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 static int fd_map; /* File descriptor for file being modified. */
44 static int mmap_failed; /* Boolean flag. */
45 static void *ehdr_curr; /* current ElfXX_Ehdr * for resource cleanup */
46 static char gpfx; /* prefix for global symbol name (sometimes '_') */
47 static struct stat sb; /* Remember .st_size, etc. */
48 static jmp_buf jmpenv; /* setjmp/longjmp per-file error escape */
49 static const char *altmcount; /* alternate mcount symbol name */
50 static int warn_on_notrace_sect; /* warn when section has mcount not being recorded */
51
52 /* setjmp() return values */
53 enum {
54 SJ_SETJMP = 0, /* hardwired first return */
55 SJ_FAIL,
56 SJ_SUCCEED
57 };
58
59 /* Per-file resource cleanup when multiple files. */
60 static void
cleanup(void)61 cleanup(void)
62 {
63 if (!mmap_failed)
64 munmap(ehdr_curr, sb.st_size);
65 else
66 free(ehdr_curr);
67 close(fd_map);
68 }
69
70 static void __attribute__((noreturn))
fail_file(void)71 fail_file(void)
72 {
73 cleanup();
74 longjmp(jmpenv, SJ_FAIL);
75 }
76
77 static void __attribute__((noreturn))
succeed_file(void)78 succeed_file(void)
79 {
80 cleanup();
81 longjmp(jmpenv, SJ_SUCCEED);
82 }
83
84 /* ulseek, uread, ...: Check return value for errors. */
85
86 static off_t
ulseek(int const fd,off_t const offset,int const whence)87 ulseek(int const fd, off_t const offset, int const whence)
88 {
89 off_t const w = lseek(fd, offset, whence);
90 if (w == (off_t)-1) {
91 perror("lseek");
92 fail_file();
93 }
94 return w;
95 }
96
97 static size_t
uread(int const fd,void * const buf,size_t const count)98 uread(int const fd, void *const buf, size_t const count)
99 {
100 size_t const n = read(fd, buf, count);
101 if (n != count) {
102 perror("read");
103 fail_file();
104 }
105 return n;
106 }
107
108 static size_t
uwrite(int const fd,void const * const buf,size_t const count)109 uwrite(int const fd, void const *const buf, size_t const count)
110 {
111 size_t const n = write(fd, buf, count);
112 if (n != count) {
113 perror("write");
114 fail_file();
115 }
116 return n;
117 }
118
119 static void *
umalloc(size_t size)120 umalloc(size_t size)
121 {
122 void *const addr = malloc(size);
123 if (addr == 0) {
124 fprintf(stderr, "malloc failed: %zu bytes\n", size);
125 fail_file();
126 }
127 return addr;
128 }
129
130 static unsigned char ideal_nop5_x86_64[5] = { 0x0f, 0x1f, 0x44, 0x00, 0x00 };
131 static unsigned char ideal_nop5_x86_32[5] = { 0x3e, 0x8d, 0x74, 0x26, 0x00 };
132 static unsigned char *ideal_nop;
133
134 static char rel_type_nop;
135
136 static int (*make_nop)(void *map, size_t const offset);
137
make_nop_x86(void * map,size_t const offset)138 static int make_nop_x86(void *map, size_t const offset)
139 {
140 uint32_t *ptr;
141 unsigned char *op;
142
143 /* Confirm we have 0xe8 0x0 0x0 0x0 0x0 */
144 ptr = map + offset;
145 if (*ptr != 0)
146 return -1;
147
148 op = map + offset - 1;
149 if (*op != 0xe8)
150 return -1;
151
152 /* convert to nop */
153 ulseek(fd_map, offset - 1, SEEK_SET);
154 uwrite(fd_map, ideal_nop, 5);
155 return 0;
156 }
157
158 /*
159 * Get the whole file as a programming convenience in order to avoid
160 * malloc+lseek+read+free of many pieces. If successful, then mmap
161 * avoids copying unused pieces; else just read the whole file.
162 * Open for both read and write; new info will be appended to the file.
163 * Use MAP_PRIVATE so that a few changes to the in-memory ElfXX_Ehdr
164 * do not propagate to the file until an explicit overwrite at the last.
165 * This preserves most aspects of consistency (all except .st_size)
166 * for simultaneous readers of the file while we are appending to it.
167 * However, multiple writers still are bad. We choose not to use
168 * locking because it is expensive and the use case of kernel build
169 * makes multiple writers unlikely.
170 */
mmap_file(char const * fname)171 static void *mmap_file(char const *fname)
172 {
173 void *addr;
174
175 fd_map = open(fname, O_RDWR);
176 if (fd_map < 0 || fstat(fd_map, &sb) < 0) {
177 perror(fname);
178 fail_file();
179 }
180 if (!S_ISREG(sb.st_mode)) {
181 fprintf(stderr, "not a regular file: %s\n", fname);
182 fail_file();
183 }
184 addr = mmap(0, sb.st_size, PROT_READ|PROT_WRITE, MAP_PRIVATE,
185 fd_map, 0);
186 mmap_failed = 0;
187 if (addr == MAP_FAILED) {
188 mmap_failed = 1;
189 addr = umalloc(sb.st_size);
190 uread(fd_map, addr, sb.st_size);
191 }
192 return addr;
193 }
194
195 /* w8rev, w8nat, ...: Handle endianness. */
196
w8rev(uint64_t const x)197 static uint64_t w8rev(uint64_t const x)
198 {
199 return ((0xff & (x >> (0 * 8))) << (7 * 8))
200 | ((0xff & (x >> (1 * 8))) << (6 * 8))
201 | ((0xff & (x >> (2 * 8))) << (5 * 8))
202 | ((0xff & (x >> (3 * 8))) << (4 * 8))
203 | ((0xff & (x >> (4 * 8))) << (3 * 8))
204 | ((0xff & (x >> (5 * 8))) << (2 * 8))
205 | ((0xff & (x >> (6 * 8))) << (1 * 8))
206 | ((0xff & (x >> (7 * 8))) << (0 * 8));
207 }
208
w4rev(uint32_t const x)209 static uint32_t w4rev(uint32_t const x)
210 {
211 return ((0xff & (x >> (0 * 8))) << (3 * 8))
212 | ((0xff & (x >> (1 * 8))) << (2 * 8))
213 | ((0xff & (x >> (2 * 8))) << (1 * 8))
214 | ((0xff & (x >> (3 * 8))) << (0 * 8));
215 }
216
w2rev(uint16_t const x)217 static uint32_t w2rev(uint16_t const x)
218 {
219 return ((0xff & (x >> (0 * 8))) << (1 * 8))
220 | ((0xff & (x >> (1 * 8))) << (0 * 8));
221 }
222
w8nat(uint64_t const x)223 static uint64_t w8nat(uint64_t const x)
224 {
225 return x;
226 }
227
w4nat(uint32_t const x)228 static uint32_t w4nat(uint32_t const x)
229 {
230 return x;
231 }
232
w2nat(uint16_t const x)233 static uint32_t w2nat(uint16_t const x)
234 {
235 return x;
236 }
237
238 static uint64_t (*w8)(uint64_t);
239 static uint32_t (*w)(uint32_t);
240 static uint32_t (*w2)(uint16_t);
241
242 /* Names of the sections that could contain calls to mcount. */
243 static int
is_mcounted_section_name(char const * const txtname)244 is_mcounted_section_name(char const *const txtname)
245 {
246 return strcmp(".text", txtname) == 0 ||
247 strcmp(".ref.text", txtname) == 0 ||
248 strcmp(".sched.text", txtname) == 0 ||
249 strcmp(".spinlock.text", txtname) == 0 ||
250 strcmp(".irqentry.text", txtname) == 0 ||
251 strcmp(".kprobes.text", txtname) == 0 ||
252 strcmp(".text.unlikely", txtname) == 0;
253 }
254
255 /* 32 bit and 64 bit are very similar */
256 #include "recordmcount.h"
257 #define RECORD_MCOUNT_64
258 #include "recordmcount.h"
259
260 /* 64-bit EM_MIPS has weird ELF64_Rela.r_info.
261 * http://techpubs.sgi.com/library/manuals/4000/007-4658-001/pdf/007-4658-001.pdf
262 * We interpret Table 29 Relocation Operation (Elf64_Rel, Elf64_Rela) [p.40]
263 * to imply the order of the members; the spec does not say so.
264 * typedef unsigned char Elf64_Byte;
265 * fails on MIPS64 because their <elf.h> already has it!
266 */
267
268 typedef uint8_t myElf64_Byte; /* Type for a 8-bit quantity. */
269
270 union mips_r_info {
271 Elf64_Xword r_info;
272 struct {
273 Elf64_Word r_sym; /* Symbol index. */
274 myElf64_Byte r_ssym; /* Special symbol. */
275 myElf64_Byte r_type3; /* Third relocation. */
276 myElf64_Byte r_type2; /* Second relocation. */
277 myElf64_Byte r_type; /* First relocation. */
278 } r_mips;
279 };
280
MIPS64_r_sym(Elf64_Rel const * rp)281 static uint64_t MIPS64_r_sym(Elf64_Rel const *rp)
282 {
283 return w(((union mips_r_info){ .r_info = rp->r_info }).r_mips.r_sym);
284 }
285
MIPS64_r_info(Elf64_Rel * const rp,unsigned sym,unsigned type)286 static void MIPS64_r_info(Elf64_Rel *const rp, unsigned sym, unsigned type)
287 {
288 rp->r_info = ((union mips_r_info){
289 .r_mips = { .r_sym = w(sym), .r_type = type }
290 }).r_info;
291 }
292
293 static void
do_file(char const * const fname)294 do_file(char const *const fname)
295 {
296 Elf32_Ehdr *const ehdr = mmap_file(fname);
297 unsigned int reltype = 0;
298
299 ehdr_curr = ehdr;
300 w = w4nat;
301 w2 = w2nat;
302 w8 = w8nat;
303 switch (ehdr->e_ident[EI_DATA]) {
304 static unsigned int const endian = 1;
305 default:
306 fprintf(stderr, "unrecognized ELF data encoding %d: %s\n",
307 ehdr->e_ident[EI_DATA], fname);
308 fail_file();
309 break;
310 case ELFDATA2LSB:
311 if (*(unsigned char const *)&endian != 1) {
312 /* main() is big endian, file.o is little endian. */
313 w = w4rev;
314 w2 = w2rev;
315 w8 = w8rev;
316 }
317 break;
318 case ELFDATA2MSB:
319 if (*(unsigned char const *)&endian != 0) {
320 /* main() is little endian, file.o is big endian. */
321 w = w4rev;
322 w2 = w2rev;
323 w8 = w8rev;
324 }
325 break;
326 } /* end switch */
327 if (memcmp(ELFMAG, ehdr->e_ident, SELFMAG) != 0
328 || w2(ehdr->e_type) != ET_REL
329 || ehdr->e_ident[EI_VERSION] != EV_CURRENT) {
330 fprintf(stderr, "unrecognized ET_REL file %s\n", fname);
331 fail_file();
332 }
333
334 gpfx = 0;
335 switch (w2(ehdr->e_machine)) {
336 default:
337 fprintf(stderr, "unrecognized e_machine %d %s\n",
338 w2(ehdr->e_machine), fname);
339 fail_file();
340 break;
341 case EM_386:
342 reltype = R_386_32;
343 make_nop = make_nop_x86;
344 ideal_nop = ideal_nop5_x86_32;
345 mcount_adjust_32 = -1;
346 break;
347 case EM_ARM: reltype = R_ARM_ABS32;
348 altmcount = "__gnu_mcount_nc";
349 break;
350 case EM_IA_64: reltype = R_IA64_IMM64; gpfx = '_'; break;
351 case EM_METAG: reltype = R_METAG_ADDR32;
352 altmcount = "_mcount_wrapper";
353 rel_type_nop = R_METAG_NONE;
354 /* We happen to have the same requirement as MIPS */
355 is_fake_mcount32 = MIPS32_is_fake_mcount;
356 break;
357 case EM_MIPS: /* reltype: e_class */ gpfx = '_'; break;
358 case EM_PPC: reltype = R_PPC_ADDR32; gpfx = '_'; break;
359 case EM_PPC64: reltype = R_PPC64_ADDR64; gpfx = '_'; break;
360 case EM_S390: /* reltype: e_class */ gpfx = '_'; break;
361 case EM_SH: reltype = R_SH_DIR32; break;
362 case EM_SPARCV9: reltype = R_SPARC_64; gpfx = '_'; break;
363 case EM_X86_64:
364 make_nop = make_nop_x86;
365 ideal_nop = ideal_nop5_x86_64;
366 reltype = R_X86_64_64;
367 mcount_adjust_64 = -1;
368 break;
369 } /* end switch */
370
371 switch (ehdr->e_ident[EI_CLASS]) {
372 default:
373 fprintf(stderr, "unrecognized ELF class %d %s\n",
374 ehdr->e_ident[EI_CLASS], fname);
375 fail_file();
376 break;
377 case ELFCLASS32:
378 if (w2(ehdr->e_ehsize) != sizeof(Elf32_Ehdr)
379 || w2(ehdr->e_shentsize) != sizeof(Elf32_Shdr)) {
380 fprintf(stderr,
381 "unrecognized ET_REL file: %s\n", fname);
382 fail_file();
383 }
384 if (w2(ehdr->e_machine) == EM_S390) {
385 reltype = R_390_32;
386 mcount_adjust_32 = -4;
387 }
388 if (w2(ehdr->e_machine) == EM_MIPS) {
389 reltype = R_MIPS_32;
390 is_fake_mcount32 = MIPS32_is_fake_mcount;
391 }
392 do32(ehdr, fname, reltype);
393 break;
394 case ELFCLASS64: {
395 Elf64_Ehdr *const ghdr = (Elf64_Ehdr *)ehdr;
396 if (w2(ghdr->e_ehsize) != sizeof(Elf64_Ehdr)
397 || w2(ghdr->e_shentsize) != sizeof(Elf64_Shdr)) {
398 fprintf(stderr,
399 "unrecognized ET_REL file: %s\n", fname);
400 fail_file();
401 }
402 if (w2(ghdr->e_machine) == EM_S390) {
403 reltype = R_390_64;
404 mcount_adjust_64 = -8;
405 }
406 if (w2(ghdr->e_machine) == EM_MIPS) {
407 reltype = R_MIPS_64;
408 Elf64_r_sym = MIPS64_r_sym;
409 Elf64_r_info = MIPS64_r_info;
410 is_fake_mcount64 = MIPS64_is_fake_mcount;
411 }
412 do64(ghdr, fname, reltype);
413 break;
414 }
415 } /* end switch */
416
417 cleanup();
418 }
419
420 int
main(int argc,char * argv[])421 main(int argc, char *argv[])
422 {
423 const char ftrace[] = "/ftrace.o";
424 int ftrace_size = sizeof(ftrace) - 1;
425 int n_error = 0; /* gcc-4.3.0 false positive complaint */
426 int c;
427 int i;
428
429 while ((c = getopt(argc, argv, "w")) >= 0) {
430 switch (c) {
431 case 'w':
432 warn_on_notrace_sect = 1;
433 break;
434 default:
435 fprintf(stderr, "usage: recordmcount [-w] file.o...\n");
436 return 0;
437 }
438 }
439
440 if ((argc - optind) < 1) {
441 fprintf(stderr, "usage: recordmcount [-w] file.o...\n");
442 return 0;
443 }
444
445 /* Process each file in turn, allowing deep failure. */
446 for (i = optind; i < argc; i++) {
447 char *file = argv[i];
448 int const sjval = setjmp(jmpenv);
449 int len;
450
451 /*
452 * The file kernel/trace/ftrace.o references the mcount
453 * function but does not call it. Since ftrace.o should
454 * not be traced anyway, we just skip it.
455 */
456 len = strlen(file);
457 if (len >= ftrace_size &&
458 strcmp(file + (len - ftrace_size), ftrace) == 0)
459 continue;
460
461 switch (sjval) {
462 default:
463 fprintf(stderr, "internal error: %s\n", file);
464 exit(1);
465 break;
466 case SJ_SETJMP: /* normal sequence */
467 /* Avoid problems if early cleanup() */
468 fd_map = -1;
469 ehdr_curr = NULL;
470 mmap_failed = 1;
471 do_file(file);
472 break;
473 case SJ_FAIL: /* error in do_file or below */
474 ++n_error;
475 break;
476 case SJ_SUCCEED: /* premature success */
477 /* do nothing */
478 break;
479 } /* end switch */
480 }
481 return !!n_error;
482 }
483
484
485