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Marchesi" To: Kumar Kartikeya Dwivedi Cc: bpf@vger.kernel.org, Yonghong Song , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , David Vernet Subject: Re: [PATCH bpf-next v2 00/14] Exceptions - 1/2 In-Reply-To: (Kumar Kartikeya Dwivedi's message of "Wed, 23 Aug 2023 02:52:48 +0530") References: <20230809114116.3216687-1-memxor@gmail.com> Date: Wed, 23 Aug 2023 00:07:11 +0200 Message-ID: <87lee2enow.fsf@oracle.com> User-Agent: Gnus/5.13 (Gnus v5.13) Content-Type: text/plain X-ClientProxiedBy: LO4P123CA0546.GBRP123.PROD.OUTLOOK.COM (2603:10a6:600:319::17) To BYAPR10MB2888.namprd10.prod.outlook.com (2603:10b6:a03:88::32) Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BYAPR10MB2888:EE_|CH0PR10MB5017:EE_ X-MS-Office365-Filtering-Correlation-Id: c6bce61d-9826-4167-c789-08dba35c25f8 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 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X-MS-Exchange-CrossTenant-Network-Message-Id: c6bce61d-9826-4167-c789-08dba35c25f8 X-MS-Exchange-CrossTenant-AuthSource: BYAPR10MB2888.namprd10.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 22 Aug 2023 22:07:17.5275 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 4e2c6054-71cb-48f1-bd6c-3a9705aca71b X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: lIRH67WAJdS7UdEQ67QC9Oh7302cnBn5LYW/cziHyA/N6pX8zZICqeD7Qeur43Pzl29qVq0ohwuWQ9ic/2R4Cgx5h/n4ANckO4KtIxbgams= X-MS-Exchange-Transport-CrossTenantHeadersStamped: CH0PR10MB5017 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.267,Aquarius:18.0.957,Hydra:6.0.601,FMLib:17.11.176.26 definitions=2023-08-22_19,2023-08-22_01,2023-05-22_02 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 adultscore=0 spamscore=0 mlxscore=0 bulkscore=0 malwarescore=0 phishscore=0 mlxlogscore=980 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2308100000 definitions=main-2308220180 X-Proofpoint-ORIG-GUID: tXWwQaZ1pkBdT22rLiIp8Tnhg7MlZ0Yb X-Proofpoint-GUID: tXWwQaZ1pkBdT22rLiIp8Tnhg7MlZ0Yb X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_BLOCKED, RCVD_IN_MSPIKE_H5,RCVD_IN_MSPIKE_WL,SPF_HELO_NONE,SPF_NONE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net > On Wed, 9 Aug 2023 at 17:11, Kumar Kartikeya Dwivedi wrote: >> >> [...] >> >> Known issues >> ------------ >> >> * Just asm volatile ("call bpf_throw" :::) does not emit DATASEC .ksyms >> for bpf_throw, there needs to be explicit call in C for clang to emit >> the DATASEC info in BTF, leading to errors during compilation. >> > > Hi Yonghong, I'd like to ask you about this issue to figure out > whether this is something worth fixing in clang or not. > It pops up in programs which only use bpf_assert macros (which emit > the call to bpf_throw using inline assembly) and not bpf_throw kfunc > directly. > > I believe in case we emit a call bpf_throw instruction, the BPF > backend code will not see any DWARF debug info for the respective > symbol, so it will also not be able to convert it and emit anything to > .BTF section in case no direct call without asm volatile is present. > Therefore my guess is that this isn't something that can be fixed in > clang/LLVM. Besides, please keep in mind that GCC doens't have an integrated assembler, and therefore relying on clang's understanding on the instructions in inline assembly is something to avoid. > There are also options like the one below to work around it. > if ((volatile int){0}) bpf_throw(); > asm volatile ("call bpf_throw"); I can confirm the above results in a BTF entry for bpf_throw with bpf-unknown-none-gcc -gbtf.