linux-kernel - [PATCH] bpf: suppress -Wcast-function-type warning

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Message-Id: <20201026210332.3885166-1-arnd@kernel.org>
Date:   Mon, 26 Oct 2020 22:03:20 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Cc:     Arnd Bergmann <arnd@...db.de>, Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andrii@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        David Miller <davem@...emloft.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jakub Sitnicki <jakub@...udflare.com>,
        Björn Töpel <bjorn.topel@...el.com>,
        Toke Høiland-Jørgensen <toke@...hat.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Pankaj Bharadiya <pankaj.laxminarayan.bharadiya@...el.com>,
        netdev@...r.kernel.org, bpf@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] bpf: suppress -Wcast-function-type warning

From: Arnd Bergmann <arnd@...db.de>

Building with -Wextra shows lots of warnings in the bpf
code such as

kernel/bpf/verifier.c: In function ‘jit_subprogs’:
include/linux/filter.h:345:4: warning: cast between incompatible function types from ‘unsigned int (*)(const void *, const struct bpf_insn *)’ to ‘u64 (*)(u64,  u64,  u64,  u64,  u64)’ {aka ‘long long unsigned int (*)(long long unsigned int,  long long unsigned int,  long long unsigned int,  long long unsigned int,  long long unsigned int)’} [-Wcast-function-type]
  345 |   ((u64 (*)(u64, u64, u64, u64, u64))(x))
      |    ^
kernel/bpf/verifier.c:10706:16: note: in expansion of macro ‘BPF_CAST_CALL’
10706 |    insn->imm = BPF_CAST_CALL(func[subprog]->bpf_func) -
      |                ^~~~~~~~~~~~~

This appears to be intentional, so change the cast in a way that
suppresses the warning.

Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 include/linux/filter.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/filter.h b/include/linux/filter.h
index 1b62397bd124..20ba04583eaa 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -342,7 +342,7 @@ static inline bool insn_is_zext(const struct bpf_insn *insn)
 /* Function call */
 
 #define BPF_CAST_CALL(x)					\
-		((u64 (*)(u64, u64, u64, u64, u64))(x))
+		((u64 (*)(u64, u64, u64, u64, u64))(uintptr_t)(x))
 
 #define BPF_EMIT_CALL(FUNC)					\
 	((struct bpf_insn) {					\
-- 
2.27.0