1 // SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
2 /*
3 * BPF static linker
4 *
5 * Copyright (c) 2021 Facebook
6 */
7 #include <stdbool.h>
8 #include <stddef.h>
9 #include <stdio.h>
10 #include <stdlib.h>
11 #include <string.h>
12 #include <unistd.h>
13 #include <errno.h>
14 #include <linux/err.h>
15 #include <linux/btf.h>
16 #include <elf.h>
17 #include <libelf.h>
18 #include <fcntl.h>
19 #include "libbpf.h"
20 #include "btf.h"
21 #include "libbpf_internal.h"
22 #include "strset.h"
23
24 #define BTF_EXTERN_SEC ".extern"
25
26 struct src_sec {
27 const char *sec_name;
28 /* positional (not necessarily ELF) index in an array of sections */
29 int id;
30 /* positional (not necessarily ELF) index of a matching section in a final object file */
31 int dst_id;
32 /* section data offset in a matching output section */
33 int dst_off;
34 /* whether section is omitted from the final ELF file */
35 bool skipped;
36 /* whether section is an ephemeral section, not mapped to an ELF section */
37 bool ephemeral;
38
39 /* ELF info */
40 size_t sec_idx;
41 Elf_Scn *scn;
42 Elf64_Shdr *shdr;
43 Elf_Data *data;
44
45 /* corresponding BTF DATASEC type ID */
46 int sec_type_id;
47 };
48
49 struct src_obj {
50 const char *filename;
51 int fd;
52 Elf *elf;
53 /* Section header strings section index */
54 size_t shstrs_sec_idx;
55 /* SYMTAB section index */
56 size_t symtab_sec_idx;
57
58 struct btf *btf;
59 struct btf_ext *btf_ext;
60
61 /* List of sections (including ephemeral). Slot zero is unused. */
62 struct src_sec *secs;
63 int sec_cnt;
64
65 /* mapping of symbol indices from src to dst ELF */
66 int *sym_map;
67 /* mapping from the src BTF type IDs to dst ones */
68 int *btf_type_map;
69 };
70
71 /* single .BTF.ext data section */
72 struct btf_ext_sec_data {
73 size_t rec_cnt;
74 __u32 rec_sz;
75 void *recs;
76 };
77
78 struct glob_sym {
79 /* ELF symbol index */
80 int sym_idx;
81 /* associated section id for .ksyms, .kconfig, etc, but not .extern */
82 int sec_id;
83 /* extern name offset in STRTAB */
84 int name_off;
85 /* optional associated BTF type ID */
86 int btf_id;
87 /* BTF type ID to which VAR/FUNC type is pointing to; used for
88 * rewriting types when extern VAR/FUNC is resolved to a concrete
89 * definition
90 */
91 int underlying_btf_id;
92 /* sec_var index in the corresponding dst_sec, if exists */
93 int var_idx;
94
95 /* extern or resolved/global symbol */
96 bool is_extern;
97 /* weak or strong symbol, never goes back from strong to weak */
98 bool is_weak;
99 };
100
101 struct dst_sec {
102 char *sec_name;
103 /* positional (not necessarily ELF) index in an array of sections */
104 int id;
105
106 bool ephemeral;
107
108 /* ELF info */
109 size_t sec_idx;
110 Elf_Scn *scn;
111 Elf64_Shdr *shdr;
112 Elf_Data *data;
113
114 /* final output section size */
115 int sec_sz;
116 /* final output contents of the section */
117 void *raw_data;
118
119 /* corresponding STT_SECTION symbol index in SYMTAB */
120 int sec_sym_idx;
121
122 /* section's DATASEC variable info, emitted on BTF finalization */
123 bool has_btf;
124 int sec_var_cnt;
125 struct btf_var_secinfo *sec_vars;
126
127 /* section's .BTF.ext data */
128 struct btf_ext_sec_data func_info;
129 struct btf_ext_sec_data line_info;
130 struct btf_ext_sec_data core_relo_info;
131 };
132
133 struct bpf_linker {
134 char *filename;
135 int fd;
136 Elf *elf;
137 Elf64_Ehdr *elf_hdr;
138
139 /* Output sections metadata */
140 struct dst_sec *secs;
141 int sec_cnt;
142
143 struct strset *strtab_strs; /* STRTAB unique strings */
144 size_t strtab_sec_idx; /* STRTAB section index */
145 size_t symtab_sec_idx; /* SYMTAB section index */
146
147 struct btf *btf;
148 struct btf_ext *btf_ext;
149
150 /* global (including extern) ELF symbols */
151 int glob_sym_cnt;
152 struct glob_sym *glob_syms;
153 };
154
155 #define pr_warn_elf(fmt, ...) \
156 libbpf_print(LIBBPF_WARN, "libbpf: " fmt ": %s\n", ##__VA_ARGS__, elf_errmsg(-1))
157
158 static int init_output_elf(struct bpf_linker *linker, const char *file);
159
160 static int linker_load_obj_file(struct bpf_linker *linker, const char *filename,
161 const struct bpf_linker_file_opts *opts,
162 struct src_obj *obj);
163 static int linker_sanity_check_elf(struct src_obj *obj);
164 static int linker_sanity_check_elf_symtab(struct src_obj *obj, struct src_sec *sec);
165 static int linker_sanity_check_elf_relos(struct src_obj *obj, struct src_sec *sec);
166 static int linker_sanity_check_btf(struct src_obj *obj);
167 static int linker_sanity_check_btf_ext(struct src_obj *obj);
168 static int linker_fixup_btf(struct src_obj *obj);
169 static int linker_append_sec_data(struct bpf_linker *linker, struct src_obj *obj);
170 static int linker_append_elf_syms(struct bpf_linker *linker, struct src_obj *obj);
171 static int linker_append_elf_sym(struct bpf_linker *linker, struct src_obj *obj,
172 Elf64_Sym *sym, const char *sym_name, int src_sym_idx);
173 static int linker_append_elf_relos(struct bpf_linker *linker, struct src_obj *obj);
174 static int linker_append_btf(struct bpf_linker *linker, struct src_obj *obj);
175 static int linker_append_btf_ext(struct bpf_linker *linker, struct src_obj *obj);
176
177 static int finalize_btf(struct bpf_linker *linker);
178 static int finalize_btf_ext(struct bpf_linker *linker);
179
bpf_linker__free(struct bpf_linker * linker)180 void bpf_linker__free(struct bpf_linker *linker)
181 {
182 int i;
183
184 if (!linker)
185 return;
186
187 free(linker->filename);
188
189 if (linker->elf)
190 elf_end(linker->elf);
191
192 if (linker->fd >= 0)
193 close(linker->fd);
194
195 strset__free(linker->strtab_strs);
196
197 btf__free(linker->btf);
198 btf_ext__free(linker->btf_ext);
199
200 for (i = 1; i < linker->sec_cnt; i++) {
201 struct dst_sec *sec = &linker->secs[i];
202
203 free(sec->sec_name);
204 free(sec->raw_data);
205 free(sec->sec_vars);
206
207 free(sec->func_info.recs);
208 free(sec->line_info.recs);
209 free(sec->core_relo_info.recs);
210 }
211 free(linker->secs);
212
213 free(linker->glob_syms);
214 free(linker);
215 }
216
bpf_linker__new(const char * filename,struct bpf_linker_opts * opts)217 struct bpf_linker *bpf_linker__new(const char *filename, struct bpf_linker_opts *opts)
218 {
219 struct bpf_linker *linker;
220 int err;
221
222 if (!OPTS_VALID(opts, bpf_linker_opts))
223 return errno = EINVAL, NULL;
224
225 if (elf_version(EV_CURRENT) == EV_NONE) {
226 pr_warn_elf("libelf initialization failed");
227 return errno = EINVAL, NULL;
228 }
229
230 linker = calloc(1, sizeof(*linker));
231 if (!linker)
232 return errno = ENOMEM, NULL;
233
234 linker->fd = -1;
235
236 err = init_output_elf(linker, filename);
237 if (err)
238 goto err_out;
239
240 return linker;
241
242 err_out:
243 bpf_linker__free(linker);
244 return errno = -err, NULL;
245 }
246
add_dst_sec(struct bpf_linker * linker,const char * sec_name)247 static struct dst_sec *add_dst_sec(struct bpf_linker *linker, const char *sec_name)
248 {
249 struct dst_sec *secs = linker->secs, *sec;
250 size_t new_cnt = linker->sec_cnt ? linker->sec_cnt + 1 : 2;
251
252 secs = libbpf_reallocarray(secs, new_cnt, sizeof(*secs));
253 if (!secs)
254 return NULL;
255
256 /* zero out newly allocated memory */
257 memset(secs + linker->sec_cnt, 0, (new_cnt - linker->sec_cnt) * sizeof(*secs));
258
259 linker->secs = secs;
260 linker->sec_cnt = new_cnt;
261
262 sec = &linker->secs[new_cnt - 1];
263 sec->id = new_cnt - 1;
264 sec->sec_name = strdup(sec_name);
265 if (!sec->sec_name)
266 return NULL;
267
268 return sec;
269 }
270
add_new_sym(struct bpf_linker * linker,size_t * sym_idx)271 static Elf64_Sym *add_new_sym(struct bpf_linker *linker, size_t *sym_idx)
272 {
273 struct dst_sec *symtab = &linker->secs[linker->symtab_sec_idx];
274 Elf64_Sym *syms, *sym;
275 size_t sym_cnt = symtab->sec_sz / sizeof(*sym);
276
277 syms = libbpf_reallocarray(symtab->raw_data, sym_cnt + 1, sizeof(*sym));
278 if (!syms)
279 return NULL;
280
281 sym = &syms[sym_cnt];
282 memset(sym, 0, sizeof(*sym));
283
284 symtab->raw_data = syms;
285 symtab->sec_sz += sizeof(*sym);
286 symtab->shdr->sh_size += sizeof(*sym);
287 symtab->data->d_size += sizeof(*sym);
288
289 if (sym_idx)
290 *sym_idx = sym_cnt;
291
292 return sym;
293 }
294
init_output_elf(struct bpf_linker * linker,const char * file)295 static int init_output_elf(struct bpf_linker *linker, const char *file)
296 {
297 int err, str_off;
298 Elf64_Sym *init_sym;
299 struct dst_sec *sec;
300
301 linker->filename = strdup(file);
302 if (!linker->filename)
303 return -ENOMEM;
304
305 linker->fd = open(file, O_WRONLY | O_CREAT | O_TRUNC | O_CLOEXEC, 0644);
306 if (linker->fd < 0) {
307 err = -errno;
308 pr_warn("failed to create '%s': %d\n", file, err);
309 return err;
310 }
311
312 linker->elf = elf_begin(linker->fd, ELF_C_WRITE, NULL);
313 if (!linker->elf) {
314 pr_warn_elf("failed to create ELF object");
315 return -EINVAL;
316 }
317
318 /* ELF header */
319 linker->elf_hdr = elf64_newehdr(linker->elf);
320 if (!linker->elf_hdr) {
321 pr_warn_elf("failed to create ELF header");
322 return -EINVAL;
323 }
324
325 linker->elf_hdr->e_machine = EM_BPF;
326 linker->elf_hdr->e_type = ET_REL;
327 #if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
328 linker->elf_hdr->e_ident[EI_DATA] = ELFDATA2LSB;
329 #elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
330 linker->elf_hdr->e_ident[EI_DATA] = ELFDATA2MSB;
331 #else
332 #error "Unknown __BYTE_ORDER__"
333 #endif
334
335 /* STRTAB */
336 /* initialize strset with an empty string to conform to ELF */
337 linker->strtab_strs = strset__new(INT_MAX, "", sizeof(""));
338 if (libbpf_get_error(linker->strtab_strs))
339 return libbpf_get_error(linker->strtab_strs);
340
341 sec = add_dst_sec(linker, ".strtab");
342 if (!sec)
343 return -ENOMEM;
344
345 sec->scn = elf_newscn(linker->elf);
346 if (!sec->scn) {
347 pr_warn_elf("failed to create STRTAB section");
348 return -EINVAL;
349 }
350
351 sec->shdr = elf64_getshdr(sec->scn);
352 if (!sec->shdr)
353 return -EINVAL;
354
355 sec->data = elf_newdata(sec->scn);
356 if (!sec->data) {
357 pr_warn_elf("failed to create STRTAB data");
358 return -EINVAL;
359 }
360
361 str_off = strset__add_str(linker->strtab_strs, sec->sec_name);
362 if (str_off < 0)
363 return str_off;
364
365 sec->sec_idx = elf_ndxscn(sec->scn);
366 linker->elf_hdr->e_shstrndx = sec->sec_idx;
367 linker->strtab_sec_idx = sec->sec_idx;
368
369 sec->shdr->sh_name = str_off;
370 sec->shdr->sh_type = SHT_STRTAB;
371 sec->shdr->sh_flags = SHF_STRINGS;
372 sec->shdr->sh_offset = 0;
373 sec->shdr->sh_link = 0;
374 sec->shdr->sh_info = 0;
375 sec->shdr->sh_addralign = 1;
376 sec->shdr->sh_size = sec->sec_sz = 0;
377 sec->shdr->sh_entsize = 0;
378
379 /* SYMTAB */
380 sec = add_dst_sec(linker, ".symtab");
381 if (!sec)
382 return -ENOMEM;
383
384 sec->scn = elf_newscn(linker->elf);
385 if (!sec->scn) {
386 pr_warn_elf("failed to create SYMTAB section");
387 return -EINVAL;
388 }
389
390 sec->shdr = elf64_getshdr(sec->scn);
391 if (!sec->shdr)
392 return -EINVAL;
393
394 sec->data = elf_newdata(sec->scn);
395 if (!sec->data) {
396 pr_warn_elf("failed to create SYMTAB data");
397 return -EINVAL;
398 }
399
400 str_off = strset__add_str(linker->strtab_strs, sec->sec_name);
401 if (str_off < 0)
402 return str_off;
403
404 sec->sec_idx = elf_ndxscn(sec->scn);
405 linker->symtab_sec_idx = sec->sec_idx;
406
407 sec->shdr->sh_name = str_off;
408 sec->shdr->sh_type = SHT_SYMTAB;
409 sec->shdr->sh_flags = 0;
410 sec->shdr->sh_offset = 0;
411 sec->shdr->sh_link = linker->strtab_sec_idx;
412 /* sh_info should be one greater than the index of the last local
413 * symbol (i.e., binding is STB_LOCAL). But why and who cares?
414 */
415 sec->shdr->sh_info = 0;
416 sec->shdr->sh_addralign = 8;
417 sec->shdr->sh_entsize = sizeof(Elf64_Sym);
418
419 /* .BTF */
420 linker->btf = btf__new_empty();
421 err = libbpf_get_error(linker->btf);
422 if (err)
423 return err;
424
425 /* add the special all-zero symbol */
426 init_sym = add_new_sym(linker, NULL);
427 if (!init_sym)
428 return -EINVAL;
429
430 init_sym->st_name = 0;
431 init_sym->st_info = 0;
432 init_sym->st_other = 0;
433 init_sym->st_shndx = SHN_UNDEF;
434 init_sym->st_value = 0;
435 init_sym->st_size = 0;
436
437 return 0;
438 }
439
bpf_linker__add_file(struct bpf_linker * linker,const char * filename,const struct bpf_linker_file_opts * opts)440 int bpf_linker__add_file(struct bpf_linker *linker, const char *filename,
441 const struct bpf_linker_file_opts *opts)
442 {
443 struct src_obj obj = {};
444 int err = 0;
445
446 if (!OPTS_VALID(opts, bpf_linker_file_opts))
447 return libbpf_err(-EINVAL);
448
449 if (!linker->elf)
450 return libbpf_err(-EINVAL);
451
452 err = err ?: linker_load_obj_file(linker, filename, opts, &obj);
453 err = err ?: linker_append_sec_data(linker, &obj);
454 err = err ?: linker_append_elf_syms(linker, &obj);
455 err = err ?: linker_append_elf_relos(linker, &obj);
456 err = err ?: linker_append_btf(linker, &obj);
457 err = err ?: linker_append_btf_ext(linker, &obj);
458
459 /* free up src_obj resources */
460 free(obj.btf_type_map);
461 btf__free(obj.btf);
462 btf_ext__free(obj.btf_ext);
463 free(obj.secs);
464 free(obj.sym_map);
465 if (obj.elf)
466 elf_end(obj.elf);
467 if (obj.fd >= 0)
468 close(obj.fd);
469
470 return libbpf_err(err);
471 }
472
is_dwarf_sec_name(const char * name)473 static bool is_dwarf_sec_name(const char *name)
474 {
475 /* approximation, but the actual list is too long */
476 return strncmp(name, ".debug_", sizeof(".debug_") - 1) == 0;
477 }
478
is_ignored_sec(struct src_sec * sec)479 static bool is_ignored_sec(struct src_sec *sec)
480 {
481 Elf64_Shdr *shdr = sec->shdr;
482 const char *name = sec->sec_name;
483
484 /* no special handling of .strtab */
485 if (shdr->sh_type == SHT_STRTAB)
486 return true;
487
488 /* ignore .llvm_addrsig section as well */
489 if (shdr->sh_type == SHT_LLVM_ADDRSIG)
490 return true;
491
492 /* no subprograms will lead to an empty .text section, ignore it */
493 if (shdr->sh_type == SHT_PROGBITS && shdr->sh_size == 0 &&
494 strcmp(sec->sec_name, ".text") == 0)
495 return true;
496
497 /* DWARF sections */
498 if (is_dwarf_sec_name(sec->sec_name))
499 return true;
500
501 if (strncmp(name, ".rel", sizeof(".rel") - 1) == 0) {
502 name += sizeof(".rel") - 1;
503 /* DWARF section relocations */
504 if (is_dwarf_sec_name(name))
505 return true;
506
507 /* .BTF and .BTF.ext don't need relocations */
508 if (strcmp(name, BTF_ELF_SEC) == 0 ||
509 strcmp(name, BTF_EXT_ELF_SEC) == 0)
510 return true;
511 }
512
513 return false;
514 }
515
add_src_sec(struct src_obj * obj,const char * sec_name)516 static struct src_sec *add_src_sec(struct src_obj *obj, const char *sec_name)
517 {
518 struct src_sec *secs = obj->secs, *sec;
519 size_t new_cnt = obj->sec_cnt ? obj->sec_cnt + 1 : 2;
520
521 secs = libbpf_reallocarray(secs, new_cnt, sizeof(*secs));
522 if (!secs)
523 return NULL;
524
525 /* zero out newly allocated memory */
526 memset(secs + obj->sec_cnt, 0, (new_cnt - obj->sec_cnt) * sizeof(*secs));
527
528 obj->secs = secs;
529 obj->sec_cnt = new_cnt;
530
531 sec = &obj->secs[new_cnt - 1];
532 sec->id = new_cnt - 1;
533 sec->sec_name = sec_name;
534
535 return sec;
536 }
537
linker_load_obj_file(struct bpf_linker * linker,const char * filename,const struct bpf_linker_file_opts * opts,struct src_obj * obj)538 static int linker_load_obj_file(struct bpf_linker *linker, const char *filename,
539 const struct bpf_linker_file_opts *opts,
540 struct src_obj *obj)
541 {
542 #if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
543 const int host_endianness = ELFDATA2LSB;
544 #elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
545 const int host_endianness = ELFDATA2MSB;
546 #else
547 #error "Unknown __BYTE_ORDER__"
548 #endif
549 int err = 0;
550 Elf_Scn *scn;
551 Elf_Data *data;
552 Elf64_Ehdr *ehdr;
553 Elf64_Shdr *shdr;
554 struct src_sec *sec;
555
556 pr_debug("linker: adding object file '%s'...\n", filename);
557
558 obj->filename = filename;
559
560 obj->fd = open(filename, O_RDONLY | O_CLOEXEC);
561 if (obj->fd < 0) {
562 err = -errno;
563 pr_warn("failed to open file '%s': %d\n", filename, err);
564 return err;
565 }
566 obj->elf = elf_begin(obj->fd, ELF_C_READ_MMAP, NULL);
567 if (!obj->elf) {
568 err = -errno;
569 pr_warn_elf("failed to parse ELF file '%s'", filename);
570 return err;
571 }
572
573 /* Sanity check ELF file high-level properties */
574 ehdr = elf64_getehdr(obj->elf);
575 if (!ehdr) {
576 err = -errno;
577 pr_warn_elf("failed to get ELF header for %s", filename);
578 return err;
579 }
580 if (ehdr->e_ident[EI_DATA] != host_endianness) {
581 err = -EOPNOTSUPP;
582 pr_warn_elf("unsupported byte order of ELF file %s", filename);
583 return err;
584 }
585 if (ehdr->e_type != ET_REL
586 || ehdr->e_machine != EM_BPF
587 || ehdr->e_ident[EI_CLASS] != ELFCLASS64) {
588 err = -EOPNOTSUPP;
589 pr_warn_elf("unsupported kind of ELF file %s", filename);
590 return err;
591 }
592
593 if (elf_getshdrstrndx(obj->elf, &obj->shstrs_sec_idx)) {
594 err = -errno;
595 pr_warn_elf("failed to get SHSTRTAB section index for %s", filename);
596 return err;
597 }
598
599 scn = NULL;
600 while ((scn = elf_nextscn(obj->elf, scn)) != NULL) {
601 size_t sec_idx = elf_ndxscn(scn);
602 const char *sec_name;
603
604 shdr = elf64_getshdr(scn);
605 if (!shdr) {
606 err = -errno;
607 pr_warn_elf("failed to get section #%zu header for %s",
608 sec_idx, filename);
609 return err;
610 }
611
612 sec_name = elf_strptr(obj->elf, obj->shstrs_sec_idx, shdr->sh_name);
613 if (!sec_name) {
614 err = -errno;
615 pr_warn_elf("failed to get section #%zu name for %s",
616 sec_idx, filename);
617 return err;
618 }
619
620 data = elf_getdata(scn, 0);
621 if (!data) {
622 err = -errno;
623 pr_warn_elf("failed to get section #%zu (%s) data from %s",
624 sec_idx, sec_name, filename);
625 return err;
626 }
627
628 sec = add_src_sec(obj, sec_name);
629 if (!sec)
630 return -ENOMEM;
631
632 sec->scn = scn;
633 sec->shdr = shdr;
634 sec->data = data;
635 sec->sec_idx = elf_ndxscn(scn);
636
637 if (is_ignored_sec(sec)) {
638 sec->skipped = true;
639 continue;
640 }
641
642 switch (shdr->sh_type) {
643 case SHT_SYMTAB:
644 if (obj->symtab_sec_idx) {
645 err = -EOPNOTSUPP;
646 pr_warn("multiple SYMTAB sections found, not supported\n");
647 return err;
648 }
649 obj->symtab_sec_idx = sec_idx;
650 break;
651 case SHT_STRTAB:
652 /* we'll construct our own string table */
653 break;
654 case SHT_PROGBITS:
655 if (strcmp(sec_name, BTF_ELF_SEC) == 0) {
656 obj->btf = btf__new(data->d_buf, shdr->sh_size);
657 err = libbpf_get_error(obj->btf);
658 if (err) {
659 pr_warn("failed to parse .BTF from %s: %d\n", filename, err);
660 return err;
661 }
662 sec->skipped = true;
663 continue;
664 }
665 if (strcmp(sec_name, BTF_EXT_ELF_SEC) == 0) {
666 obj->btf_ext = btf_ext__new(data->d_buf, shdr->sh_size);
667 err = libbpf_get_error(obj->btf_ext);
668 if (err) {
669 pr_warn("failed to parse .BTF.ext from '%s': %d\n", filename, err);
670 return err;
671 }
672 sec->skipped = true;
673 continue;
674 }
675
676 /* data & code */
677 break;
678 case SHT_NOBITS:
679 /* BSS */
680 break;
681 case SHT_REL:
682 /* relocations */
683 break;
684 default:
685 pr_warn("unrecognized section #%zu (%s) in %s\n",
686 sec_idx, sec_name, filename);
687 err = -EINVAL;
688 return err;
689 }
690 }
691
692 err = err ?: linker_sanity_check_elf(obj);
693 err = err ?: linker_sanity_check_btf(obj);
694 err = err ?: linker_sanity_check_btf_ext(obj);
695 err = err ?: linker_fixup_btf(obj);
696
697 return err;
698 }
699
linker_sanity_check_elf(struct src_obj * obj)700 static int linker_sanity_check_elf(struct src_obj *obj)
701 {
702 struct src_sec *sec;
703 int i, err;
704
705 if (!obj->symtab_sec_idx) {
706 pr_warn("ELF is missing SYMTAB section in %s\n", obj->filename);
707 return -EINVAL;
708 }
709 if (!obj->shstrs_sec_idx) {
710 pr_warn("ELF is missing section headers STRTAB section in %s\n", obj->filename);
711 return -EINVAL;
712 }
713
714 for (i = 1; i < obj->sec_cnt; i++) {
715 sec = &obj->secs[i];
716
717 if (sec->sec_name[0] == '\0') {
718 pr_warn("ELF section #%zu has empty name in %s\n", sec->sec_idx, obj->filename);
719 return -EINVAL;
720 }
721
722 if (sec->shdr->sh_addralign && !is_pow_of_2(sec->shdr->sh_addralign))
723 return -EINVAL;
724 if (sec->shdr->sh_addralign != sec->data->d_align)
725 return -EINVAL;
726
727 if (sec->shdr->sh_size != sec->data->d_size)
728 return -EINVAL;
729
730 switch (sec->shdr->sh_type) {
731 case SHT_SYMTAB:
732 err = linker_sanity_check_elf_symtab(obj, sec);
733 if (err)
734 return err;
735 break;
736 case SHT_STRTAB:
737 break;
738 case SHT_PROGBITS:
739 if (sec->shdr->sh_flags & SHF_EXECINSTR) {
740 if (sec->shdr->sh_size % sizeof(struct bpf_insn) != 0)
741 return -EINVAL;
742 }
743 break;
744 case SHT_NOBITS:
745 break;
746 case SHT_REL:
747 err = linker_sanity_check_elf_relos(obj, sec);
748 if (err)
749 return err;
750 break;
751 case SHT_LLVM_ADDRSIG:
752 break;
753 default:
754 pr_warn("ELF section #%zu (%s) has unrecognized type %zu in %s\n",
755 sec->sec_idx, sec->sec_name, (size_t)sec->shdr->sh_type, obj->filename);
756 return -EINVAL;
757 }
758 }
759
760 return 0;
761 }
762
linker_sanity_check_elf_symtab(struct src_obj * obj,struct src_sec * sec)763 static int linker_sanity_check_elf_symtab(struct src_obj *obj, struct src_sec *sec)
764 {
765 struct src_sec *link_sec;
766 Elf64_Sym *sym;
767 int i, n;
768
769 if (sec->shdr->sh_entsize != sizeof(Elf64_Sym))
770 return -EINVAL;
771 if (sec->shdr->sh_size % sec->shdr->sh_entsize != 0)
772 return -EINVAL;
773
774 if (!sec->shdr->sh_link || sec->shdr->sh_link >= obj->sec_cnt) {
775 pr_warn("ELF SYMTAB section #%zu points to missing STRTAB section #%zu in %s\n",
776 sec->sec_idx, (size_t)sec->shdr->sh_link, obj->filename);
777 return -EINVAL;
778 }
779 link_sec = &obj->secs[sec->shdr->sh_link];
780 if (link_sec->shdr->sh_type != SHT_STRTAB) {
781 pr_warn("ELF SYMTAB section #%zu points to invalid STRTAB section #%zu in %s\n",
782 sec->sec_idx, (size_t)sec->shdr->sh_link, obj->filename);
783 return -EINVAL;
784 }
785
786 n = sec->shdr->sh_size / sec->shdr->sh_entsize;
787 sym = sec->data->d_buf;
788 for (i = 0; i < n; i++, sym++) {
789 int sym_type = ELF64_ST_TYPE(sym->st_info);
790 int sym_bind = ELF64_ST_BIND(sym->st_info);
791 int sym_vis = ELF64_ST_VISIBILITY(sym->st_other);
792
793 if (i == 0) {
794 if (sym->st_name != 0 || sym->st_info != 0
795 || sym->st_other != 0 || sym->st_shndx != 0
796 || sym->st_value != 0 || sym->st_size != 0) {
797 pr_warn("ELF sym #0 is invalid in %s\n", obj->filename);
798 return -EINVAL;
799 }
800 continue;
801 }
802 if (sym_bind != STB_LOCAL && sym_bind != STB_GLOBAL && sym_bind != STB_WEAK) {
803 pr_warn("ELF sym #%d in section #%zu has unsupported symbol binding %d\n",
804 i, sec->sec_idx, sym_bind);
805 return -EINVAL;
806 }
807 if (sym_vis != STV_DEFAULT && sym_vis != STV_HIDDEN) {
808 pr_warn("ELF sym #%d in section #%zu has unsupported symbol visibility %d\n",
809 i, sec->sec_idx, sym_vis);
810 return -EINVAL;
811 }
812 if (sym->st_shndx == 0) {
813 if (sym_type != STT_NOTYPE || sym_bind == STB_LOCAL
814 || sym->st_value != 0 || sym->st_size != 0) {
815 pr_warn("ELF sym #%d is invalid extern symbol in %s\n",
816 i, obj->filename);
817
818 return -EINVAL;
819 }
820 continue;
821 }
822 if (sym->st_shndx < SHN_LORESERVE && sym->st_shndx >= obj->sec_cnt) {
823 pr_warn("ELF sym #%d in section #%zu points to missing section #%zu in %s\n",
824 i, sec->sec_idx, (size_t)sym->st_shndx, obj->filename);
825 return -EINVAL;
826 }
827 if (sym_type == STT_SECTION) {
828 if (sym->st_value != 0)
829 return -EINVAL;
830 continue;
831 }
832 }
833
834 return 0;
835 }
836
linker_sanity_check_elf_relos(struct src_obj * obj,struct src_sec * sec)837 static int linker_sanity_check_elf_relos(struct src_obj *obj, struct src_sec *sec)
838 {
839 struct src_sec *link_sec, *sym_sec;
840 Elf64_Rel *relo;
841 int i, n;
842
843 if (sec->shdr->sh_entsize != sizeof(Elf64_Rel))
844 return -EINVAL;
845 if (sec->shdr->sh_size % sec->shdr->sh_entsize != 0)
846 return -EINVAL;
847
848 /* SHT_REL's sh_link should point to SYMTAB */
849 if (sec->shdr->sh_link != obj->symtab_sec_idx) {
850 pr_warn("ELF relo section #%zu points to invalid SYMTAB section #%zu in %s\n",
851 sec->sec_idx, (size_t)sec->shdr->sh_link, obj->filename);
852 return -EINVAL;
853 }
854
855 /* SHT_REL's sh_info points to relocated section */
856 if (!sec->shdr->sh_info || sec->shdr->sh_info >= obj->sec_cnt) {
857 pr_warn("ELF relo section #%zu points to missing section #%zu in %s\n",
858 sec->sec_idx, (size_t)sec->shdr->sh_info, obj->filename);
859 return -EINVAL;
860 }
861 link_sec = &obj->secs[sec->shdr->sh_info];
862
863 /* .rel<secname> -> <secname> pattern is followed */
864 if (strncmp(sec->sec_name, ".rel", sizeof(".rel") - 1) != 0
865 || strcmp(sec->sec_name + sizeof(".rel") - 1, link_sec->sec_name) != 0) {
866 pr_warn("ELF relo section #%zu name has invalid name in %s\n",
867 sec->sec_idx, obj->filename);
868 return -EINVAL;
869 }
870
871 /* don't further validate relocations for ignored sections */
872 if (link_sec->skipped)
873 return 0;
874
875 /* relocatable section is data or instructions */
876 if (link_sec->shdr->sh_type != SHT_PROGBITS && link_sec->shdr->sh_type != SHT_NOBITS) {
877 pr_warn("ELF relo section #%zu points to invalid section #%zu in %s\n",
878 sec->sec_idx, (size_t)sec->shdr->sh_info, obj->filename);
879 return -EINVAL;
880 }
881
882 /* check sanity of each relocation */
883 n = sec->shdr->sh_size / sec->shdr->sh_entsize;
884 relo = sec->data->d_buf;
885 sym_sec = &obj->secs[obj->symtab_sec_idx];
886 for (i = 0; i < n; i++, relo++) {
887 size_t sym_idx = ELF64_R_SYM(relo->r_info);
888 size_t sym_type = ELF64_R_TYPE(relo->r_info);
889
890 if (sym_type != R_BPF_64_64 && sym_type != R_BPF_64_32 &&
891 sym_type != R_BPF_64_ABS64 && sym_type != R_BPF_64_ABS32) {
892 pr_warn("ELF relo #%d in section #%zu has unexpected type %zu in %s\n",
893 i, sec->sec_idx, sym_type, obj->filename);
894 return -EINVAL;
895 }
896
897 if (!sym_idx || sym_idx * sizeof(Elf64_Sym) >= sym_sec->shdr->sh_size) {
898 pr_warn("ELF relo #%d in section #%zu points to invalid symbol #%zu in %s\n",
899 i, sec->sec_idx, sym_idx, obj->filename);
900 return -EINVAL;
901 }
902
903 if (link_sec->shdr->sh_flags & SHF_EXECINSTR) {
904 if (relo->r_offset % sizeof(struct bpf_insn) != 0) {
905 pr_warn("ELF relo #%d in section #%zu points to missing symbol #%zu in %s\n",
906 i, sec->sec_idx, sym_idx, obj->filename);
907 return -EINVAL;
908 }
909 }
910 }
911
912 return 0;
913 }
914
check_btf_type_id(__u32 * type_id,void * ctx)915 static int check_btf_type_id(__u32 *type_id, void *ctx)
916 {
917 struct btf *btf = ctx;
918
919 if (*type_id >= btf__type_cnt(btf))
920 return -EINVAL;
921
922 return 0;
923 }
924
check_btf_str_off(__u32 * str_off,void * ctx)925 static int check_btf_str_off(__u32 *str_off, void *ctx)
926 {
927 struct btf *btf = ctx;
928 const char *s;
929
930 s = btf__str_by_offset(btf, *str_off);
931
932 if (!s)
933 return -EINVAL;
934
935 return 0;
936 }
937
linker_sanity_check_btf(struct src_obj * obj)938 static int linker_sanity_check_btf(struct src_obj *obj)
939 {
940 struct btf_type *t;
941 int i, n, err = 0;
942
943 if (!obj->btf)
944 return 0;
945
946 n = btf__type_cnt(obj->btf);
947 for (i = 1; i < n; i++) {
948 t = btf_type_by_id(obj->btf, i);
949
950 err = err ?: btf_type_visit_type_ids(t, check_btf_type_id, obj->btf);
951 err = err ?: btf_type_visit_str_offs(t, check_btf_str_off, obj->btf);
952 if (err)
953 return err;
954 }
955
956 return 0;
957 }
958
linker_sanity_check_btf_ext(struct src_obj * obj)959 static int linker_sanity_check_btf_ext(struct src_obj *obj)
960 {
961 int err = 0;
962
963 if (!obj->btf_ext)
964 return 0;
965
966 /* can't use .BTF.ext without .BTF */
967 if (!obj->btf)
968 return -EINVAL;
969
970 err = err ?: btf_ext_visit_type_ids(obj->btf_ext, check_btf_type_id, obj->btf);
971 err = err ?: btf_ext_visit_str_offs(obj->btf_ext, check_btf_str_off, obj->btf);
972 if (err)
973 return err;
974
975 return 0;
976 }
977
init_sec(struct bpf_linker * linker,struct dst_sec * dst_sec,struct src_sec * src_sec)978 static int init_sec(struct bpf_linker *linker, struct dst_sec *dst_sec, struct src_sec *src_sec)
979 {
980 Elf_Scn *scn;
981 Elf_Data *data;
982 Elf64_Shdr *shdr;
983 int name_off;
984
985 dst_sec->sec_sz = 0;
986 dst_sec->sec_idx = 0;
987 dst_sec->ephemeral = src_sec->ephemeral;
988
989 /* ephemeral sections are just thin section shells lacking most parts */
990 if (src_sec->ephemeral)
991 return 0;
992
993 scn = elf_newscn(linker->elf);
994 if (!scn)
995 return -ENOMEM;
996 data = elf_newdata(scn);
997 if (!data)
998 return -ENOMEM;
999 shdr = elf64_getshdr(scn);
1000 if (!shdr)
1001 return -ENOMEM;
1002
1003 dst_sec->scn = scn;
1004 dst_sec->shdr = shdr;
1005 dst_sec->data = data;
1006 dst_sec->sec_idx = elf_ndxscn(scn);
1007
1008 name_off = strset__add_str(linker->strtab_strs, src_sec->sec_name);
1009 if (name_off < 0)
1010 return name_off;
1011
1012 shdr->sh_name = name_off;
1013 shdr->sh_type = src_sec->shdr->sh_type;
1014 shdr->sh_flags = src_sec->shdr->sh_flags;
1015 shdr->sh_size = 0;
1016 /* sh_link and sh_info have different meaning for different types of
1017 * sections, so we leave it up to the caller code to fill them in, if
1018 * necessary
1019 */
1020 shdr->sh_link = 0;
1021 shdr->sh_info = 0;
1022 shdr->sh_addralign = src_sec->shdr->sh_addralign;
1023 shdr->sh_entsize = src_sec->shdr->sh_entsize;
1024
1025 data->d_type = src_sec->data->d_type;
1026 data->d_size = 0;
1027 data->d_buf = NULL;
1028 data->d_align = src_sec->data->d_align;
1029 data->d_off = 0;
1030
1031 return 0;
1032 }
1033
find_dst_sec_by_name(struct bpf_linker * linker,const char * sec_name)1034 static struct dst_sec *find_dst_sec_by_name(struct bpf_linker *linker, const char *sec_name)
1035 {
1036 struct dst_sec *sec;
1037 int i;
1038
1039 for (i = 1; i < linker->sec_cnt; i++) {
1040 sec = &linker->secs[i];
1041
1042 if (strcmp(sec->sec_name, sec_name) == 0)
1043 return sec;
1044 }
1045
1046 return NULL;
1047 }
1048
secs_match(struct dst_sec * dst,struct src_sec * src)1049 static bool secs_match(struct dst_sec *dst, struct src_sec *src)
1050 {
1051 if (dst->ephemeral || src->ephemeral)
1052 return true;
1053
1054 if (dst->shdr->sh_type != src->shdr->sh_type) {
1055 pr_warn("sec %s types mismatch\n", dst->sec_name);
1056 return false;
1057 }
1058 if (dst->shdr->sh_flags != src->shdr->sh_flags) {
1059 pr_warn("sec %s flags mismatch\n", dst->sec_name);
1060 return false;
1061 }
1062 if (dst->shdr->sh_entsize != src->shdr->sh_entsize) {
1063 pr_warn("sec %s entsize mismatch\n", dst->sec_name);
1064 return false;
1065 }
1066
1067 return true;
1068 }
1069
sec_content_is_same(struct dst_sec * dst_sec,struct src_sec * src_sec)1070 static bool sec_content_is_same(struct dst_sec *dst_sec, struct src_sec *src_sec)
1071 {
1072 if (dst_sec->sec_sz != src_sec->shdr->sh_size)
1073 return false;
1074 if (memcmp(dst_sec->raw_data, src_sec->data->d_buf, dst_sec->sec_sz) != 0)
1075 return false;
1076 return true;
1077 }
1078
extend_sec(struct bpf_linker * linker,struct dst_sec * dst,struct src_sec * src)1079 static int extend_sec(struct bpf_linker *linker, struct dst_sec *dst, struct src_sec *src)
1080 {
1081 void *tmp;
1082 size_t dst_align, src_align;
1083 size_t dst_align_sz, dst_final_sz;
1084 int err;
1085
1086 /* Ephemeral source section doesn't contribute anything to ELF
1087 * section data.
1088 */
1089 if (src->ephemeral)
1090 return 0;
1091
1092 /* Some sections (like .maps) can contain both externs (and thus be
1093 * ephemeral) and non-externs (map definitions). So it's possible that
1094 * it has to be "upgraded" from ephemeral to non-ephemeral when the
1095 * first non-ephemeral entity appears. In such case, we add ELF
1096 * section, data, etc.
1097 */
1098 if (dst->ephemeral) {
1099 err = init_sec(linker, dst, src);
1100 if (err)
1101 return err;
1102 }
1103
1104 dst_align = dst->shdr->sh_addralign;
1105 src_align = src->shdr->sh_addralign;
1106 if (dst_align == 0)
1107 dst_align = 1;
1108 if (dst_align < src_align)
1109 dst_align = src_align;
1110
1111 dst_align_sz = (dst->sec_sz + dst_align - 1) / dst_align * dst_align;
1112
1113 /* no need to re-align final size */
1114 dst_final_sz = dst_align_sz + src->shdr->sh_size;
1115
1116 if (src->shdr->sh_type != SHT_NOBITS) {
1117 tmp = realloc(dst->raw_data, dst_final_sz);
1118 /* If dst_align_sz == 0, realloc() behaves in a special way:
1119 * 1. When dst->raw_data is NULL it returns:
1120 * "either NULL or a pointer suitable to be passed to free()" [1].
1121 * 2. When dst->raw_data is not-NULL it frees dst->raw_data and returns NULL,
1122 * thus invalidating any "pointer suitable to be passed to free()" obtained
1123 * at step (1).
1124 *
1125 * The dst_align_sz > 0 check avoids error exit after (2), otherwise
1126 * dst->raw_data would be freed again in bpf_linker__free().
1127 *
1128 * [1] man 3 realloc
1129 */
1130 if (!tmp && dst_align_sz > 0)
1131 return -ENOMEM;
1132 dst->raw_data = tmp;
1133
1134 /* pad dst section, if it's alignment forced size increase */
1135 memset(dst->raw_data + dst->sec_sz, 0, dst_align_sz - dst->sec_sz);
1136 /* now copy src data at a properly aligned offset */
1137 memcpy(dst->raw_data + dst_align_sz, src->data->d_buf, src->shdr->sh_size);
1138 }
1139
1140 dst->sec_sz = dst_final_sz;
1141 dst->shdr->sh_size = dst_final_sz;
1142 dst->data->d_size = dst_final_sz;
1143
1144 dst->shdr->sh_addralign = dst_align;
1145 dst->data->d_align = dst_align;
1146
1147 src->dst_off = dst_align_sz;
1148
1149 return 0;
1150 }
1151
is_data_sec(struct src_sec * sec)1152 static bool is_data_sec(struct src_sec *sec)
1153 {
1154 if (!sec || sec->skipped)
1155 return false;
1156 /* ephemeral sections are data sections, e.g., .kconfig, .ksyms */
1157 if (sec->ephemeral)
1158 return true;
1159 return sec->shdr->sh_type == SHT_PROGBITS || sec->shdr->sh_type == SHT_NOBITS;
1160 }
1161
is_relo_sec(struct src_sec * sec)1162 static bool is_relo_sec(struct src_sec *sec)
1163 {
1164 if (!sec || sec->skipped || sec->ephemeral)
1165 return false;
1166 return sec->shdr->sh_type == SHT_REL;
1167 }
1168
linker_append_sec_data(struct bpf_linker * linker,struct src_obj * obj)1169 static int linker_append_sec_data(struct bpf_linker *linker, struct src_obj *obj)
1170 {
1171 int i, err;
1172
1173 for (i = 1; i < obj->sec_cnt; i++) {
1174 struct src_sec *src_sec;
1175 struct dst_sec *dst_sec;
1176
1177 src_sec = &obj->secs[i];
1178 if (!is_data_sec(src_sec))
1179 continue;
1180
1181 dst_sec = find_dst_sec_by_name(linker, src_sec->sec_name);
1182 if (!dst_sec) {
1183 dst_sec = add_dst_sec(linker, src_sec->sec_name);
1184 if (!dst_sec)
1185 return -ENOMEM;
1186 err = init_sec(linker, dst_sec, src_sec);
1187 if (err) {
1188 pr_warn("failed to init section '%s'\n", src_sec->sec_name);
1189 return err;
1190 }
1191 } else {
1192 if (!secs_match(dst_sec, src_sec)) {
1193 pr_warn("ELF sections %s are incompatible\n", src_sec->sec_name);
1194 return -1;
1195 }
1196
1197 /* "license" and "version" sections are deduped */
1198 if (strcmp(src_sec->sec_name, "license") == 0
1199 || strcmp(src_sec->sec_name, "version") == 0) {
1200 if (!sec_content_is_same(dst_sec, src_sec)) {
1201 pr_warn("non-identical contents of section '%s' are not supported\n", src_sec->sec_name);
1202 return -EINVAL;
1203 }
1204 src_sec->skipped = true;
1205 src_sec->dst_id = dst_sec->id;
1206 continue;
1207 }
1208 }
1209
1210 /* record mapped section index */
1211 src_sec->dst_id = dst_sec->id;
1212
1213 err = extend_sec(linker, dst_sec, src_sec);
1214 if (err)
1215 return err;
1216 }
1217
1218 return 0;
1219 }
1220
linker_append_elf_syms(struct bpf_linker * linker,struct src_obj * obj)1221 static int linker_append_elf_syms(struct bpf_linker *linker, struct src_obj *obj)
1222 {
1223 struct src_sec *symtab = &obj->secs[obj->symtab_sec_idx];
1224 Elf64_Sym *sym = symtab->data->d_buf;
1225 int i, n = symtab->shdr->sh_size / symtab->shdr->sh_entsize, err;
1226 int str_sec_idx = symtab->shdr->sh_link;
1227 const char *sym_name;
1228
1229 obj->sym_map = calloc(n + 1, sizeof(*obj->sym_map));
1230 if (!obj->sym_map)
1231 return -ENOMEM;
1232
1233 for (i = 0; i < n; i++, sym++) {
1234 /* We already validated all-zero symbol #0 and we already
1235 * appended it preventively to the final SYMTAB, so skip it.
1236 */
1237 if (i == 0)
1238 continue;
1239
1240 sym_name = elf_strptr(obj->elf, str_sec_idx, sym->st_name);
1241 if (!sym_name) {
1242 pr_warn("can't fetch symbol name for symbol #%d in '%s'\n", i, obj->filename);
1243 return -EINVAL;
1244 }
1245
1246 err = linker_append_elf_sym(linker, obj, sym, sym_name, i);
1247 if (err)
1248 return err;
1249 }
1250
1251 return 0;
1252 }
1253
get_sym_by_idx(struct bpf_linker * linker,size_t sym_idx)1254 static Elf64_Sym *get_sym_by_idx(struct bpf_linker *linker, size_t sym_idx)
1255 {
1256 struct dst_sec *symtab = &linker->secs[linker->symtab_sec_idx];
1257 Elf64_Sym *syms = symtab->raw_data;
1258
1259 return &syms[sym_idx];
1260 }
1261
find_glob_sym(struct bpf_linker * linker,const char * sym_name)1262 static struct glob_sym *find_glob_sym(struct bpf_linker *linker, const char *sym_name)
1263 {
1264 struct glob_sym *glob_sym;
1265 const char *name;
1266 int i;
1267
1268 for (i = 0; i < linker->glob_sym_cnt; i++) {
1269 glob_sym = &linker->glob_syms[i];
1270 name = strset__data(linker->strtab_strs) + glob_sym->name_off;
1271
1272 if (strcmp(name, sym_name) == 0)
1273 return glob_sym;
1274 }
1275
1276 return NULL;
1277 }
1278
add_glob_sym(struct bpf_linker * linker)1279 static struct glob_sym *add_glob_sym(struct bpf_linker *linker)
1280 {
1281 struct glob_sym *syms, *sym;
1282
1283 syms = libbpf_reallocarray(linker->glob_syms, linker->glob_sym_cnt + 1,
1284 sizeof(*linker->glob_syms));
1285 if (!syms)
1286 return NULL;
1287
1288 sym = &syms[linker->glob_sym_cnt];
1289 memset(sym, 0, sizeof(*sym));
1290 sym->var_idx = -1;
1291
1292 linker->glob_syms = syms;
1293 linker->glob_sym_cnt++;
1294
1295 return sym;
1296 }
1297
glob_sym_btf_matches(const char * sym_name,bool exact,const struct btf * btf1,__u32 id1,const struct btf * btf2,__u32 id2)1298 static bool glob_sym_btf_matches(const char *sym_name, bool exact,
1299 const struct btf *btf1, __u32 id1,
1300 const struct btf *btf2, __u32 id2)
1301 {
1302 const struct btf_type *t1, *t2;
1303 bool is_static1, is_static2;
1304 const char *n1, *n2;
1305 int i, n;
1306
1307 recur:
1308 n1 = n2 = NULL;
1309 t1 = skip_mods_and_typedefs(btf1, id1, &id1);
1310 t2 = skip_mods_and_typedefs(btf2, id2, &id2);
1311
1312 /* check if only one side is FWD, otherwise handle with common logic */
1313 if (!exact && btf_is_fwd(t1) != btf_is_fwd(t2)) {
1314 n1 = btf__str_by_offset(btf1, t1->name_off);
1315 n2 = btf__str_by_offset(btf2, t2->name_off);
1316 if (strcmp(n1, n2) != 0) {
1317 pr_warn("global '%s': incompatible forward declaration names '%s' and '%s'\n",
1318 sym_name, n1, n2);
1319 return false;
1320 }
1321 /* validate if FWD kind matches concrete kind */
1322 if (btf_is_fwd(t1)) {
1323 if (btf_kflag(t1) && btf_is_union(t2))
1324 return true;
1325 if (!btf_kflag(t1) && btf_is_struct(t2))
1326 return true;
1327 pr_warn("global '%s': incompatible %s forward declaration and concrete kind %s\n",
1328 sym_name, btf_kflag(t1) ? "union" : "struct", btf_kind_str(t2));
1329 } else {
1330 if (btf_kflag(t2) && btf_is_union(t1))
1331 return true;
1332 if (!btf_kflag(t2) && btf_is_struct(t1))
1333 return true;
1334 pr_warn("global '%s': incompatible %s forward declaration and concrete kind %s\n",
1335 sym_name, btf_kflag(t2) ? "union" : "struct", btf_kind_str(t1));
1336 }
1337 return false;
1338 }
1339
1340 if (btf_kind(t1) != btf_kind(t2)) {
1341 pr_warn("global '%s': incompatible BTF kinds %s and %s\n",
1342 sym_name, btf_kind_str(t1), btf_kind_str(t2));
1343 return false;
1344 }
1345
1346 switch (btf_kind(t1)) {
1347 case BTF_KIND_STRUCT:
1348 case BTF_KIND_UNION:
1349 case BTF_KIND_ENUM:
1350 case BTF_KIND_ENUM64:
1351 case BTF_KIND_FWD:
1352 case BTF_KIND_FUNC:
1353 case BTF_KIND_VAR:
1354 n1 = btf__str_by_offset(btf1, t1->name_off);
1355 n2 = btf__str_by_offset(btf2, t2->name_off);
1356 if (strcmp(n1, n2) != 0) {
1357 pr_warn("global '%s': incompatible %s names '%s' and '%s'\n",
1358 sym_name, btf_kind_str(t1), n1, n2);
1359 return false;
1360 }
1361 break;
1362 default:
1363 break;
1364 }
1365
1366 switch (btf_kind(t1)) {
1367 case BTF_KIND_UNKN: /* void */
1368 case BTF_KIND_FWD:
1369 return true;
1370 case BTF_KIND_INT:
1371 case BTF_KIND_FLOAT:
1372 case BTF_KIND_ENUM:
1373 case BTF_KIND_ENUM64:
1374 /* ignore encoding for int and enum values for enum */
1375 if (t1->size != t2->size) {
1376 pr_warn("global '%s': incompatible %s '%s' size %u and %u\n",
1377 sym_name, btf_kind_str(t1), n1, t1->size, t2->size);
1378 return false;
1379 }
1380 return true;
1381 case BTF_KIND_PTR:
1382 /* just validate overall shape of the referenced type, so no
1383 * contents comparison for struct/union, and allowd fwd vs
1384 * struct/union
1385 */
1386 exact = false;
1387 id1 = t1->type;
1388 id2 = t2->type;
1389 goto recur;
1390 case BTF_KIND_ARRAY:
1391 /* ignore index type and array size */
1392 id1 = btf_array(t1)->type;
1393 id2 = btf_array(t2)->type;
1394 goto recur;
1395 case BTF_KIND_FUNC:
1396 /* extern and global linkages are compatible */
1397 is_static1 = btf_func_linkage(t1) == BTF_FUNC_STATIC;
1398 is_static2 = btf_func_linkage(t2) == BTF_FUNC_STATIC;
1399 if (is_static1 != is_static2) {
1400 pr_warn("global '%s': incompatible func '%s' linkage\n", sym_name, n1);
1401 return false;
1402 }
1403
1404 id1 = t1->type;
1405 id2 = t2->type;
1406 goto recur;
1407 case BTF_KIND_VAR:
1408 /* extern and global linkages are compatible */
1409 is_static1 = btf_var(t1)->linkage == BTF_VAR_STATIC;
1410 is_static2 = btf_var(t2)->linkage == BTF_VAR_STATIC;
1411 if (is_static1 != is_static2) {
1412 pr_warn("global '%s': incompatible var '%s' linkage\n", sym_name, n1);
1413 return false;
1414 }
1415
1416 id1 = t1->type;
1417 id2 = t2->type;
1418 goto recur;
1419 case BTF_KIND_STRUCT:
1420 case BTF_KIND_UNION: {
1421 const struct btf_member *m1, *m2;
1422
1423 if (!exact)
1424 return true;
1425
1426 if (btf_vlen(t1) != btf_vlen(t2)) {
1427 pr_warn("global '%s': incompatible number of %s fields %u and %u\n",
1428 sym_name, btf_kind_str(t1), btf_vlen(t1), btf_vlen(t2));
1429 return false;
1430 }
1431
1432 n = btf_vlen(t1);
1433 m1 = btf_members(t1);
1434 m2 = btf_members(t2);
1435 for (i = 0; i < n; i++, m1++, m2++) {
1436 n1 = btf__str_by_offset(btf1, m1->name_off);
1437 n2 = btf__str_by_offset(btf2, m2->name_off);
1438 if (strcmp(n1, n2) != 0) {
1439 pr_warn("global '%s': incompatible field #%d names '%s' and '%s'\n",
1440 sym_name, i, n1, n2);
1441 return false;
1442 }
1443 if (m1->offset != m2->offset) {
1444 pr_warn("global '%s': incompatible field #%d ('%s') offsets\n",
1445 sym_name, i, n1);
1446 return false;
1447 }
1448 if (!glob_sym_btf_matches(sym_name, exact, btf1, m1->type, btf2, m2->type))
1449 return false;
1450 }
1451
1452 return true;
1453 }
1454 case BTF_KIND_FUNC_PROTO: {
1455 const struct btf_param *m1, *m2;
1456
1457 if (btf_vlen(t1) != btf_vlen(t2)) {
1458 pr_warn("global '%s': incompatible number of %s params %u and %u\n",
1459 sym_name, btf_kind_str(t1), btf_vlen(t1), btf_vlen(t2));
1460 return false;
1461 }
1462
1463 n = btf_vlen(t1);
1464 m1 = btf_params(t1);
1465 m2 = btf_params(t2);
1466 for (i = 0; i < n; i++, m1++, m2++) {
1467 /* ignore func arg names */
1468 if (!glob_sym_btf_matches(sym_name, exact, btf1, m1->type, btf2, m2->type))
1469 return false;
1470 }
1471
1472 /* now check return type as well */
1473 id1 = t1->type;
1474 id2 = t2->type;
1475 goto recur;
1476 }
1477
1478 /* skip_mods_and_typedefs() make this impossible */
1479 case BTF_KIND_TYPEDEF:
1480 case BTF_KIND_VOLATILE:
1481 case BTF_KIND_CONST:
1482 case BTF_KIND_RESTRICT:
1483 /* DATASECs are never compared with each other */
1484 case BTF_KIND_DATASEC:
1485 default:
1486 pr_warn("global '%s': unsupported BTF kind %s\n",
1487 sym_name, btf_kind_str(t1));
1488 return false;
1489 }
1490 }
1491
map_defs_match(const char * sym_name,const struct btf * main_btf,const struct btf_map_def * main_def,const struct btf_map_def * main_inner_def,const struct btf * extra_btf,const struct btf_map_def * extra_def,const struct btf_map_def * extra_inner_def)1492 static bool map_defs_match(const char *sym_name,
1493 const struct btf *main_btf,
1494 const struct btf_map_def *main_def,
1495 const struct btf_map_def *main_inner_def,
1496 const struct btf *extra_btf,
1497 const struct btf_map_def *extra_def,
1498 const struct btf_map_def *extra_inner_def)
1499 {
1500 const char *reason;
1501
1502 if (main_def->map_type != extra_def->map_type) {
1503 reason = "type";
1504 goto mismatch;
1505 }
1506
1507 /* check key type/size match */
1508 if (main_def->key_size != extra_def->key_size) {
1509 reason = "key_size";
1510 goto mismatch;
1511 }
1512 if (!!main_def->key_type_id != !!extra_def->key_type_id) {
1513 reason = "key type";
1514 goto mismatch;
1515 }
1516 if ((main_def->parts & MAP_DEF_KEY_TYPE)
1517 && !glob_sym_btf_matches(sym_name, true /*exact*/,
1518 main_btf, main_def->key_type_id,
1519 extra_btf, extra_def->key_type_id)) {
1520 reason = "key type";
1521 goto mismatch;
1522 }
1523
1524 /* validate value type/size match */
1525 if (main_def->value_size != extra_def->value_size) {
1526 reason = "value_size";
1527 goto mismatch;
1528 }
1529 if (!!main_def->value_type_id != !!extra_def->value_type_id) {
1530 reason = "value type";
1531 goto mismatch;
1532 }
1533 if ((main_def->parts & MAP_DEF_VALUE_TYPE)
1534 && !glob_sym_btf_matches(sym_name, true /*exact*/,
1535 main_btf, main_def->value_type_id,
1536 extra_btf, extra_def->value_type_id)) {
1537 reason = "key type";
1538 goto mismatch;
1539 }
1540
1541 if (main_def->max_entries != extra_def->max_entries) {
1542 reason = "max_entries";
1543 goto mismatch;
1544 }
1545 if (main_def->map_flags != extra_def->map_flags) {
1546 reason = "map_flags";
1547 goto mismatch;
1548 }
1549 if (main_def->numa_node != extra_def->numa_node) {
1550 reason = "numa_node";
1551 goto mismatch;
1552 }
1553 if (main_def->pinning != extra_def->pinning) {
1554 reason = "pinning";
1555 goto mismatch;
1556 }
1557
1558 if ((main_def->parts & MAP_DEF_INNER_MAP) != (extra_def->parts & MAP_DEF_INNER_MAP)) {
1559 reason = "inner map";
1560 goto mismatch;
1561 }
1562
1563 if (main_def->parts & MAP_DEF_INNER_MAP) {
1564 char inner_map_name[128];
1565
1566 snprintf(inner_map_name, sizeof(inner_map_name), "%s.inner", sym_name);
1567
1568 return map_defs_match(inner_map_name,
1569 main_btf, main_inner_def, NULL,
1570 extra_btf, extra_inner_def, NULL);
1571 }
1572
1573 return true;
1574
1575 mismatch:
1576 pr_warn("global '%s': map %s mismatch\n", sym_name, reason);
1577 return false;
1578 }
1579
glob_map_defs_match(const char * sym_name,struct bpf_linker * linker,struct glob_sym * glob_sym,struct src_obj * obj,Elf64_Sym * sym,int btf_id)1580 static bool glob_map_defs_match(const char *sym_name,
1581 struct bpf_linker *linker, struct glob_sym *glob_sym,
1582 struct src_obj *obj, Elf64_Sym *sym, int btf_id)
1583 {
1584 struct btf_map_def dst_def = {}, dst_inner_def = {};
1585 struct btf_map_def src_def = {}, src_inner_def = {};
1586 const struct btf_type *t;
1587 int err;
1588
1589 t = btf__type_by_id(obj->btf, btf_id);
1590 if (!btf_is_var(t)) {
1591 pr_warn("global '%s': invalid map definition type [%d]\n", sym_name, btf_id);
1592 return false;
1593 }
1594 t = skip_mods_and_typedefs(obj->btf, t->type, NULL);
1595
1596 err = parse_btf_map_def(sym_name, obj->btf, t, true /*strict*/, &src_def, &src_inner_def);
1597 if (err) {
1598 pr_warn("global '%s': invalid map definition\n", sym_name);
1599 return false;
1600 }
1601
1602 /* re-parse existing map definition */
1603 t = btf__type_by_id(linker->btf, glob_sym->btf_id);
1604 t = skip_mods_and_typedefs(linker->btf, t->type, NULL);
1605 err = parse_btf_map_def(sym_name, linker->btf, t, true /*strict*/, &dst_def, &dst_inner_def);
1606 if (err) {
1607 /* this should not happen, because we already validated it */
1608 pr_warn("global '%s': invalid dst map definition\n", sym_name);
1609 return false;
1610 }
1611
1612 /* Currently extern map definition has to be complete and match
1613 * concrete map definition exactly. This restriction might be lifted
1614 * in the future.
1615 */
1616 return map_defs_match(sym_name, linker->btf, &dst_def, &dst_inner_def,
1617 obj->btf, &src_def, &src_inner_def);
1618 }
1619
glob_syms_match(const char * sym_name,struct bpf_linker * linker,struct glob_sym * glob_sym,struct src_obj * obj,Elf64_Sym * sym,size_t sym_idx,int btf_id)1620 static bool glob_syms_match(const char *sym_name,
1621 struct bpf_linker *linker, struct glob_sym *glob_sym,
1622 struct src_obj *obj, Elf64_Sym *sym, size_t sym_idx, int btf_id)
1623 {
1624 const struct btf_type *src_t;
1625
1626 /* if we are dealing with externs, BTF types describing both global
1627 * and extern VARs/FUNCs should be completely present in all files
1628 */
1629 if (!glob_sym->btf_id || !btf_id) {
1630 pr_warn("BTF info is missing for global symbol '%s'\n", sym_name);
1631 return false;
1632 }
1633
1634 src_t = btf__type_by_id(obj->btf, btf_id);
1635 if (!btf_is_var(src_t) && !btf_is_func(src_t)) {
1636 pr_warn("only extern variables and functions are supported, but got '%s' for '%s'\n",
1637 btf_kind_str(src_t), sym_name);
1638 return false;
1639 }
1640
1641 /* deal with .maps definitions specially */
1642 if (glob_sym->sec_id && strcmp(linker->secs[glob_sym->sec_id].sec_name, MAPS_ELF_SEC) == 0)
1643 return glob_map_defs_match(sym_name, linker, glob_sym, obj, sym, btf_id);
1644
1645 if (!glob_sym_btf_matches(sym_name, true /*exact*/,
1646 linker->btf, glob_sym->btf_id, obj->btf, btf_id))
1647 return false;
1648
1649 return true;
1650 }
1651
btf_is_non_static(const struct btf_type * t)1652 static bool btf_is_non_static(const struct btf_type *t)
1653 {
1654 return (btf_is_var(t) && btf_var(t)->linkage != BTF_VAR_STATIC)
1655 || (btf_is_func(t) && btf_func_linkage(t) != BTF_FUNC_STATIC);
1656 }
1657
find_glob_sym_btf(struct src_obj * obj,Elf64_Sym * sym,const char * sym_name,int * out_btf_sec_id,int * out_btf_id)1658 static int find_glob_sym_btf(struct src_obj *obj, Elf64_Sym *sym, const char *sym_name,
1659 int *out_btf_sec_id, int *out_btf_id)
1660 {
1661 int i, j, n, m, btf_id = 0;
1662 const struct btf_type *t;
1663 const struct btf_var_secinfo *vi;
1664 const char *name;
1665
1666 if (!obj->btf) {
1667 pr_warn("failed to find BTF info for object '%s'\n", obj->filename);
1668 return -EINVAL;
1669 }
1670
1671 n = btf__type_cnt(obj->btf);
1672 for (i = 1; i < n; i++) {
1673 t = btf__type_by_id(obj->btf, i);
1674
1675 /* some global and extern FUNCs and VARs might not be associated with any
1676 * DATASEC, so try to detect them in the same pass
1677 */
1678 if (btf_is_non_static(t)) {
1679 name = btf__str_by_offset(obj->btf, t->name_off);
1680 if (strcmp(name, sym_name) != 0)
1681 continue;
1682
1683 /* remember and still try to find DATASEC */
1684 btf_id = i;
1685 continue;
1686 }
1687
1688 if (!btf_is_datasec(t))
1689 continue;
1690
1691 vi = btf_var_secinfos(t);
1692 for (j = 0, m = btf_vlen(t); j < m; j++, vi++) {
1693 t = btf__type_by_id(obj->btf, vi->type);
1694 name = btf__str_by_offset(obj->btf, t->name_off);
1695
1696 if (strcmp(name, sym_name) != 0)
1697 continue;
1698 if (btf_is_var(t) && btf_var(t)->linkage == BTF_VAR_STATIC)
1699 continue;
1700 if (btf_is_func(t) && btf_func_linkage(t) == BTF_FUNC_STATIC)
1701 continue;
1702
1703 if (btf_id && btf_id != vi->type) {
1704 pr_warn("global/extern '%s' BTF is ambiguous: both types #%d and #%u match\n",
1705 sym_name, btf_id, vi->type);
1706 return -EINVAL;
1707 }
1708
1709 *out_btf_sec_id = i;
1710 *out_btf_id = vi->type;
1711
1712 return 0;
1713 }
1714 }
1715
1716 /* free-floating extern or global FUNC */
1717 if (btf_id) {
1718 *out_btf_sec_id = 0;
1719 *out_btf_id = btf_id;
1720 return 0;
1721 }
1722
1723 pr_warn("failed to find BTF info for global/extern symbol '%s'\n", sym_name);
1724 return -ENOENT;
1725 }
1726
find_src_sec_by_name(struct src_obj * obj,const char * sec_name)1727 static struct src_sec *find_src_sec_by_name(struct src_obj *obj, const char *sec_name)
1728 {
1729 struct src_sec *sec;
1730 int i;
1731
1732 for (i = 1; i < obj->sec_cnt; i++) {
1733 sec = &obj->secs[i];
1734
1735 if (strcmp(sec->sec_name, sec_name) == 0)
1736 return sec;
1737 }
1738
1739 return NULL;
1740 }
1741
complete_extern_btf_info(struct btf * dst_btf,int dst_id,struct btf * src_btf,int src_id)1742 static int complete_extern_btf_info(struct btf *dst_btf, int dst_id,
1743 struct btf *src_btf, int src_id)
1744 {
1745 struct btf_type *dst_t = btf_type_by_id(dst_btf, dst_id);
1746 struct btf_type *src_t = btf_type_by_id(src_btf, src_id);
1747 struct btf_param *src_p, *dst_p;
1748 const char *s;
1749 int i, n, off;
1750
1751 /* We already made sure that source and destination types (FUNC or
1752 * VAR) match in terms of types and argument names.
1753 */
1754 if (btf_is_var(dst_t)) {
1755 btf_var(dst_t)->linkage = BTF_VAR_GLOBAL_ALLOCATED;
1756 return 0;
1757 }
1758
1759 dst_t->info = btf_type_info(BTF_KIND_FUNC, BTF_FUNC_GLOBAL, 0);
1760
1761 /* now onto FUNC_PROTO types */
1762 src_t = btf_type_by_id(src_btf, src_t->type);
1763 dst_t = btf_type_by_id(dst_btf, dst_t->type);
1764
1765 /* Fill in all the argument names, which for extern FUNCs are missing.
1766 * We'll end up with two copies of FUNCs/VARs for externs, but that
1767 * will be taken care of by BTF dedup at the very end.
1768 * It might be that BTF types for extern in one file has less/more BTF
1769 * information (e.g., FWD instead of full STRUCT/UNION information),
1770 * but that should be (in most cases, subject to BTF dedup rules)
1771 * handled and resolved by BTF dedup algorithm as well, so we won't
1772 * worry about it. Our only job is to make sure that argument names
1773 * are populated on both sides, otherwise BTF dedup will pedantically
1774 * consider them different.
1775 */
1776 src_p = btf_params(src_t);
1777 dst_p = btf_params(dst_t);
1778 for (i = 0, n = btf_vlen(dst_t); i < n; i++, src_p++, dst_p++) {
1779 if (!src_p->name_off)
1780 continue;
1781
1782 /* src_btf has more complete info, so add name to dst_btf */
1783 s = btf__str_by_offset(src_btf, src_p->name_off);
1784 off = btf__add_str(dst_btf, s);
1785 if (off < 0)
1786 return off;
1787 dst_p->name_off = off;
1788 }
1789 return 0;
1790 }
1791
sym_update_bind(Elf64_Sym * sym,int sym_bind)1792 static void sym_update_bind(Elf64_Sym *sym, int sym_bind)
1793 {
1794 sym->st_info = ELF64_ST_INFO(sym_bind, ELF64_ST_TYPE(sym->st_info));
1795 }
1796
sym_update_type(Elf64_Sym * sym,int sym_type)1797 static void sym_update_type(Elf64_Sym *sym, int sym_type)
1798 {
1799 sym->st_info = ELF64_ST_INFO(ELF64_ST_BIND(sym->st_info), sym_type);
1800 }
1801
sym_update_visibility(Elf64_Sym * sym,int sym_vis)1802 static void sym_update_visibility(Elf64_Sym *sym, int sym_vis)
1803 {
1804 /* libelf doesn't provide setters for ST_VISIBILITY,
1805 * but it is stored in the lower 2 bits of st_other
1806 */
1807 sym->st_other &= ~0x03;
1808 sym->st_other |= sym_vis;
1809 }
1810
linker_append_elf_sym(struct bpf_linker * linker,struct src_obj * obj,Elf64_Sym * sym,const char * sym_name,int src_sym_idx)1811 static int linker_append_elf_sym(struct bpf_linker *linker, struct src_obj *obj,
1812 Elf64_Sym *sym, const char *sym_name, int src_sym_idx)
1813 {
1814 struct src_sec *src_sec = NULL;
1815 struct dst_sec *dst_sec = NULL;
1816 struct glob_sym *glob_sym = NULL;
1817 int name_off, sym_type, sym_bind, sym_vis, err;
1818 int btf_sec_id = 0, btf_id = 0;
1819 size_t dst_sym_idx;
1820 Elf64_Sym *dst_sym;
1821 bool sym_is_extern;
1822
1823 sym_type = ELF64_ST_TYPE(sym->st_info);
1824 sym_bind = ELF64_ST_BIND(sym->st_info);
1825 sym_vis = ELF64_ST_VISIBILITY(sym->st_other);
1826 sym_is_extern = sym->st_shndx == SHN_UNDEF;
1827
1828 if (sym_is_extern) {
1829 if (!obj->btf) {
1830 pr_warn("externs without BTF info are not supported\n");
1831 return -ENOTSUP;
1832 }
1833 } else if (sym->st_shndx < SHN_LORESERVE) {
1834 src_sec = &obj->secs[sym->st_shndx];
1835 if (src_sec->skipped)
1836 return 0;
1837 dst_sec = &linker->secs[src_sec->dst_id];
1838
1839 /* allow only one STT_SECTION symbol per section */
1840 if (sym_type == STT_SECTION && dst_sec->sec_sym_idx) {
1841 obj->sym_map[src_sym_idx] = dst_sec->sec_sym_idx;
1842 return 0;
1843 }
1844 }
1845
1846 if (sym_bind == STB_LOCAL)
1847 goto add_sym;
1848
1849 /* find matching BTF info */
1850 err = find_glob_sym_btf(obj, sym, sym_name, &btf_sec_id, &btf_id);
1851 if (err)
1852 return err;
1853
1854 if (sym_is_extern && btf_sec_id) {
1855 const char *sec_name = NULL;
1856 const struct btf_type *t;
1857
1858 t = btf__type_by_id(obj->btf, btf_sec_id);
1859 sec_name = btf__str_by_offset(obj->btf, t->name_off);
1860
1861 /* Clang puts unannotated extern vars into
1862 * '.extern' BTF DATASEC. Treat them the same
1863 * as unannotated extern funcs (which are
1864 * currently not put into any DATASECs).
1865 * Those don't have associated src_sec/dst_sec.
1866 */
1867 if (strcmp(sec_name, BTF_EXTERN_SEC) != 0) {
1868 src_sec = find_src_sec_by_name(obj, sec_name);
1869 if (!src_sec) {
1870 pr_warn("failed to find matching ELF sec '%s'\n", sec_name);
1871 return -ENOENT;
1872 }
1873 dst_sec = &linker->secs[src_sec->dst_id];
1874 }
1875 }
1876
1877 glob_sym = find_glob_sym(linker, sym_name);
1878 if (glob_sym) {
1879 /* Preventively resolve to existing symbol. This is
1880 * needed for further relocation symbol remapping in
1881 * the next step of linking.
1882 */
1883 obj->sym_map[src_sym_idx] = glob_sym->sym_idx;
1884
1885 /* If both symbols are non-externs, at least one of
1886 * them has to be STB_WEAK, otherwise they are in
1887 * a conflict with each other.
1888 */
1889 if (!sym_is_extern && !glob_sym->is_extern
1890 && !glob_sym->is_weak && sym_bind != STB_WEAK) {
1891 pr_warn("conflicting non-weak symbol #%d (%s) definition in '%s'\n",
1892 src_sym_idx, sym_name, obj->filename);
1893 return -EINVAL;
1894 }
1895
1896 if (!glob_syms_match(sym_name, linker, glob_sym, obj, sym, src_sym_idx, btf_id))
1897 return -EINVAL;
1898
1899 dst_sym = get_sym_by_idx(linker, glob_sym->sym_idx);
1900
1901 /* If new symbol is strong, then force dst_sym to be strong as
1902 * well; this way a mix of weak and non-weak extern
1903 * definitions will end up being strong.
1904 */
1905 if (sym_bind == STB_GLOBAL) {
1906 /* We still need to preserve type (NOTYPE or
1907 * OBJECT/FUNC, depending on whether the symbol is
1908 * extern or not)
1909 */
1910 sym_update_bind(dst_sym, STB_GLOBAL);
1911 glob_sym->is_weak = false;
1912 }
1913
1914 /* Non-default visibility is "contaminating", with stricter
1915 * visibility overwriting more permissive ones, even if more
1916 * permissive visibility comes from just an extern definition.
1917 * Currently only STV_DEFAULT and STV_HIDDEN are allowed and
1918 * ensured by ELF symbol sanity checks above.
1919 */
1920 if (sym_vis > ELF64_ST_VISIBILITY(dst_sym->st_other))
1921 sym_update_visibility(dst_sym, sym_vis);
1922
1923 /* If the new symbol is extern, then regardless if
1924 * existing symbol is extern or resolved global, just
1925 * keep the existing one untouched.
1926 */
1927 if (sym_is_extern)
1928 return 0;
1929
1930 /* If existing symbol is a strong resolved symbol, bail out,
1931 * because we lost resolution battle have nothing to
1932 * contribute. We already checked abover that there is no
1933 * strong-strong conflict. We also already tightened binding
1934 * and visibility, so nothing else to contribute at that point.
1935 */
1936 if (!glob_sym->is_extern && sym_bind == STB_WEAK)
1937 return 0;
1938
1939 /* At this point, new symbol is strong non-extern,
1940 * so overwrite glob_sym with new symbol information.
1941 * Preserve binding and visibility.
1942 */
1943 sym_update_type(dst_sym, sym_type);
1944 dst_sym->st_shndx = dst_sec->sec_idx;
1945 dst_sym->st_value = src_sec->dst_off + sym->st_value;
1946 dst_sym->st_size = sym->st_size;
1947
1948 /* see comment below about dst_sec->id vs dst_sec->sec_idx */
1949 glob_sym->sec_id = dst_sec->id;
1950 glob_sym->is_extern = false;
1951
1952 if (complete_extern_btf_info(linker->btf, glob_sym->btf_id,
1953 obj->btf, btf_id))
1954 return -EINVAL;
1955
1956 /* request updating VAR's/FUNC's underlying BTF type when appending BTF type */
1957 glob_sym->underlying_btf_id = 0;
1958
1959 obj->sym_map[src_sym_idx] = glob_sym->sym_idx;
1960 return 0;
1961 }
1962
1963 add_sym:
1964 name_off = strset__add_str(linker->strtab_strs, sym_name);
1965 if (name_off < 0)
1966 return name_off;
1967
1968 dst_sym = add_new_sym(linker, &dst_sym_idx);
1969 if (!dst_sym)
1970 return -ENOMEM;
1971
1972 dst_sym->st_name = name_off;
1973 dst_sym->st_info = sym->st_info;
1974 dst_sym->st_other = sym->st_other;
1975 dst_sym->st_shndx = dst_sec ? dst_sec->sec_idx : sym->st_shndx;
1976 dst_sym->st_value = (src_sec ? src_sec->dst_off : 0) + sym->st_value;
1977 dst_sym->st_size = sym->st_size;
1978
1979 obj->sym_map[src_sym_idx] = dst_sym_idx;
1980
1981 if (sym_type == STT_SECTION && dst_sym) {
1982 dst_sec->sec_sym_idx = dst_sym_idx;
1983 dst_sym->st_value = 0;
1984 }
1985
1986 if (sym_bind != STB_LOCAL) {
1987 glob_sym = add_glob_sym(linker);
1988 if (!glob_sym)
1989 return -ENOMEM;
1990
1991 glob_sym->sym_idx = dst_sym_idx;
1992 /* we use dst_sec->id (and not dst_sec->sec_idx), because
1993 * ephemeral sections (.kconfig, .ksyms, etc) don't have
1994 * sec_idx (as they don't have corresponding ELF section), but
1995 * still have id. .extern doesn't have even ephemeral section
1996 * associated with it, so dst_sec->id == dst_sec->sec_idx == 0.
1997 */
1998 glob_sym->sec_id = dst_sec ? dst_sec->id : 0;
1999 glob_sym->name_off = name_off;
2000 /* we will fill btf_id in during BTF merging step */
2001 glob_sym->btf_id = 0;
2002 glob_sym->is_extern = sym_is_extern;
2003 glob_sym->is_weak = sym_bind == STB_WEAK;
2004 }
2005
2006 return 0;
2007 }
2008
linker_append_elf_relos(struct bpf_linker * linker,struct src_obj * obj)2009 static int linker_append_elf_relos(struct bpf_linker *linker, struct src_obj *obj)
2010 {
2011 struct src_sec *src_symtab = &obj->secs[obj->symtab_sec_idx];
2012 int i, err;
2013
2014 for (i = 1; i < obj->sec_cnt; i++) {
2015 struct src_sec *src_sec, *src_linked_sec;
2016 struct dst_sec *dst_sec, *dst_linked_sec;
2017 Elf64_Rel *src_rel, *dst_rel;
2018 int j, n;
2019
2020 src_sec = &obj->secs[i];
2021 if (!is_relo_sec(src_sec))
2022 continue;
2023
2024 /* shdr->sh_info points to relocatable section */
2025 src_linked_sec = &obj->secs[src_sec->shdr->sh_info];
2026 if (src_linked_sec->skipped)
2027 continue;
2028
2029 dst_sec = find_dst_sec_by_name(linker, src_sec->sec_name);
2030 if (!dst_sec) {
2031 dst_sec = add_dst_sec(linker, src_sec->sec_name);
2032 if (!dst_sec)
2033 return -ENOMEM;
2034 err = init_sec(linker, dst_sec, src_sec);
2035 if (err) {
2036 pr_warn("failed to init section '%s'\n", src_sec->sec_name);
2037 return err;
2038 }
2039 } else if (!secs_match(dst_sec, src_sec)) {
2040 pr_warn("sections %s are not compatible\n", src_sec->sec_name);
2041 return -1;
2042 }
2043
2044 /* shdr->sh_link points to SYMTAB */
2045 dst_sec->shdr->sh_link = linker->symtab_sec_idx;
2046
2047 /* shdr->sh_info points to relocated section */
2048 dst_linked_sec = &linker->secs[src_linked_sec->dst_id];
2049 dst_sec->shdr->sh_info = dst_linked_sec->sec_idx;
2050
2051 src_sec->dst_id = dst_sec->id;
2052 err = extend_sec(linker, dst_sec, src_sec);
2053 if (err)
2054 return err;
2055
2056 src_rel = src_sec->data->d_buf;
2057 dst_rel = dst_sec->raw_data + src_sec->dst_off;
2058 n = src_sec->shdr->sh_size / src_sec->shdr->sh_entsize;
2059 for (j = 0; j < n; j++, src_rel++, dst_rel++) {
2060 size_t src_sym_idx, dst_sym_idx, sym_type;
2061 Elf64_Sym *src_sym;
2062
2063 src_sym_idx = ELF64_R_SYM(src_rel->r_info);
2064 src_sym = src_symtab->data->d_buf + sizeof(*src_sym) * src_sym_idx;
2065
2066 dst_sym_idx = obj->sym_map[src_sym_idx];
2067 dst_rel->r_offset += src_linked_sec->dst_off;
2068 sym_type = ELF64_R_TYPE(src_rel->r_info);
2069 dst_rel->r_info = ELF64_R_INFO(dst_sym_idx, sym_type);
2070
2071 if (ELF64_ST_TYPE(src_sym->st_info) == STT_SECTION) {
2072 struct src_sec *sec = &obj->secs[src_sym->st_shndx];
2073 struct bpf_insn *insn;
2074
2075 if (src_linked_sec->shdr->sh_flags & SHF_EXECINSTR) {
2076 /* calls to the very first static function inside
2077 * .text section at offset 0 will
2078 * reference section symbol, not the
2079 * function symbol. Fix that up,
2080 * otherwise it won't be possible to
2081 * relocate calls to two different
2082 * static functions with the same name
2083 * (rom two different object files)
2084 */
2085 insn = dst_linked_sec->raw_data + dst_rel->r_offset;
2086 if (insn->code == (BPF_JMP | BPF_CALL))
2087 insn->imm += sec->dst_off / sizeof(struct bpf_insn);
2088 else
2089 insn->imm += sec->dst_off;
2090 } else {
2091 pr_warn("relocation against STT_SECTION in non-exec section is not supported!\n");
2092 return -EINVAL;
2093 }
2094 }
2095
2096 }
2097 }
2098
2099 return 0;
2100 }
2101
find_sym_by_name(struct src_obj * obj,size_t sec_idx,int sym_type,const char * sym_name)2102 static Elf64_Sym *find_sym_by_name(struct src_obj *obj, size_t sec_idx,
2103 int sym_type, const char *sym_name)
2104 {
2105 struct src_sec *symtab = &obj->secs[obj->symtab_sec_idx];
2106 Elf64_Sym *sym = symtab->data->d_buf;
2107 int i, n = symtab->shdr->sh_size / symtab->shdr->sh_entsize;
2108 int str_sec_idx = symtab->shdr->sh_link;
2109 const char *name;
2110
2111 for (i = 0; i < n; i++, sym++) {
2112 if (sym->st_shndx != sec_idx)
2113 continue;
2114 if (ELF64_ST_TYPE(sym->st_info) != sym_type)
2115 continue;
2116
2117 name = elf_strptr(obj->elf, str_sec_idx, sym->st_name);
2118 if (!name)
2119 return NULL;
2120
2121 if (strcmp(sym_name, name) != 0)
2122 continue;
2123
2124 return sym;
2125 }
2126
2127 return NULL;
2128 }
2129
linker_fixup_btf(struct src_obj * obj)2130 static int linker_fixup_btf(struct src_obj *obj)
2131 {
2132 const char *sec_name;
2133 struct src_sec *sec;
2134 int i, j, n, m;
2135
2136 if (!obj->btf)
2137 return 0;
2138
2139 n = btf__type_cnt(obj->btf);
2140 for (i = 1; i < n; i++) {
2141 struct btf_var_secinfo *vi;
2142 struct btf_type *t;
2143
2144 t = btf_type_by_id(obj->btf, i);
2145 if (btf_kind(t) != BTF_KIND_DATASEC)
2146 continue;
2147
2148 sec_name = btf__str_by_offset(obj->btf, t->name_off);
2149 sec = find_src_sec_by_name(obj, sec_name);
2150 if (sec) {
2151 /* record actual section size, unless ephemeral */
2152 if (sec->shdr)
2153 t->size = sec->shdr->sh_size;
2154 } else {
2155 /* BTF can have some sections that are not represented
2156 * in ELF, e.g., .kconfig, .ksyms, .extern, which are used
2157 * for special extern variables.
2158 *
2159 * For all but one such special (ephemeral)
2160 * sections, we pre-create "section shells" to be able
2161 * to keep track of extra per-section metadata later
2162 * (e.g., those BTF extern variables).
2163 *
2164 * .extern is even more special, though, because it
2165 * contains extern variables that need to be resolved
2166 * by static linker, not libbpf and kernel. When such
2167 * externs are resolved, we are going to remove them
2168 * from .extern BTF section and might end up not
2169 * needing it at all. Each resolved extern should have
2170 * matching non-extern VAR/FUNC in other sections.
2171 *
2172 * We do support leaving some of the externs
2173 * unresolved, though, to support cases of building
2174 * libraries, which will later be linked against final
2175 * BPF applications. So if at finalization we still
2176 * see unresolved externs, we'll create .extern
2177 * section on our own.
2178 */
2179 if (strcmp(sec_name, BTF_EXTERN_SEC) == 0)
2180 continue;
2181
2182 sec = add_src_sec(obj, sec_name);
2183 if (!sec)
2184 return -ENOMEM;
2185
2186 sec->ephemeral = true;
2187 sec->sec_idx = 0; /* will match UNDEF shndx in ELF */
2188 }
2189
2190 /* remember ELF section and its BTF type ID match */
2191 sec->sec_type_id = i;
2192
2193 /* fix up variable offsets */
2194 vi = btf_var_secinfos(t);
2195 for (j = 0, m = btf_vlen(t); j < m; j++, vi++) {
2196 const struct btf_type *vt = btf__type_by_id(obj->btf, vi->type);
2197 const char *var_name;
2198 int var_linkage;
2199 Elf64_Sym *sym;
2200
2201 /* could be a variable or function */
2202 if (!btf_is_var(vt))
2203 continue;
2204
2205 var_name = btf__str_by_offset(obj->btf, vt->name_off);
2206 var_linkage = btf_var(vt)->linkage;
2207
2208 /* no need to patch up static or extern vars */
2209 if (var_linkage != BTF_VAR_GLOBAL_ALLOCATED)
2210 continue;
2211
2212 sym = find_sym_by_name(obj, sec->sec_idx, STT_OBJECT, var_name);
2213 if (!sym) {
2214 pr_warn("failed to find symbol for variable '%s' in section '%s'\n", var_name, sec_name);
2215 return -ENOENT;
2216 }
2217
2218 vi->offset = sym->st_value;
2219 }
2220 }
2221
2222 return 0;
2223 }
2224
remap_type_id(__u32 * type_id,void * ctx)2225 static int remap_type_id(__u32 *type_id, void *ctx)
2226 {
2227 int *id_map = ctx;
2228 int new_id = id_map[*type_id];
2229
2230 /* Error out if the type wasn't remapped. Ignore VOID which stays VOID. */
2231 if (new_id == 0 && *type_id != 0) {
2232 pr_warn("failed to find new ID mapping for original BTF type ID %u\n", *type_id);
2233 return -EINVAL;
2234 }
2235
2236 *type_id = id_map[*type_id];
2237
2238 return 0;
2239 }
2240
linker_append_btf(struct bpf_linker * linker,struct src_obj * obj)2241 static int linker_append_btf(struct bpf_linker *linker, struct src_obj *obj)
2242 {
2243 const struct btf_type *t;
2244 int i, j, n, start_id, id;
2245 const char *name;
2246
2247 if (!obj->btf)
2248 return 0;
2249
2250 start_id = btf__type_cnt(linker->btf);
2251 n = btf__type_cnt(obj->btf);
2252
2253 obj->btf_type_map = calloc(n + 1, sizeof(int));
2254 if (!obj->btf_type_map)
2255 return -ENOMEM;
2256
2257 for (i = 1; i < n; i++) {
2258 struct glob_sym *glob_sym = NULL;
2259
2260 t = btf__type_by_id(obj->btf, i);
2261
2262 /* DATASECs are handled specially below */
2263 if (btf_kind(t) == BTF_KIND_DATASEC)
2264 continue;
2265
2266 if (btf_is_non_static(t)) {
2267 /* there should be glob_sym already */
2268 name = btf__str_by_offset(obj->btf, t->name_off);
2269 glob_sym = find_glob_sym(linker, name);
2270
2271 /* VARs without corresponding glob_sym are those that
2272 * belong to skipped/deduplicated sections (i.e.,
2273 * license and version), so just skip them
2274 */
2275 if (!glob_sym)
2276 continue;
2277
2278 /* linker_append_elf_sym() might have requested
2279 * updating underlying type ID, if extern was resolved
2280 * to strong symbol or weak got upgraded to non-weak
2281 */
2282 if (glob_sym->underlying_btf_id == 0)
2283 glob_sym->underlying_btf_id = -t->type;
2284
2285 /* globals from previous object files that match our
2286 * VAR/FUNC already have a corresponding associated
2287 * BTF type, so just make sure to use it
2288 */
2289 if (glob_sym->btf_id) {
2290 /* reuse existing BTF type for global var/func */
2291 obj->btf_type_map[i] = glob_sym->btf_id;
2292 continue;
2293 }
2294 }
2295
2296 id = btf__add_type(linker->btf, obj->btf, t);
2297 if (id < 0) {
2298 pr_warn("failed to append BTF type #%d from file '%s'\n", i, obj->filename);
2299 return id;
2300 }
2301
2302 obj->btf_type_map[i] = id;
2303
2304 /* record just appended BTF type for var/func */
2305 if (glob_sym) {
2306 glob_sym->btf_id = id;
2307 glob_sym->underlying_btf_id = -t->type;
2308 }
2309 }
2310
2311 /* remap all the types except DATASECs */
2312 n = btf__type_cnt(linker->btf);
2313 for (i = start_id; i < n; i++) {
2314 struct btf_type *dst_t = btf_type_by_id(linker->btf, i);
2315
2316 if (btf_type_visit_type_ids(dst_t, remap_type_id, obj->btf_type_map))
2317 return -EINVAL;
2318 }
2319
2320 /* Rewrite VAR/FUNC underlying types (i.e., FUNC's FUNC_PROTO and VAR's
2321 * actual type), if necessary
2322 */
2323 for (i = 0; i < linker->glob_sym_cnt; i++) {
2324 struct glob_sym *glob_sym = &linker->glob_syms[i];
2325 struct btf_type *glob_t;
2326
2327 if (glob_sym->underlying_btf_id >= 0)
2328 continue;
2329
2330 glob_sym->underlying_btf_id = obj->btf_type_map[-glob_sym->underlying_btf_id];
2331
2332 glob_t = btf_type_by_id(linker->btf, glob_sym->btf_id);
2333 glob_t->type = glob_sym->underlying_btf_id;
2334 }
2335
2336 /* append DATASEC info */
2337 for (i = 1; i < obj->sec_cnt; i++) {
2338 struct src_sec *src_sec;
2339 struct dst_sec *dst_sec;
2340 const struct btf_var_secinfo *src_var;
2341 struct btf_var_secinfo *dst_var;
2342
2343 src_sec = &obj->secs[i];
2344 if (!src_sec->sec_type_id || src_sec->skipped)
2345 continue;
2346 dst_sec = &linker->secs[src_sec->dst_id];
2347
2348 /* Mark section as having BTF regardless of the presence of
2349 * variables. In some cases compiler might generate empty BTF
2350 * with no variables information. E.g., when promoting local
2351 * array/structure variable initial values and BPF object
2352 * file otherwise has no read-only static variables in
2353 * .rodata. We need to preserve such empty BTF and just set
2354 * correct section size.
2355 */
2356 dst_sec->has_btf = true;
2357
2358 t = btf__type_by_id(obj->btf, src_sec->sec_type_id);
2359 src_var = btf_var_secinfos(t);
2360 n = btf_vlen(t);
2361 for (j = 0; j < n; j++, src_var++) {
2362 void *sec_vars = dst_sec->sec_vars;
2363 int new_id = obj->btf_type_map[src_var->type];
2364 struct glob_sym *glob_sym = NULL;
2365
2366 t = btf_type_by_id(linker->btf, new_id);
2367 if (btf_is_non_static(t)) {
2368 name = btf__str_by_offset(linker->btf, t->name_off);
2369 glob_sym = find_glob_sym(linker, name);
2370 if (glob_sym->sec_id != dst_sec->id) {
2371 pr_warn("global '%s': section mismatch %d vs %d\n",
2372 name, glob_sym->sec_id, dst_sec->id);
2373 return -EINVAL;
2374 }
2375 }
2376
2377 /* If there is already a member (VAR or FUNC) mapped
2378 * to the same type, don't add a duplicate entry.
2379 * This will happen when multiple object files define
2380 * the same extern VARs/FUNCs.
2381 */
2382 if (glob_sym && glob_sym->var_idx >= 0) {
2383 __s64 sz;
2384
2385 dst_var = &dst_sec->sec_vars[glob_sym->var_idx];
2386 /* Because underlying BTF type might have
2387 * changed, so might its size have changed, so
2388 * re-calculate and update it in sec_var.
2389 */
2390 sz = btf__resolve_size(linker->btf, glob_sym->underlying_btf_id);
2391 if (sz < 0) {
2392 pr_warn("global '%s': failed to resolve size of underlying type: %d\n",
2393 name, (int)sz);
2394 return -EINVAL;
2395 }
2396 dst_var->size = sz;
2397 continue;
2398 }
2399
2400 sec_vars = libbpf_reallocarray(sec_vars,
2401 dst_sec->sec_var_cnt + 1,
2402 sizeof(*dst_sec->sec_vars));
2403 if (!sec_vars)
2404 return -ENOMEM;
2405
2406 dst_sec->sec_vars = sec_vars;
2407 dst_sec->sec_var_cnt++;
2408
2409 dst_var = &dst_sec->sec_vars[dst_sec->sec_var_cnt - 1];
2410 dst_var->type = obj->btf_type_map[src_var->type];
2411 dst_var->size = src_var->size;
2412 dst_var->offset = src_sec->dst_off + src_var->offset;
2413
2414 if (glob_sym)
2415 glob_sym->var_idx = dst_sec->sec_var_cnt - 1;
2416 }
2417 }
2418
2419 return 0;
2420 }
2421
add_btf_ext_rec(struct btf_ext_sec_data * ext_data,const void * src_rec)2422 static void *add_btf_ext_rec(struct btf_ext_sec_data *ext_data, const void *src_rec)
2423 {
2424 void *tmp;
2425
2426 tmp = libbpf_reallocarray(ext_data->recs, ext_data->rec_cnt + 1, ext_data->rec_sz);
2427 if (!tmp)
2428 return NULL;
2429 ext_data->recs = tmp;
2430
2431 tmp += ext_data->rec_cnt * ext_data->rec_sz;
2432 memcpy(tmp, src_rec, ext_data->rec_sz);
2433
2434 ext_data->rec_cnt++;
2435
2436 return tmp;
2437 }
2438
linker_append_btf_ext(struct bpf_linker * linker,struct src_obj * obj)2439 static int linker_append_btf_ext(struct bpf_linker *linker, struct src_obj *obj)
2440 {
2441 const struct btf_ext_info_sec *ext_sec;
2442 const char *sec_name, *s;
2443 struct src_sec *src_sec;
2444 struct dst_sec *dst_sec;
2445 int rec_sz, str_off, i;
2446
2447 if (!obj->btf_ext)
2448 return 0;
2449
2450 rec_sz = obj->btf_ext->func_info.rec_size;
2451 for_each_btf_ext_sec(&obj->btf_ext->func_info, ext_sec) {
2452 struct bpf_func_info_min *src_rec, *dst_rec;
2453
2454 sec_name = btf__name_by_offset(obj->btf, ext_sec->sec_name_off);
2455 src_sec = find_src_sec_by_name(obj, sec_name);
2456 if (!src_sec) {
2457 pr_warn("can't find section '%s' referenced from .BTF.ext\n", sec_name);
2458 return -EINVAL;
2459 }
2460 dst_sec = &linker->secs[src_sec->dst_id];
2461
2462 if (dst_sec->func_info.rec_sz == 0)
2463 dst_sec->func_info.rec_sz = rec_sz;
2464 if (dst_sec->func_info.rec_sz != rec_sz) {
2465 pr_warn("incompatible .BTF.ext record sizes for section '%s'\n", sec_name);
2466 return -EINVAL;
2467 }
2468
2469 for_each_btf_ext_rec(&obj->btf_ext->func_info, ext_sec, i, src_rec) {
2470 dst_rec = add_btf_ext_rec(&dst_sec->func_info, src_rec);
2471 if (!dst_rec)
2472 return -ENOMEM;
2473
2474 dst_rec->insn_off += src_sec->dst_off;
2475 dst_rec->type_id = obj->btf_type_map[dst_rec->type_id];
2476 }
2477 }
2478
2479 rec_sz = obj->btf_ext->line_info.rec_size;
2480 for_each_btf_ext_sec(&obj->btf_ext->line_info, ext_sec) {
2481 struct bpf_line_info_min *src_rec, *dst_rec;
2482
2483 sec_name = btf__name_by_offset(obj->btf, ext_sec->sec_name_off);
2484 src_sec = find_src_sec_by_name(obj, sec_name);
2485 if (!src_sec) {
2486 pr_warn("can't find section '%s' referenced from .BTF.ext\n", sec_name);
2487 return -EINVAL;
2488 }
2489 dst_sec = &linker->secs[src_sec->dst_id];
2490
2491 if (dst_sec->line_info.rec_sz == 0)
2492 dst_sec->line_info.rec_sz = rec_sz;
2493 if (dst_sec->line_info.rec_sz != rec_sz) {
2494 pr_warn("incompatible .BTF.ext record sizes for section '%s'\n", sec_name);
2495 return -EINVAL;
2496 }
2497
2498 for_each_btf_ext_rec(&obj->btf_ext->line_info, ext_sec, i, src_rec) {
2499 dst_rec = add_btf_ext_rec(&dst_sec->line_info, src_rec);
2500 if (!dst_rec)
2501 return -ENOMEM;
2502
2503 dst_rec->insn_off += src_sec->dst_off;
2504
2505 s = btf__str_by_offset(obj->btf, src_rec->file_name_off);
2506 str_off = btf__add_str(linker->btf, s);
2507 if (str_off < 0)
2508 return -ENOMEM;
2509 dst_rec->file_name_off = str_off;
2510
2511 s = btf__str_by_offset(obj->btf, src_rec->line_off);
2512 str_off = btf__add_str(linker->btf, s);
2513 if (str_off < 0)
2514 return -ENOMEM;
2515 dst_rec->line_off = str_off;
2516
2517 /* dst_rec->line_col is fine */
2518 }
2519 }
2520
2521 rec_sz = obj->btf_ext->core_relo_info.rec_size;
2522 for_each_btf_ext_sec(&obj->btf_ext->core_relo_info, ext_sec) {
2523 struct bpf_core_relo *src_rec, *dst_rec;
2524
2525 sec_name = btf__name_by_offset(obj->btf, ext_sec->sec_name_off);
2526 src_sec = find_src_sec_by_name(obj, sec_name);
2527 if (!src_sec) {
2528 pr_warn("can't find section '%s' referenced from .BTF.ext\n", sec_name);
2529 return -EINVAL;
2530 }
2531 dst_sec = &linker->secs[src_sec->dst_id];
2532
2533 if (dst_sec->core_relo_info.rec_sz == 0)
2534 dst_sec->core_relo_info.rec_sz = rec_sz;
2535 if (dst_sec->core_relo_info.rec_sz != rec_sz) {
2536 pr_warn("incompatible .BTF.ext record sizes for section '%s'\n", sec_name);
2537 return -EINVAL;
2538 }
2539
2540 for_each_btf_ext_rec(&obj->btf_ext->core_relo_info, ext_sec, i, src_rec) {
2541 dst_rec = add_btf_ext_rec(&dst_sec->core_relo_info, src_rec);
2542 if (!dst_rec)
2543 return -ENOMEM;
2544
2545 dst_rec->insn_off += src_sec->dst_off;
2546 dst_rec->type_id = obj->btf_type_map[dst_rec->type_id];
2547
2548 s = btf__str_by_offset(obj->btf, src_rec->access_str_off);
2549 str_off = btf__add_str(linker->btf, s);
2550 if (str_off < 0)
2551 return -ENOMEM;
2552 dst_rec->access_str_off = str_off;
2553
2554 /* dst_rec->kind is fine */
2555 }
2556 }
2557
2558 return 0;
2559 }
2560
bpf_linker__finalize(struct bpf_linker * linker)2561 int bpf_linker__finalize(struct bpf_linker *linker)
2562 {
2563 struct dst_sec *sec;
2564 size_t strs_sz;
2565 const void *strs;
2566 int err, i;
2567
2568 if (!linker->elf)
2569 return libbpf_err(-EINVAL);
2570
2571 err = finalize_btf(linker);
2572 if (err)
2573 return libbpf_err(err);
2574
2575 /* Finalize strings */
2576 strs_sz = strset__data_size(linker->strtab_strs);
2577 strs = strset__data(linker->strtab_strs);
2578
2579 sec = &linker->secs[linker->strtab_sec_idx];
2580 sec->data->d_align = 1;
2581 sec->data->d_off = 0LL;
2582 sec->data->d_buf = (void *)strs;
2583 sec->data->d_type = ELF_T_BYTE;
2584 sec->data->d_size = strs_sz;
2585 sec->shdr->sh_size = strs_sz;
2586
2587 for (i = 1; i < linker->sec_cnt; i++) {
2588 sec = &linker->secs[i];
2589
2590 /* STRTAB is handled specially above */
2591 if (sec->sec_idx == linker->strtab_sec_idx)
2592 continue;
2593
2594 /* special ephemeral sections (.ksyms, .kconfig, etc) */
2595 if (!sec->scn)
2596 continue;
2597
2598 sec->data->d_buf = sec->raw_data;
2599 }
2600
2601 /* Finalize ELF layout */
2602 if (elf_update(linker->elf, ELF_C_NULL) < 0) {
2603 err = -errno;
2604 pr_warn_elf("failed to finalize ELF layout");
2605 return libbpf_err(err);
2606 }
2607
2608 /* Write out final ELF contents */
2609 if (elf_update(linker->elf, ELF_C_WRITE) < 0) {
2610 err = -errno;
2611 pr_warn_elf("failed to write ELF contents");
2612 return libbpf_err(err);
2613 }
2614
2615 elf_end(linker->elf);
2616 close(linker->fd);
2617
2618 linker->elf = NULL;
2619 linker->fd = -1;
2620
2621 return 0;
2622 }
2623
emit_elf_data_sec(struct bpf_linker * linker,const char * sec_name,size_t align,const void * raw_data,size_t raw_sz)2624 static int emit_elf_data_sec(struct bpf_linker *linker, const char *sec_name,
2625 size_t align, const void *raw_data, size_t raw_sz)
2626 {
2627 Elf_Scn *scn;
2628 Elf_Data *data;
2629 Elf64_Shdr *shdr;
2630 int name_off;
2631
2632 name_off = strset__add_str(linker->strtab_strs, sec_name);
2633 if (name_off < 0)
2634 return name_off;
2635
2636 scn = elf_newscn(linker->elf);
2637 if (!scn)
2638 return -ENOMEM;
2639 data = elf_newdata(scn);
2640 if (!data)
2641 return -ENOMEM;
2642 shdr = elf64_getshdr(scn);
2643 if (!shdr)
2644 return -EINVAL;
2645
2646 shdr->sh_name = name_off;
2647 shdr->sh_type = SHT_PROGBITS;
2648 shdr->sh_flags = 0;
2649 shdr->sh_size = raw_sz;
2650 shdr->sh_link = 0;
2651 shdr->sh_info = 0;
2652 shdr->sh_addralign = align;
2653 shdr->sh_entsize = 0;
2654
2655 data->d_type = ELF_T_BYTE;
2656 data->d_size = raw_sz;
2657 data->d_buf = (void *)raw_data;
2658 data->d_align = align;
2659 data->d_off = 0;
2660
2661 return 0;
2662 }
2663
finalize_btf(struct bpf_linker * linker)2664 static int finalize_btf(struct bpf_linker *linker)
2665 {
2666 LIBBPF_OPTS(btf_dedup_opts, opts);
2667 struct btf *btf = linker->btf;
2668 const void *raw_data;
2669 int i, j, id, err;
2670 __u32 raw_sz;
2671
2672 /* bail out if no BTF data was produced */
2673 if (btf__type_cnt(linker->btf) == 1)
2674 return 0;
2675
2676 for (i = 1; i < linker->sec_cnt; i++) {
2677 struct dst_sec *sec = &linker->secs[i];
2678
2679 if (!sec->has_btf)
2680 continue;
2681
2682 id = btf__add_datasec(btf, sec->sec_name, sec->sec_sz);
2683 if (id < 0) {
2684 pr_warn("failed to add consolidated BTF type for datasec '%s': %d\n",
2685 sec->sec_name, id);
2686 return id;
2687 }
2688
2689 for (j = 0; j < sec->sec_var_cnt; j++) {
2690 struct btf_var_secinfo *vi = &sec->sec_vars[j];
2691
2692 if (btf__add_datasec_var_info(btf, vi->type, vi->offset, vi->size))
2693 return -EINVAL;
2694 }
2695 }
2696
2697 err = finalize_btf_ext(linker);
2698 if (err) {
2699 pr_warn(".BTF.ext generation failed: %d\n", err);
2700 return err;
2701 }
2702
2703 opts.btf_ext = linker->btf_ext;
2704 err = btf__dedup(linker->btf, &opts);
2705 if (err) {
2706 pr_warn("BTF dedup failed: %d\n", err);
2707 return err;
2708 }
2709
2710 /* Emit .BTF section */
2711 raw_data = btf__raw_data(linker->btf, &raw_sz);
2712 if (!raw_data)
2713 return -ENOMEM;
2714
2715 err = emit_elf_data_sec(linker, BTF_ELF_SEC, 8, raw_data, raw_sz);
2716 if (err) {
2717 pr_warn("failed to write out .BTF ELF section: %d\n", err);
2718 return err;
2719 }
2720
2721 /* Emit .BTF.ext section */
2722 if (linker->btf_ext) {
2723 raw_data = btf_ext__get_raw_data(linker->btf_ext, &raw_sz);
2724 if (!raw_data)
2725 return -ENOMEM;
2726
2727 err = emit_elf_data_sec(linker, BTF_EXT_ELF_SEC, 8, raw_data, raw_sz);
2728 if (err) {
2729 pr_warn("failed to write out .BTF.ext ELF section: %d\n", err);
2730 return err;
2731 }
2732 }
2733
2734 return 0;
2735 }
2736
emit_btf_ext_data(struct bpf_linker * linker,void * output,const char * sec_name,struct btf_ext_sec_data * sec_data)2737 static int emit_btf_ext_data(struct bpf_linker *linker, void *output,
2738 const char *sec_name, struct btf_ext_sec_data *sec_data)
2739 {
2740 struct btf_ext_info_sec *sec_info;
2741 void *cur = output;
2742 int str_off;
2743 size_t sz;
2744
2745 if (!sec_data->rec_cnt)
2746 return 0;
2747
2748 str_off = btf__add_str(linker->btf, sec_name);
2749 if (str_off < 0)
2750 return -ENOMEM;
2751
2752 sec_info = cur;
2753 sec_info->sec_name_off = str_off;
2754 sec_info->num_info = sec_data->rec_cnt;
2755 cur += sizeof(struct btf_ext_info_sec);
2756
2757 sz = sec_data->rec_cnt * sec_data->rec_sz;
2758 memcpy(cur, sec_data->recs, sz);
2759 cur += sz;
2760
2761 return cur - output;
2762 }
2763
finalize_btf_ext(struct bpf_linker * linker)2764 static int finalize_btf_ext(struct bpf_linker *linker)
2765 {
2766 size_t funcs_sz = 0, lines_sz = 0, core_relos_sz = 0, total_sz = 0;
2767 size_t func_rec_sz = 0, line_rec_sz = 0, core_relo_rec_sz = 0;
2768 struct btf_ext_header *hdr;
2769 void *data, *cur;
2770 int i, err, sz;
2771
2772 /* validate that all sections have the same .BTF.ext record sizes
2773 * and calculate total data size for each type of data (func info,
2774 * line info, core relos)
2775 */
2776 for (i = 1; i < linker->sec_cnt; i++) {
2777 struct dst_sec *sec = &linker->secs[i];
2778
2779 if (sec->func_info.rec_cnt) {
2780 if (func_rec_sz == 0)
2781 func_rec_sz = sec->func_info.rec_sz;
2782 if (func_rec_sz != sec->func_info.rec_sz) {
2783 pr_warn("mismatch in func_info record size %zu != %u\n",
2784 func_rec_sz, sec->func_info.rec_sz);
2785 return -EINVAL;
2786 }
2787
2788 funcs_sz += sizeof(struct btf_ext_info_sec) + func_rec_sz * sec->func_info.rec_cnt;
2789 }
2790 if (sec->line_info.rec_cnt) {
2791 if (line_rec_sz == 0)
2792 line_rec_sz = sec->line_info.rec_sz;
2793 if (line_rec_sz != sec->line_info.rec_sz) {
2794 pr_warn("mismatch in line_info record size %zu != %u\n",
2795 line_rec_sz, sec->line_info.rec_sz);
2796 return -EINVAL;
2797 }
2798
2799 lines_sz += sizeof(struct btf_ext_info_sec) + line_rec_sz * sec->line_info.rec_cnt;
2800 }
2801 if (sec->core_relo_info.rec_cnt) {
2802 if (core_relo_rec_sz == 0)
2803 core_relo_rec_sz = sec->core_relo_info.rec_sz;
2804 if (core_relo_rec_sz != sec->core_relo_info.rec_sz) {
2805 pr_warn("mismatch in core_relo_info record size %zu != %u\n",
2806 core_relo_rec_sz, sec->core_relo_info.rec_sz);
2807 return -EINVAL;
2808 }
2809
2810 core_relos_sz += sizeof(struct btf_ext_info_sec) + core_relo_rec_sz * sec->core_relo_info.rec_cnt;
2811 }
2812 }
2813
2814 if (!funcs_sz && !lines_sz && !core_relos_sz)
2815 return 0;
2816
2817 total_sz += sizeof(struct btf_ext_header);
2818 if (funcs_sz) {
2819 funcs_sz += sizeof(__u32); /* record size prefix */
2820 total_sz += funcs_sz;
2821 }
2822 if (lines_sz) {
2823 lines_sz += sizeof(__u32); /* record size prefix */
2824 total_sz += lines_sz;
2825 }
2826 if (core_relos_sz) {
2827 core_relos_sz += sizeof(__u32); /* record size prefix */
2828 total_sz += core_relos_sz;
2829 }
2830
2831 cur = data = calloc(1, total_sz);
2832 if (!data)
2833 return -ENOMEM;
2834
2835 hdr = cur;
2836 hdr->magic = BTF_MAGIC;
2837 hdr->version = BTF_VERSION;
2838 hdr->flags = 0;
2839 hdr->hdr_len = sizeof(struct btf_ext_header);
2840 cur += sizeof(struct btf_ext_header);
2841
2842 /* All offsets are in bytes relative to the end of this header */
2843 hdr->func_info_off = 0;
2844 hdr->func_info_len = funcs_sz;
2845 hdr->line_info_off = funcs_sz;
2846 hdr->line_info_len = lines_sz;
2847 hdr->core_relo_off = funcs_sz + lines_sz;
2848 hdr->core_relo_len = core_relos_sz;
2849
2850 if (funcs_sz) {
2851 *(__u32 *)cur = func_rec_sz;
2852 cur += sizeof(__u32);
2853
2854 for (i = 1; i < linker->sec_cnt; i++) {
2855 struct dst_sec *sec = &linker->secs[i];
2856
2857 sz = emit_btf_ext_data(linker, cur, sec->sec_name, &sec->func_info);
2858 if (sz < 0) {
2859 err = sz;
2860 goto out;
2861 }
2862
2863 cur += sz;
2864 }
2865 }
2866
2867 if (lines_sz) {
2868 *(__u32 *)cur = line_rec_sz;
2869 cur += sizeof(__u32);
2870
2871 for (i = 1; i < linker->sec_cnt; i++) {
2872 struct dst_sec *sec = &linker->secs[i];
2873
2874 sz = emit_btf_ext_data(linker, cur, sec->sec_name, &sec->line_info);
2875 if (sz < 0) {
2876 err = sz;
2877 goto out;
2878 }
2879
2880 cur += sz;
2881 }
2882 }
2883
2884 if (core_relos_sz) {
2885 *(__u32 *)cur = core_relo_rec_sz;
2886 cur += sizeof(__u32);
2887
2888 for (i = 1; i < linker->sec_cnt; i++) {
2889 struct dst_sec *sec = &linker->secs[i];
2890
2891 sz = emit_btf_ext_data(linker, cur, sec->sec_name, &sec->core_relo_info);
2892 if (sz < 0) {
2893 err = sz;
2894 goto out;
2895 }
2896
2897 cur += sz;
2898 }
2899 }
2900
2901 linker->btf_ext = btf_ext__new(data, total_sz);
2902 err = libbpf_get_error(linker->btf_ext);
2903 if (err) {
2904 linker->btf_ext = NULL;
2905 pr_warn("failed to parse final .BTF.ext data: %d\n", err);
2906 goto out;
2907 }
2908
2909 out:
2910 free(data);
2911 return err;
2912 }
2913