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1/*
2 * genelf.c
3 * Copyright (C) 2014, Google, Inc
4 *
5 * Contributed by:
6 * Stephane Eranian <eranian@gmail.com>
7 *
8 * Released under the GPL v2. (and only v2, not any later version)
9 */
10
11#include <sys/types.h>
12#include <stdio.h>
13#include <getopt.h>
14#include <stddef.h>
15#include <libelf.h>
16#include <string.h>
17#include <stdlib.h>
18#include <inttypes.h>
19#include <limits.h>
20#include <fcntl.h>
21#include <err.h>
22#include <dwarf.h>
23
24#include "perf.h"
25#include "genelf.h"
26#include "../util/jitdump.h"
27
28#define JVMTI
29
30#define BUILD_ID_URANDOM /* different uuid for each run */
31
32#ifdef HAVE_LIBCRYPTO
33
34#define BUILD_ID_MD5
35#undef BUILD_ID_SHA /* does not seem to work well when linked with Java */
36#undef BUILD_ID_URANDOM /* different uuid for each run */
37
38#ifdef BUILD_ID_SHA
39#include <openssl/sha.h>
40#endif
41
42#ifdef BUILD_ID_MD5
43#include <openssl/md5.h>
44#endif
45#endif
46
47
48typedef struct {
49 unsigned int namesz; /* Size of entry's owner string */
50 unsigned int descsz; /* Size of the note descriptor */
51 unsigned int type; /* Interpretation of the descriptor */
52 char name[0]; /* Start of the name+desc data */
53} Elf_Note;
54
55struct options {
56 char *output;
57 int fd;
58};
59
60static char shd_string_table[] = {
61 0,
62 '.', 't', 'e', 'x', 't', 0, /* 1 */
63 '.', 's', 'h', 's', 't', 'r', 't', 'a', 'b', 0, /* 7 */
64 '.', 's', 'y', 'm', 't', 'a', 'b', 0, /* 17 */
65 '.', 's', 't', 'r', 't', 'a', 'b', 0, /* 25 */
66 '.', 'n', 'o', 't', 'e', '.', 'g', 'n', 'u', '.', 'b', 'u', 'i', 'l', 'd', '-', 'i', 'd', 0, /* 33 */
67 '.', 'd', 'e', 'b', 'u', 'g', '_', 'l', 'i', 'n', 'e', 0, /* 52 */
68 '.', 'd', 'e', 'b', 'u', 'g', '_', 'i', 'n', 'f', 'o', 0, /* 64 */
69 '.', 'd', 'e', 'b', 'u', 'g', '_', 'a', 'b', 'b', 'r', 'e', 'v', 0, /* 76 */
70};
71
72static struct buildid_note {
73 Elf_Note desc; /* descsz: size of build-id, must be multiple of 4 */
74 char name[4]; /* GNU\0 */
75 char build_id[20];
76} bnote;
77
78static Elf_Sym symtab[]={
79 /* symbol 0 MUST be the undefined symbol */
80 { .st_name = 0, /* index in sym_string table */
81 .st_info = ELF_ST_TYPE(STT_NOTYPE),
82 .st_shndx = 0, /* for now */
83 .st_value = 0x0,
84 .st_other = ELF_ST_VIS(STV_DEFAULT),
85 .st_size = 0,
86 },
87 { .st_name = 1, /* index in sym_string table */
88 .st_info = ELF_ST_BIND(STB_LOCAL) | ELF_ST_TYPE(STT_FUNC),
89 .st_shndx = 1,
90 .st_value = 0, /* for now */
91 .st_other = ELF_ST_VIS(STV_DEFAULT),
92 .st_size = 0, /* for now */
93 }
94};
95
96#ifdef BUILD_ID_URANDOM
97static void
98gen_build_id(struct buildid_note *note,
99 unsigned long load_addr __maybe_unused,
100 const void *code __maybe_unused,
101 size_t csize __maybe_unused)
102{
103 int fd;
104 size_t sz = sizeof(note->build_id);
105 ssize_t sret;
106
107 fd = open("/dev/urandom", O_RDONLY);
108 if (fd == -1)
109 err(1, "cannot access /dev/urandom for builid");
110
111 sret = read(fd, note->build_id, sz);
112
113 close(fd);
114
115 if (sret != (ssize_t)sz)
116 memset(note->build_id, 0, sz);
117}
118#endif
119
120#ifdef BUILD_ID_SHA
121static void
122gen_build_id(struct buildid_note *note,
123 unsigned long load_addr __maybe_unused,
124 const void *code,
125 size_t csize)
126{
127 if (sizeof(note->build_id) < SHA_DIGEST_LENGTH)
128 errx(1, "build_id too small for SHA1");
129
130 SHA1(code, csize, (unsigned char *)note->build_id);
131}
132#endif
133
134#ifdef BUILD_ID_MD5
135static void
136gen_build_id(struct buildid_note *note, unsigned long load_addr, const void *code, size_t csize)
137{
138 MD5_CTX context;
139
140 if (sizeof(note->build_id) < 16)
141 errx(1, "build_id too small for MD5");
142
143 MD5_Init(&context);
144 MD5_Update(&context, &load_addr, sizeof(load_addr));
145 MD5_Update(&context, code, csize);
146 MD5_Final((unsigned char *)note->build_id, &context);
147}
148#endif
149
150/*
151 * fd: file descriptor open for writing for the output file
152 * load_addr: code load address (could be zero, just used for buildid)
153 * sym: function name (for native code - used as the symbol)
154 * code: the native code
155 * csize: the code size in bytes
156 */
157int
158jit_write_elf(int fd, uint64_t load_addr, const char *sym,
159 const void *code, int csize,
160 void *debug, int nr_debug_entries)
161{
162 Elf *e;
163 Elf_Data *d;
164 Elf_Scn *scn;
165 Elf_Ehdr *ehdr;
166 Elf_Shdr *shdr;
167 char *strsym = NULL;
168 int symlen;
169 int retval = -1;
170
171 if (elf_version(EV_CURRENT) == EV_NONE) {
172 warnx("ELF initialization failed");
173 return -1;
174 }
175
176 e = elf_begin(fd, ELF_C_WRITE, NULL);
177 if (!e) {
178 warnx("elf_begin failed");
179 goto error;
180 }
181
182 /*
183 * setup ELF header
184 */
185 ehdr = elf_newehdr(e);
186 if (!ehdr) {
187 warnx("cannot get ehdr");
188 goto error;
189 }
190
191 ehdr->e_ident[EI_DATA] = GEN_ELF_ENDIAN;
192 ehdr->e_ident[EI_CLASS] = GEN_ELF_CLASS;
193 ehdr->e_machine = GEN_ELF_ARCH;
194 ehdr->e_type = ET_DYN;
195 ehdr->e_entry = GEN_ELF_TEXT_OFFSET;
196 ehdr->e_version = EV_CURRENT;
197 ehdr->e_shstrndx= 2; /* shdr index for section name */
198
199 /*
200 * setup text section
201 */
202 scn = elf_newscn(e);
203 if (!scn) {
204 warnx("cannot create section");
205 goto error;
206 }
207
208 d = elf_newdata(scn);
209 if (!d) {
210 warnx("cannot get new data");
211 goto error;
212 }
213
214 d->d_align = 16;
215 d->d_off = 0LL;
216 d->d_buf = (void *)code;
217 d->d_type = ELF_T_BYTE;
218 d->d_size = csize;
219 d->d_version = EV_CURRENT;
220
221 shdr = elf_getshdr(scn);
222 if (!shdr) {
223 warnx("cannot get section header");
224 goto error;
225 }
226
227 shdr->sh_name = 1;
228 shdr->sh_type = SHT_PROGBITS;
229 shdr->sh_addr = GEN_ELF_TEXT_OFFSET;
230 shdr->sh_flags = SHF_EXECINSTR | SHF_ALLOC;
231 shdr->sh_entsize = 0;
232
233 /*
234 * setup section headers string table
235 */
236 scn = elf_newscn(e);
237 if (!scn) {
238 warnx("cannot create section");
239 goto error;
240 }
241
242 d = elf_newdata(scn);
243 if (!d) {
244 warnx("cannot get new data");
245 goto error;
246 }
247
248 d->d_align = 1;
249 d->d_off = 0LL;
250 d->d_buf = shd_string_table;
251 d->d_type = ELF_T_BYTE;
252 d->d_size = sizeof(shd_string_table);
253 d->d_version = EV_CURRENT;
254
255 shdr = elf_getshdr(scn);
256 if (!shdr) {
257 warnx("cannot get section header");
258 goto error;
259 }
260
261 shdr->sh_name = 7; /* offset of '.shstrtab' in shd_string_table */
262 shdr->sh_type = SHT_STRTAB;
263 shdr->sh_flags = 0;
264 shdr->sh_entsize = 0;
265
266 /*
267 * setup symtab section
268 */
269 symtab[1].st_size = csize;
270 symtab[1].st_value = GEN_ELF_TEXT_OFFSET;
271
272 scn = elf_newscn(e);
273 if (!scn) {
274 warnx("cannot create section");
275 goto error;
276 }
277
278 d = elf_newdata(scn);
279 if (!d) {
280 warnx("cannot get new data");
281 goto error;
282 }
283
284 d->d_align = 8;
285 d->d_off = 0LL;
286 d->d_buf = symtab;
287 d->d_type = ELF_T_SYM;
288 d->d_size = sizeof(symtab);
289 d->d_version = EV_CURRENT;
290
291 shdr = elf_getshdr(scn);
292 if (!shdr) {
293 warnx("cannot get section header");
294 goto error;
295 }
296
297 shdr->sh_name = 17; /* offset of '.symtab' in shd_string_table */
298 shdr->sh_type = SHT_SYMTAB;
299 shdr->sh_flags = 0;
300 shdr->sh_entsize = sizeof(Elf_Sym);
301 shdr->sh_link = 4; /* index of .strtab section */
302
303 /*
304 * setup symbols string table
305 * 2 = 1 for 0 in 1st entry, 1 for the 0 at end of symbol for 2nd entry
306 */
307 symlen = 2 + strlen(sym);
308 strsym = calloc(1, symlen);
309 if (!strsym) {
310 warnx("cannot allocate strsym");
311 goto error;
312 }
313 strcpy(strsym + 1, sym);
314
315 scn = elf_newscn(e);
316 if (!scn) {
317 warnx("cannot create section");
318 goto error;
319 }
320
321 d = elf_newdata(scn);
322 if (!d) {
323 warnx("cannot get new data");
324 goto error;
325 }
326
327 d->d_align = 1;
328 d->d_off = 0LL;
329 d->d_buf = strsym;
330 d->d_type = ELF_T_BYTE;
331 d->d_size = symlen;
332 d->d_version = EV_CURRENT;
333
334 shdr = elf_getshdr(scn);
335 if (!shdr) {
336 warnx("cannot get section header");
337 goto error;
338 }
339
340 shdr->sh_name = 25; /* offset in shd_string_table */
341 shdr->sh_type = SHT_STRTAB;
342 shdr->sh_flags = 0;
343 shdr->sh_entsize = 0;
344
345 /*
346 * setup build-id section
347 */
348 scn = elf_newscn(e);
349 if (!scn) {
350 warnx("cannot create section");
351 goto error;
352 }
353
354 d = elf_newdata(scn);
355 if (!d) {
356 warnx("cannot get new data");
357 goto error;
358 }
359
360 /*
361 * build-id generation
362 */
363 gen_build_id(&bnote, load_addr, code, csize);
364 bnote.desc.namesz = sizeof(bnote.name); /* must include 0 termination */
365 bnote.desc.descsz = sizeof(bnote.build_id);
366 bnote.desc.type = NT_GNU_BUILD_ID;
367 strcpy(bnote.name, "GNU");
368
369 d->d_align = 4;
370 d->d_off = 0LL;
371 d->d_buf = &bnote;
372 d->d_type = ELF_T_BYTE;
373 d->d_size = sizeof(bnote);
374 d->d_version = EV_CURRENT;
375
376 shdr = elf_getshdr(scn);
377 if (!shdr) {
378 warnx("cannot get section header");
379 goto error;
380 }
381
382 shdr->sh_name = 33; /* offset in shd_string_table */
383 shdr->sh_type = SHT_NOTE;
384 shdr->sh_addr = 0x0;
385 shdr->sh_flags = SHF_ALLOC;
386 shdr->sh_size = sizeof(bnote);
387 shdr->sh_entsize = 0;
388
389 if (debug && nr_debug_entries) {
390 retval = jit_add_debug_info(e, load_addr, debug, nr_debug_entries);
391 if (retval)
392 goto error;
393 } else {
394 if (elf_update(e, ELF_C_WRITE) < 0) {
395 warnx("elf_update 4 failed");
396 goto error;
397 }
398 }
399
400 retval = 0;
401error:
402 (void)elf_end(e);
403
404 free(strsym);
405
406
407 return retval;
408}
409
410#ifndef JVMTI
411
412static unsigned char x86_code[] = {
413 0xBB, 0x2A, 0x00, 0x00, 0x00, /* movl $42, %ebx */
414 0xB8, 0x01, 0x00, 0x00, 0x00, /* movl $1, %eax */
415 0xCD, 0x80 /* int $0x80 */
416};
417
418static struct options options;
419
420int main(int argc, char **argv)
421{
422 int c, fd, ret;
423
424 while ((c = getopt(argc, argv, "o:h")) != -1) {
425 switch (c) {
426 case 'o':
427 options.output = optarg;
428 break;
429 case 'h':
430 printf("Usage: genelf -o output_file [-h]\n");
431 return 0;
432 default:
433 errx(1, "unknown option");
434 }
435 }
436
437 fd = open(options.output, O_CREAT|O_TRUNC|O_RDWR, 0666);
438 if (fd == -1)
439 err(1, "cannot create file %s", options.output);
440
441 ret = jit_write_elf(fd, "main", x86_code, sizeof(x86_code));
442 close(fd);
443
444 if (ret != 0)
445 unlink(options.output);
446
447 return ret;
448}
449#endif