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Tue, 5 Sep 2023 19:27:00 +0000 Date: Tue, 5 Sep 2023 21:26:53 +0200 From: Maciej Fijalkowski To: Leon Hwang CC: , , , , , , Subject: Re: [RFC PATCH bpf-next v4 1/4] bpf, x64: Comment tail_call_cnt initialisation Message-ID: References: <20230903151448.61696-1-hffilwlqm@gmail.com> <20230903151448.61696-2-hffilwlqm@gmail.com> Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20230903151448.61696-2-hffilwlqm@gmail.com> X-ClientProxiedBy: FR2P281CA0151.DEUP281.PROD.OUTLOOK.COM (2603:10a6:d10:98::14) To DM4PR11MB6117.namprd11.prod.outlook.com (2603:10b6:8:b3::19) 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: DM4PR11MB6117:EE_|SJ2PR11MB8297:EE_ X-MS-Office365-Filtering-Correlation-Id: e0e4559e-2810-4f0a-9c7e-08dbae46135f X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:DM4PR11MB6117.namprd11.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230031)(7916004)(136003)(366004)(376002)(396003)(39860400002)(346002)(1800799009)(451199024)(186009)(41300700001)(33716001)(82960400001)(86362001)(6666004)(83380400001)(966005)(38100700002)(478600001)(26005)(9686003)(6512007)(6486002)(6506007)(66556008)(66476007)(2906002)(316002)(6916009)(66946007)(5660300002)(8936002)(44832011)(4326008)(8676002);DIR:OUT;SFP:1102; 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We should be trying to provide fixes as small as possible IMHO. Having this as a separate commit also breaks logistics of this set as the fix + selftest should be routed towards bpf tree, whereas this particular commit is rather a bpf-next candidate. PTAL at https://www.kernel.org/doc/html/latest/bpf/bpf_devel_QA.html > --- > arch/x86/net/bpf_jit_comp.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c > index a5930042139d3..bcca1c9b9a027 100644 > --- a/arch/x86/net/bpf_jit_comp.c > +++ b/arch/x86/net/bpf_jit_comp.c > @@ -303,8 +303,12 @@ static void emit_prologue(u8 **pprog, u32 stack_depth, bool ebpf_from_cbpf, > prog += X86_PATCH_SIZE; > if (!ebpf_from_cbpf) { > if (tail_call_reachable && !is_subprog) > + /* When it's the entry of the whole tailcall context, > + * zeroing rax means initialising tail_call_cnt. > + */ > EMIT2(0x31, 0xC0); /* xor eax, eax */ > else > + /* Keep the same instruction layout. */ > EMIT2(0x66, 0x90); /* nop2 */ > } > EMIT1(0x55); /* push rbp */ > -- > 2.41.0 >