1 /*
2 * recordmcount.c: construct a table of the locations of calls to 'mcount'
3 * so that ftrace can find them quickly.
4 * Copyright 2009 John F. Reiser <jreiser@BitWagon.com>. All rights reserved.
5 * Licensed under the GNU General Public License, version 2 (GPLv2).
6 *
7 * Restructured to fit Linux format, as well as other updates:
8 * Copyright 2010 Steven Rostedt <srostedt@redhat.com>, Red Hat Inc.
9 */
10
11 /*
12 * Strategy: alter the .o file in-place.
13 *
14 * Append a new STRTAB that has the new section names, followed by a new array
15 * ElfXX_Shdr[] that has the new section headers, followed by the section
16 * contents for __mcount_loc and its relocations. The old shstrtab strings,
17 * and the old ElfXX_Shdr[] array, remain as "garbage" (commonly, a couple
18 * kilobytes.) Subsequent processing by /bin/ld (or the kernel module loader)
19 * will ignore the garbage regions, because they are not designated by the
20 * new .e_shoff nor the new ElfXX_Shdr[]. [In order to remove the garbage,
21 * then use "ld -r" to create a new file that omits the garbage.]
22 */
23
24 #include <sys/types.h>
25 #include <sys/mman.h>
26 #include <sys/stat.h>
27 #include <getopt.h>
28 #include <elf.h>
29 #include <fcntl.h>
30 #include <setjmp.h>
31 #include <stdio.h>
32 #include <stdlib.h>
33 #include <string.h>
34 #include <unistd.h>
35
36 #ifndef EM_AARCH64
37 #define EM_AARCH64 183
38 #define R_AARCH64_NONE 0
39 #define R_AARCH64_ABS64 257
40 #endif
41
42 static int fd_map; /* File descriptor for file being modified. */
43 static int mmap_failed; /* Boolean flag. */
44 static char gpfx; /* prefix for global symbol name (sometimes '_') */
45 static struct stat sb; /* Remember .st_size, etc. */
46 static jmp_buf jmpenv; /* setjmp/longjmp per-file error escape */
47 static const char *altmcount; /* alternate mcount symbol name */
48 static int warn_on_notrace_sect; /* warn when section has mcount not being recorded */
49 static void *file_map; /* pointer of the mapped file */
50 static void *file_end; /* pointer to the end of the mapped file */
51 static int file_updated; /* flag to state file was changed */
52 static void *file_ptr; /* current file pointer location */
53 static void *file_append; /* added to the end of the file */
54 static size_t file_append_size; /* how much is added to end of file */
55
56 /* setjmp() return values */
57 enum {
58 SJ_SETJMP = 0, /* hardwired first return */
59 SJ_FAIL,
60 SJ_SUCCEED
61 };
62
63 /* Per-file resource cleanup when multiple files. */
64 static void
cleanup(void)65 cleanup(void)
66 {
67 if (!mmap_failed)
68 munmap(file_map, sb.st_size);
69 else
70 free(file_map);
71 file_map = NULL;
72 free(file_append);
73 file_append = NULL;
74 file_append_size = 0;
75 file_updated = 0;
76 }
77
78 static void __attribute__((noreturn))
fail_file(void)79 fail_file(void)
80 {
81 cleanup();
82 longjmp(jmpenv, SJ_FAIL);
83 }
84
85 static void __attribute__((noreturn))
succeed_file(void)86 succeed_file(void)
87 {
88 cleanup();
89 longjmp(jmpenv, SJ_SUCCEED);
90 }
91
92 /* ulseek, uread, ...: Check return value for errors. */
93
94 static off_t
ulseek(int const fd,off_t const offset,int const whence)95 ulseek(int const fd, off_t const offset, int const whence)
96 {
97 switch (whence) {
98 case SEEK_SET:
99 file_ptr = file_map + offset;
100 break;
101 case SEEK_CUR:
102 file_ptr += offset;
103 break;
104 case SEEK_END:
105 file_ptr = file_map + (sb.st_size - offset);
106 break;
107 }
108 if (file_ptr < file_map) {
109 fprintf(stderr, "lseek: seek before file\n");
110 fail_file();
111 }
112 return file_ptr - file_map;
113 }
114
115 static size_t
uread(int const fd,void * const buf,size_t const count)116 uread(int const fd, void *const buf, size_t const count)
117 {
118 size_t const n = read(fd, buf, count);
119 if (n != count) {
120 perror("read");
121 fail_file();
122 }
123 return n;
124 }
125
126 static size_t
uwrite(int const fd,void const * const buf,size_t const count)127 uwrite(int const fd, void const *const buf, size_t const count)
128 {
129 size_t cnt = count;
130 off_t idx = 0;
131
132 file_updated = 1;
133
134 if (file_ptr + count >= file_end) {
135 off_t aoffset = (file_ptr + count) - file_end;
136
137 if (aoffset > file_append_size) {
138 file_append = realloc(file_append, aoffset);
139 file_append_size = aoffset;
140 }
141 if (!file_append) {
142 perror("write");
143 fail_file();
144 }
145 if (file_ptr < file_end) {
146 cnt = file_end - file_ptr;
147 } else {
148 cnt = 0;
149 idx = aoffset - count;
150 }
151 }
152
153 if (cnt)
154 memcpy(file_ptr, buf, cnt);
155
156 if (cnt < count)
157 memcpy(file_append + idx, buf + cnt, count - cnt);
158
159 file_ptr += count;
160 return count;
161 }
162
163 static void *
umalloc(size_t size)164 umalloc(size_t size)
165 {
166 void *const addr = malloc(size);
167 if (addr == 0) {
168 fprintf(stderr, "malloc failed: %zu bytes\n", size);
169 fail_file();
170 }
171 return addr;
172 }
173
174 static unsigned char ideal_nop5_x86_64[5] = { 0x0f, 0x1f, 0x44, 0x00, 0x00 };
175 static unsigned char ideal_nop5_x86_32[5] = { 0x3e, 0x8d, 0x74, 0x26, 0x00 };
176 static unsigned char *ideal_nop;
177
178 static char rel_type_nop;
179
180 static int (*make_nop)(void *map, size_t const offset);
181
make_nop_x86(void * map,size_t const offset)182 static int make_nop_x86(void *map, size_t const offset)
183 {
184 uint32_t *ptr;
185 unsigned char *op;
186
187 /* Confirm we have 0xe8 0x0 0x0 0x0 0x0 */
188 ptr = map + offset;
189 if (*ptr != 0)
190 return -1;
191
192 op = map + offset - 1;
193 if (*op != 0xe8)
194 return -1;
195
196 /* convert to nop */
197 ulseek(fd_map, offset - 1, SEEK_SET);
198 uwrite(fd_map, ideal_nop, 5);
199 return 0;
200 }
201
202 static unsigned char ideal_nop4_arm_le[4] = { 0x00, 0x00, 0xa0, 0xe1 }; /* mov r0, r0 */
203 static unsigned char ideal_nop4_arm_be[4] = { 0xe1, 0xa0, 0x00, 0x00 }; /* mov r0, r0 */
204 static unsigned char *ideal_nop4_arm;
205
206 static unsigned char bl_mcount_arm_le[4] = { 0xfe, 0xff, 0xff, 0xeb }; /* bl */
207 static unsigned char bl_mcount_arm_be[4] = { 0xeb, 0xff, 0xff, 0xfe }; /* bl */
208 static unsigned char *bl_mcount_arm;
209
210 static unsigned char push_arm_le[4] = { 0x04, 0xe0, 0x2d, 0xe5 }; /* push {lr} */
211 static unsigned char push_arm_be[4] = { 0xe5, 0x2d, 0xe0, 0x04 }; /* push {lr} */
212 static unsigned char *push_arm;
213
214 static unsigned char ideal_nop2_thumb_le[2] = { 0x00, 0xbf }; /* nop */
215 static unsigned char ideal_nop2_thumb_be[2] = { 0xbf, 0x00 }; /* nop */
216 static unsigned char *ideal_nop2_thumb;
217
218 static unsigned char push_bl_mcount_thumb_le[6] = { 0x00, 0xb5, 0xff, 0xf7, 0xfe, 0xff }; /* push {lr}, bl */
219 static unsigned char push_bl_mcount_thumb_be[6] = { 0xb5, 0x00, 0xf7, 0xff, 0xff, 0xfe }; /* push {lr}, bl */
220 static unsigned char *push_bl_mcount_thumb;
221
make_nop_arm(void * map,size_t const offset)222 static int make_nop_arm(void *map, size_t const offset)
223 {
224 char *ptr;
225 int cnt = 1;
226 int nop_size;
227 size_t off = offset;
228
229 ptr = map + offset;
230 if (memcmp(ptr, bl_mcount_arm, 4) == 0) {
231 if (memcmp(ptr - 4, push_arm, 4) == 0) {
232 off -= 4;
233 cnt = 2;
234 }
235 ideal_nop = ideal_nop4_arm;
236 nop_size = 4;
237 } else if (memcmp(ptr - 2, push_bl_mcount_thumb, 6) == 0) {
238 cnt = 3;
239 nop_size = 2;
240 off -= 2;
241 ideal_nop = ideal_nop2_thumb;
242 } else
243 return -1;
244
245 /* Convert to nop */
246 ulseek(fd_map, off, SEEK_SET);
247
248 do {
249 uwrite(fd_map, ideal_nop, nop_size);
250 } while (--cnt > 0);
251
252 return 0;
253 }
254
255 static unsigned char ideal_nop4_arm64[4] = {0x1f, 0x20, 0x03, 0xd5};
make_nop_arm64(void * map,size_t const offset)256 static int make_nop_arm64(void *map, size_t const offset)
257 {
258 uint32_t *ptr;
259
260 ptr = map + offset;
261 /* bl <_mcount> is 0x94000000 before relocation */
262 if (*ptr != 0x94000000)
263 return -1;
264
265 /* Convert to nop */
266 ulseek(fd_map, offset, SEEK_SET);
267 uwrite(fd_map, ideal_nop, 4);
268 return 0;
269 }
270
271 /*
272 * Get the whole file as a programming convenience in order to avoid
273 * malloc+lseek+read+free of many pieces. If successful, then mmap
274 * avoids copying unused pieces; else just read the whole file.
275 * Open for both read and write; new info will be appended to the file.
276 * Use MAP_PRIVATE so that a few changes to the in-memory ElfXX_Ehdr
277 * do not propagate to the file until an explicit overwrite at the last.
278 * This preserves most aspects of consistency (all except .st_size)
279 * for simultaneous readers of the file while we are appending to it.
280 * However, multiple writers still are bad. We choose not to use
281 * locking because it is expensive and the use case of kernel build
282 * makes multiple writers unlikely.
283 */
mmap_file(char const * fname)284 static void *mmap_file(char const *fname)
285 {
286 fd_map = open(fname, O_RDONLY);
287 if (fd_map < 0 || fstat(fd_map, &sb) < 0) {
288 perror(fname);
289 fail_file();
290 }
291 if (!S_ISREG(sb.st_mode)) {
292 fprintf(stderr, "not a regular file: %s\n", fname);
293 fail_file();
294 }
295 file_map = mmap(0, sb.st_size, PROT_READ|PROT_WRITE, MAP_PRIVATE,
296 fd_map, 0);
297 mmap_failed = 0;
298 if (file_map == MAP_FAILED) {
299 mmap_failed = 1;
300 file_map = umalloc(sb.st_size);
301 uread(fd_map, file_map, sb.st_size);
302 }
303 close(fd_map);
304
305 file_end = file_map + sb.st_size;
306
307 return file_map;
308 }
309
write_file(const char * fname)310 static void write_file(const char *fname)
311 {
312 char tmp_file[strlen(fname) + 4];
313 size_t n;
314
315 if (!file_updated)
316 return;
317
318 sprintf(tmp_file, "%s.rc", fname);
319
320 /*
321 * After reading the entire file into memory, delete it
322 * and write it back, to prevent weird side effects of modifying
323 * an object file in place.
324 */
325 fd_map = open(tmp_file, O_WRONLY | O_TRUNC | O_CREAT, sb.st_mode);
326 if (fd_map < 0) {
327 perror(fname);
328 fail_file();
329 }
330 n = write(fd_map, file_map, sb.st_size);
331 if (n != sb.st_size) {
332 perror("write");
333 fail_file();
334 }
335 if (file_append_size) {
336 n = write(fd_map, file_append, file_append_size);
337 if (n != file_append_size) {
338 perror("write");
339 fail_file();
340 }
341 }
342 close(fd_map);
343 if (rename(tmp_file, fname) < 0) {
344 perror(fname);
345 fail_file();
346 }
347 }
348
349 /* w8rev, w8nat, ...: Handle endianness. */
350
w8rev(uint64_t const x)351 static uint64_t w8rev(uint64_t const x)
352 {
353 return ((0xff & (x >> (0 * 8))) << (7 * 8))
354 | ((0xff & (x >> (1 * 8))) << (6 * 8))
355 | ((0xff & (x >> (2 * 8))) << (5 * 8))
356 | ((0xff & (x >> (3 * 8))) << (4 * 8))
357 | ((0xff & (x >> (4 * 8))) << (3 * 8))
358 | ((0xff & (x >> (5 * 8))) << (2 * 8))
359 | ((0xff & (x >> (6 * 8))) << (1 * 8))
360 | ((0xff & (x >> (7 * 8))) << (0 * 8));
361 }
362
w4rev(uint32_t const x)363 static uint32_t w4rev(uint32_t const x)
364 {
365 return ((0xff & (x >> (0 * 8))) << (3 * 8))
366 | ((0xff & (x >> (1 * 8))) << (2 * 8))
367 | ((0xff & (x >> (2 * 8))) << (1 * 8))
368 | ((0xff & (x >> (3 * 8))) << (0 * 8));
369 }
370
w2rev(uint16_t const x)371 static uint32_t w2rev(uint16_t const x)
372 {
373 return ((0xff & (x >> (0 * 8))) << (1 * 8))
374 | ((0xff & (x >> (1 * 8))) << (0 * 8));
375 }
376
w8nat(uint64_t const x)377 static uint64_t w8nat(uint64_t const x)
378 {
379 return x;
380 }
381
w4nat(uint32_t const x)382 static uint32_t w4nat(uint32_t const x)
383 {
384 return x;
385 }
386
w2nat(uint16_t const x)387 static uint32_t w2nat(uint16_t const x)
388 {
389 return x;
390 }
391
392 static uint64_t (*w8)(uint64_t);
393 static uint32_t (*w)(uint32_t);
394 static uint32_t (*w2)(uint16_t);
395
396 /* Names of the sections that could contain calls to mcount. */
397 static int
is_mcounted_section_name(char const * const txtname)398 is_mcounted_section_name(char const *const txtname)
399 {
400 return strcmp(".text", txtname) == 0 ||
401 strcmp(".init.text", txtname) == 0 ||
402 strcmp(".ref.text", txtname) == 0 ||
403 strcmp(".sched.text", txtname) == 0 ||
404 strcmp(".spinlock.text", txtname) == 0 ||
405 strcmp(".irqentry.text", txtname) == 0 ||
406 strcmp(".softirqentry.text", txtname) == 0 ||
407 strcmp(".kprobes.text", txtname) == 0 ||
408 strcmp(".cpuidle.text", txtname) == 0 ||
409 strcmp(".text.unlikely", txtname) == 0;
410 }
411
412 /* 32 bit and 64 bit are very similar */
413 #include "recordmcount.h"
414 #define RECORD_MCOUNT_64
415 #include "recordmcount.h"
416
417 /* 64-bit EM_MIPS has weird ELF64_Rela.r_info.
418 * http://techpubs.sgi.com/library/manuals/4000/007-4658-001/pdf/007-4658-001.pdf
419 * We interpret Table 29 Relocation Operation (Elf64_Rel, Elf64_Rela) [p.40]
420 * to imply the order of the members; the spec does not say so.
421 * typedef unsigned char Elf64_Byte;
422 * fails on MIPS64 because their <elf.h> already has it!
423 */
424
425 typedef uint8_t myElf64_Byte; /* Type for a 8-bit quantity. */
426
427 union mips_r_info {
428 Elf64_Xword r_info;
429 struct {
430 Elf64_Word r_sym; /* Symbol index. */
431 myElf64_Byte r_ssym; /* Special symbol. */
432 myElf64_Byte r_type3; /* Third relocation. */
433 myElf64_Byte r_type2; /* Second relocation. */
434 myElf64_Byte r_type; /* First relocation. */
435 } r_mips;
436 };
437
MIPS64_r_sym(Elf64_Rel const * rp)438 static uint64_t MIPS64_r_sym(Elf64_Rel const *rp)
439 {
440 return w(((union mips_r_info){ .r_info = rp->r_info }).r_mips.r_sym);
441 }
442
MIPS64_r_info(Elf64_Rel * const rp,unsigned sym,unsigned type)443 static void MIPS64_r_info(Elf64_Rel *const rp, unsigned sym, unsigned type)
444 {
445 rp->r_info = ((union mips_r_info){
446 .r_mips = { .r_sym = w(sym), .r_type = type }
447 }).r_info;
448 }
449
450 static void
do_file(char const * const fname)451 do_file(char const *const fname)
452 {
453 Elf32_Ehdr *const ehdr = mmap_file(fname);
454 unsigned int reltype = 0;
455
456 w = w4nat;
457 w2 = w2nat;
458 w8 = w8nat;
459 switch (ehdr->e_ident[EI_DATA]) {
460 static unsigned int const endian = 1;
461 default:
462 fprintf(stderr, "unrecognized ELF data encoding %d: %s\n",
463 ehdr->e_ident[EI_DATA], fname);
464 fail_file();
465 break;
466 case ELFDATA2LSB:
467 if (*(unsigned char const *)&endian != 1) {
468 /* main() is big endian, file.o is little endian. */
469 w = w4rev;
470 w2 = w2rev;
471 w8 = w8rev;
472 }
473 ideal_nop4_arm = ideal_nop4_arm_le;
474 bl_mcount_arm = bl_mcount_arm_le;
475 push_arm = push_arm_le;
476 ideal_nop2_thumb = ideal_nop2_thumb_le;
477 push_bl_mcount_thumb = push_bl_mcount_thumb_le;
478 break;
479 case ELFDATA2MSB:
480 if (*(unsigned char const *)&endian != 0) {
481 /* main() is little endian, file.o is big endian. */
482 w = w4rev;
483 w2 = w2rev;
484 w8 = w8rev;
485 }
486 ideal_nop4_arm = ideal_nop4_arm_be;
487 bl_mcount_arm = bl_mcount_arm_be;
488 push_arm = push_arm_be;
489 ideal_nop2_thumb = ideal_nop2_thumb_be;
490 push_bl_mcount_thumb = push_bl_mcount_thumb_be;
491 break;
492 } /* end switch */
493 if (memcmp(ELFMAG, ehdr->e_ident, SELFMAG) != 0
494 || w2(ehdr->e_type) != ET_REL
495 || ehdr->e_ident[EI_VERSION] != EV_CURRENT) {
496 fprintf(stderr, "unrecognized ET_REL file %s\n", fname);
497 fail_file();
498 }
499
500 gpfx = 0;
501 switch (w2(ehdr->e_machine)) {
502 default:
503 fprintf(stderr, "unrecognized e_machine %u %s\n",
504 w2(ehdr->e_machine), fname);
505 fail_file();
506 break;
507 case EM_386:
508 reltype = R_386_32;
509 rel_type_nop = R_386_NONE;
510 make_nop = make_nop_x86;
511 ideal_nop = ideal_nop5_x86_32;
512 mcount_adjust_32 = -1;
513 break;
514 case EM_ARM: reltype = R_ARM_ABS32;
515 altmcount = "__gnu_mcount_nc";
516 make_nop = make_nop_arm;
517 rel_type_nop = R_ARM_NONE;
518 break;
519 case EM_AARCH64:
520 reltype = R_AARCH64_ABS64;
521 make_nop = make_nop_arm64;
522 rel_type_nop = R_AARCH64_NONE;
523 ideal_nop = ideal_nop4_arm64;
524 gpfx = '_';
525 break;
526 case EM_IA_64: reltype = R_IA64_IMM64; gpfx = '_'; break;
527 case EM_MIPS: /* reltype: e_class */ gpfx = '_'; break;
528 case EM_PPC: reltype = R_PPC_ADDR32; gpfx = '_'; break;
529 case EM_PPC64: reltype = R_PPC64_ADDR64; gpfx = '_'; break;
530 case EM_S390: /* reltype: e_class */ gpfx = '_'; break;
531 case EM_SH: reltype = R_SH_DIR32; break;
532 case EM_SPARCV9: reltype = R_SPARC_64; gpfx = '_'; break;
533 case EM_X86_64:
534 make_nop = make_nop_x86;
535 ideal_nop = ideal_nop5_x86_64;
536 reltype = R_X86_64_64;
537 rel_type_nop = R_X86_64_NONE;
538 mcount_adjust_64 = -1;
539 break;
540 } /* end switch */
541
542 switch (ehdr->e_ident[EI_CLASS]) {
543 default:
544 fprintf(stderr, "unrecognized ELF class %d %s\n",
545 ehdr->e_ident[EI_CLASS], fname);
546 fail_file();
547 break;
548 case ELFCLASS32:
549 if (w2(ehdr->e_ehsize) != sizeof(Elf32_Ehdr)
550 || w2(ehdr->e_shentsize) != sizeof(Elf32_Shdr)) {
551 fprintf(stderr,
552 "unrecognized ET_REL file: %s\n", fname);
553 fail_file();
554 }
555 if (w2(ehdr->e_machine) == EM_MIPS) {
556 reltype = R_MIPS_32;
557 is_fake_mcount32 = MIPS32_is_fake_mcount;
558 }
559 do32(ehdr, fname, reltype);
560 break;
561 case ELFCLASS64: {
562 Elf64_Ehdr *const ghdr = (Elf64_Ehdr *)ehdr;
563 if (w2(ghdr->e_ehsize) != sizeof(Elf64_Ehdr)
564 || w2(ghdr->e_shentsize) != sizeof(Elf64_Shdr)) {
565 fprintf(stderr,
566 "unrecognized ET_REL file: %s\n", fname);
567 fail_file();
568 }
569 if (w2(ghdr->e_machine) == EM_S390) {
570 reltype = R_390_64;
571 mcount_adjust_64 = -14;
572 }
573 if (w2(ghdr->e_machine) == EM_MIPS) {
574 reltype = R_MIPS_64;
575 Elf64_r_sym = MIPS64_r_sym;
576 Elf64_r_info = MIPS64_r_info;
577 is_fake_mcount64 = MIPS64_is_fake_mcount;
578 }
579 do64(ghdr, fname, reltype);
580 break;
581 }
582 } /* end switch */
583
584 write_file(fname);
585 cleanup();
586 }
587
588 int
main(int argc,char * argv[])589 main(int argc, char *argv[])
590 {
591 const char ftrace[] = "/ftrace.o";
592 int ftrace_size = sizeof(ftrace) - 1;
593 int n_error = 0; /* gcc-4.3.0 false positive complaint */
594 int c;
595 int i;
596
597 while ((c = getopt(argc, argv, "w")) >= 0) {
598 switch (c) {
599 case 'w':
600 warn_on_notrace_sect = 1;
601 break;
602 default:
603 fprintf(stderr, "usage: recordmcount [-w] file.o...\n");
604 return 0;
605 }
606 }
607
608 if ((argc - optind) < 1) {
609 fprintf(stderr, "usage: recordmcount [-w] file.o...\n");
610 return 0;
611 }
612
613 /* Process each file in turn, allowing deep failure. */
614 for (i = optind; i < argc; i++) {
615 char *file = argv[i];
616 int const sjval = setjmp(jmpenv);
617 int len;
618
619 /*
620 * The file kernel/trace/ftrace.o references the mcount
621 * function but does not call it. Since ftrace.o should
622 * not be traced anyway, we just skip it.
623 */
624 len = strlen(file);
625 if (len >= ftrace_size &&
626 strcmp(file + (len - ftrace_size), ftrace) == 0)
627 continue;
628
629 switch (sjval) {
630 default:
631 fprintf(stderr, "internal error: %s\n", file);
632 exit(1);
633 break;
634 case SJ_SETJMP: /* normal sequence */
635 /* Avoid problems if early cleanup() */
636 fd_map = -1;
637 mmap_failed = 1;
638 file_map = NULL;
639 file_ptr = NULL;
640 file_updated = 0;
641 do_file(file);
642 break;
643 case SJ_FAIL: /* error in do_file or below */
644 fprintf(stderr, "%s: failed\n", file);
645 ++n_error;
646 break;
647 case SJ_SUCCEED: /* premature success */
648 /* do nothing */
649 break;
650 } /* end switch */
651 }
652 return !!n_error;
653 }
654
