From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wm1-f48.google.com (mail-wm1-f48.google.com [209.85.128.48]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 3580A3845D8 for ; Fri, 12 Jun 2026 10:18:52 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.48 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781259533; cv=none; b=QBtCpyqVPjwlw9MVDTATxYCReqvH764hDKvrBDAjRzAB/jLUsNYSLlfpI/Zv8R//DOmYYWiiMbq2IW3QX47F0FXEstmz4AILpiqD4vQJIJ6247LZgeaJEQylmApCd3c55ai0AiRIBJlXNMDkbthbSKXOnGoqNzRUiawoFtztaT4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781259533; c=relaxed/simple; bh=Iu+WsPA3d5zC/vpm66sf0PXFm63IcdCvAGgoL0vzIyI=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=OiwB5xuKSX5v9NXOPRz3ezuQBmVOv81h/gP2K1heFdXIm3Pf7trS3RM65IvugnaYCAEYx1q2raPjnlQTvdAJl6GB5jXPdpMT+hFrbCWlBEj+FnfzzUeshTrl6Z6p1H9o+e0xz3ZBs80Z89CWBsl/osrtrsPS6k3CVk2PdJ1QCRI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=suse.com; spf=pass smtp.mailfrom=suse.com; dkim=pass (2048-bit key) header.d=suse.com header.i=@suse.com header.b=bBME3aOj; arc=none smtp.client-ip=209.85.128.48 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=suse.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=suse.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=suse.com header.i=@suse.com header.b="bBME3aOj" Received: by mail-wm1-f48.google.com with SMTP id 5b1f17b1804b1-490b8a97b11so9319255e9.0 for ; Fri, 12 Jun 2026 03:18:51 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=google; t=1781259530; x=1781864330; darn=vger.kernel.org; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=wZYS51t2QXr2ZWiJCJ2esfR2JgSuWZes3mVwU5icUks=; b=bBME3aOjy09Ne3TOuJciwQgMQrD3QA56oZBnha0V1aiAml8vZFjlLytwRDLcbAjTfK gs0paoiXwr+SoduVvkIUms0MRhDY4psKxnYztyMXaCgHdKmYEU1TrRrQrbGmf78LFKLy Nb7MwXBQq6cZ5ahJc1jkRoGezwCEYiQdNVic+lM3Sq67OQ6+JDEzb5aqGGVaMTwwdG8l Y1dVVIssm8yet7XPKGHJgxwSWw7e8nfefziTDbuAI1WXNifv4/FxN7bnwKl7QZznlsK+ /L52yU+EIT8vhOhbInFxE4932yW9o6b9QOztuVi07hqQf1r1TUk1zeLIEwTU7TKGdYaS IVHg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1781259530; x=1781864330; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-gg:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=wZYS51t2QXr2ZWiJCJ2esfR2JgSuWZes3mVwU5icUks=; b=Gh1Gv4Dp3P4Ej//Paw+0PE9SH6p/8uOp5PzZXEdUtvM/sK77mg397gq7/S6E/KlkQZ RUPT7jqqdEp0/CHtYTD1fZN8Y6uq5H77rqO0dOvcmmJGQuaORxyhBtf5hCWtCwlvOc3G /nv3qD2Gxm6EUUQE3gDrrCaxLPdNYXALKIuTwN2X/kSaFzy53mP1p7/SOHzwb9aic+wf X/zVgU8wvBa+CWbNSvu1T4cJ0fYzBhyDCC72Skn8tzWYN23S6Iu48dcou4lmsYkuvF3J UNj6mUTpd6uEeNlNsoDHJtsBjTTtQSz/PRpv4F3qwg/C0AvuMr1IoahyPMjgepgsZgQI G34w== X-Forwarded-Encrypted: i=1; AFNElJ8OzjJXmfFmNiiYdAZL5TKlLdjhIBol3an6EPA2gt0tdUdPBpVLAxCjBnyvmtJSkfXtX4mXG2A=@vger.kernel.org X-Gm-Message-State: AOJu0Yx7J2GeU9cDa5P3lDkM9/dA/srgn9pkDYJEAE14KVi6pPdb0dzb OT608q6cWAk0wlmgz9Pdaimfw2g/AsDlNLhHvfX8xjTkWnAp5AYME2TTEMVozlU4fmw= X-Gm-Gg: Acq92OFbT/oI7PiwKGTtDIdsAJ+jnSLI3iCKRqBOt3P1P0r5xnRqLza+5vcsUwOdvgG 13Uqq03k6itM5SR/zdHr+91xeyc0ziVErdjiVQwQyNi2AYqzwERI4HOsCtKuVELyst/57z9MORJ 00vLjJyEpJhAerjJvXehfAmjhED7q4hGUYexwGRe3SXDyxdUeQ3pF15I9epiK4QRBtTShSBRHaI ARTt6yByrYM3LCAr5ounwphmx5RrmtbnHtsXySYOBm9vJLm+0rUxdQT95j8hxiawxXpLjhZx9YB 7wq4R2gS7iN1wiOpdVrjMsRCSzlr9uPlYcvz79wuw4zghdJQQiTmDz9XbHZYp0eok9zCuClyPPY wFcZYERwMauxZRV5p5WPNEb48O6JxvOnuLQgOYPD3HA/ec4o3BPorDmuVzrgCCpi0MA0kG51UJ8 m20eNisAYKo/BN9riltukwIrlBJGd8PXQVP+RRqZ+s X-Received: by 2002:a05:600c:5493:b0:490:3c15:7146 with SMTP id 5b1f17b1804b1-490ec4f26ecmr26968165e9.19.1781259530302; Fri, 12 Jun 2026 03:18:50 -0700 (PDT) Received: from u94a (27-51-56-85.adsl.fetnet.net. [27.51.56.85]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-3081eb95342sm2857806eec.29.2026.06.12.03.18.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 12 Jun 2026 03:18:48 -0700 (PDT) Date: Fri, 12 Jun 2026 18:18:39 +0800 From: Shung-Hsi Yu To: Alexei Starovoitov Cc: Zhenzhong Wu , bpf@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, ast@kernel.org, daniel@iogearbox.net, john.fastabend@gmail.com, andrii@kernel.org, martin.lau@linux.dev, song@kernel.org, yonghong.song@linux.dev, kpsingh@kernel.org, haoluo@google.com, jolsa@kernel.org, menglong8.dong@gmail.com, eddyz87@gmail.com, stable@vger.kernel.org, mykolal@fb.com, tamird@kernel.org Subject: Re: [PATCH bpf-next] selftests/bpf: add helper retval linked scalar pruning selftest Message-ID: References: <20260611160749.391279-1-jt26wzz@gmail.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Thu, Jun 11, 2026 at 09:55:55AM -0700, Alexei Starovoitov wrote: > On Thu Jun 11, 2026 at 9:07 AM PDT, Zhenzhong Wu wrote: > > Add a verifier runtime test for a branch pattern where a helper return > > value and a related scalar stay live across the same control-flow > > sequence. Rust/Aya-generated eBPF can naturally produce this shape when > > a match on a helper status keeps data derived before the helper call > > live across the same branches. Such code commonly uses the helper return > > value in r0, where 0 means success, producing an r0 == 0 / r0 != 0 > > branch shape. [...] > > +SEC("tc") > > +__description("helper retval linked scalar pruning") > > +__success __retval(0) > > +__naked void helper_retval_linked_scalar_pruning(void) > > +{ > > + asm volatile ( > > + "r7 = *(u32 *)(r1 + %[__sk_buff_data_end]);" > > + "r5 = *(u32 *)(r1 + %[__sk_buff_data]);" > > + "r7 -= r5;" > > + "r2 = 0;" > > + "r3 = r10;" > > + "r3 += -8;" > > + "r4 = 1;" > > + "call %[bpf_skb_load_bytes];" > > + "r0 += 1;" > > + "r6 = 1;" > > + /* success path keeps r7 independent; failure path links r7 to r0. */ > > + "if r0 == 1 goto l0_%=;" > > this exercises linked registers with BPF_ADD_CONST logic. > We already have such tests. Why do we need this one? > How is it different? BPF_ADD_CONST wasn't what was meant to be tested. The main logic is r7.id == r0.id only happens on "if r0 == 1 goto l0_%=" fall through, and does not have such link otherwise. I only check tests added in commit c0087d59e504 ("selftests/bpf: tests for per-insn sync_linked_regs() precision tracking"), but it doesn't seem like such conditional linking was tested. The other rational is that this seem like a common pattern that is genereated from Rust-based BPF program. > > + /* success path keeps r7 independent; failure path links r7 to r0. */ > > + "if r0 == 1 goto l0_%=;" > > + "r7 = r0;" ^^^^^^^ conditional scalar linking > > +"l0_%=: if r0 != 1 goto l1_%=;" > > + "r7 <<= 32;" > > + "r7 >>= 32;" > > + "if r7 != %[test_data_len] goto l1_%=;" > > + "r0 = 0;" > > + "exit;" > > +"l1_%=: r0 = r6;" > > + "exit;" > > + : > > + : __imm(bpf_skb_load_bytes), > > + __imm_const(__sk_buff_data, offsetof(struct __sk_buff, data)), > > + __imm_const(__sk_buff_data_end, offsetof(struct __sk_buff, data_end)), > > + __imm_const(test_data_len, TEST_DATA_LEN) > > + : __clobber_all); > > +} [...]