From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=91.218.175.181 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793664968; b=X+z71Pwgmc5wtqOM6Nn+4UAf+z9ATnZuuxQTkgk0SN4UAkwv37Y5Yi2pg1tYxfNfgNzg 1vBTX72d1YHDIZ+/3bKgZYVDaBKWBf/uuoxvdeWEhZXQdO5/uCI9dU7ZKYiuyblC7R8VN uGsVaXKTV46Ud286OXZlsQ8wVHHCouN9KK0uzVkzfNOu97ICHYN3UtXA25M0E2/uN2pFe VfrBcbMkLt2+FAShKuVOynjUrs1XdAtOWdLVfi9Uq5T+8Xp9g3s2d6WrDlhLmL/Pld/Eg fx5VI4GeNZcOzsspUVHxG3/QYrW5GokT2e8EYj84NwhGbid2HWgo3B4cQRBtBp7Md3g== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793664968; h=DMARC-Filter:X-Envelope-To:DKIM-Signature:X-Envelope-To:Received: X-Mizu-Trace-ID:X-Migadu-Flow:Message-ID:Date:MIME-Version:User-Agent: Subject:To:Cc:References:From:Content-Language:In-Reply-To: Content-Type:Content-Transfer-Encoding; bh=/uPT4vdHUQZrtGUWIDhvkzHSaxat7xD3UNSEdtv7bHA=; b=keTdZW1WKPyj4iVd8l3lq8CjBf+Qth6aIdYAIltuiSYVrE6GSP9lPvOsPkzARcyCgBJh RD+MobzsRD4ye/zQXa4igfvCzLEwx/LNXDOvptVdk3Nld1Jh0itRWwRiDncKQWvnQidH7 NnyhnkoYTtzHOXDTd0dj1Zd1ZcsczMgGlPwYHuk6/2vqo6VOekmdTumBauF7gC/uhqY1C VIRP0T6ipbU9bmgYK4ZDM+6mXylBrdeBKBYVxXfeTx48LPD+VEpnSfc7rwP+evXj5SVgo nL6J9H2l1QGboQzftqtar7akg9MNmqSTEQ6p0SXKTOv9Lu2OXHaAEFZuiLqpW8UlwTg== 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=HNf0zk5b; arc=none smtp.remote-ip=91.218.175.181 Received: from mta0.migadu.com (out-181.mta0.migadu.com [91.218.175.181]) (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 6BE82606A32C for ; Tue, 3 Nov 2026 00:16:06 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 6BE82606A32C 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=HNf0zk5b X-Envelope-To: bpf@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=0XIP2nwc6eaTMkjHzyVrBh3ylA4dDdfFpXWL7zb1+wc=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1793664965; v=1; x=1794269765; b=HNf0zk5b7JsjzBN040M2Q4qRLual1HyMagKRSCTOiXIVNdyUcptondMSoT65ys2Jq6H2mLgY OvU8PZyXkLzYRrKNMtmw5TN4pLHpIseYXiMIhO2IPrgsgi5v4v48dSQ9KS3nvM+RzpKzfmzjcfW 7npEsvXbD7EKdYEn0wclsWrA= X-Envelope-To: bpf@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id ca924cd7e3058c18; Tue, 03 Nov 2026 00:16:04 +0000 X-Mizu-Trace-ID: ca924cd7e3058c18 X-Migadu-Flow: FLOW_OUT Message-ID: <7c603b2b-6fcc-41d7-84e3-31e8af005776@linux.dev> Date: Mon, 2 Nov 2026 16:15:55 -0800 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 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH bpf-next v3 4/8] selftests/bpf: make arena_base() opaque to GCC's -Warray-bounds To: Alexei Starovoitov , bpf@vger.kernel.org Cc: 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 References: <20261102220717.4079739-1-vineet.gupta@linux.dev> <20261102220717.4079739-5-vineet.gupta@linux.dev> From: Vineet Gupta Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 11/2/26 2:38 PM, Alexei Starovoitov wrote: > On Mon, Nov 02, 2026 at 02:07 PM Vineet Gupta wrote: >> 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. > stream.c already has barrier_var() for both compilers. > > How about this one instead: Yeah definitely much better. Just to be clear the intent of series is to not make current compiler look better o anything. As I mentioned in the cover, this was during in my in-works arena compiler testing, .... Thx for the quick feedback. -Vineet > 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 82aafe8..0eba529 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 +49,16 @@ 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; > > -#define arena_base(map) ((void __arena *)((struct bpf_arena *)(map))->user_vm_start) > +/* > + * The map definition is smaller than struct bpf_arena. > + * barrier_var() hides that from -Warray-bounds of GCC. > + */ > +#define arena_base(map) \ > + ({ \ > + struct bpf_arena *___arena = (void *)(map); \ > + barrier_var(___arena); \ > + (void __arena *)___arena->user_vm_start; \ > + }) > > #else /* when compiled as user space code */ > > diff --git a/tools/testing/selftests/bpf/progs/stream.c b/tools/testing/selftests/bpf/progs/stream.c > index 1ae015c..b4d88d0 100644 > --- a/tools/testing/selftests/bpf/progs/stream.c > +++ b/tools/testing/selftests/bpf/progs/stream.c > @@ -178,16 +178,8 @@ __stderr("Call trace:\n" > "|[ \t]+[^\n]+\n)*}}") > int stream_arena_write_fault(void *ctx) > { > - struct bpf_arena *ptr = (void *)&arena; > - u64 user_vm_start; > + u64 user_vm_start = (u64)arena_base(&arena); > > - /* Prevent GCC bounds warning: casting &arena to struct bpf_arena * > - * triggers bounds checking since the map definition is smaller than struct > - * bpf_arena. barrier_var() makes the pointer opaque to GCC, preventing the > - * bounds analysis > - */ > - barrier_var(ptr); > - user_vm_start = ptr->user_vm_start; > fault_addr = user_vm_start + 0x7fff; > bpf_addr_space_cast(user_vm_start, 0, 1); > asm volatile ( > @@ -212,16 +204,8 @@ __stderr("Call trace:\n" > "|[ \t]+[^\n]+\n)*}}") > int stream_arena_read_fault(void *ctx) > { > - struct bpf_arena *ptr = (void *)&arena; > - u64 user_vm_start; > + u64 user_vm_start = (u64)arena_base(&arena); > > - /* Prevent GCC bounds warning: casting &arena to struct bpf_arena * > - * triggers bounds checking since the map definition is smaller than struct > - * bpf_arena. barrier_var() makes the pointer opaque to GCC, preventing the > - * bounds analysis > - */ > - barrier_var(ptr); > - user_vm_start = ptr->user_vm_start; > fault_addr = user_vm_start + 0x7fff; > bpf_addr_space_cast(user_vm_start, 0, 1); > asm volatile ( > @@ -252,17 +236,9 @@ int stream_arena_load_acquire_fault(void *ctx) > .off = 0x7fff, > .imm = 0x100, /* BPF_LOAD_ACQ */ > }; > - struct bpf_arena *ptr = (void *)&arena; > - u64 user_vm_start, val; > + u64 user_vm_start = (u64)arena_base(&arena); > + u64 val; > > - /* > - * Prevent GCC bounds warning: casting &arena to struct bpf_arena * > - * triggers bounds checking since the map definition is smaller than > - * struct bpf_arena. barrier_var() makes the pointer opaque to GCC, > - * preventing the bounds analysis. > - */ > - barrier_var(ptr); > - user_vm_start = ptr->user_vm_start; > fault_addr = user_vm_start + 0x7fff; > bpf_addr_space_cast(user_vm_start, 0, 1); > asm volatile ( > @@ -296,17 +272,9 @@ int stream_arena_xchg_fault(void *ctx) > .off = 0x7fff, > .imm = 0xe1, /* BPF_XCHG */ > }; > - struct bpf_arena *ptr = (void *)&arena; > - u64 user_vm_start, val; > + u64 user_vm_start = (u64)arena_base(&arena); > + u64 val; > > - /* > - * Prevent GCC bounds warning: casting &arena to struct bpf_arena * > - * triggers bounds checking since the map definition is smaller than > - * struct bpf_arena. barrier_var() makes the pointer opaque to GCC, > - * preventing the bounds analysis. > - */ > - barrier_var(ptr); > - user_vm_start = ptr->user_vm_start; > fault_addr = user_vm_start + 0x7fff; > bpf_addr_space_cast(user_vm_start, 0, 1); > /* > @@ -346,17 +314,9 @@ int stream_arena_cmpxchg_fault(void *ctx) > .off = 0x7fff, > .imm = 0xf1, /* BPF_CMPXCHG */ > }; > - struct bpf_arena *ptr = (void *)&arena; > - u64 user_vm_start, val; > + u64 user_vm_start = (u64)arena_base(&arena); > + u64 val; > > - /* > - * Prevent GCC bounds warning: casting &arena to struct bpf_arena * > - * triggers bounds checking since the map definition is smaller than > - * struct bpf_arena. barrier_var() makes the pointer opaque to GCC, > - * preventing the bounds analysis. > - */ > - barrier_var(ptr); > - user_vm_start = ptr->user_vm_start; > fault_addr = user_vm_start + 0x7fff; > bpf_addr_space_cast(user_vm_start, 0, 1); > /*