libbpf: Fix BTF-defined map's __type macro handling of arrays

Due to a quirky C syntax of declaring pointers to array or function
prototype, existing __type() macro doesn't work with map key/value types
that are array or function prototype. One has to create a typedef first
and use it to specify key/value type for a BPF map.  By using typeof(),
pointer to type is now handled uniformly for all kinds of types. Convert
one of self-tests as a demonstration.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20191004040211.2434033-1-andriin@fb.com

tools/testing/selftests/bpf/bpf_helpers.h

@@ -3,7 +3,7 @@
 #define __BPF_HELPERS__
 
 #define __uint(name, val) int (*name)[val]
-#define __type(name, val) val *name
+#define __type(name, val) typeof(val) *name
 
 /* helper macro to print out debug messages */
 #define bpf_printk(fmt, ...)				\

tools/testing/selftests/bpf/progs/test_get_stack_rawtp.c

@@ -47,12 +47,11 @@ struct {
  * issue and avoid complicated C programming massaging.
  * This is an acceptable workaround since there is one entry here.
  */
-typedef __u64 raw_stack_trace_t[2 * MAX_STACK_RAWTP];
 struct {
 	__uint(type, BPF_MAP_TYPE_PERCPU_ARRAY);
 	__uint(max_entries, 1);
 	__type(key, __u32);
-	__type(value, raw_stack_trace_t);
+	__type(value, __u64[2 * MAX_STACK_RAWTP]);
 } rawdata_map SEC(".maps");
 
 SEC("raw_tracepoint/sys_enter")