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_METAG
37 /* Remove this when these make it to the standard system elf.h. */
38 #define EM_METAG 174
39 #define R_METAG_ADDR32 2
40 #define R_METAG_NONE 3
41 #endif
42
43 #ifndef EM_AARCH64
44 #define EM_AARCH64 183
45 #define R_AARCH64_NONE 0
46 #define R_AARCH64_ABS64 257
47 #endif
48
49 static int fd_map; /* File descriptor for file being modified. */
50 static int mmap_failed; /* Boolean flag. */
51 static void *ehdr_curr; /* current ElfXX_Ehdr * for resource cleanup */
52 static char gpfx; /* prefix for global symbol name (sometimes '_') */
53 static struct stat sb; /* Remember .st_size, etc. */
54 static jmp_buf jmpenv; /* setjmp/longjmp per-file error escape */
55 static const char *altmcount; /* alternate mcount symbol name */
56 static int warn_on_notrace_sect; /* warn when section has mcount not being recorded */
57
58 /* setjmp() return values */
59 enum {
60 SJ_SETJMP = 0, /* hardwired first return */
61 SJ_FAIL,
62 SJ_SUCCEED
63 };
64
65 /* Per-file resource cleanup when multiple files. */
66 static void
cleanup(void)67 cleanup(void)
68 {
69 if (!mmap_failed)
70 munmap(ehdr_curr, sb.st_size);
71 else
72 free(ehdr_curr);
73 close(fd_map);
74 }
75
76 static void __attribute__((noreturn))
fail_file(void)77 fail_file(void)
78 {
79 cleanup();
80 longjmp(jmpenv, SJ_FAIL);
81 }
82
83 static void __attribute__((noreturn))
succeed_file(void)84 succeed_file(void)
85 {
86 cleanup();
87 longjmp(jmpenv, SJ_SUCCEED);
88 }
89
90 /* ulseek, uread, ...: Check return value for errors. */
91
92 static off_t
ulseek(int const fd,off_t const offset,int const whence)93 ulseek(int const fd, off_t const offset, int const whence)
94 {
95 off_t const w = lseek(fd, offset, whence);
96 if (w == (off_t)-1) {
97 perror("lseek");
98 fail_file();
99 }
100 return w;
101 }
102
103 static size_t
uread(int const fd,void * const buf,size_t const count)104 uread(int const fd, void *const buf, size_t const count)
105 {
106 size_t const n = read(fd, buf, count);
107 if (n != count) {
108 perror("read");
109 fail_file();
110 }
111 return n;
112 }
113
114 static size_t
uwrite(int const fd,void const * const buf,size_t const count)115 uwrite(int const fd, void const *const buf, size_t const count)
116 {
117 size_t const n = write(fd, buf, count);
118 if (n != count) {
119 perror("write");
120 fail_file();
121 }
122 return n;
123 }
124
125 static void *
umalloc(size_t size)126 umalloc(size_t size)
127 {
128 void *const addr = malloc(size);
129 if (addr == 0) {
130 fprintf(stderr, "malloc failed: %zu bytes\n", size);
131 fail_file();
132 }
133 return addr;
134 }
135
136 static unsigned char ideal_nop5_x86_64[5] = { 0x0f, 0x1f, 0x44, 0x00, 0x00 };
137 static unsigned char ideal_nop5_x86_32[5] = { 0x3e, 0x8d, 0x74, 0x26, 0x00 };
138 static unsigned char *ideal_nop;
139
140 static char rel_type_nop;
141
142 static int (*make_nop)(void *map, size_t const offset);
143
make_nop_x86(void * map,size_t const offset)144 static int make_nop_x86(void *map, size_t const offset)
145 {
146 uint32_t *ptr;
147 unsigned char *op;
148
149 /* Confirm we have 0xe8 0x0 0x0 0x0 0x0 */
150 ptr = map + offset;
151 if (*ptr != 0)
152 return -1;
153
154 op = map + offset - 1;
155 if (*op != 0xe8)
156 return -1;
157
158 /* convert to nop */
159 ulseek(fd_map, offset - 1, SEEK_SET);
160 uwrite(fd_map, ideal_nop, 5);
161 return 0;
162 }
163
164 static unsigned char ideal_nop4_arm64[4] = {0x1f, 0x20, 0x03, 0xd5};
make_nop_arm64(void * map,size_t const offset)165 static int make_nop_arm64(void *map, size_t const offset)
166 {
167 uint32_t *ptr;
168
169 ptr = map + offset;
170 /* bl <_mcount> is 0x94000000 before relocation */
171 if (*ptr != 0x94000000)
172 return -1;
173
174 /* Convert to nop */
175 ulseek(fd_map, offset, SEEK_SET);
176 uwrite(fd_map, ideal_nop, 4);
177 return 0;
178 }
179
180 /*
181 * Get the whole file as a programming convenience in order to avoid
182 * malloc+lseek+read+free of many pieces. If successful, then mmap
183 * avoids copying unused pieces; else just read the whole file.
184 * Open for both read and write; new info will be appended to the file.
185 * Use MAP_PRIVATE so that a few changes to the in-memory ElfXX_Ehdr
186 * do not propagate to the file until an explicit overwrite at the last.
187 * This preserves most aspects of consistency (all except .st_size)
188 * for simultaneous readers of the file while we are appending to it.
189 * However, multiple writers still are bad. We choose not to use
190 * locking because it is expensive and the use case of kernel build
191 * makes multiple writers unlikely.
192 */
mmap_file(char const * fname)193 static void *mmap_file(char const *fname)
194 {
195 void *addr;
196
197 fd_map = open(fname, O_RDWR);
198 if (fd_map < 0 || fstat(fd_map, &sb) < 0) {
199 perror(fname);
200 fail_file();
201 }
202 if (!S_ISREG(sb.st_mode)) {
203 fprintf(stderr, "not a regular file: %s\n", fname);
204 fail_file();
205 }
206 addr = mmap(0, sb.st_size, PROT_READ|PROT_WRITE, MAP_PRIVATE,
207 fd_map, 0);
208 mmap_failed = 0;
209 if (addr == MAP_FAILED) {
210 mmap_failed = 1;
211 addr = umalloc(sb.st_size);
212 uread(fd_map, addr, sb.st_size);
213 }
214 return addr;
215 }
216
217 /* w8rev, w8nat, ...: Handle endianness. */
218
w8rev(uint64_t const x)219 static uint64_t w8rev(uint64_t const x)
220 {
221 return ((0xff & (x >> (0 * 8))) << (7 * 8))
222 | ((0xff & (x >> (1 * 8))) << (6 * 8))
223 | ((0xff & (x >> (2 * 8))) << (5 * 8))
224 | ((0xff & (x >> (3 * 8))) << (4 * 8))
225 | ((0xff & (x >> (4 * 8))) << (3 * 8))
226 | ((0xff & (x >> (5 * 8))) << (2 * 8))
227 | ((0xff & (x >> (6 * 8))) << (1 * 8))
228 | ((0xff & (x >> (7 * 8))) << (0 * 8));
229 }
230
w4rev(uint32_t const x)231 static uint32_t w4rev(uint32_t const x)
232 {
233 return ((0xff & (x >> (0 * 8))) << (3 * 8))
234 | ((0xff & (x >> (1 * 8))) << (2 * 8))
235 | ((0xff & (x >> (2 * 8))) << (1 * 8))
236 | ((0xff & (x >> (3 * 8))) << (0 * 8));
237 }
238
w2rev(uint16_t const x)239 static uint32_t w2rev(uint16_t const x)
240 {
241 return ((0xff & (x >> (0 * 8))) << (1 * 8))
242 | ((0xff & (x >> (1 * 8))) << (0 * 8));
243 }
244
w8nat(uint64_t const x)245 static uint64_t w8nat(uint64_t const x)
246 {
247 return x;
248 }
249
w4nat(uint32_t const x)250 static uint32_t w4nat(uint32_t const x)
251 {
252 return x;
253 }
254
w2nat(uint16_t const x)255 static uint32_t w2nat(uint16_t const x)
256 {
257 return x;
258 }
259
260 static uint64_t (*w8)(uint64_t);
261 static uint32_t (*w)(uint32_t);
262 static uint32_t (*w2)(uint16_t);
263
264 /* Names of the sections that could contain calls to mcount. */
265 static int
is_mcounted_section_name(char const * const txtname)266 is_mcounted_section_name(char const *const txtname)
267 {
268 return strcmp(".text", txtname) == 0 ||
269 strcmp(".ref.text", txtname) == 0 ||
270 strcmp(".sched.text", txtname) == 0 ||
271 strcmp(".spinlock.text", txtname) == 0 ||
272 strcmp(".irqentry.text", txtname) == 0 ||
273 strcmp(".kprobes.text", txtname) == 0 ||
274 strcmp(".text.unlikely", txtname) == 0;
275 }
276
277 /* 32 bit and 64 bit are very similar */
278 #include "recordmcount.h"
279 #define RECORD_MCOUNT_64
280 #include "recordmcount.h"
281
282 /* 64-bit EM_MIPS has weird ELF64_Rela.r_info.
283 * http://techpubs.sgi.com/library/manuals/4000/007-4658-001/pdf/007-4658-001.pdf
284 * We interpret Table 29 Relocation Operation (Elf64_Rel, Elf64_Rela) [p.40]
285 * to imply the order of the members; the spec does not say so.
286 * typedef unsigned char Elf64_Byte;
287 * fails on MIPS64 because their <elf.h> already has it!
288 */
289
290 typedef uint8_t myElf64_Byte; /* Type for a 8-bit quantity. */
291
292 union mips_r_info {
293 Elf64_Xword r_info;
294 struct {
295 Elf64_Word r_sym; /* Symbol index. */
296 myElf64_Byte r_ssym; /* Special symbol. */
297 myElf64_Byte r_type3; /* Third relocation. */
298 myElf64_Byte r_type2; /* Second relocation. */
299 myElf64_Byte r_type; /* First relocation. */
300 } r_mips;
301 };
302
MIPS64_r_sym(Elf64_Rel const * rp)303 static uint64_t MIPS64_r_sym(Elf64_Rel const *rp)
304 {
305 return w(((union mips_r_info){ .r_info = rp->r_info }).r_mips.r_sym);
306 }
307
MIPS64_r_info(Elf64_Rel * const rp,unsigned sym,unsigned type)308 static void MIPS64_r_info(Elf64_Rel *const rp, unsigned sym, unsigned type)
309 {
310 rp->r_info = ((union mips_r_info){
311 .r_mips = { .r_sym = w(sym), .r_type = type }
312 }).r_info;
313 }
314
315 static void
do_file(char const * const fname)316 do_file(char const *const fname)
317 {
318 Elf32_Ehdr *const ehdr = mmap_file(fname);
319 unsigned int reltype = 0;
320
321 ehdr_curr = ehdr;
322 w = w4nat;
323 w2 = w2nat;
324 w8 = w8nat;
325 switch (ehdr->e_ident[EI_DATA]) {
326 static unsigned int const endian = 1;
327 default:
328 fprintf(stderr, "unrecognized ELF data encoding %d: %s\n",
329 ehdr->e_ident[EI_DATA], fname);
330 fail_file();
331 break;
332 case ELFDATA2LSB:
333 if (*(unsigned char const *)&endian != 1) {
334 /* main() is big endian, file.o is little endian. */
335 w = w4rev;
336 w2 = w2rev;
337 w8 = w8rev;
338 }
339 break;
340 case ELFDATA2MSB:
341 if (*(unsigned char const *)&endian != 0) {
342 /* main() is little endian, file.o is big endian. */
343 w = w4rev;
344 w2 = w2rev;
345 w8 = w8rev;
346 }
347 break;
348 } /* end switch */
349 if (memcmp(ELFMAG, ehdr->e_ident, SELFMAG) != 0
350 || w2(ehdr->e_type) != ET_REL
351 || ehdr->e_ident[EI_VERSION] != EV_CURRENT) {
352 fprintf(stderr, "unrecognized ET_REL file %s\n", fname);
353 fail_file();
354 }
355
356 gpfx = 0;
357 switch (w2(ehdr->e_machine)) {
358 default:
359 fprintf(stderr, "unrecognized e_machine %d %s\n",
360 w2(ehdr->e_machine), fname);
361 fail_file();
362 break;
363 case EM_386:
364 reltype = R_386_32;
365 make_nop = make_nop_x86;
366 ideal_nop = ideal_nop5_x86_32;
367 mcount_adjust_32 = -1;
368 break;
369 case EM_ARM: reltype = R_ARM_ABS32;
370 altmcount = "__gnu_mcount_nc";
371 break;
372 case EM_AARCH64:
373 reltype = R_AARCH64_ABS64;
374 make_nop = make_nop_arm64;
375 rel_type_nop = R_AARCH64_NONE;
376 ideal_nop = ideal_nop4_arm64;
377 gpfx = '_';
378 break;
379 case EM_IA_64: reltype = R_IA64_IMM64; gpfx = '_'; break;
380 case EM_METAG: reltype = R_METAG_ADDR32;
381 altmcount = "_mcount_wrapper";
382 rel_type_nop = R_METAG_NONE;
383 /* We happen to have the same requirement as MIPS */
384 is_fake_mcount32 = MIPS32_is_fake_mcount;
385 break;
386 case EM_MIPS: /* reltype: e_class */ gpfx = '_'; break;
387 case EM_PPC: reltype = R_PPC_ADDR32; gpfx = '_'; break;
388 case EM_PPC64: reltype = R_PPC64_ADDR64; gpfx = '_'; break;
389 case EM_S390: /* reltype: e_class */ gpfx = '_'; break;
390 case EM_SH: reltype = R_SH_DIR32; break;
391 case EM_SPARCV9: reltype = R_SPARC_64; gpfx = '_'; break;
392 case EM_X86_64:
393 make_nop = make_nop_x86;
394 ideal_nop = ideal_nop5_x86_64;
395 reltype = R_X86_64_64;
396 mcount_adjust_64 = -1;
397 break;
398 } /* end switch */
399
400 switch (ehdr->e_ident[EI_CLASS]) {
401 default:
402 fprintf(stderr, "unrecognized ELF class %d %s\n",
403 ehdr->e_ident[EI_CLASS], fname);
404 fail_file();
405 break;
406 case ELFCLASS32:
407 if (w2(ehdr->e_ehsize) != sizeof(Elf32_Ehdr)
408 || w2(ehdr->e_shentsize) != sizeof(Elf32_Shdr)) {
409 fprintf(stderr,
410 "unrecognized ET_REL file: %s\n", fname);
411 fail_file();
412 }
413 if (w2(ehdr->e_machine) == EM_MIPS) {
414 reltype = R_MIPS_32;
415 is_fake_mcount32 = MIPS32_is_fake_mcount;
416 }
417 do32(ehdr, fname, reltype);
418 break;
419 case ELFCLASS64: {
420 Elf64_Ehdr *const ghdr = (Elf64_Ehdr *)ehdr;
421 if (w2(ghdr->e_ehsize) != sizeof(Elf64_Ehdr)
422 || w2(ghdr->e_shentsize) != sizeof(Elf64_Shdr)) {
423 fprintf(stderr,
424 "unrecognized ET_REL file: %s\n", fname);
425 fail_file();
426 }
427 if (w2(ghdr->e_machine) == EM_S390) {
428 reltype = R_390_64;
429 mcount_adjust_64 = -14;
430 }
431 if (w2(ghdr->e_machine) == EM_MIPS) {
432 reltype = R_MIPS_64;
433 Elf64_r_sym = MIPS64_r_sym;
434 Elf64_r_info = MIPS64_r_info;
435 is_fake_mcount64 = MIPS64_is_fake_mcount;
436 }
437 do64(ghdr, fname, reltype);
438 break;
439 }
440 } /* end switch */
441
442 cleanup();
443 }
444
445 int
main(int argc,char * argv[])446 main(int argc, char *argv[])
447 {
448 const char ftrace[] = "/ftrace.o";
449 int ftrace_size = sizeof(ftrace) - 1;
450 int n_error = 0; /* gcc-4.3.0 false positive complaint */
451 int c;
452 int i;
453
454 while ((c = getopt(argc, argv, "w")) >= 0) {
455 switch (c) {
456 case 'w':
457 warn_on_notrace_sect = 1;
458 break;
459 default:
460 fprintf(stderr, "usage: recordmcount [-w] file.o...\n");
461 return 0;
462 }
463 }
464
465 if ((argc - optind) < 1) {
466 fprintf(stderr, "usage: recordmcount [-w] file.o...\n");
467 return 0;
468 }
469
470 /* Process each file in turn, allowing deep failure. */
471 for (i = optind; i < argc; i++) {
472 char *file = argv[i];
473 int const sjval = setjmp(jmpenv);
474 int len;
475
476 /*
477 * The file kernel/trace/ftrace.o references the mcount
478 * function but does not call it. Since ftrace.o should
479 * not be traced anyway, we just skip it.
480 */
481 len = strlen(file);
482 if (len >= ftrace_size &&
483 strcmp(file + (len - ftrace_size), ftrace) == 0)
484 continue;
485
486 switch (sjval) {
487 default:
488 fprintf(stderr, "internal error: %s\n", file);
489 exit(1);
490 break;
491 case SJ_SETJMP: /* normal sequence */
492 /* Avoid problems if early cleanup() */
493 fd_map = -1;
494 ehdr_curr = NULL;
495 mmap_failed = 1;
496 do_file(file);
497 break;
498 case SJ_FAIL: /* error in do_file or below */
499 ++n_error;
500 break;
501 case SJ_SUCCEED: /* premature success */
502 /* do nothing */
503 break;
504 } /* end switch */
505 }
506 return !!n_error;
507 }
508