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