Merge branch 'selftests-bpf-fix-expression-result-unused-warnings-with-icecc'

Ilya Leoshkevich says:

====================
selftests/bpf: Fix "expression result unused" warnings with icecc

v3: https://lore.kernel.org/bpf/[email protected]/
v3 -> v4: Go back to the original solution (Yonghong, Alexei).

v2: https://lore.kernel.org/bpf/[email protected]/
v2 -> v3: Do not touch libbpf, explain how having two function
          declarations works (Andrii).
          Fix bpf-gcc build (CI).

v1: https://lore.kernel.org/bpf/[email protected]/
v1 -> v2: Annotate bpf_obj_new_impl() with __must_check (Alexei).
          Add an explanation about icecc.

I took another look at the "expression result unused" warnings I've
been seeing, and it turned out that the root cause was the icecc
compiler wrapper and what I consider a clang bug. Back then I've
reported that the problem was reproducible with plain clang, but now
I see that it was clearly a mixup, sorry about that.

The solution is to add a few awkward (void) casts. I've added a
detailed explanation of why they are helpful to the commit message.
====================

Link: https://patch.msgid.link/[email protected]
Signed-off-by: Alexei Starovoitov <[email protected]>

Author: Alexei Starovoitov

tools/testing/selftests/bpf/progs/bpf_arena_spin_lock.h

@@ -302,7 +302,7 @@ int arena_spin_lock_slowpath(arena_spinlock_t __arena __arg_arena *lock, u32 val
 	 * barriers.
 	 */
 	if (val & _Q_LOCKED_MASK)
-		smp_cond_load_acquire_label(&lock->locked, !VAL, release_err);
+		(void)smp_cond_load_acquire_label(&lock->locked, !VAL, release_err);
 
 	/*
 	 * take ownership and clear the pending bit.
@@ -380,7 +380,7 @@ int arena_spin_lock_slowpath(arena_spinlock_t __arena __arg_arena *lock, u32 val
 		/* Link @node into the waitqueue. */
 		WRITE_ONCE(prev->next, node);
 
-		arch_mcs_spin_lock_contended_label(&node->locked, release_node_err);
+		(void)arch_mcs_spin_lock_contended_label(&node->locked, release_node_err);
 
 		/*
 		 * While waiting for the MCS lock, the next pointer may have

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

@@ -226,8 +226,7 @@ int obj_new_no_composite(void *ctx)
 SEC("?tc")
 int obj_new_no_struct(void *ctx)
 {
-
-	bpf_obj_new(union { int data; unsigned udata; });
+	(void)bpf_obj_new(union { int data; unsigned udata; });
 	return 0;
 }
 
@@ -252,7 +251,7 @@ int new_null_ret(void *ctx)
 SEC("?tc")
 int obj_new_acq(void *ctx)
 {
-	bpf_obj_new(struct foo);
+	(void)bpf_obj_new(struct foo);
 	return 0;
 }