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Mon, 5 Oct 2020 16:04:49 +0000 Subject: Re: [PATCH] use valid btf in bpf_program__set_attach_target(prog, 0, ...); To: Luigi Rizzo , , Eelco Chaudron , Daniel Borkmann CC: References: <20201005134100.302271-1-lrizzo@google.com> From: Yonghong Song Message-ID: <102ef3d8-e9fa-24c6-af96-b0d62ccf57c2@fb.com> Date: Mon, 5 Oct 2020 09:04:45 -0700 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:68.0) Gecko/20100101 Thunderbird/68.12.1 In-Reply-To: <20201005134100.302271-1-lrizzo@google.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [2620:10d:c090:400::5:91d2] X-ClientProxiedBy: MWHPR1601CA0010.namprd16.prod.outlook.com (2603:10b6:300:da::20) To DM6PR15MB4090.namprd15.prod.outlook.com (2603:10b6:5:c2::18) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [IPv6:2620:10d:c085:21cf::1273] (2620:10d:c090:400::5:91d2) by MWHPR1601CA0010.namprd16.prod.outlook.com (2603:10b6:300:da::20) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3412.20 via Frontend Transport; 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X-MS-Exchange-AntiSpam-MessageData: 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 X-MS-Exchange-CrossTenant-Network-Message-Id: 5f4cb15f-a0b5-4c68-75ba-08d86948629e X-MS-Exchange-CrossTenant-AuthSource: DM6PR15MB4090.namprd15.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 05 Oct 2020 16:04:48.9466 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 8ae927fe-1255-47a7-a2af-5f3a069daaa2 X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: SGAfOUB8JgWVB4Q6FVE1E3cWqDsaBFGck8o3zXeEBZrGtWnUeVspyiexzHz9SkY1 X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM6PR15MB3595 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.235,18.0.687 definitions=2020-10-05_11:2020-10-05,2020-10-05 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 lowpriorityscore=0 spamscore=0 mlxlogscore=999 clxscore=1011 suspectscore=2 adultscore=0 impostorscore=0 malwarescore=0 bulkscore=0 phishscore=0 mlxscore=0 priorityscore=1501 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2010050117 X-FB-Internal: deliver Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On 10/5/20 6:41 AM, Luigi Rizzo wrote: > bpf_program__set_attach_target() will always fail with fd=0 (attach to a > kernel symbol) because obj->btf_vmlinux is NULL and there is no way to > set it. > > Fix this by explicitly calling libbpf_find_kernel_btf() in the function. > > Signed-off-by: Luigi Rizzo > --- > tools/lib/bpf/libbpf.c | 9 ++++++--- > 1 file changed, 6 insertions(+), 3 deletions(-) > > diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c > index a4f55f8a460d..3a63db86666f 100644 > --- a/tools/lib/bpf/libbpf.c > +++ b/tools/lib/bpf/libbpf.c > @@ -10352,10 +10352,13 @@ int bpf_program__set_attach_target(struct bpf_program *prog, > if (attach_prog_fd) > btf_id = libbpf_find_prog_btf_id(attach_func_name, > attach_prog_fd); > - else > - btf_id = __find_vmlinux_btf_id(prog->obj->btf_vmlinux, > - attach_func_name, > + else { > + struct btf *btf = libbpf_find_kernel_btf(); > + > + btf_id = __find_vmlinux_btf_id(btf, attach_func_name, > prog->expected_attach_type); > + btf__free(btf); > + } Doesn't feel this is right fix. In libbpf, we have API function libbpf_find_vmlinux_btf_id just doing the above. Also, could you point out why btf_vmlinux is NULL? Is this related to fd = 0? We probably should fix the problem there since what if other API functions like bpf_program__set_attach_target() wants btf_vmlinux. We should not duplicate this logic to other API functions. > > if (btf_id < 0) > return btf_id; >