1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * recordmcount.c: construct a table of the locations of calls to 'mcount'
4 * so that ftrace can find them quickly.
5 * Copyright 2009 John F. Reiser <jreiser@BitWagon.com>. All rights reserved.
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 <stdio.h>
31 #include <stdlib.h>
32 #include <string.h>
33 #include <unistd.h>
34
35 #ifndef EM_AARCH64
36 #define EM_AARCH64 183
37 #define R_AARCH64_NONE 0
38 #define R_AARCH64_ABS64 257
39 #endif
40
41 static int fd_map; /* File descriptor for file being modified. */
42 static int mmap_failed; /* Boolean flag. */
43 static char gpfx; /* prefix for global symbol name (sometimes '_') */
44 static struct stat sb; /* Remember .st_size, etc. */
45 static const char *altmcount; /* alternate mcount symbol name */
46 static int warn_on_notrace_sect; /* warn when section has mcount not being recorded */
47 static void *file_map; /* pointer of the mapped file */
48 static void *file_end; /* pointer to the end of the mapped file */
49 static int file_updated; /* flag to state file was changed */
50 static void *file_ptr; /* current file pointer location */
51
52 static void *file_append; /* added to the end of the file */
53 static size_t file_append_size; /* how much is added to end of file */
54
55 /* Per-file resource cleanup when multiple files. */
file_append_cleanup(void)56 static void file_append_cleanup(void)
57 {
58 free(file_append);
59 file_append = NULL;
60 file_append_size = 0;
61 file_updated = 0;
62 }
63
mmap_cleanup(void)64 static void mmap_cleanup(void)
65 {
66 if (!mmap_failed)
67 munmap(file_map, sb.st_size);
68 else
69 free(file_map);
70 file_map = NULL;
71 }
72
73 /* ulseek, uwrite, ...: Check return value for errors. */
74
ulseek(off_t const offset,int const whence)75 static off_t ulseek(off_t const offset, int const whence)
76 {
77 switch (whence) {
78 case SEEK_SET:
79 file_ptr = file_map + offset;
80 break;
81 case SEEK_CUR:
82 file_ptr += offset;
83 break;
84 case SEEK_END:
85 file_ptr = file_map + (sb.st_size - offset);
86 break;
87 }
88 if (file_ptr < file_map) {
89 fprintf(stderr, "lseek: seek before file\n");
90 return -1;
91 }
92 return file_ptr - file_map;
93 }
94
uwrite(void const * const buf,size_t const count)95 static ssize_t uwrite(void const *const buf, size_t const count)
96 {
97 size_t cnt = count;
98 off_t idx = 0;
99
100 file_updated = 1;
101
102 if (file_ptr + count >= file_end) {
103 off_t aoffset = (file_ptr + count) - file_end;
104
105 if (aoffset > file_append_size) {
106 file_append = realloc(file_append, aoffset);
107 file_append_size = aoffset;
108 }
109 if (!file_append) {
110 perror("write");
111 file_append_cleanup();
112 mmap_cleanup();
113 return -1;
114 }
115 if (file_ptr < file_end) {
116 cnt = file_end - file_ptr;
117 } else {
118 cnt = 0;
119 idx = aoffset - count;
120 }
121 }
122
123 if (cnt)
124 memcpy(file_ptr, buf, cnt);
125
126 if (cnt < count)
127 memcpy(file_append + idx, buf + cnt, count - cnt);
128
129 file_ptr += count;
130 return count;
131 }
132
umalloc(size_t size)133 static void * umalloc(size_t size)
134 {
135 void *const addr = malloc(size);
136 if (addr == 0) {
137 fprintf(stderr, "malloc failed: %zu bytes\n", size);
138 file_append_cleanup();
139 mmap_cleanup();
140 return NULL;
141 }
142 return addr;
143 }
144
145 /*
146 * Get the whole file as a programming convenience in order to avoid
147 * malloc+lseek+read+free of many pieces. If successful, then mmap
148 * avoids copying unused pieces; else just read the whole file.
149 * Open for both read and write; new info will be appended to the file.
150 * Use MAP_PRIVATE so that a few changes to the in-memory ElfXX_Ehdr
151 * do not propagate to the file until an explicit overwrite at the last.
152 * This preserves most aspects of consistency (all except .st_size)
153 * for simultaneous readers of the file while we are appending to it.
154 * However, multiple writers still are bad. We choose not to use
155 * locking because it is expensive and the use case of kernel build
156 * makes multiple writers unlikely.
157 */
mmap_file(char const * fname)158 static void *mmap_file(char const *fname)
159 {
160 /* Avoid problems if early cleanup() */
161 fd_map = -1;
162 mmap_failed = 1;
163 file_map = NULL;
164 file_ptr = NULL;
165 file_updated = 0;
166 sb.st_size = 0;
167
168 fd_map = open(fname, O_RDONLY);
169 if (fd_map < 0) {
170 perror(fname);
171 return NULL;
172 }
173 if (fstat(fd_map, &sb) < 0) {
174 perror(fname);
175 goto out;
176 }
177 if (!S_ISREG(sb.st_mode)) {
178 fprintf(stderr, "not a regular file: %s\n", fname);
179 goto out;
180 }
181 file_map = mmap(0, sb.st_size, PROT_READ|PROT_WRITE, MAP_PRIVATE,
182 fd_map, 0);
183 if (file_map == MAP_FAILED) {
184 mmap_failed = 1;
185 file_map = umalloc(sb.st_size);
186 if (!file_map) {
187 perror(fname);
188 goto out;
189 }
190 if (read(fd_map, file_map, sb.st_size) != sb.st_size) {
191 perror(fname);
192 free(file_map);
193 file_map = NULL;
194 goto out;
195 }
196 } else
197 mmap_failed = 0;
198 out:
199 close(fd_map);
200 fd_map = -1;
201
202 file_end = file_map + sb.st_size;
203
204 return file_map;
205 }
206
207
208 static unsigned char ideal_nop5_x86_64[5] = { 0x0f, 0x1f, 0x44, 0x00, 0x00 };
209 static unsigned char ideal_nop5_x86_32[5] = { 0x3e, 0x8d, 0x74, 0x26, 0x00 };
210 static unsigned char *ideal_nop;
211
212 static char rel_type_nop;
213
214 static int (*make_nop)(void *map, size_t const offset);
215
make_nop_x86(void * map,size_t const offset)216 static int make_nop_x86(void *map, size_t const offset)
217 {
218 uint32_t *ptr;
219 unsigned char *op;
220
221 /* Confirm we have 0xe8 0x0 0x0 0x0 0x0 */
222 ptr = map + offset;
223 if (*ptr != 0)
224 return -1;
225
226 op = map + offset - 1;
227 if (*op != 0xe8)
228 return -1;
229
230 /* convert to nop */
231 if (ulseek(offset - 1, SEEK_SET) < 0)
232 return -1;
233 if (uwrite(ideal_nop, 5) < 0)
234 return -1;
235 return 0;
236 }
237
238 static unsigned char ideal_nop4_arm_le[4] = { 0x00, 0x00, 0xa0, 0xe1 }; /* mov r0, r0 */
239 static unsigned char ideal_nop4_arm_be[4] = { 0xe1, 0xa0, 0x00, 0x00 }; /* mov r0, r0 */
240 static unsigned char *ideal_nop4_arm;
241
242 static unsigned char bl_mcount_arm_le[4] = { 0xfe, 0xff, 0xff, 0xeb }; /* bl */
243 static unsigned char bl_mcount_arm_be[4] = { 0xeb, 0xff, 0xff, 0xfe }; /* bl */
244 static unsigned char *bl_mcount_arm;
245
246 static unsigned char push_arm_le[4] = { 0x04, 0xe0, 0x2d, 0xe5 }; /* push {lr} */
247 static unsigned char push_arm_be[4] = { 0xe5, 0x2d, 0xe0, 0x04 }; /* push {lr} */
248 static unsigned char *push_arm;
249
250 static unsigned char ideal_nop2_thumb_le[2] = { 0x00, 0xbf }; /* nop */
251 static unsigned char ideal_nop2_thumb_be[2] = { 0xbf, 0x00 }; /* nop */
252 static unsigned char *ideal_nop2_thumb;
253
254 static unsigned char push_bl_mcount_thumb_le[6] = { 0x00, 0xb5, 0xff, 0xf7, 0xfe, 0xff }; /* push {lr}, bl */
255 static unsigned char push_bl_mcount_thumb_be[6] = { 0xb5, 0x00, 0xf7, 0xff, 0xff, 0xfe }; /* push {lr}, bl */
256 static unsigned char *push_bl_mcount_thumb;
257
make_nop_arm(void * map,size_t const offset)258 static int make_nop_arm(void *map, size_t const offset)
259 {
260 char *ptr;
261 int cnt = 1;
262 int nop_size;
263 size_t off = offset;
264
265 ptr = map + offset;
266 if (memcmp(ptr, bl_mcount_arm, 4) == 0) {
267 if (memcmp(ptr - 4, push_arm, 4) == 0) {
268 off -= 4;
269 cnt = 2;
270 }
271 ideal_nop = ideal_nop4_arm;
272 nop_size = 4;
273 } else if (memcmp(ptr - 2, push_bl_mcount_thumb, 6) == 0) {
274 cnt = 3;
275 nop_size = 2;
276 off -= 2;
277 ideal_nop = ideal_nop2_thumb;
278 } else
279 return -1;
280
281 /* Convert to nop */
282 if (ulseek(off, SEEK_SET) < 0)
283 return -1;
284
285 do {
286 if (uwrite(ideal_nop, nop_size) < 0)
287 return -1;
288 } while (--cnt > 0);
289
290 return 0;
291 }
292
293 static unsigned char ideal_nop4_arm64[4] = {0x1f, 0x20, 0x03, 0xd5};
make_nop_arm64(void * map,size_t const offset)294 static int make_nop_arm64(void *map, size_t const offset)
295 {
296 uint32_t *ptr;
297
298 ptr = map + offset;
299 /* bl <_mcount> is 0x94000000 before relocation */
300 if (*ptr != 0x94000000)
301 return -1;
302
303 /* Convert to nop */
304 if (ulseek(offset, SEEK_SET) < 0)
305 return -1;
306 if (uwrite(ideal_nop, 4) < 0)
307 return -1;
308 return 0;
309 }
310
write_file(const char * fname)311 static int write_file(const char *fname)
312 {
313 char tmp_file[strlen(fname) + 4];
314 size_t n;
315
316 if (!file_updated)
317 return 0;
318
319 sprintf(tmp_file, "%s.rc", fname);
320
321 /*
322 * After reading the entire file into memory, delete it
323 * and write it back, to prevent weird side effects of modifying
324 * an object file in place.
325 */
326 fd_map = open(tmp_file, O_WRONLY | O_TRUNC | O_CREAT, sb.st_mode);
327 if (fd_map < 0) {
328 perror(fname);
329 return -1;
330 }
331 n = write(fd_map, file_map, sb.st_size);
332 if (n != sb.st_size) {
333 perror("write");
334 close(fd_map);
335 return -1;
336 }
337 if (file_append_size) {
338 n = write(fd_map, file_append, file_append_size);
339 if (n != file_append_size) {
340 perror("write");
341 close(fd_map);
342 return -1;
343 }
344 }
345 close(fd_map);
346 if (rename(tmp_file, fname) < 0) {
347 perror(fname);
348 return -1;
349 }
350 return 0;
351 }
352
353 /* w8rev, w8nat, ...: Handle endianness. */
354
w8rev(uint64_t const x)355 static uint64_t w8rev(uint64_t const x)
356 {
357 return ((0xff & (x >> (0 * 8))) << (7 * 8))
358 | ((0xff & (x >> (1 * 8))) << (6 * 8))
359 | ((0xff & (x >> (2 * 8))) << (5 * 8))
360 | ((0xff & (x >> (3 * 8))) << (4 * 8))
361 | ((0xff & (x >> (4 * 8))) << (3 * 8))
362 | ((0xff & (x >> (5 * 8))) << (2 * 8))
363 | ((0xff & (x >> (6 * 8))) << (1 * 8))
364 | ((0xff & (x >> (7 * 8))) << (0 * 8));
365 }
366
w4rev(uint32_t const x)367 static uint32_t w4rev(uint32_t const x)
368 {
369 return ((0xff & (x >> (0 * 8))) << (3 * 8))
370 | ((0xff & (x >> (1 * 8))) << (2 * 8))
371 | ((0xff & (x >> (2 * 8))) << (1 * 8))
372 | ((0xff & (x >> (3 * 8))) << (0 * 8));
373 }
374
w2rev(uint16_t const x)375 static uint32_t w2rev(uint16_t const x)
376 {
377 return ((0xff & (x >> (0 * 8))) << (1 * 8))
378 | ((0xff & (x >> (1 * 8))) << (0 * 8));
379 }
380
w8nat(uint64_t const x)381 static uint64_t w8nat(uint64_t const x)
382 {
383 return x;
384 }
385
w4nat(uint32_t const x)386 static uint32_t w4nat(uint32_t const x)
387 {
388 return x;
389 }
390
w2nat(uint16_t const x)391 static uint32_t w2nat(uint16_t const x)
392 {
393 return x;
394 }
395
396 static uint64_t (*w8)(uint64_t);
397 static uint32_t (*w)(uint32_t);
398 static uint32_t (*w2)(uint16_t);
399
400 /* Names of the sections that could contain calls to mcount. */
is_mcounted_section_name(char const * const txtname)401 static int is_mcounted_section_name(char const *const txtname)
402 {
403 return strncmp(".text", txtname, 5) == 0 ||
404 strcmp(".init.text", txtname) == 0 ||
405 strcmp(".ref.text", txtname) == 0 ||
406 strcmp(".sched.text", txtname) == 0 ||
407 strcmp(".spinlock.text", txtname) == 0 ||
408 strcmp(".irqentry.text", txtname) == 0 ||
409 strcmp(".softirqentry.text", txtname) == 0 ||
410 strcmp(".kprobes.text", txtname) == 0 ||
411 strcmp(".cpuidle.text", txtname) == 0;
412 }
413
414 static char const *already_has_rel_mcount = "success"; /* our work here is done! */
415
416 /* 32 bit and 64 bit are very similar */
417 #include "recordmcount.h"
418 #define RECORD_MCOUNT_64
419 #include "recordmcount.h"
420
421 /* 64-bit EM_MIPS has weird ELF64_Rela.r_info.
422 * http://techpubs.sgi.com/library/manuals/4000/007-4658-001/pdf/007-4658-001.pdf
423 * We interpret Table 29 Relocation Operation (Elf64_Rel, Elf64_Rela) [p.40]
424 * to imply the order of the members; the spec does not say so.
425 * typedef unsigned char Elf64_Byte;
426 * fails on MIPS64 because their <elf.h> already has it!
427 */
428
429 typedef uint8_t myElf64_Byte; /* Type for a 8-bit quantity. */
430
431 union mips_r_info {
432 Elf64_Xword r_info;
433 struct {
434 Elf64_Word r_sym; /* Symbol index. */
435 myElf64_Byte r_ssym; /* Special symbol. */
436 myElf64_Byte r_type3; /* Third relocation. */
437 myElf64_Byte r_type2; /* Second relocation. */
438 myElf64_Byte r_type; /* First relocation. */
439 } r_mips;
440 };
441
MIPS64_r_sym(Elf64_Rel const * rp)442 static uint64_t MIPS64_r_sym(Elf64_Rel const *rp)
443 {
444 return w(((union mips_r_info){ .r_info = rp->r_info }).r_mips.r_sym);
445 }
446
MIPS64_r_info(Elf64_Rel * const rp,unsigned sym,unsigned type)447 static void MIPS64_r_info(Elf64_Rel *const rp, unsigned sym, unsigned type)
448 {
449 rp->r_info = ((union mips_r_info){
450 .r_mips = { .r_sym = w(sym), .r_type = type }
451 }).r_info;
452 }
453
do_file(char const * const fname)454 static int do_file(char const *const fname)
455 {
456 unsigned int reltype = 0;
457 Elf32_Ehdr *ehdr;
458 int rc = -1;
459
460 ehdr = mmap_file(fname);
461 if (!ehdr)
462 goto out;
463
464 w = w4nat;
465 w2 = w2nat;
466 w8 = w8nat;
467 switch (ehdr->e_ident[EI_DATA]) {
468 static unsigned int const endian = 1;
469 default:
470 fprintf(stderr, "unrecognized ELF data encoding %d: %s\n",
471 ehdr->e_ident[EI_DATA], fname);
472 goto out;
473 case ELFDATA2LSB:
474 if (*(unsigned char const *)&endian != 1) {
475 /* main() is big endian, file.o is little endian. */
476 w = w4rev;
477 w2 = w2rev;
478 w8 = w8rev;
479 }
480 ideal_nop4_arm = ideal_nop4_arm_le;
481 bl_mcount_arm = bl_mcount_arm_le;
482 push_arm = push_arm_le;
483 ideal_nop2_thumb = ideal_nop2_thumb_le;
484 push_bl_mcount_thumb = push_bl_mcount_thumb_le;
485 break;
486 case ELFDATA2MSB:
487 if (*(unsigned char const *)&endian != 0) {
488 /* main() is little endian, file.o is big endian. */
489 w = w4rev;
490 w2 = w2rev;
491 w8 = w8rev;
492 }
493 ideal_nop4_arm = ideal_nop4_arm_be;
494 bl_mcount_arm = bl_mcount_arm_be;
495 push_arm = push_arm_be;
496 ideal_nop2_thumb = ideal_nop2_thumb_be;
497 push_bl_mcount_thumb = push_bl_mcount_thumb_be;
498 break;
499 } /* end switch */
500 if (memcmp(ELFMAG, ehdr->e_ident, SELFMAG) != 0 ||
501 w2(ehdr->e_type) != ET_REL ||
502 ehdr->e_ident[EI_VERSION] != EV_CURRENT) {
503 fprintf(stderr, "unrecognized ET_REL file %s\n", fname);
504 goto out;
505 }
506
507 gpfx = '_';
508 switch (w2(ehdr->e_machine)) {
509 default:
510 fprintf(stderr, "unrecognized e_machine %u %s\n",
511 w2(ehdr->e_machine), fname);
512 goto out;
513 case EM_386:
514 reltype = R_386_32;
515 rel_type_nop = R_386_NONE;
516 make_nop = make_nop_x86;
517 ideal_nop = ideal_nop5_x86_32;
518 mcount_adjust_32 = -1;
519 gpfx = 0;
520 break;
521 case EM_ARM:
522 reltype = R_ARM_ABS32;
523 altmcount = "__gnu_mcount_nc";
524 make_nop = make_nop_arm;
525 rel_type_nop = R_ARM_NONE;
526 gpfx = 0;
527 break;
528 case EM_AARCH64:
529 reltype = R_AARCH64_ABS64;
530 make_nop = make_nop_arm64;
531 rel_type_nop = R_AARCH64_NONE;
532 ideal_nop = ideal_nop4_arm64;
533 break;
534 case EM_IA_64: reltype = R_IA64_IMM64; break;
535 case EM_MIPS: /* reltype: e_class */ break;
536 case EM_PPC: reltype = R_PPC_ADDR32; break;
537 case EM_PPC64: reltype = R_PPC64_ADDR64; break;
538 case EM_S390: /* reltype: e_class */ break;
539 case EM_SH: reltype = R_SH_DIR32; gpfx = 0; break;
540 case EM_SPARCV9: reltype = R_SPARC_64; break;
541 case EM_X86_64:
542 make_nop = make_nop_x86;
543 ideal_nop = ideal_nop5_x86_64;
544 reltype = R_X86_64_64;
545 rel_type_nop = R_X86_64_NONE;
546 mcount_adjust_64 = -1;
547 gpfx = 0;
548 break;
549 } /* end switch */
550
551 switch (ehdr->e_ident[EI_CLASS]) {
552 default:
553 fprintf(stderr, "unrecognized ELF class %d %s\n",
554 ehdr->e_ident[EI_CLASS], fname);
555 goto out;
556 case ELFCLASS32:
557 if (w2(ehdr->e_ehsize) != sizeof(Elf32_Ehdr)
558 || w2(ehdr->e_shentsize) != sizeof(Elf32_Shdr)) {
559 fprintf(stderr,
560 "unrecognized ET_REL file: %s\n", fname);
561 goto out;
562 }
563 if (w2(ehdr->e_machine) == EM_MIPS) {
564 reltype = R_MIPS_32;
565 is_fake_mcount32 = MIPS32_is_fake_mcount;
566 }
567 if (do32(ehdr, fname, reltype) < 0)
568 goto out;
569 break;
570 case ELFCLASS64: {
571 Elf64_Ehdr *const ghdr = (Elf64_Ehdr *)ehdr;
572 if (w2(ghdr->e_ehsize) != sizeof(Elf64_Ehdr)
573 || w2(ghdr->e_shentsize) != sizeof(Elf64_Shdr)) {
574 fprintf(stderr,
575 "unrecognized ET_REL file: %s\n", fname);
576 goto out;
577 }
578 if (w2(ghdr->e_machine) == EM_S390) {
579 reltype = R_390_64;
580 mcount_adjust_64 = -14;
581 }
582 if (w2(ghdr->e_machine) == EM_MIPS) {
583 reltype = R_MIPS_64;
584 Elf64_r_sym = MIPS64_r_sym;
585 Elf64_r_info = MIPS64_r_info;
586 is_fake_mcount64 = MIPS64_is_fake_mcount;
587 }
588 if (do64(ghdr, fname, reltype) < 0)
589 goto out;
590 break;
591 }
592 } /* end switch */
593
594 rc = write_file(fname);
595 out:
596 file_append_cleanup();
597 mmap_cleanup();
598 return rc;
599 }
600
main(int argc,char * argv[])601 int main(int argc, char *argv[])
602 {
603 const char ftrace[] = "/ftrace.o";
604 int ftrace_size = sizeof(ftrace) - 1;
605 int n_error = 0; /* gcc-4.3.0 false positive complaint */
606 int c;
607 int i;
608
609 while ((c = getopt(argc, argv, "w")) >= 0) {
610 switch (c) {
611 case 'w':
612 warn_on_notrace_sect = 1;
613 break;
614 default:
615 fprintf(stderr, "usage: recordmcount [-w] file.o...\n");
616 return 0;
617 }
618 }
619
620 if ((argc - optind) < 1) {
621 fprintf(stderr, "usage: recordmcount [-w] file.o...\n");
622 return 0;
623 }
624
625 /* Process each file in turn, allowing deep failure. */
626 for (i = optind; i < argc; i++) {
627 char *file = argv[i];
628 int len;
629
630 /*
631 * The file kernel/trace/ftrace.o references the mcount
632 * function but does not call it. Since ftrace.o should
633 * not be traced anyway, we just skip it.
634 */
635 len = strlen(file);
636 if (len >= ftrace_size &&
637 strcmp(file + (len - ftrace_size), ftrace) == 0)
638 continue;
639
640 if (do_file(file)) {
641 fprintf(stderr, "%s: failed\n", file);
642 ++n_error;
643 }
644 }
645 return !!n_error;
646 }
647
