[PATCH bpf-next v3 2/9] selftests/bpf: Add test for scalar/arena pointer addition

[Emil Tsalapatis <emil@etsalapatis.com>]

From: Emil Tsalapatis <etsal@meta.com>

Add a selftest that ensures scalar += ptr_to_arena instructions
are accepted by the verifier.

Signed-off-by: Emil Tsalapatis <emil@etsalapatis.com>
---
 .../selftests/bpf/progs/verifier_arena.c      | 29 +++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/tools/testing/selftests/bpf/progs/verifier_arena.c b/tools/testing/selftests/bpf/progs/verifier_arena.c
index c4b8daac4388..450e8f1181cd 100644
--- a/tools/testing/selftests/bpf/progs/verifier_arena.c
+++ b/tools/testing/selftests/bpf/progs/verifier_arena.c
@@ -477,4 +477,33 @@ int arena_kfuncs_under_bpf_lock(void *ctx)
 
 	return 0;
 }
+/*
+ * Test that scalar += PTR_TO_ARENA correctly upgrades the
+ * destination register to a PTR_TO_ARENA.
+ */
+SEC("syscall")
+__success __retval(0)
+int scalar_add_arena_ptr(void *ctx)
+{
+#if defined(__BPF_FEATURE_ADDR_SPACE_CAST)
+	int __arena *result, *arena_ptr;
+
+	/* Needed for the verifier to link the arena to the subprog. */
+	volatile char __arena *base = arena_base(&arena);
+
+	/* Passing base here to avoid optimizing it out during compilation. */
+	asm volatile (
+		"%[arena_ptr] = 8192;"
+		"%[arena_ptr] = addr_space_cast(%[arena_ptr], 0x0, 0x1);"
+		"%[result] = 12;"
+		"%[result] += %[arena_ptr];"
+		: [result] "=r"(result),
+		  [arena_ptr] "=&r"(arena_ptr)
+		: "r"(base)
+		:
+	);
+#endif
+	return 0;
+}
+
 char _license[] SEC("license") = "GPL";
-- 
2.53.0