selftests/bpf: Add tests for the new type-tag based __arena identifier

Add selftests that combine the new type-based __arena identifier with
the volatile qualifier both in functions' arguments and return values.
This way we test both that they are recognized as arena arguments and
that they are not sensitive to the position they are placed in the type
compared to other qualifiers.

Signed-off-by: Emil Tsalapatis <emil@etsalapatis.com>
Link: https://lore.kernel.org/r/20260602004120.17087-7-emil@etsalapatis.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Author: etsal

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

@@ -607,4 +607,71 @@ int non_arena_ptr_add_to_arena_ptr(void *ctx)
 
 #endif
 
+static __noinline
+u32 __arena *check_arena_arg_nonglobal(u32 __arena *arg)
+{
+	volatile u32 val = *arg;
+
+	*arg = val + 1;
+
+	return arg;
+}
+
+__weak
+u32 __arena *check_arena_arg_global(u32 __arena *arg)
+{
+	volatile u32 val = *arg;
+
+	*arg = val + 1;
+
+	return arg;
+}
+
+__weak
+u32 volatile __arena *check_arena_arg_quals1(u32 volatile __arena *arg1, u32 __arena volatile *arg2)
+{
+	*arg1 = *arg1 + 1;
+	*arg2 = *arg1 + 1;
+
+	return arg2;
+}
+
+__weak
+u32 __arena volatile *check_arena_arg_quals2(u32 volatile __arena *arg1, u32 __arena volatile *arg2)
+{
+	*arg1 = *arg1 + 1;
+	*arg2 = *arg2 + 1;
+
+	return arg2;
+}
+
+SEC("syscall")
+__success __retval(0)
+int check_arena_arg_ret(void *ctx)
+{
+	u32 __arena *page = bpf_arena_alloc_pages(&arena, NULL, 1, NUMA_NO_NODE, 0);
+	u32 __arena *arg = page;
+	u32 __arena volatile *arg1;
+	u32 __arena volatile *ret1;
+	u32 volatile __arena *arg2;
+	u32 volatile __arena *ret2;
+
+	if (!arg)
+		return 1;
+
+	/* Make sure we use {arg, ret}{1, 2}. */
+
+	arg = check_arena_arg_nonglobal(page);
+	arg = check_arena_arg_global(arg);
+
+	arg1 = arg2 = page;
+	ret1 = check_arena_arg_quals1(arg1, arg2);
+	ret2 = check_arena_arg_quals2(arg1, arg2);
+
+	if (!(*ret1 ||*ret2))
+		return -EINVAL;
+
+	return 0;
+}
+
 char _license[] SEC("license") = "GPL";