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 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 (w == (off_t)-1) {
  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 (addr == 0) {
 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 (fd_map < 0 || fstat(fd_map, &sb) < 0) {
 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 (addr == MAP_FAILED) {
 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 strcmp(".text",           txtname) == 0 ||
 210                 strcmp(".ref.text",      txtname) == 0 ||
 211                 strcmp(".sched.text",    txtname) == 0 ||
 212                 strcmp(".spinlock.text", txtname) == 0 ||
 213                 strcmp(".irqentry.text", txtname) == 0 ||
 214                 strcmp(".kprobes.text", txtname) == 0 ||
 215                 strcmp(".text.unlikely", txtname) == 0;
 216 }
 217
 218 /* 32 bit and 64 bit are very similar */
 219 #include "recordmcount.h"
 220 #define RECORD_MCOUNT_64
 221 #include "recordmcount.h"
 222
 223 /* 64-bit EM_MIPS has weird ELF64_Rela.r_info.
 224  * http://techpubs.sgi.com/library/manuals/4000/007-4658-001/pdf/007-4658-001.pdf
 225  * We interpret Table 29 Relocation Operation (Elf64_Rel, Elf64_Rela) [p.40]
 226  * to imply the order of the members; the spec does not say so.
 227  *      typedef unsigned char Elf64_Byte;
 228  * fails on MIPS64 because their <elf.h> already has it!
 229  */
 230
 231 typedef uint8_t myElf64_Byte;           /* Type for a 8-bit quantity.  */
 232
 233 union mips_r_info {
 234         Elf64_Xword r_info;
 235         struct {
 236                 Elf64_Word r_sym;               /* Symbol index.  */
 237                 myElf64_Byte r_ssym;            /* Special symbol.  */
 238                 myElf64_Byte r_type3;           /* Third relocation.  */
 239                 myElf64_Byte r_type2;           /* Second relocation.  */
 240                 myElf64_Byte r_type;            /* First relocation.  */
 241         } r_mips;
 242 };
 243
 244 static uint64_t MIPS64_r_sym(Elf64_Rel const *rp)
 245 {
 246         return w(((union mips_r_info){ .r_info = rp->r_info }).r_mips.r_sym);
 247 }
 248
 249 static void MIPS64_r_info(Elf64_Rel *const rp, unsigned sym, unsigned type)
 250 {
 251         rp->r_info = ((union mips_r_info){
 252                 .r_mips = { .r_sym = w(sym), .r_type = type }
 253         }).r_info;
 254 }
 255
 256 static void
 257 do_file(char const *const fname)
 258 {
 259         Elf32_Ehdr *const ehdr = mmap_file(fname);
 260         unsigned int reltype = 0;
 261
 262         ehdr_curr = ehdr;
 263         w = w4nat;
 264         w2 = w2nat;
 265         w8 = w8nat;
 266         switch (ehdr->e_ident[EI_DATA]) {
 267                 static unsigned int const endian = 1;
 268         default:
 269                 fprintf(stderr, "unrecognized ELF data encoding %d: %s\n",
 270                         ehdr->e_ident[EI_DATA], fname);
 271                 fail_file();
 272                 break;
 273         case ELFDATA2LSB:
 274                 if (*(unsigned char const *)&endian != 1) {
 275                         /* main() is big endian, file.o is little endian. */
 276                         w = w4rev;
 277                         w2 = w2rev;
 278                         w8 = w8rev;
 279                 }
 280                 break;
 281         case ELFDATA2MSB:
 282                 if (*(unsigned char const *)&endian != 0) {
 283                         /* main() is little endian, file.o is big endian. */
 284                         w = w4rev;
 285                         w2 = w2rev;
 286                         w8 = w8rev;
 287                 }
 288                 break;
 289         }  /* end switch */
 290         if (memcmp(ELFMAG, ehdr->e_ident, SELFMAG) != 0
 291         ||  w2(ehdr->e_type) != ET_REL
 292         ||  ehdr->e_ident[EI_VERSION] != EV_CURRENT) {
 293                 fprintf(stderr, "unrecognized ET_REL file %s\n", fname);
 294                 fail_file();
 295         }
 296
 297         gpfx = 0;
 298         switch (w2(ehdr->e_machine)) {
 299         default:
 300                 fprintf(stderr, "unrecognized e_machine %d %s\n",
 301                         w2(ehdr->e_machine), fname);
 302                 fail_file();
 303                 break;
 304         case EM_386:     reltype = R_386_32;                   break;
 305         case EM_ARM:     reltype = R_ARM_ABS32;
 306                          altmcount = "__gnu_mcount_nc";
 307                          break;
 308         case EM_IA_64:   reltype = R_IA64_IMM64;   gpfx = '_'; break;
 309         case EM_MIPS:    /* reltype: e_class    */ gpfx = '_'; break;
 310         case EM_PPC:     reltype = R_PPC_ADDR32;   gpfx = '_'; break;
 311         case EM_PPC64:   reltype = R_PPC64_ADDR64; gpfx = '_'; break;
 312         case EM_S390:    /* reltype: e_class    */ gpfx = '_'; break;
 313         case EM_SH:      reltype = R_SH_DIR32;                 break;
 314         case EM_SPARCV9: reltype = R_SPARC_64;     gpfx = '_'; break;
 315         case EM_X86_64:  reltype = R_X86_64_64;                break;
 316         }  /* end switch */
 317
 318         switch (ehdr->e_ident[EI_CLASS]) {
 319         default:
 320                 fprintf(stderr, "unrecognized ELF class %d %s\n",
 321                         ehdr->e_ident[EI_CLASS], fname);
 322                 fail_file();
 323                 break;
 324         case ELFCLASS32:
 325                 if (w2(ehdr->e_ehsize) != sizeof(Elf32_Ehdr)
 326                 ||  w2(ehdr->e_shentsize) != sizeof(Elf32_Shdr)) {
 327                         fprintf(stderr,
 328                                 "unrecognized ET_REL file: %s\n", fname);
 329                         fail_file();
 330                 }
 331                 if (w2(ehdr->e_machine) == EM_S390)
 332                         reltype = R_390_32;
 333                 if (w2(ehdr->e_machine) == EM_MIPS) {
 334                         reltype = R_MIPS_32;
 335                         is_fake_mcount32 = MIPS32_is_fake_mcount;
 336                 }
 337                 do32(ehdr, fname, reltype);
 338                 break;
 339         case ELFCLASS64: {
 340                 Elf64_Ehdr *const ghdr = (Elf64_Ehdr *)ehdr;
 341                 if (w2(ghdr->e_ehsize) != sizeof(Elf64_Ehdr)
 342                 ||  w2(ghdr->e_shentsize) != sizeof(Elf64_Shdr)) {
 343                         fprintf(stderr,
 344                                 "unrecognized ET_REL file: %s\n", fname);
 345                         fail_file();
 346                 }
 347                 if (w2(ghdr->e_machine) == EM_S390)
 348                         reltype = R_390_64;
 349                 if (w2(ghdr->e_machine) == EM_MIPS) {
 350                         reltype = R_MIPS_64;
 351                         Elf64_r_sym = MIPS64_r_sym;
 352                         Elf64_r_info = MIPS64_r_info;
 353                         is_fake_mcount64 = MIPS64_is_fake_mcount;
 354                 }
 355                 do64(ghdr, fname, reltype);
 356                 break;
 357         }
 358         }  /* end switch */
 359
 360         cleanup();
 361 }
 362
 363 int
 364 main(int argc, char const *argv[])
 365 {
 366         const char ftrace[] = "/ftrace.o";
 367         int ftrace_size = sizeof(ftrace) - 1;
 368         int n_error = 0;  /* gcc-4.3.0 false positive complaint */
 369
 370         if (argc <= 1) {
 371                 fprintf(stderr, "usage: recordmcount file.o...\n");
 372                 return 0;
 373         }
 374
 375         /* Process each file in turn, allowing deep failure. */
 376         for (--argc, ++argv; argc > 0; --argc, ++argv) {
 377                 int const sjval = setjmp(jmpenv);
 378                 int len;
 379
 380                 /*
 381                  * The file kernel/trace/ftrace.o references the mcount
 382                  * function but does not call it. Since ftrace.o should
 383                  * not be traced anyway, we just skip it.
 384                  */
 385                 len = strlen(argv[0]);
 386                 if (len >= ftrace_size &&
 387                     strcmp(argv[0] + (len - ftrace_size), ftrace) == 0)
 388                         continue;
 389
 390                 switch (sjval) {
 391                 default:
 392                         fprintf(stderr, "internal error: %s\n", argv[0]);
 393                         exit(1);
 394                         break;
 395                 case SJ_SETJMP:    /* normal sequence */
 396                         /* Avoid problems if early cleanup() */
 397                         fd_map = -1;
 398                         ehdr_curr = NULL;
 399                         mmap_failed = 1;
 400                         do_file(argv[0]);
 401                         break;
 402                 case SJ_FAIL:    /* error in do_file or below */
 403                         ++n_error;
 404                         break;
 405                 case SJ_SUCCEED:    /* premature success */
 406                         /* do nothing */
 407                         break;
 408                 }  /* end switch */
 409         }
 410         return !!n_error;
 411 }
 412
 413