linux-kernel - [PATCH bpf-next] bpf: fix 'dubious one-bit signed bitfield' warnings

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Date:   Sun, 10 Jul 2022 10:35:23 +0200
From:   Matthieu Baerts <matthieu.baerts@...sares.net>
To:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        Eduard Zingerman <eddyz87@...il.com>
Cc:     mptcp@...ts.linux.dev,
        Matthieu Baerts <matthieu.baerts@...sares.net>,
        bpf@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH bpf-next] bpf: fix 'dubious one-bit signed bitfield' warnings

Our CI[1] reported these warnings when using Sparse:

  $ touch net/mptcp/bpf.c
  $ make C=1 net/mptcp/bpf.o
  net/mptcp/bpf.c: note: in included file:
  include/linux/bpf_verifier.h:348:26: error: dubious one-bit signed bitfield
  include/linux/bpf_verifier.h:349:29: error: dubious one-bit signed bitfield

These two fields from the new 'bpf_loop_inline_state' structure are used
as booleans. Instead of declaring two 'unsigned int', we can declare
them as 'bool'.

While at it, also set 'state->initialized' to 'true' instead of '1' to
make it clearer it is linked to a 'bool' type.

[1] https://github.com/multipath-tcp/mptcp_net-next/actions/runs/2643588487

Fixes: 1ade23711971 ("bpf: Inline calls to bpf_loop when callback is known")
Signed-off-by: Matthieu Baerts <matthieu.baerts@...sares.net>
---
 include/linux/bpf_verifier.h | 8 ++++----
 kernel/bpf/verifier.c        | 2 +-
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 81b19669efba..2ac424641cc3 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -345,10 +345,10 @@ struct bpf_verifier_state_list {
 };
 
 struct bpf_loop_inline_state {
-	int initialized:1; /* set to true upon first entry */
-	int fit_for_inline:1; /* true if callback function is the same
-			       * at each call and flags are always zero
-			       */
+	bool initialized; /* set to true upon first entry */
+	bool fit_for_inline; /* true if callback function is the same
+			      * at each call and flags are always zero
+			      */
 	u32 callback_subprogno; /* valid when fit_for_inline is true */
 };
 
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 328cfab3af60..4fa49d852a59 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -7144,7 +7144,7 @@ static void update_loop_inline_state(struct bpf_verifier_env *env, u32 subprogno
 	struct bpf_loop_inline_state *state = &cur_aux(env)->loop_inline_state;
 
 	if (!state->initialized) {
-		state->initialized = 1;
+		state->initialized = true;
 		state->fit_for_inline = loop_flag_is_zero(env);
 		state->callback_subprogno = subprogno;
 		return;
-- 
2.36.1