From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-177.mta0.migadu.com (out-177.mta0.migadu.com [91.218.175.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id CB4E4314A95 for ; Fri, 23 Jan 2026 08:16:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.177 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769156180; cv=none; b=iQMFD/KjR1PXVOKixXBzsIu5GKXtIg5P1MzctgaNW5Q/H6VSG7mrc+W7+nOQcVyvsreXDY0PFwYtI57UB9nAbUdA4Q6+M2LxlY1b+w8PtACU4x2YPRMksWLgawDgya3BQlTn+9VYKqwrdMPYmThMX0i/yRq+T3JNF6dCSUI4jOE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769156180; c=relaxed/simple; bh=BsTbk9PK/Dho8o57iGK8Ji2OTakuElTTQ+Nej8bohjM=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=qFcg55+psPZ547ULkv4TpppOrbQzhXhv/QRDNFWi92ZSXKwDIx7ptM/UL2xw0CXQxVUGRdLnZdxH4M7vFwpoBXjfQF9Wl3w4SIyIIpIQNtkNdzobj8wkwH9GTHnkEK/nlp14QBWYU4OYR4MU6GdCt1J/I37BB5SwdB2hfU5HN/I= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=vEr63Vax; arc=none smtp.client-ip=91.218.175.177 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) header.d=linux.dev header.i=@linux.dev header.b="vEr63Vax" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1769156166; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=s5/gOBon1dhydrWDZXwZcbC1y+hCYJIaCL2aKChxtag=; b=vEr63VaxWe8PUFcQkZqOMUJb88ZZobeFvXZ5re+ha18e8e9XToG54pm+B9mgR7TndTRpnJ Z7CVTe8VJw3ADiCjhwMTFmn0grkAqkpjTbh0cwXrBd9nJSv49ToBnt+4fI2m0lDhU4G1WJ RifQIWCxdui44PHAXUK/JzfCSAiJUHE= From: Menglong Dong To: menglong8.dong@gmail.com, andrii@kernel.org, bot+bpf-ci@kernel.org Cc: daniel@iogearbox.net, martin.lau@linux.dev, eddyz87@gmail.com, song@kernel.org, yonghong.song@linux.dev, john.fastabend@gmail.com, kpsingh@kernel.org, sdf@fomichev.me, haoluo@google.com, jolsa@kernel.org, davem@davemloft.net, dsahern@kernel.org, tglx@linutronix.de, mingo@redhat.com, jiang.biao@linux.dev, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, bpf@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, ast@kernel.org, andrii@kernel.org, daniel@iogearbox.net, martin.lau@kernel.org, eddyz87@gmail.com, yonghong.song@linux.dev, clm@meta.com, ihor.solodrai@linux.dev Subject: Re: [PATCH bpf-next v11 04/12] bpf: support fsession for bpf_session_is_return Date: Fri, 23 Jan 2026 16:15:50 +0800 Message-ID: <5071572.31r3eYUQgx@7940hx> In-Reply-To: References: <20260123073532.238985-5-dongml2@chinatelecom.cn> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="utf-8" X-Migadu-Flow: FLOW_OUT On 2026/1/23 16:07 bot+bpf-ci@kernel.org write: > > diff --git a/include/linux/bpf.h b/include/linux/bpf.h > > index 41228b0add52..29eecd79352e 100644 > > --- a/include/linux/bpf.h > > +++ b/include/linux/bpf.h > > @@ -1229,6 +1229,8 @@ enum { > > #endif > > }; > > > > +#define BPF_TRAMP_IS_RETURN_SHIFT 63 > > + > > struct bpf_tramp_links { > > > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > > index 19fd16697262..2ae8f29b854f 100644 > > --- a/kernel/bpf/verifier.c > > +++ b/kernel/bpf/verifier.c > > @@ -23011,6 +23011,19 @@ static int fixup_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn, > > desc->func_id == special_kfunc_list[KF_bpf_rdonly_cast]) { > > insn_buf[0] = BPF_MOV64_REG(BPF_REG_0, BPF_REG_1); > > *cnt = 1; > > + } else if (desc->func_id == special_kfunc_list[KF_bpf_session_is_return] && > > + env->prog->expected_attach_type == BPF_TRACE_FSESSION) { > > + /* > > + * inline the bpf_session_is_return() for fsession: > > + * bool bpf_session_is_return(void *ctx) > > + * { > > + * return (((u64 *)ctx)[-1] >> BPF_TRAMP_IS_RETURN_SHIFT) & 1; > > + * } > > + */ > > + insn_buf[0] = BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1, -8); > > + insn_buf[1] = BPF_ALU64_IMM(BPF_RSH, BPF_REG_0, BPF_TRAMP_IS_RETURN_SHIFT); > > + insn_buf[2] = BPF_ALU64_IMM(BPF_AND, BPF_REG_0, 1); > > + *cnt = 3; > > + } > > The inline implementation reads bit 63 of ctx[-1] to check the is_return > flag. However, looking at the x86 trampoline code in > arch/x86/net/bpf_jit_comp.c, the trampoline only stores nr_regs in ctx[-1]: > > emit_mov_imm64(&prog, BPF_REG_0, 0, (u32) nr_regs); > emit_stx(&prog, BPF_DW, BPF_REG_FP, BPF_REG_0, -nregs_off); > > The is_return flag (bit 63) is never set by the current trampoline code. > This means bpf_session_is_return() will always return 0 for fsession > programs, even when executing at the return point. > > I see this is fixed later in the series by commit ba766b26e776 ("bpf,x86: > add fsession support for x86_64") which adds: > > func_meta |= (1ULL << BPF_TRAMP_IS_RETURN_SHIFT); > if (bpf_fsession_cnt(tlinks)) > emit_store_stack_imm64(&prog, BPF_REG_0, -func_meta_off, func_meta); > > Should this commit be squashed with the x86 trampoline changes to ensure > the feature works correctly at each point in the series? As I said before, this patch implement the common part of the fsession. and we implement the architecture specific code for x86_64 in the later patch. > > [ ... ] > > > --- > AI reviewed your patch. Please fix the bug or email reply why it's not a bug. > See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md > > CI run summary: https://github.com/kernel-patches/bpf/actions/runs/21278745581 >