tools/perf/util/bpf-loader.c

   1 /*
   2  * bpf-loader.c
   3  *
   4  * Copyright (C) 2015 Wang Nan <wangnan0@huawei.com>
   5  * Copyright (C) 2015 Huawei Inc.
   6  */
   7
   8 #include <linux/bpf.h>
   9 #include <bpf/libbpf.h>
  10 #include <linux/err.h>
  11 #include <linux/string.h>
  12 #include "perf.h"
  13 #include "debug.h"
  14 #include "bpf-loader.h"
  15 #include "bpf-prologue.h"
  16 #include "llvm-utils.h"
  17 #include "probe-event.h"
  18 #include "probe-finder.h" // for MAX_PROBES
  19 #include "llvm-utils.h"
  20
  21 #define DEFINE_PRINT_FN(name, level) \
  22 static int libbpf_##name(const char *fmt, ...)  \
  23 {                                               \
  24         va_list args;                           \
  25         int ret;                                \
  26                                                 \
  27         va_start(args, fmt);                    \
  28         ret = veprintf(level, verbose, pr_fmt(fmt), args);\
  29         va_end(args);                           \
  30         return ret;                             \
  31 }
  32
  33 DEFINE_PRINT_FN(warning, 1)
  34 DEFINE_PRINT_FN(info, 1)
  35 DEFINE_PRINT_FN(debug, 1)
  36
  37 struct bpf_prog_priv {
  38         struct perf_probe_event pev;
  39         bool need_prologue;
  40         struct bpf_insn *insns_buf;
  41 };
  42
  43 static bool libbpf_initialized;
  44
  45 struct bpf_object *
  46 bpf__prepare_load_buffer(void *obj_buf, size_t obj_buf_sz, const char *name)
  47 {
  48         struct bpf_object *obj;
  49
  50         if (!libbpf_initialized) {
  51                 libbpf_set_print(libbpf_warning,
  52                                  libbpf_info,
  53                                  libbpf_debug);
  54                 libbpf_initialized = true;
  55         }
  56
  57         obj = bpf_object__open_buffer(obj_buf, obj_buf_sz, name);
  58         if (IS_ERR(obj)) {
  59                 pr_debug("bpf: failed to load buffer\n");
  60                 return ERR_PTR(-EINVAL);
  61         }
  62
  63         return obj;
  64 }
  65
  66 struct bpf_object *bpf__prepare_load(const char *filename, bool source)
  67 {
  68         struct bpf_object *obj;
  69
  70         if (!libbpf_initialized) {
  71                 libbpf_set_print(libbpf_warning,
  72                                  libbpf_info,
  73                                  libbpf_debug);
  74                 libbpf_initialized = true;
  75         }
  76
  77         if (source) {
  78                 int err;
  79                 void *obj_buf;
  80                 size_t obj_buf_sz;
  81
  82                 err = llvm__compile_bpf(filename, &obj_buf, &obj_buf_sz);
  83                 if (err)
  84                         return ERR_PTR(-BPF_LOADER_ERRNO__COMPILE);
  85                 obj = bpf_object__open_buffer(obj_buf, obj_buf_sz, filename);
  86                 free(obj_buf);
  87         } else
  88                 obj = bpf_object__open(filename);
  89
  90         if (IS_ERR(obj)) {
  91                 pr_debug("bpf: failed to load %s\n", filename);
  92                 return obj;
  93         }
  94
  95         return obj;
  96 }
  97
  98 void bpf__clear(void)
  99 {
 100         struct bpf_object *obj, *tmp;
 101
 102         bpf_object__for_each_safe(obj, tmp) {
 103                 bpf__unprobe(obj);
 104                 bpf_object__close(obj);
 105         }
 106 }
 107
 108 static void
 109 bpf_prog_priv__clear(struct bpf_program *prog __maybe_unused,
 110                      void *_priv)
 111 {
 112         struct bpf_prog_priv *priv = _priv;
 113
 114         cleanup_perf_probe_events(&priv->pev, 1);
 115         zfree(&priv->insns_buf);
 116         free(priv);
 117 }
 118
 119 static int
 120 config__exec(const char *value, struct perf_probe_event *pev)
 121 {
 122         pev->uprobes = true;
 123         pev->target = strdup(value);
 124         if (!pev->target)
 125                 return -ENOMEM;
 126         return 0;
 127 }
 128
 129 static int
 130 config__module(const char *value, struct perf_probe_event *pev)
 131 {
 132         pev->uprobes = false;
 133         pev->target = strdup(value);
 134         if (!pev->target)
 135                 return -ENOMEM;
 136         return 0;
 137 }
 138
 139 static int
 140 config__bool(const char *value,
 141              bool *pbool, bool invert)
 142 {
 143         int err;
 144         bool bool_value;
 145
 146         if (!pbool)
 147                 return -EINVAL;
 148
 149         err = strtobool(value, &bool_value);
 150         if (err)
 151                 return err;
 152
 153         *pbool = invert ? !bool_value : bool_value;
 154         return 0;
 155 }
 156
 157 static int
 158 config__inlines(const char *value,
 159                 struct perf_probe_event *pev __maybe_unused)
 160 {
 161         return config__bool(value, &probe_conf.no_inlines, true);
 162 }
 163
 164 static int
 165 config__force(const char *value,
 166               struct perf_probe_event *pev __maybe_unused)
 167 {
 168         return config__bool(value, &probe_conf.force_add, false);
 169 }
 170
 171 static struct {
 172         const char *key;
 173         const char *usage;
 174         const char *desc;
 175         int (*func)(const char *, struct perf_probe_event *);
 176 } bpf_config_terms[] = {
 177         {
 178                 .key    = "exec",
 179                 .usage  = "exec=<full path of file>",
 180                 .desc   = "Set uprobe target",
 181                 .func   = config__exec,
 182         },
 183         {
 184                 .key    = "module",
 185                 .usage  = "module=<module name>    ",
 186                 .desc   = "Set kprobe module",
 187                 .func   = config__module,
 188         },
 189         {
 190                 .key    = "inlines",
 191                 .usage  = "inlines=[yes|no]        ",
 192                 .desc   = "Probe at inline symbol",
 193                 .func   = config__inlines,
 194         },
 195         {
 196                 .key    = "force",
 197                 .usage  = "force=[yes|no]          ",
 198                 .desc   = "Forcibly add events with existing name",
 199                 .func   = config__force,
 200         },
 201 };
 202
 203 static int
 204 do_config(const char *key, const char *value,
 205           struct perf_probe_event *pev)
 206 {
 207         unsigned int i;
 208
 209         pr_debug("config bpf program: %s=%s\n", key, value);
 210         for (i = 0; i < ARRAY_SIZE(bpf_config_terms); i++)
 211                 if (strcmp(key, bpf_config_terms[i].key) == 0)
 212                         return bpf_config_terms[i].func(value, pev);
 213
 214         pr_debug("BPF: ERROR: invalid config option in object: %s=%s\n",
 215                  key, value);
 216
 217         pr_debug("\nHint: Currently valid options are:\n");
 218         for (i = 0; i < ARRAY_SIZE(bpf_config_terms); i++)
 219                 pr_debug("\t%s:\t%s\n", bpf_config_terms[i].usage,
 220                          bpf_config_terms[i].desc);
 221         pr_debug("\n");
 222
 223         return -BPF_LOADER_ERRNO__CONFIG_TERM;
 224 }
 225
 226 static const char *
 227 parse_config_kvpair(const char *config_str, struct perf_probe_event *pev)
 228 {
 229         char *text = strdup(config_str);
 230         char *sep, *line;
 231         const char *main_str = NULL;
 232         int err = 0;
 233
 234         if (!text) {
 235                 pr_debug("No enough memory: dup config_str failed\n");
 236                 return ERR_PTR(-ENOMEM);
 237         }
 238
 239         line = text;
 240         while ((sep = strchr(line, ';'))) {
 241                 char *equ;
 242
 243                 *sep = '\0';
 244                 equ = strchr(line, '=');
 245                 if (!equ) {
 246                         pr_warning("WARNING: invalid config in BPF object: %s\n",
 247                                    line);
 248                         pr_warning("\tShould be 'key=value'.\n");
 249                         goto nextline;
 250                 }
 251                 *equ = '\0';
 252
 253                 err = do_config(line, equ + 1, pev);
 254                 if (err)
 255                         break;
 256 nextline:
 257                 line = sep + 1;
 258         }
 259
 260         if (!err)
 261                 main_str = config_str + (line - text);
 262         free(text);
 263
 264         return err ? ERR_PTR(err) : main_str;
 265 }
 266
 267 static int
 268 parse_config(const char *config_str, struct perf_probe_event *pev)
 269 {
 270         int err;
 271         const char *main_str = parse_config_kvpair(config_str, pev);
 272
 273         if (IS_ERR(main_str))
 274                 return PTR_ERR(main_str);
 275
 276         err = parse_perf_probe_command(main_str, pev);
 277         if (err < 0) {
 278                 pr_debug("bpf: '%s' is not a valid config string\n",
 279                          config_str);
 280                 /* parse failed, don't need clear pev. */
 281                 return -BPF_LOADER_ERRNO__CONFIG;
 282         }
 283         return 0;
 284 }
 285
 286 static int
 287 config_bpf_program(struct bpf_program *prog)
 288 {
 289         struct perf_probe_event *pev = NULL;
 290         struct bpf_prog_priv *priv = NULL;
 291         const char *config_str;
 292         int err;
 293
 294         /* Initialize per-program probing setting */
 295         probe_conf.no_inlines = false;
 296         probe_conf.force_add = false;
 297
 298         config_str = bpf_program__title(prog, false);
 299         if (IS_ERR(config_str)) {
 300                 pr_debug("bpf: unable to get title for program\n");
 301                 return PTR_ERR(config_str);
 302         }
 303
 304         priv = calloc(sizeof(*priv), 1);
 305         if (!priv) {
 306                 pr_debug("bpf: failed to alloc priv\n");
 307                 return -ENOMEM;
 308         }
 309         pev = &priv->pev;
 310
 311         pr_debug("bpf: config program '%s'\n", config_str);
 312         err = parse_config(config_str, pev);
 313         if (err)
 314                 goto errout;
 315
 316         if (pev->group && strcmp(pev->group, PERF_BPF_PROBE_GROUP)) {
 317                 pr_debug("bpf: '%s': group for event is set and not '%s'.\n",
 318                          config_str, PERF_BPF_PROBE_GROUP);
 319                 err = -BPF_LOADER_ERRNO__GROUP;
 320                 goto errout;
 321         } else if (!pev->group)
 322                 pev->group = strdup(PERF_BPF_PROBE_GROUP);
 323
 324         if (!pev->group) {
 325                 pr_debug("bpf: strdup failed\n");
 326                 err = -ENOMEM;
 327                 goto errout;
 328         }
 329
 330         if (!pev->event) {
 331                 pr_debug("bpf: '%s': event name is missing. Section name should be 'key=value'\n",
 332                          config_str);
 333                 err = -BPF_LOADER_ERRNO__EVENTNAME;
 334                 goto errout;
 335         }
 336         pr_debug("bpf: config '%s' is ok\n", config_str);
 337
 338         err = bpf_program__set_private(prog, priv, bpf_prog_priv__clear);
 339         if (err) {
 340                 pr_debug("Failed to set priv for program '%s'\n", config_str);
 341                 goto errout;
 342         }
 343
 344         return 0;
 345
 346 errout:
 347         if (pev)
 348                 clear_perf_probe_event(pev);
 349         free(priv);
 350         return err;
 351 }
 352
 353 static int bpf__prepare_probe(void)
 354 {
 355         static int err = 0;
 356         static bool initialized = false;
 357
 358         /*
 359          * Make err static, so if init failed the first, bpf__prepare_probe()
 360          * fails each time without calling init_probe_symbol_maps multiple
 361          * times.
 362          */
 363         if (initialized)
 364                 return err;
 365
 366         initialized = true;
 367         err = init_probe_symbol_maps(false);
 368         if (err < 0)
 369                 pr_debug("Failed to init_probe_symbol_maps\n");
 370         probe_conf.max_probes = MAX_PROBES;
 371         return err;
 372 }
 373
 374 static int
 375 preproc_gen_prologue(struct bpf_program *prog, int n,
 376                      struct bpf_insn *orig_insns, int orig_insns_cnt,
 377                      struct bpf_prog_prep_result *res)
 378 {
 379         struct probe_trace_event *tev;
 380         struct perf_probe_event *pev;
 381         struct bpf_prog_priv *priv;
 382         struct bpf_insn *buf;
 383         size_t prologue_cnt = 0;
 384         int err;
 385
 386         err = bpf_program__get_private(prog, (void **)&priv);
 387         if (err || !priv)
 388                 goto errout;
 389
 390         pev = &priv->pev;
 391
 392         if (n < 0 || n >= pev->ntevs)
 393                 goto errout;
 394
 395         tev = &pev->tevs[n];
 396
 397         buf = priv->insns_buf;
 398         err = bpf__gen_prologue(tev->args, tev->nargs,
 399                                 buf, &prologue_cnt,
 400                                 BPF_MAXINSNS - orig_insns_cnt);
 401         if (err) {
 402                 const char *title;
 403
 404                 title = bpf_program__title(prog, false);
 405                 if (!title)
 406                         title = "[unknown]";
 407
 408                 pr_debug("Failed to generate prologue for program %s\n",
 409                          title);
 410                 return err;
 411         }
 412
 413         memcpy(&buf[prologue_cnt], orig_insns,
 414                sizeof(struct bpf_insn) * orig_insns_cnt);
 415
 416         res->new_insn_ptr = buf;
 417         res->new_insn_cnt = prologue_cnt + orig_insns_cnt;
 418         res->pfd = NULL;
 419         return 0;
 420
 421 errout:
 422         pr_debug("Internal error in preproc_gen_prologue\n");
 423         return -BPF_LOADER_ERRNO__PROLOGUE;
 424 }
 425
 426 static int hook_load_preprocessor(struct bpf_program *prog)
 427 {
 428         struct perf_probe_event *pev;
 429         struct bpf_prog_priv *priv;
 430         bool need_prologue = false;
 431         int err, i;
 432
 433         err = bpf_program__get_private(prog, (void **)&priv);
 434         if (err || !priv) {
 435                 pr_debug("Internal error when hook preprocessor\n");
 436                 return -BPF_LOADER_ERRNO__INTERNAL;
 437         }
 438
 439         pev = &priv->pev;
 440         for (i = 0; i < pev->ntevs; i++) {
 441                 struct probe_trace_event *tev = &pev->tevs[i];
 442
 443                 if (tev->nargs > 0) {
 444                         need_prologue = true;
 445                         break;
 446                 }
 447         }
 448
 449         /*
 450          * Since all tevs don't have argument, we don't need generate
 451          * prologue.
 452          */
 453         if (!need_prologue) {
 454                 priv->need_prologue = false;
 455                 return 0;
 456         }
 457
 458         priv->need_prologue = true;
 459         priv->insns_buf = malloc(sizeof(struct bpf_insn) * BPF_MAXINSNS);
 460         if (!priv->insns_buf) {
 461                 pr_debug("No enough memory: alloc insns_buf failed\n");
 462                 return -ENOMEM;
 463         }
 464
 465         err = bpf_program__set_prep(prog, pev->ntevs,
 466                                     preproc_gen_prologue);
 467         return err;
 468 }
 469
 470 int bpf__probe(struct bpf_object *obj)
 471 {
 472         int err = 0;
 473         struct bpf_program *prog;
 474         struct bpf_prog_priv *priv;
 475         struct perf_probe_event *pev;
 476
 477         err = bpf__prepare_probe();
 478         if (err) {
 479                 pr_debug("bpf__prepare_probe failed\n");
 480                 return err;
 481         }
 482
 483         bpf_object__for_each_program(prog, obj) {
 484                 err = config_bpf_program(prog);
 485                 if (err)
 486                         goto out;
 487
 488                 err = bpf_program__get_private(prog, (void **)&priv);
 489                 if (err || !priv)
 490                         goto out;
 491                 pev = &priv->pev;
 492
 493                 err = convert_perf_probe_events(pev, 1);
 494                 if (err < 0) {
 495                         pr_debug("bpf_probe: failed to convert perf probe events");
 496                         goto out;
 497                 }
 498
 499                 err = apply_perf_probe_events(pev, 1);
 500                 if (err < 0) {
 501                         pr_debug("bpf_probe: failed to apply perf probe events");
 502                         goto out;
 503                 }
 504
 505                 /*
 506                  * After probing, let's consider prologue, which
 507                  * adds program fetcher to BPF programs.
 508                  *
 509                  * hook_load_preprocessorr() hooks pre-processor
 510                  * to bpf_program, let it generate prologue
 511                  * dynamically during loading.
 512                  */
 513                 err = hook_load_preprocessor(prog);
 514                 if (err)
 515                         goto out;
 516         }
 517 out:
 518         return err < 0 ? err : 0;
 519 }
 520
 521 #define EVENTS_WRITE_BUFSIZE  4096
 522 int bpf__unprobe(struct bpf_object *obj)
 523 {
 524         int err, ret = 0;
 525         struct bpf_program *prog;
 526         struct bpf_prog_priv *priv;
 527
 528         bpf_object__for_each_program(prog, obj) {
 529                 int i;
 530
 531                 err = bpf_program__get_private(prog, (void **)&priv);
 532                 if (err || !priv)
 533                         continue;
 534
 535                 for (i = 0; i < priv->pev.ntevs; i++) {
 536                         struct probe_trace_event *tev = &priv->pev.tevs[i];
 537                         char name_buf[EVENTS_WRITE_BUFSIZE];
 538                         struct strfilter *delfilter;
 539
 540                         snprintf(name_buf, EVENTS_WRITE_BUFSIZE,
 541                                  "%s:%s", tev->group, tev->event);
 542                         name_buf[EVENTS_WRITE_BUFSIZE - 1] = '\0';
 543
 544                         delfilter = strfilter__new(name_buf, NULL);
 545                         if (!delfilter) {
 546                                 pr_debug("Failed to create filter for unprobing\n");
 547                                 ret = -ENOMEM;
 548                                 continue;
 549                         }
 550
 551                         err = del_perf_probe_events(delfilter);
 552                         strfilter__delete(delfilter);
 553                         if (err) {
 554                                 pr_debug("Failed to delete %s\n", name_buf);
 555                                 ret = err;
 556                                 continue;
 557                         }
 558                 }
 559         }
 560         return ret;
 561 }
 562
 563 int bpf__load(struct bpf_object *obj)
 564 {
 565         int err;
 566
 567         err = bpf_object__load(obj);
 568         if (err) {
 569                 pr_debug("bpf: load objects failed\n");
 570                 return err;
 571         }
 572         return 0;
 573 }
 574
 575 int bpf__foreach_tev(struct bpf_object *obj,
 576                      bpf_prog_iter_callback_t func,
 577                      void *arg)
 578 {
 579         struct bpf_program *prog;
 580         int err;
 581
 582         bpf_object__for_each_program(prog, obj) {
 583                 struct probe_trace_event *tev;
 584                 struct perf_probe_event *pev;
 585                 struct bpf_prog_priv *priv;
 586                 int i, fd;
 587
 588                 err = bpf_program__get_private(prog,
 589                                 (void **)&priv);
 590                 if (err || !priv) {
 591                         pr_debug("bpf: failed to get private field\n");
 592                         return -BPF_LOADER_ERRNO__INTERNAL;
 593                 }
 594
 595                 pev = &priv->pev;
 596                 for (i = 0; i < pev->ntevs; i++) {
 597                         tev = &pev->tevs[i];
 598
 599                         if (priv->need_prologue)
 600                                 fd = bpf_program__nth_fd(prog, i);
 601                         else
 602                                 fd = bpf_program__fd(prog);
 603
 604                         if (fd < 0) {
 605                                 pr_debug("bpf: failed to get file descriptor\n");
 606                                 return fd;
 607                         }
 608
 609                         err = (*func)(tev, fd, arg);
 610                         if (err) {
 611                                 pr_debug("bpf: call back failed, stop iterate\n");
 612                                 return err;
 613                         }
 614                 }
 615         }
 616         return 0;
 617 }
 618
 619 #define ERRNO_OFFSET(e)         ((e) - __BPF_LOADER_ERRNO__START)
 620 #define ERRCODE_OFFSET(c)       ERRNO_OFFSET(BPF_LOADER_ERRNO__##c)
 621 #define NR_ERRNO        (__BPF_LOADER_ERRNO__END - __BPF_LOADER_ERRNO__START)
 622
 623 static const char *bpf_loader_strerror_table[NR_ERRNO] = {
 624         [ERRCODE_OFFSET(CONFIG)]        = "Invalid config string",
 625         [ERRCODE_OFFSET(GROUP)]         = "Invalid group name",
 626         [ERRCODE_OFFSET(EVENTNAME)]     = "No event name found in config string",
 627         [ERRCODE_OFFSET(INTERNAL)]      = "BPF loader internal error",
 628         [ERRCODE_OFFSET(COMPILE)]       = "Error when compiling BPF scriptlet",
 629         [ERRCODE_OFFSET(CONFIG_TERM)]   = "Invalid config term in config string",
 630         [ERRCODE_OFFSET(PROLOGUE)]      = "Failed to generate prologue",
 631         [ERRCODE_OFFSET(PROLOGUE2BIG)]  = "Prologue too big for program",
 632         [ERRCODE_OFFSET(PROLOGUEOOB)]   = "Offset out of bound for prologue",
 633 };
 634
 635 static int
 636 bpf_loader_strerror(int err, char *buf, size_t size)
 637 {
 638         char sbuf[STRERR_BUFSIZE];
 639         const char *msg;
 640
 641         if (!buf || !size)
 642                 return -1;
 643
 644         err = err > 0 ? err : -err;
 645
 646         if (err >= __LIBBPF_ERRNO__START)
 647                 return libbpf_strerror(err, buf, size);
 648
 649         if (err >= __BPF_LOADER_ERRNO__START && err < __BPF_LOADER_ERRNO__END) {
 650                 msg = bpf_loader_strerror_table[ERRNO_OFFSET(err)];
 651                 snprintf(buf, size, "%s", msg);
 652                 buf[size - 1] = '\0';
 653                 return 0;
 654         }
 655
 656         if (err >= __BPF_LOADER_ERRNO__END)
 657                 snprintf(buf, size, "Unknown bpf loader error %d", err);
 658         else
 659                 snprintf(buf, size, "%s",
 660                          strerror_r(err, sbuf, sizeof(sbuf)));
 661
 662         buf[size - 1] = '\0';
 663         return -1;
 664 }
 665
 666 #define bpf__strerror_head(err, buf, size) \
 667         char sbuf[STRERR_BUFSIZE], *emsg;\
 668         if (!size)\
 669                 return 0;\
 670         if (err < 0)\
 671                 err = -err;\
 672         bpf_loader_strerror(err, sbuf, sizeof(sbuf));\
 673         emsg = sbuf;\
 674         switch (err) {\
 675         default:\
 676                 scnprintf(buf, size, "%s", emsg);\
 677                 break;
 678
 679 #define bpf__strerror_entry(val, fmt...)\
 680         case val: {\
 681                 scnprintf(buf, size, fmt);\
 682                 break;\
 683         }
 684
 685 #define bpf__strerror_end(buf, size)\
 686         }\
 687         buf[size - 1] = '\0';
 688
 689 int bpf__strerror_prepare_load(const char *filename, bool source,
 690                                int err, char *buf, size_t size)
 691 {
 692         size_t n;
 693         int ret;
 694
 695         n = snprintf(buf, size, "Failed to load %s%s: ",
 696                          filename, source ? " from source" : "");
 697         if (n >= size) {
 698                 buf[size - 1] = '\0';
 699                 return 0;
 700         }
 701         buf += n;
 702         size -= n;
 703
 704         ret = bpf_loader_strerror(err, buf, size);
 705         buf[size - 1] = '\0';
 706         return ret;
 707 }
 708
 709 int bpf__strerror_probe(struct bpf_object *obj __maybe_unused,
 710                         int err, char *buf, size_t size)
 711 {
 712         bpf__strerror_head(err, buf, size);
 713         case BPF_LOADER_ERRNO__CONFIG_TERM: {
 714                 scnprintf(buf, size, "%s (add -v to see detail)", emsg);
 715                 break;
 716         }
 717         bpf__strerror_entry(EEXIST, "Probe point exist. Try 'perf probe -d \"*\"' and set 'force=yes'");
 718         bpf__strerror_entry(EACCES, "You need to be root");
 719         bpf__strerror_entry(EPERM, "You need to be root, and /proc/sys/kernel/kptr_restrict should be 0");
 720         bpf__strerror_entry(ENOENT, "You need to check probing points in BPF file");
 721         bpf__strerror_end(buf, size);
 722         return 0;
 723 }
 724
 725 int bpf__strerror_load(struct bpf_object *obj,
 726                        int err, char *buf, size_t size)
 727 {
 728         bpf__strerror_head(err, buf, size);
 729         case LIBBPF_ERRNO__KVER: {
 730                 unsigned int obj_kver = bpf_object__get_kversion(obj);
 731                 unsigned int real_kver;
 732
 733                 if (fetch_kernel_version(&real_kver, NULL, 0)) {
 734                         scnprintf(buf, size, "Unable to fetch kernel version");
 735                         break;
 736                 }
 737
 738                 if (obj_kver != real_kver) {
 739                         scnprintf(buf, size,
 740                                   "'version' ("KVER_FMT") doesn't match running kernel ("KVER_FMT")",
 741                                   KVER_PARAM(obj_kver),
 742                                   KVER_PARAM(real_kver));
 743                         break;
 744                 }
 745
 746                 scnprintf(buf, size, "Failed to load program for unknown reason");
 747                 break;
 748         }
 749         bpf__strerror_end(buf, size);
 750         return 0;
 751 }