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1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * genelf.c
4 * Copyright (C) 2014, Google, Inc
5 *
6 * Contributed by:
7 * Stephane Eranian <eranian@gmail.com>
8 */
9
10#include <sys/types.h>
11#include <stdio.h>
12#include <getopt.h>
13#include <stddef.h>
14#include <libelf.h>
15#include <string.h>
16#include <stdlib.h>
17#include <unistd.h>
18#include <inttypes.h>
19#include <limits.h>
20#include <fcntl.h>
21#include <err.h>
22#ifdef HAVE_DWARF_SUPPORT
23#include <dwarf.h>
24#endif
25
26#include "genelf.h"
27#include "../util/jitdump.h"
28#include <linux/compiler.h>
29
30#ifndef NT_GNU_BUILD_ID
31#define NT_GNU_BUILD_ID 3
32#endif
33
34#define JVMTI
35
36#define BUILD_ID_URANDOM /* different uuid for each run */
37
38#ifdef HAVE_LIBCRYPTO
39
40#define BUILD_ID_MD5
41#undef BUILD_ID_SHA /* does not seem to work well when linked with Java */
42#undef BUILD_ID_URANDOM /* different uuid for each run */
43
44#ifdef BUILD_ID_SHA
45#include <openssl/sha.h>
46#endif
47
48#ifdef BUILD_ID_MD5
49#include <openssl/md5.h>
50#endif
51#endif
52
53
54typedef struct {
55 unsigned int namesz; /* Size of entry's owner string */
56 unsigned int descsz; /* Size of the note descriptor */
57 unsigned int type; /* Interpretation of the descriptor */
58 char name[0]; /* Start of the name+desc data */
59} Elf_Note;
60
61struct options {
62 char *output;
63 int fd;
64};
65
66static char shd_string_table[] = {
67 0,
68 '.', 't', 'e', 'x', 't', 0, /* 1 */
69 '.', 's', 'h', 's', 't', 'r', 't', 'a', 'b', 0, /* 7 */
70 '.', 's', 'y', 'm', 't', 'a', 'b', 0, /* 17 */
71 '.', 's', 't', 'r', 't', 'a', 'b', 0, /* 25 */
72 '.', 'n', 'o', 't', 'e', '.', 'g', 'n', 'u', '.', 'b', 'u', 'i', 'l', 'd', '-', 'i', 'd', 0, /* 33 */
73 '.', 'd', 'e', 'b', 'u', 'g', '_', 'l', 'i', 'n', 'e', 0, /* 52 */
74 '.', 'd', 'e', 'b', 'u', 'g', '_', 'i', 'n', 'f', 'o', 0, /* 64 */
75 '.', 'd', 'e', 'b', 'u', 'g', '_', 'a', 'b', 'b', 'r', 'e', 'v', 0, /* 76 */
76 '.', 'e', 'h', '_', 'f', 'r', 'a', 'm', 'e', '_', 'h', 'd', 'r', 0, /* 90 */
77 '.', 'e', 'h', '_', 'f', 'r', 'a', 'm', 'e', 0, /* 104 */
78};
79
80static struct buildid_note {
81 Elf_Note desc; /* descsz: size of build-id, must be multiple of 4 */
82 char name[4]; /* GNU\0 */
83 char build_id[20];
84} bnote;
85
86static Elf_Sym symtab[]={
87 /* symbol 0 MUST be the undefined symbol */
88 { .st_name = 0, /* index in sym_string table */
89 .st_info = ELF_ST_TYPE(STT_NOTYPE),
90 .st_shndx = 0, /* for now */
91 .st_value = 0x0,
92 .st_other = ELF_ST_VIS(STV_DEFAULT),
93 .st_size = 0,
94 },
95 { .st_name = 1, /* index in sym_string table */
96 .st_info = ELF_ST_BIND(STB_LOCAL) | ELF_ST_TYPE(STT_FUNC),
97 .st_shndx = 1,
98 .st_value = 0, /* for now */
99 .st_other = ELF_ST_VIS(STV_DEFAULT),
100 .st_size = 0, /* for now */
101 }
102};
103
104#ifdef BUILD_ID_URANDOM
105static void
106gen_build_id(struct buildid_note *note,
107 unsigned long load_addr __maybe_unused,
108 const void *code __maybe_unused,
109 size_t csize __maybe_unused)
110{
111 int fd;
112 size_t sz = sizeof(note->build_id);
113 ssize_t sret;
114
115 fd = open("/dev/urandom", O_RDONLY);
116 if (fd == -1)
117 err(1, "cannot access /dev/urandom for buildid");
118
119 sret = read(fd, note->build_id, sz);
120
121 close(fd);
122
123 if (sret != (ssize_t)sz)
124 memset(note->build_id, 0, sz);
125}
126#endif
127
128#ifdef BUILD_ID_SHA
129static void
130gen_build_id(struct buildid_note *note,
131 unsigned long load_addr __maybe_unused,
132 const void *code,
133 size_t csize)
134{
135 if (sizeof(note->build_id) < SHA_DIGEST_LENGTH)
136 errx(1, "build_id too small for SHA1");
137
138 SHA1(code, csize, (unsigned char *)note->build_id);
139}
140#endif
141
142#ifdef BUILD_ID_MD5
143static void
144gen_build_id(struct buildid_note *note, unsigned long load_addr, const void *code, size_t csize)
145{
146 MD5_CTX context;
147
148 if (sizeof(note->build_id) < 16)
149 errx(1, "build_id too small for MD5");
150
151 MD5_Init(&context);
152 MD5_Update(&context, &load_addr, sizeof(load_addr));
153 MD5_Update(&context, code, csize);
154 MD5_Final((unsigned char *)note->build_id, &context);
155}
156#endif
157
158static int
159jit_add_eh_frame_info(Elf *e, void* unwinding, uint64_t unwinding_header_size,
160 uint64_t unwinding_size, uint64_t base_offset)
161{
162 Elf_Data *d;
163 Elf_Scn *scn;
164 Elf_Shdr *shdr;
165 uint64_t unwinding_table_size = unwinding_size - unwinding_header_size;
166
167 /*
168 * setup eh_frame section
169 */
170 scn = elf_newscn(e);
171 if (!scn) {
172 warnx("cannot create section");
173 return -1;
174 }
175
176 d = elf_newdata(scn);
177 if (!d) {
178 warnx("cannot get new data");
179 return -1;
180 }
181
182 d->d_align = 8;
183 d->d_off = 0LL;
184 d->d_buf = unwinding;
185 d->d_type = ELF_T_BYTE;
186 d->d_size = unwinding_table_size;
187 d->d_version = EV_CURRENT;
188
189 shdr = elf_getshdr(scn);
190 if (!shdr) {
191 warnx("cannot get section header");
192 return -1;
193 }
194
195 shdr->sh_name = 104;
196 shdr->sh_type = SHT_PROGBITS;
197 shdr->sh_addr = base_offset;
198 shdr->sh_flags = SHF_ALLOC;
199 shdr->sh_entsize = 0;
200
201 /*
202 * setup eh_frame_hdr section
203 */
204 scn = elf_newscn(e);
205 if (!scn) {
206 warnx("cannot create section");
207 return -1;
208 }
209
210 d = elf_newdata(scn);
211 if (!d) {
212 warnx("cannot get new data");
213 return -1;
214 }
215
216 d->d_align = 4;
217 d->d_off = 0LL;
218 d->d_buf = unwinding + unwinding_table_size;
219 d->d_type = ELF_T_BYTE;
220 d->d_size = unwinding_header_size;
221 d->d_version = EV_CURRENT;
222
223 shdr = elf_getshdr(scn);
224 if (!shdr) {
225 warnx("cannot get section header");
226 return -1;
227 }
228
229 shdr->sh_name = 90;
230 shdr->sh_type = SHT_PROGBITS;
231 shdr->sh_addr = base_offset + unwinding_table_size;
232 shdr->sh_flags = SHF_ALLOC;
233 shdr->sh_entsize = 0;
234
235 return 0;
236}
237
238/*
239 * fd: file descriptor open for writing for the output file
240 * load_addr: code load address (could be zero, just used for buildid)
241 * sym: function name (for native code - used as the symbol)
242 * code: the native code
243 * csize: the code size in bytes
244 */
245int
246jit_write_elf(int fd, uint64_t load_addr, const char *sym,
247 const void *code, int csize,
248 void *debug __maybe_unused, int nr_debug_entries __maybe_unused,
249 void *unwinding, uint64_t unwinding_header_size, uint64_t unwinding_size)
250{
251 Elf *e;
252 Elf_Data *d;
253 Elf_Scn *scn;
254 Elf_Ehdr *ehdr;
255 Elf_Shdr *shdr;
256 uint64_t eh_frame_base_offset;
257 char *strsym = NULL;
258 int symlen;
259 int retval = -1;
260
261 if (elf_version(EV_CURRENT) == EV_NONE) {
262 warnx("ELF initialization failed");
263 return -1;
264 }
265
266 e = elf_begin(fd, ELF_C_WRITE, NULL);
267 if (!e) {
268 warnx("elf_begin failed");
269 goto error;
270 }
271
272 /*
273 * setup ELF header
274 */
275 ehdr = elf_newehdr(e);
276 if (!ehdr) {
277 warnx("cannot get ehdr");
278 goto error;
279 }
280
281 ehdr->e_ident[EI_DATA] = GEN_ELF_ENDIAN;
282 ehdr->e_ident[EI_CLASS] = GEN_ELF_CLASS;
283 ehdr->e_machine = GEN_ELF_ARCH;
284 ehdr->e_type = ET_DYN;
285 ehdr->e_entry = GEN_ELF_TEXT_OFFSET;
286 ehdr->e_version = EV_CURRENT;
287 ehdr->e_shstrndx= unwinding ? 4 : 2; /* shdr index for section name */
288
289 /*
290 * setup text section
291 */
292 scn = elf_newscn(e);
293 if (!scn) {
294 warnx("cannot create section");
295 goto error;
296 }
297
298 d = elf_newdata(scn);
299 if (!d) {
300 warnx("cannot get new data");
301 goto error;
302 }
303
304 d->d_align = 16;
305 d->d_off = 0LL;
306 d->d_buf = (void *)code;
307 d->d_type = ELF_T_BYTE;
308 d->d_size = csize;
309 d->d_version = EV_CURRENT;
310
311 shdr = elf_getshdr(scn);
312 if (!shdr) {
313 warnx("cannot get section header");
314 goto error;
315 }
316
317 shdr->sh_name = 1;
318 shdr->sh_type = SHT_PROGBITS;
319 shdr->sh_addr = GEN_ELF_TEXT_OFFSET;
320 shdr->sh_flags = SHF_EXECINSTR | SHF_ALLOC;
321 shdr->sh_entsize = 0;
322
323 /*
324 * Setup .eh_frame_hdr and .eh_frame
325 */
326 if (unwinding) {
327 eh_frame_base_offset = ALIGN_8(GEN_ELF_TEXT_OFFSET + csize);
328 retval = jit_add_eh_frame_info(e, unwinding,
329 unwinding_header_size, unwinding_size,
330 eh_frame_base_offset);
331 if (retval)
332 goto error;
333 }
334
335 /*
336 * setup section headers string table
337 */
338 scn = elf_newscn(e);
339 if (!scn) {
340 warnx("cannot create section");
341 goto error;
342 }
343
344 d = elf_newdata(scn);
345 if (!d) {
346 warnx("cannot get new data");
347 goto error;
348 }
349
350 d->d_align = 1;
351 d->d_off = 0LL;
352 d->d_buf = shd_string_table;
353 d->d_type = ELF_T_BYTE;
354 d->d_size = sizeof(shd_string_table);
355 d->d_version = EV_CURRENT;
356
357 shdr = elf_getshdr(scn);
358 if (!shdr) {
359 warnx("cannot get section header");
360 goto error;
361 }
362
363 shdr->sh_name = 7; /* offset of '.shstrtab' in shd_string_table */
364 shdr->sh_type = SHT_STRTAB;
365 shdr->sh_flags = 0;
366 shdr->sh_entsize = 0;
367
368 /*
369 * setup symtab section
370 */
371 symtab[1].st_size = csize;
372 symtab[1].st_value = GEN_ELF_TEXT_OFFSET;
373
374 scn = elf_newscn(e);
375 if (!scn) {
376 warnx("cannot create section");
377 goto error;
378 }
379
380 d = elf_newdata(scn);
381 if (!d) {
382 warnx("cannot get new data");
383 goto error;
384 }
385
386 d->d_align = 8;
387 d->d_off = 0LL;
388 d->d_buf = symtab;
389 d->d_type = ELF_T_SYM;
390 d->d_size = sizeof(symtab);
391 d->d_version = EV_CURRENT;
392
393 shdr = elf_getshdr(scn);
394 if (!shdr) {
395 warnx("cannot get section header");
396 goto error;
397 }
398
399 shdr->sh_name = 17; /* offset of '.symtab' in shd_string_table */
400 shdr->sh_type = SHT_SYMTAB;
401 shdr->sh_flags = 0;
402 shdr->sh_entsize = sizeof(Elf_Sym);
403 shdr->sh_link = unwinding ? 6 : 4; /* index of .strtab section */
404
405 /*
406 * setup symbols string table
407 * 2 = 1 for 0 in 1st entry, 1 for the 0 at end of symbol for 2nd entry
408 */
409 symlen = 2 + strlen(sym);
410 strsym = calloc(1, symlen);
411 if (!strsym) {
412 warnx("cannot allocate strsym");
413 goto error;
414 }
415 strcpy(strsym + 1, sym);
416
417 scn = elf_newscn(e);
418 if (!scn) {
419 warnx("cannot create section");
420 goto error;
421 }
422
423 d = elf_newdata(scn);
424 if (!d) {
425 warnx("cannot get new data");
426 goto error;
427 }
428
429 d->d_align = 1;
430 d->d_off = 0LL;
431 d->d_buf = strsym;
432 d->d_type = ELF_T_BYTE;
433 d->d_size = symlen;
434 d->d_version = EV_CURRENT;
435
436 shdr = elf_getshdr(scn);
437 if (!shdr) {
438 warnx("cannot get section header");
439 goto error;
440 }
441
442 shdr->sh_name = 25; /* offset in shd_string_table */
443 shdr->sh_type = SHT_STRTAB;
444 shdr->sh_flags = 0;
445 shdr->sh_entsize = 0;
446
447 /*
448 * setup build-id section
449 */
450 scn = elf_newscn(e);
451 if (!scn) {
452 warnx("cannot create section");
453 goto error;
454 }
455
456 d = elf_newdata(scn);
457 if (!d) {
458 warnx("cannot get new data");
459 goto error;
460 }
461
462 /*
463 * build-id generation
464 */
465 gen_build_id(&bnote, load_addr, code, csize);
466 bnote.desc.namesz = sizeof(bnote.name); /* must include 0 termination */
467 bnote.desc.descsz = sizeof(bnote.build_id);
468 bnote.desc.type = NT_GNU_BUILD_ID;
469 strcpy(bnote.name, "GNU");
470
471 d->d_align = 4;
472 d->d_off = 0LL;
473 d->d_buf = &bnote;
474 d->d_type = ELF_T_BYTE;
475 d->d_size = sizeof(bnote);
476 d->d_version = EV_CURRENT;
477
478 shdr = elf_getshdr(scn);
479 if (!shdr) {
480 warnx("cannot get section header");
481 goto error;
482 }
483
484 shdr->sh_name = 33; /* offset in shd_string_table */
485 shdr->sh_type = SHT_NOTE;
486 shdr->sh_addr = 0x0;
487 shdr->sh_flags = SHF_ALLOC;
488 shdr->sh_size = sizeof(bnote);
489 shdr->sh_entsize = 0;
490
491#ifdef HAVE_DWARF_SUPPORT
492 if (debug && nr_debug_entries) {
493 retval = jit_add_debug_info(e, load_addr, debug, nr_debug_entries);
494 if (retval)
495 goto error;
496 } else
497#endif
498 {
499 if (elf_update(e, ELF_C_WRITE) < 0) {
500 warnx("elf_update 4 failed");
501 goto error;
502 }
503 }
504
505 retval = 0;
506error:
507 (void)elf_end(e);
508
509 free(strsym);
510
511
512 return retval;
513}
514
515#ifndef JVMTI
516
517static unsigned char x86_code[] = {
518 0xBB, 0x2A, 0x00, 0x00, 0x00, /* movl $42, %ebx */
519 0xB8, 0x01, 0x00, 0x00, 0x00, /* movl $1, %eax */
520 0xCD, 0x80 /* int $0x80 */
521};
522
523static struct options options;
524
525int main(int argc, char **argv)
526{
527 int c, fd, ret;
528
529 while ((c = getopt(argc, argv, "o:h")) != -1) {
530 switch (c) {
531 case 'o':
532 options.output = optarg;
533 break;
534 case 'h':
535 printf("Usage: genelf -o output_file [-h]\n");
536 return 0;
537 default:
538 errx(1, "unknown option");
539 }
540 }
541
542 fd = open(options.output, O_CREAT|O_TRUNC|O_RDWR, 0666);
543 if (fd == -1)
544 err(1, "cannot create file %s", options.output);
545
546 ret = jit_write_elf(fd, "main", x86_code, sizeof(x86_code));
547 close(fd);
548
549 if (ret != 0)
550 unlink(options.output);
551
552 return ret;
553}
554#endif