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Thu, 18 Jun 2020 23:51:24 +0000 Date: Thu, 18 Jun 2020 16:51:22 -0700 From: Andrey Ignatov To: Martin KaFai Lau CC: , , , Subject: Re: [PATCH bpf-next 4/6] bpf: Support access to bpf map fields Message-ID: <20200618235122.GB47103@rdna-mbp.dhcp.thefacebook.com> References: <53fdc8f0c100fc50c8aa5fbc798d659e3dd77e92.1592426215.git.rdna@fb.com> <20200618061841.f52jaacsacazotkq@kafai-mbp.dhcp.thefacebook.com> <20200618194236.GA47103@rdna-mbp.dhcp.thefacebook.com> Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20200618194236.GA47103@rdna-mbp.dhcp.thefacebook.com> User-Agent: Mutt/1.12.1 (2019-06-15) X-ClientProxiedBy: BYAPR05CA0062.namprd05.prod.outlook.com (2603:10b6:a03:74::39) To BYAPR15MB4119.namprd15.prod.outlook.com (2603:10b6:a02:cd::20) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from localhost (2620:10d:c090:400::5:142a) by BYAPR05CA0062.namprd05.prod.outlook.com (2603:10b6:a03:74::39) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3131.12 via Frontend Transport; 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X-MS-Exchange-AntiSpam-MessageData: bczd52irTYbLCiFj2zLWwJD9I1fZsAIofFmWYzvP97xbpSDSEo3p8Jqm8jw614wnECu/ozPxBbhYiX4McTTo8zPg/3O/5Gs3LfFzMDdtsD558mlnbfQjhoWrdEbUNXElQAdx1DAQmgaiwjLcnXcnREZFhWd6R7oaProbxMPzLoSXKK4XQcFsrRIvluETMauV8rujuot/iGssSSAnai7NpPSrUi9OfHw/FoWVbddcAYFwaXsqC32LLORiyDcnHLTmb0S/cXDSuKUcV3UchpRe35ibML/2vQwWaOuKL1kDfADTW9xGIWAW/cLsO3Ep00IkAjTlSetDoXClFOgqA9Jh8d1kbw0U4lYjapzEISapHMIbFOq2xB7ILEjruKAMyX6FwlYirgcaPxtnllMW6SeA07RWvi0WAsWYVK3qSDdmFlf9HIvU+PNGrkIakuaJ/F5LhRPUJzOyFNAKF7cVW8FQEPSIv/RLiSjgnKRenpZxzu8TtYbP2zxk98GlRxQEcDylBhvTjL9uiDNeTWb/2e1A2g== X-MS-Exchange-CrossTenant-Network-Message-Id: 254dd05d-3407-4956-b98f-08d813e28232 X-MS-Exchange-CrossTenant-OriginalArrivalTime: 18 Jun 2020 23:51:24.4542 (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: izo24TuKMJWfPtgFTSVpuJOMNgLhL42p/fiBdy2yRncvTFvpqU8FoSj8u12g5MDY X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR15MB3190 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.216,18.0.687 definitions=2020-06-18_21:2020-06-18,2020-06-18 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 malwarescore=0 impostorscore=0 cotscore=-2147483648 suspectscore=0 adultscore=0 spamscore=0 clxscore=1015 priorityscore=1501 mlxscore=0 phishscore=0 lowpriorityscore=0 bulkscore=0 mlxlogscore=999 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2004280000 definitions=main-2006180183 X-FB-Internal: deliver Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org Andrey Ignatov [Thu, 2020-06-18 12:42 -0700]: > Martin KaFai Lau [Wed, 2020-06-17 23:18 -0700]: > > On Wed, Jun 17, 2020 at 01:43:45PM -0700, Andrey Ignatov wrote: > > [ ... ] > > > diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c > > > index e5c5305e859c..fa21b1e766ae 100644 > > > --- a/kernel/bpf/btf.c > > > +++ b/kernel/bpf/btf.c > > > @@ -3577,6 +3577,67 @@ btf_get_prog_ctx_type(struct bpf_verifier_log *log, struct btf *btf, > > > return ctx_type; > > > } > > > > > > +#define BPF_PROG_TYPE(_id, _name, prog_ctx_type, kern_ctx_type) > > > +#define BPF_LINK_TYPE(_id, _name) > > > +static const struct bpf_map_ops * const btf_vmlinux_map_ops[] = { > > > +#define BPF_MAP_TYPE(_id, _ops) \ > > > + [_id] = &_ops, > > > +#include > > > +#undef BPF_MAP_TYPE > > > +}; > > > +static u32 btf_vmlinux_map_ids[] = { > > > +#define BPF_MAP_TYPE(_id, _ops) \ > > > + [_id] = (u32)-1, > > > +#include > > > +#undef BPF_MAP_TYPE > > > +}; > > > +#undef BPF_PROG_TYPE > > > +#undef BPF_LINK_TYPE > > > + > > > +static int btf_vmlinux_map_ids_init(const struct btf *btf, > > > + struct bpf_verifier_log *log) > > > +{ > > > + int base_btf_id, btf_id, i; > > > + const char *btf_name; > > > + > > > + base_btf_id = btf_find_by_name_kind(btf, "bpf_map", BTF_KIND_STRUCT); > > > + if (base_btf_id < 0) > > > + return base_btf_id; > > > + > > > + BUILD_BUG_ON(ARRAY_SIZE(btf_vmlinux_map_ops) != > > > + ARRAY_SIZE(btf_vmlinux_map_ids)); > > > + > > > + for (i = 0; i < ARRAY_SIZE(btf_vmlinux_map_ops); ++i) { > > > + if (!btf_vmlinux_map_ops[i]) > > > + continue; > > > + btf_name = btf_vmlinux_map_ops[i]->map_btf_name; > > > + if (!btf_name) { > > > + btf_vmlinux_map_ids[i] = base_btf_id; > > > + continue; > > > + } > > > + btf_id = btf_find_by_name_kind(btf, btf_name, BTF_KIND_STRUCT); > > > + if (btf_id < 0) > > > + return btf_id; > > > + btf_vmlinux_map_ids[i] = btf_id; > > Since map_btf_name is already in map_ops, how about storing map_btf_id in > > map_ops also? > > btf_id 0 is "void" which is as good as -1, so there is no need > > to modify all map_ops to init map_btf_id to -1. > > Yeah, btf_id == 0 being a valid id was the reason I used -1. > > I realized that having a map type specific struct with btf_id == 0 > should be practically impossible, but is it guaranteed to always be > "void" or it just happened so and can change in the future? > > If both this and having one more field in bpf_map_ops is not a problem, > I'll move it to bpf_map_ops. Nope, I can't do it. All `struct bpf_map_ops` are global `const`, i.e. rodata and a try cast `const` away and change them causes a panic. Simple user space repro: % cat 1.c #include struct map_ops { int a; }; const struct map_ops ops = { .a = 1, }; int main(void) { struct map_ops *ops_rw = (struct map_ops *)&ops; printf("before a=%d\n", ops_rw->a); ops_rw->a = 3; printf(" afrer a=%d\n", ops_rw->a); } % clang -O2 -Wall -Wextra -pedantic -pedantic-errors -g 1.c && ./a.out before a=1 Segmentation fault (core dumped) % objdump -t a.out | grep -w ops 0000000000400600 g O .rodata 0000000000000004 ops -- Andrey Ignatov