scripts/recordmcount.c

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