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Marchesi" To: Yonghong Song Cc: bpf@vger.kernel.org, david.faust@oracle.com, James Hilliard , Nick Desaulniers , David Malcolm , Julia Lawall , elena.zannoni@oracle.com Subject: Re: BTF tag support in DWARF (notes for today's BPF Office Hours) In-Reply-To: (Yonghong Song's message of "Sun, 22 Jan 2023 09:53:51 -0800") References: <87r0w9jjoq.fsf@oracle.com> <877cy0j0kt.fsf@oracle.com> Date: Mon, 23 Jan 2023 16:50:11 +0100 Message-ID: <873581i72k.fsf@oracle.com> User-Agent: Gnus/5.13 (Gnus v5.13) Content-Type: text/plain X-ClientProxiedBy: LO2P265CA0466.GBRP265.PROD.OUTLOOK.COM (2603:10a6:600:a2::22) To BYAPR10MB2888.namprd10.prod.outlook.com (2603:10b6:a03:88::32) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BYAPR10MB2888:EE_|PH7PR10MB6107:EE_ X-MS-Office365-Filtering-Correlation-Id: b6cb25aa-04a4-47c5-c846-08dafd59861b X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; X-Microsoft-Antispam-Message-Info: TeebgeBwERYPe/7/faBiQ31hGNF5h+I7jIIoTskbiwLrjZt4LEPV4GjmIRrSCSRdhrKGAMyy14D3h+4wmbGNUb/bZUIgoob/6RYvWNQqXDRXLvGwpi66mulWd+hVmImfgGrwNQs7gviCs9mll8bohjTRx95BOGfFwjHLBNFundL5wjSsEIKmIZCn1apD1zHSIPjvXZWEThpYLqT+jqoZoxQh7ggI120g8yhThsfiyBZvtYsTo6q7v4MVuqS5i2vOIWp90NUZjxLyoV1ohf5r1jXvVzXBCkyTy3KD/IcwG1BjwAnNH9bS1GsPCC/qWrDWV5Uydat0JCDVXTw4RDfuN5IBO8TC1NxapENQJmFVKWuvlSmELSrT45h5fgFM6qCIUI9ekxkqT2XOyAGU0BmrsyC02ZMq7cmZ9EjpC9kkwJuyQBR58dCQDA5xJZomsfENziDDGZh99yVt43LaVuirhinrUVf6Pw5HILytL8rzsA+lNRJ8rIObXxwbZCBL+fsGiq5dkAchNls1Vxlsh38pt6PZXWinXnVy9YzL36mSQFa5FhaIbgkOzUSfUMq3iwm/BffKxI9G8wehIMVMGlIXVoIqhS5DKYahyH8XNvaIaP9H96eq2/+A76GfvxVmdNIFENo8Nb0c5MkEkUxXblFB+YE2d/wUVO08JMA+GeU4DT4= X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:BYAPR10MB2888.namprd10.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230022)(396003)(346002)(136003)(376002)(366004)(39860400002)(451199015)(6486002)(186003)(26005)(2906002)(6512007)(54906003)(2616005)(316002)(478600001)(966005)(6666004)(38100700002)(36756003)(107886003)(53546011)(6506007)(86362001)(83380400001)(41300700001)(4326008)(5660300002)(8936002)(66556008)(6916009)(66476007)(66946007)(8676002);DIR:OUT;SFP:1101; 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Marchesi wrote: >> We agreed in the meeting to implement Solution 2 below in both GCC >> and >> clang. >> The DW_TAG_LLVM_annotation DIE number will be changed in order to >> make >> it possible for pahole to handle the current tags. The number of the >> new tag will be shared by both GCC and clang. > > w.r.t c2x attribute syntax discussion in 01/19 office hour discussion. > > I have checked clang c2x syntax w.r.t. > btf_type_tag and btf_decl_tag. They are both supported > with clang 15 and 16. > > See: > https://clang.llvm.org/docs/AttributeReference.html > > The c2x btf_decl_tag attr syntax is [[clang::btf_decl_tag("")]]. > The c2x btf_type_tag attr syntax is [[clang::btf_type_tag("")]]. > > $ cat t.c > int [[clang::btf_type_tag("aa")]] * [[clang::btf_type_tag("bb")]] *f; > [[clang::btf_decl_tag("cc")]] int foo() { return 5; } > int bar() { return foo(); } > $ clang -std=c2x -g -O2 -c t.c > $ llvm-dwarfdump t.o | grep btf | grep tag > DW_AT_name ("btf_type_tag") > DW_AT_name ("btf_type_tag") > DW_AT_name ("btf_decl_tag") > > I double checked and the c2x syntax above generates the *same* > type IR and dwarf compared to __attribute__ style attributes. > > [...] Thanks for checking. That matches our impression that C2X type attributes actually order the same way than sparse type annotations, at least in the cases we are interested on.