From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=91.218.175.220 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793220147; b=VPPrdGpRZW1uYBfz69Oqpa17xcei+Zjw48B1k1rv2QC1qmmo8rtuIiw7OhlBrx/AglyS pxhNVHw8histQ+rFXB6CfnW60IWRrQYTMsnw1sOCwlPKc4ruBimKQsKPTTJ0hrHwUP7Qp TI4v+99fgOhguT3V7b3Wavq8Rxmrd1Krk7tXpeeCzGJ84mJa8cpQlnSnxuKq+eKZb+Wyh UAx8IyhWaiZWMoiofew/QgTvtNFtKGr9FgF1fAoQjmjCc8eK/Jrxo7OYC5IcNPvVOo4+w DeKCL70Hds9JjIhNUFbSGH4RgbOTVQQDBGid558SS/dCPDw6J/Fau/53T1gZNd1kpZw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793220147; 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:In-Reply-To:References:MIME-Version: Content-Transfer-Encoding; bh=TqZMShUwObQw8SKTj74MIhBW352zXxbZoagijRnRZsU=; b=nBZhmWTt6+lttgn5M7+7N4O1lPf5AcENGEz2p7PZ6yfJpDPJH8J6iRNxsRcyCJuXS0jk ugYKfweQSL0/NHbExq7pYUn49CyTskhXuSD2dx/tlLybPJRxzSd0ZY16PNtt4ezrBatOw sfdyYA4NSBQ7U9RCvy0odOSZeenLohokdmTfl+dWrnl2ZMB35Q6YWMWKvfC4aFoA6X/hp yU9U2Q/9t/qyA+8RxCTmc6dfg2Ji8MaDd6RJBPnDIJblV6fPrhlQIr6roOJRAZ2jMEFT4 Ivdvz6TkRsod7LyGBFBWdH2Pr8pZSoKx4gybL0QxZuwj6w5UdoNs36IRnyJoI97bMiQ== 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=wSnkai6V; arc=none smtp.remote-ip=91.218.175.220 Received: from mta0.migadu.com (out-220.mta0.migadu.com [91.218.175.220]) (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 CA18760A2620 for ; Wed, 28 Oct 2026 20:42:26 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org CA18760A2620 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=wSnkai6V X-Envelope-To: bpf@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=1793220144; v=1; x=1793824944; b=wSnkai6VeJCpNKAhA625hQB948WhheNWZxUw0SCRY/OHoBGek5Ty+8RWLiVbcf12cfH1MgEj v9Y0vbZ0f3NSQoybNxGAMVEP86oB2ZhzKRTRBWNJv1WYxT6hM5M7XGJPuzWkX6r99d53XypKRZz zazY3nvj/qru5TY5YmOaiqWE= X-Envelope-To: bpf@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id 58ae1e1d1c5ddfdf; Wed, 28 Oct 2026 20:42:24 +0000 X-Mizu-Trace-ID: 58ae1e1d1c5ddfdf 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 v2 4/8] selftests/bpf: make arena_base() opaque to GCC's -Warray-bounds Date: Wed, 28 Oct 2026 13:41:54 -0700 Message-ID: <20261028204158.1021284-5-vineet.gupta@linux.dev> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261028204158.1021284-1-vineet.gupta@linux.dev> References: <20261028204158.1021284-1-vineet.gupta@linux.dev> X-Mailing-List: bpf@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