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 <elf.h> 28 #include <fcntl.h> 29 #include <setjmp.h> 30 #include <stdio.h> 31 #include <stdlib.h> 32 #include <string.h> 33 #include <unistd.h> 34 35 static int fd_map; /* File descriptor for file being modified. */ 36 static int mmap_failed; /* Boolean flag. */ 37 static void *ehdr_curr; /* current ElfXX_Ehdr * for resource cleanup */ 38 static char gpfx; /* prefix for global symbol name (sometimes '_') */ 39 static struct stat sb; /* Remember .st_size, etc. */ 40 static jmp_buf jmpenv; /* setjmp/longjmp per-file error escape */ 41 static const char *altmcount; /* alternate mcount symbol name */ 42 43 /* setjmp() return values */ 44 enum { 45 SJ_SETJMP = 0, /* hardwired first return */ 46 SJ_FAIL, 47 SJ_SUCCEED 48 }; 49 50 /* Per-file resource cleanup when multiple files. */ 51 static void 52 cleanup(void) 53 { 54 if (!mmap_failed) 55 munmap(ehdr_curr, sb.st_size); 56 else 57 free(ehdr_curr); 58 close(fd_map); 59 } 60 61 static void __attribute__((noreturn)) 62 fail_file(void) 63 { 64 cleanup(); 65 longjmp(jmpenv, SJ_FAIL); 66 } 67 68 static void __attribute__((noreturn)) 69 succeed_file(void) 70 { 71 cleanup(); 72 longjmp(jmpenv, SJ_SUCCEED); 73 } 74 75 /* ulseek, uread, ...: Check return value for errors. */ 76 77 static off_t 78 ulseek(int const fd, off_t const offset, int const whence) 79 { 80 off_t const w = lseek(fd, offset, whence); 81 if ((off_t)-1 == w) { 82 perror("lseek"); 83 fail_file(); 84 } 85 return w; 86 } 87 88 static size_t 89 uread(int const fd, void *const buf, size_t const count) 90 { 91 size_t const n = read(fd, buf, count); 92 if (n != count) { 93 perror("read"); 94 fail_file(); 95 } 96 return n; 97 } 98 99 static size_t 100 uwrite(int const fd, void const *const buf, size_t const count) 101 { 102 size_t const n = write(fd, buf, count); 103 if (n != count) { 104 perror("write"); 105 fail_file(); 106 } 107 return n; 108 } 109 110 static void * 111 umalloc(size_t size) 112 { 113 void *const addr = malloc(size); 114 if (0 == addr) { 115 fprintf(stderr, "malloc failed: %zu bytes\n", size); 116 fail_file(); 117 } 118 return addr; 119 } 120 121 /* 122 * Get the whole file as a programming convenience in order to avoid 123 * malloc+lseek+read+free of many pieces. If successful, then mmap 124 * avoids copying unused pieces; else just read the whole file. 125 * Open for both read and write; new info will be appended to the file. 126 * Use MAP_PRIVATE so that a few changes to the in-memory ElfXX_Ehdr 127 * do not propagate to the file until an explicit overwrite at the last. 128 * This preserves most aspects of consistency (all except .st_size) 129 * for simultaneous readers of the file while we are appending to it. 130 * However, multiple writers still are bad. We choose not to use 131 * locking because it is expensive and the use case of kernel build 132 * makes multiple writers unlikely. 133 */ 134 static void *mmap_file(char const *fname) 135 { 136 void *addr; 137 138 fd_map = open(fname, O_RDWR); 139 if (0 > fd_map || 0 > fstat(fd_map, &sb)) { 140 perror(fname); 141 fail_file(); 142 } 143 if (!S_ISREG(sb.st_mode)) { 144 fprintf(stderr, "not a regular file: %s\n", fname); 145 fail_file(); 146 } 147 addr = mmap(0, sb.st_size, PROT_READ|PROT_WRITE, MAP_PRIVATE, 148 fd_map, 0); 149 mmap_failed = 0; 150 if (MAP_FAILED == addr) { 151 mmap_failed = 1; 152 addr = umalloc(sb.st_size); 153 uread(fd_map, addr, sb.st_size); 154 } 155 return addr; 156 } 157 158 /* w8rev, w8nat, ...: Handle endianness. */ 159 160 static uint64_t w8rev(uint64_t const x) 161 { 162 return ((0xff & (x >> (0 * 8))) << (7 * 8)) 163 | ((0xff & (x >> (1 * 8))) << (6 * 8)) 164 | ((0xff & (x >> (2 * 8))) << (5 * 8)) 165 | ((0xff & (x >> (3 * 8))) << (4 * 8)) 166 | ((0xff & (x >> (4 * 8))) << (3 * 8)) 167 | ((0xff & (x >> (5 * 8))) << (2 * 8)) 168 | ((0xff & (x >> (6 * 8))) << (1 * 8)) 169 | ((0xff & (x >> (7 * 8))) << (0 * 8)); 170 } 171 172 static uint32_t w4rev(uint32_t const x) 173 { 174 return ((0xff & (x >> (0 * 8))) << (3 * 8)) 175 | ((0xff & (x >> (1 * 8))) << (2 * 8)) 176 | ((0xff & (x >> (2 * 8))) << (1 * 8)) 177 | ((0xff & (x >> (3 * 8))) << (0 * 8)); 178 } 179 180 static uint32_t w2rev(uint16_t const x) 181 { 182 return ((0xff & (x >> (0 * 8))) << (1 * 8)) 183 | ((0xff & (x >> (1 * 8))) << (0 * 8)); 184 } 185 186 static uint64_t w8nat(uint64_t const x) 187 { 188 return x; 189 } 190 191 static uint32_t w4nat(uint32_t const x) 192 { 193 return x; 194 } 195 196 static uint32_t w2nat(uint16_t const x) 197 { 198 return x; 199 } 200 201 static uint64_t (*w8)(uint64_t); 202 static uint32_t (*w)(uint32_t); 203 static uint32_t (*w2)(uint16_t); 204 205 /* Names of the sections that could contain calls to mcount. */ 206 static int 207 is_mcounted_section_name(char const *const txtname) 208 { 209 return 0 == strcmp(".text", txtname) || 210 0 == strcmp(".sched.text", txtname) || 211 0 == strcmp(".spinlock.text", txtname) || 212 0 == strcmp(".irqentry.text", txtname) || 213 0 == strcmp(".text.unlikely", txtname); 214 } 215 216 /* 32 bit and 64 bit are very similar */ 217 #include "recordmcount.h" 218 #define RECORD_MCOUNT_64 219 #include "recordmcount.h" 220 221 /* 64-bit EM_MIPS has weird ELF64_Rela.r_info. 222 * http://techpubs.sgi.com/library/manuals/4000/007-4658-001/pdf/007-4658-001.pdf 223 * We interpret Table 29 Relocation Operation (Elf64_Rel, Elf64_Rela) [p.40] 224 * to imply the order of the members; the spec does not say so. 225 * typedef unsigned char Elf64_Byte; 226 * fails on MIPS64 because their <elf.h> already has it! 227 */ 228 229 typedef uint8_t myElf64_Byte; /* Type for a 8-bit quantity. */ 230 231 union mips_r_info { 232 Elf64_Xword r_info; 233 struct { 234 Elf64_Word r_sym; /* Symbol index. */ 235 myElf64_Byte r_ssym; /* Special symbol. */ 236 myElf64_Byte r_type3; /* Third relocation. */ 237 myElf64_Byte r_type2; /* Second relocation. */ 238 myElf64_Byte r_type; /* First relocation. */ 239 } r_mips; 240 }; 241 242 static uint64_t MIPS64_r_sym(Elf64_Rel const *rp) 243 { 244 return w(((union mips_r_info){ .r_info = rp->r_info }).r_mips.r_sym); 245 } 246 247 static void MIPS64_r_info(Elf64_Rel *const rp, unsigned sym, unsigned type) 248 { 249 rp->r_info = ((union mips_r_info){ 250 .r_mips = { .r_sym = w(sym), .r_type = type } 251 }).r_info; 252 } 253 254 static void 255 do_file(char const *const fname) 256 { 257 Elf32_Ehdr *const ehdr = mmap_file(fname); 258 unsigned int reltype = 0; 259 260 ehdr_curr = ehdr; 261 w = w4nat; 262 w2 = w2nat; 263 w8 = w8nat; 264 switch (ehdr->e_ident[EI_DATA]) { 265 static unsigned int const endian = 1; 266 default: { 267 fprintf(stderr, "unrecognized ELF data encoding %d: %s\n", 268 ehdr->e_ident[EI_DATA], fname); 269 fail_file(); 270 } break; 271 case ELFDATA2LSB: { 272 if (1 != *(unsigned char const *)&endian) { 273 /* main() is big endian, file.o is little endian. */ 274 w = w4rev; 275 w2 = w2rev; 276 w8 = w8rev; 277 } 278 } break; 279 case ELFDATA2MSB: { 280 if (0 != *(unsigned char const *)&endian) { 281 /* main() is little endian, file.o is big endian. */ 282 w = w4rev; 283 w2 = w2rev; 284 w8 = w8rev; 285 } 286 } break; 287 } /* end switch */ 288 if (0 != memcmp(ELFMAG, ehdr->e_ident, SELFMAG) 289 || ET_REL != w2(ehdr->e_type) 290 || EV_CURRENT != ehdr->e_ident[EI_VERSION]) { 291 fprintf(stderr, "unrecognized ET_REL file %s\n", fname); 292 fail_file(); 293 } 294 295 gpfx = 0; 296 switch (w2(ehdr->e_machine)) { 297 default: { 298 fprintf(stderr, "unrecognized e_machine %d %s\n", 299 w2(ehdr->e_machine), fname); 300 fail_file(); 301 } break; 302 case EM_386: reltype = R_386_32; break; 303 case EM_ARM: reltype = R_ARM_ABS32; 304 altmcount = "__gnu_mcount_nc"; 305 break; 306 case EM_IA_64: reltype = R_IA64_IMM64; gpfx = '_'; break; 307 case EM_MIPS: /* reltype: e_class */ gpfx = '_'; break; 308 case EM_PPC: reltype = R_PPC_ADDR32; gpfx = '_'; break; 309 case EM_PPC64: reltype = R_PPC64_ADDR64; gpfx = '_'; break; 310 case EM_S390: /* reltype: e_class */ gpfx = '_'; break; 311 case EM_SH: reltype = R_SH_DIR32; break; 312 case EM_SPARCV9: reltype = R_SPARC_64; gpfx = '_'; break; 313 case EM_X86_64: reltype = R_X86_64_64; break; 314 } /* end switch */ 315 316 switch (ehdr->e_ident[EI_CLASS]) { 317 default: { 318 fprintf(stderr, "unrecognized ELF class %d %s\n", 319 ehdr->e_ident[EI_CLASS], fname); 320 fail_file(); 321 } break; 322 case ELFCLASS32: { 323 if (sizeof(Elf32_Ehdr) != w2(ehdr->e_ehsize) 324 || sizeof(Elf32_Shdr) != w2(ehdr->e_shentsize)) { 325 fprintf(stderr, 326 "unrecognized ET_REL file: %s\n", fname); 327 fail_file(); 328 } 329 if (EM_S390 == w2(ehdr->e_machine)) 330 reltype = R_390_32; 331 if (EM_MIPS == w2(ehdr->e_machine)) { 332 reltype = R_MIPS_32; 333 is_fake_mcount32 = MIPS32_is_fake_mcount; 334 } 335 do32(ehdr, fname, reltype); 336 } break; 337 case ELFCLASS64: { 338 Elf64_Ehdr *const ghdr = (Elf64_Ehdr *)ehdr; 339 if (sizeof(Elf64_Ehdr) != w2(ghdr->e_ehsize) 340 || sizeof(Elf64_Shdr) != w2(ghdr->e_shentsize)) { 341 fprintf(stderr, 342 "unrecognized ET_REL file: %s\n", fname); 343 fail_file(); 344 } 345 if (EM_S390 == w2(ghdr->e_machine)) 346 reltype = R_390_64; 347 if (EM_MIPS == w2(ghdr->e_machine)) { 348 reltype = R_MIPS_64; 349 Elf64_r_sym = MIPS64_r_sym; 350 Elf64_r_info = MIPS64_r_info; 351 is_fake_mcount64 = MIPS64_is_fake_mcount; 352 } 353 do64(ghdr, fname, reltype); 354 } break; 355 } /* end switch */ 356 357 cleanup(); 358 } 359 360 int 361 main(int argc, char const *argv[]) 362 { 363 const char ftrace[] = "/ftrace.o"; 364 int ftrace_size = sizeof(ftrace) - 1; 365 int n_error = 0; /* gcc-4.3.0 false positive complaint */ 366 367 if (argc <= 1) { 368 fprintf(stderr, "usage: recordmcount file.o...\n"); 369 return 0; 370 } 371 372 /* Process each file in turn, allowing deep failure. */ 373 for (--argc, ++argv; 0 < argc; --argc, ++argv) { 374 int const sjval = setjmp(jmpenv); 375 int len; 376 377 /* 378 * The file kernel/trace/ftrace.o references the mcount 379 * function but does not call it. Since ftrace.o should 380 * not be traced anyway, we just skip it. 381 */ 382 len = strlen(argv[0]); 383 if (len >= ftrace_size && 384 strcmp(argv[0] + (len - ftrace_size), ftrace) == 0) 385 continue; 386 387 switch (sjval) { 388 default: { 389 fprintf(stderr, "internal error: %s\n", argv[0]); 390 exit(1); 391 } break; 392 case SJ_SETJMP: { /* normal sequence */ 393 /* Avoid problems if early cleanup() */ 394 fd_map = -1; 395 ehdr_curr = NULL; 396 mmap_failed = 1; 397 do_file(argv[0]); 398 } break; 399 case SJ_FAIL: { /* error in do_file or below */ 400 ++n_error; 401 } break; 402 case SJ_SUCCEED: { /* premature success */ 403 /* do nothing */ 404 } break; 405 } /* end switch */ 406 } 407 return !!n_error; 408 } 409 410 411