From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=91.218.175.1 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793145897; b=Vo3WULBfsurGss7vMMN2WLHagMS2OeSfJC5lSkONoTgxg43Wpms09oQJjMKOcCv/KOxv uU+cQc+6hosmMSdKXrii5cPh9/RL2vN+yCiRC1CxOShTaqpnhvtchd8KzYNjQ/H/hLyst yXfML8Q5KkfBQAJkhMxt4gNBc5kTSjE/TEHTjA3RZwZAfTgTvBa8l+IwH8r4y4jfzZTHs /Qq2FC/sVGqFUfB9wOLoSuwWSqEV/LoZFYJFHOv8amHGM4Sg2e4Jp9sh+4Xe6iEsZD9/S akrjho5mPq1x4EckQ1tag60hm/7qu8TisQYGolvMpAOr8CtaeRMlPtqNjpIhQWqsPhg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793145897; h=DMARC-Filter:X-Envelope-To:DKIM-Signature:X-Envelope-To:Received: X-Mizu-Trace-ID:X-Migadu-Flow:From:To:Cc:Subject:Date:Message-ID: X-Mailer:MIME-Version:Content-Transfer-Encoding; bh=TqZMShUwObQw8SKTj74MIhBW352zXxbZoagijRnRZsU=; b=os15dQVmjEDF48A5b/2KKatgEovqmP2HybP1khuHG7nmg/+XxjgxPCiBWSgka9Hh7Zjo vXZXn7cunUkl/mh1GUizuDRKKVL7sTV0FSvnnBV9bXWNnK/sQsgsYhxmtIRygUbGJCiTZ U7RD08IDgXUlV0OQtHWKb8yURF7EzLlHpePxWfcpvCTF0tDY6yOQCT7A5xnAWKWwWuF17 Rb7T2qA2vt9TBMTogk2A1z6Q1t/AHVGoGfbGvbpPUwqNBCjVco+P3raRDB5hUTnc1k3IN lgQpuc3Y9KQuHF/zLzEKMyahKjpFPrhsmLrV9QlQhIDe7GMQgbh+Xs4QZXqNgJCmn3g== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=GjeFvKhQ; arc=none smtp.remote-ip=91.218.175.1 Received: from mta0.migadu.com (out-1.mta0.migadu.com [91.218.175.1]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 34D33606A31D for ; Wed, 28 Oct 2026 00:04:55 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 34D33606A31D Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=GjeFvKhQ X-Envelope-To: linux-kselftest@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=kG6PSTw+cy6dHxyAq6KmUby801uCfZJf2HXQ109G+h4=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1793145894; v=1; x=1793750694; b=GjeFvKhQQdRdbZqtb1W4VbUmEEBaYv2YNplwdRLmz4uu6BtWgTcA0rQO/SccAbWJJjBRSFHj IHK2icPF5/CR1rhvqvN6kYGrGpt3q6KEgJGfOYTmmU6hCxzYWx808T8EVb0bTz2WD8gSckAJBBB 8Ko39EIY94ugCople+C7vu2Y= X-Envelope-To: linux-kselftest@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id 76a2d9e2e1102b84; Wed, 28 Oct 2026 00:04:54 +0000 X-Mizu-Trace-ID: 76a2d9e2e1102b84 X-Migadu-Flow: FLOW_OUT From: Vineet Gupta To: bpf@vger.kernel.org Cc: ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, eddyz87@gmail.com, memxor@gmail.com, martin.lau@linux.dev, song@kernel.org, yonghong.song@linux.dev, jolsa@kernel.org, emil@etsalapatis.com, ihor.solodrai@linux.dev, john.fastabend@gmail.com, shuah@kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, jose.marchesi@oracle.com, david.faust@oss.qualcomm.com, Vineet Gupta Subject: [PATCH bpf-next v1 4/7] selftests/bpf: make arena_base() opaque to GCC's -Warray-bounds Date: Tue, 27 Oct 2026 17:04:08 -0700 Message-ID: <20261028000411.4010967-5-vineet.gupta@linux.dev> X-Mailer: git-send-email 2.56.0 X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit arena_base() casts the map definition to the kernel's struct bpf_arena and reads user_vm_start out of it. In the object file that definition is only the 32-byte BTF placeholder the loader rewrites, so the access is past the end of the object and GCC says so: libarena/include/bpf_arena_common.h:52:69: error: array subscript 'struct bpf_arena[0]' is partly outside array bounds of 'struct [1]' [-Werror=array-bounds=] 52 | #define arena_base(map) ((void __arena *)((struct bpf_arena *)(map))->user_vm_start) progs/arena_race.c:58:30: note: in expansion of macro 'arena_base' GCC is right; clang has the same warning but does not apply it to a member access through a cast. With BPF_CFLAGS carrying -Werror this is a build failure, today, for every prog that calls arena_base() and is compiled by a GCC with arena support: verifier_arena.c, verifier_arena_large.c, verifier_arena_globals1.c, verifier_arena_globals2.c and arena_race.c. Make the pointer opaque instead, which is what progs/stream.c already does for its own open-coded copy of the same access. The bounds analysis then has nothing to reason about, and every caller is covered without a per-file opt-out that has to be maintained -- arena_race.c was added without one and broke the bpf_gcc build. The barrier is behind #ifdef __clang__ so clang keeps the plain macro. It does not need it, and the barrier is not free: it blocks reuse of the map address, so each call site reloads it. Across the five progs and 20 call sites that is +35 instructions under GCC (2528 -> 2563), about 1.4% on those objects and nothing elsewhere. Clang output is unchanged, bit for bit. Signed-off-by: Vineet Gupta --- .../bpf/libarena/include/bpf_arena_common.h | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/tools/testing/selftests/bpf/libarena/include/bpf_arena_common.h b/tools/testing/selftests/bpf/libarena/include/bpf_arena_common.h index 82aafe879fae..4f2c6050215f 100644 --- a/tools/testing/selftests/bpf/libarena/include/bpf_arena_common.h +++ b/tools/testing/selftests/bpf/libarena/include/bpf_arena_common.h @@ -49,7 +49,23 @@ void __arena* bpf_arena_alloc_pages(void *map, void __arena *addr, __u32 page_cn int bpf_arena_reserve_pages(void *map, void __arena *addr, __u32 page_cnt) __ksym __weak; void bpf_arena_free_pages(void *map, void __arena *ptr, __u32 page_cnt) __ksym __weak; +/* + * GCC's -Warray-bounds fires on the member access: the map definition the + * object file carries is smaller than struct bpf_arena. Make the pointer + * opaque to it, as the open-coded form in progs/stream.c already does. + * clang does not warn and does not need the barrier, which costs a reload + * of the map address at every call site. + */ +#ifdef __clang__ #define arena_base(map) ((void __arena *)((struct bpf_arena *)(map))->user_vm_start) +#else +#define arena_base(map) \ +({ \ + struct bpf_arena *__ma = (void *)(map); \ + barrier_var(__ma); \ + (void __arena *)__ma->user_vm_start; \ +}) +#endif #else /* when compiled as user space code */ -- 2.53.0-Meta