypeOfValue, num_entries)                 \
+    DEFINE_BPF_MAP_NO_ACCESSORS(the_map, TYPE, TypeOfKey, TypeOfValue, num_entries)        \
+                                                                                           \
+    static inline __always_inline __unused TypeOfValue* bpf_##the_map##_lookup_elem(       \
+            TypeOfKey* k) {                                                                \
+        return unsafe_bpf_map_lookup_elem(&the_map, k);                                    \
+    };                                                                                     \
+                                                                                           \
+    static inline __always_inline __unused int bpf_##the_map##_update_elem(                \
+            TypeOfKey* k, TypeOfValue* v, unsigned long long flags) {                      \
+        return unsafe_bpf_map_update_elem(&the_map, k, v, flags);                          \
+    };                                                                                     \
+                                                                                           \
+    static inline __always_inline __unused int bpf_##the_map##_delete_elem(TypeOfKey* k) { \
+        return unsafe_bpf_map_delete_elem(&the_map, k);                                    \
+    };
+
 static int (*bpf_probe_read)(void* dst, int size, void* unsafe_ptr) = (void*) BPF_FUNC_probe_read;
 static unsigned long long (*bpf_ktime_get_ns)(void) = (void*) BPF_FUNC_ktime_get_ns;
 static int (*bpf_trace_printk)(const char* fmt, int fmt_size, ...) = (void*) BPF_FUNC_trace_printk;