openwrt/toolchain/sstrip/src/sstrip.c

   1 /* http://www.muppetlabs.com/~breadbox/software/elfkickers.html */
   2
   3 /* sstrip: Copyright (C) 1999-2001 by Brian Raiter, under the GNU
   4  * General Public License. No warranty. See COPYING for details.
   5  *
   6  * Aug 23, 2004 Hacked by Manuel Novoa III <mjn3@codepoet.org> to
   7  * handle targets of different endianness and/or elf class, making
   8  * it more useful in a cross-devel environment.
   9  */
  10
  11 /* ============== original README ===================
  12  *
  13  * sstrip is a small utility that removes the contents at the end of an
  14  * ELF file that are not part of the program's memory image.
  15  *
  16  * Most ELF executables are built with both a program header table and a
  17  * section header table. However, only the former is required in order
  18  * for the OS to load, link and execute a program. sstrip attempts to
  19  * extract the ELF header, the program header table, and its contents,
  20  * leaving everything else in the bit bucket. It can only remove parts of
  21  * the file that occur at the end, after the parts to be saved. However,
  22  * this almost always includes the section header table, and occasionally
  23  * a few random sections that are not used when running a program.
  24  *
  25  * It should be noted that the GNU bfd library is (understandably)
  26  * dependent on the section header table as an index to the file's
  27  * contents. Thus, an executable file that has no section header table
  28  * cannot be used with gdb, objdump, or any other program based upon the
  29  * bfd library, at all. In fact, the program will not even recognize the
  30  * file as a valid executable. (This limitation is noted in the source
  31  * code comments for bfd, and is marked "FIXME", so this may change at
  32  * some future date. However, I would imagine that it is a pretty
  33  * low-priority item, as executables without a section header table are
  34  * rare in the extreme.) This probably also explains why strip doesn't
  35  * offer the option to do this.
  36  *
  37  * Shared library files may also have their section header table removed.
  38  * Such a library will still function; however, it will no longer be
  39  * possible for a compiler to link a new program against it.
  40  *
  41  * As an added bonus, sstrip also tries to removes trailing zero bytes
  42  * from the end of the file. (This normally cannot be done with an
  43  * executable that has a section header table.)
  44  *
  45  * sstrip is a very simplistic program. It depends upon the common
  46  * practice of putting the parts of the file that contribute to the
  47  * memory image at the front, and the remaining material at the end. This
  48  * permits it to discard the latter material without affecting file
  49  * offsets and memory addresses in what remains. Of course, the ELF
  50  * standard permits files to be organized in almost any order, so if a
  51  * pathological linker decided to put its section headers at the top,
  52  * sstrip would be useless on such executables.
  53  */
  54
  55 #include        <stdio.h>
  56 #include        <stdlib.h>
  57 #include        <string.h>
  58 #include        <errno.h>
  59 #include        <unistd.h>
  60 #include        <fcntl.h>
  61 #include        <elf.h>
  62
  63 #ifdef __FreeBSD__
  64 /**
  65  * This seems to work on FreeBSD 5.3, should
  66  * work on all newer versions as well. I have
  67  * no idea if it will work on versions < 5.3
  68  *
  69  * Joe Estock (guru) <jestock at nutextonline.com>
  70  */
  71 #include <sys/endian.h>
  72 #define bswap_64 __bswap64
  73 #define bswap_32 __bswap32
  74 #define bswap_16 __bswap16
  75 #elif defined(__APPLE__)
  76 #include        <machine/endian.h>
  77 #include        <machine/byte_order.h>
  78 #define __BYTE_ORDER BYTE_ORDER
  79 #define __BIG_ENDIAN BIG_ENDIAN
  80 #define bswap_16(x) NXSwapShort(x)
  81 #define bswap_32(x) NXSwapInt(x)
  82 #define bswap_64(x) NXSwapLongLong(x)
  83 #else
  84 #include        <endian.h>
  85 #include        <byteswap.h>
  86 #endif
  87
  88
  89 #ifndef TRUE
  90 #define TRUE            1
  91 #define FALSE           0
  92 #endif
  93
  94 /* The name of the program.
  95  */
  96 static char const       *progname;
  97
  98 /* The name of the current file.
  99  */
 100 static char const       *filename;
 101
 102
 103 /* A simple error-handling function. FALSE is always returned for the
 104  * convenience of the caller.
 105  */
 106 static int err(char const *errmsg)
 107 {
 108         fprintf(stderr, "%s: %s: %s\n", progname, filename, errmsg);
 109         return FALSE;
 110 }
 111
 112 /* A flag to signal the need for endian reversal.
 113  */
 114 static int do_reverse_endian;
 115
 116 /* Get a value from the elf header, compensating for endianness.
 117  */
 118 #define EGET(X) \
 119         (__extension__ ({ \
 120                 uint64_t __res; \
 121                 if (!do_reverse_endian) { \
 122                         __res = (X); \
 123                 } else if (sizeof(X) == 1) { \
 124                         __res = (X); \
 125                 } else if (sizeof(X) == 2) { \
 126                         __res = bswap_16((X)); \
 127                 } else if (sizeof(X) == 4) { \
 128                         __res = bswap_32((X)); \
 129                 } else if (sizeof(X) == 8) { \
 130                         __res = bswap_64((X)); \
 131                 } else { \
 132                         fprintf(stderr, "%s: %s: EGET failed for size %d\n", \
 133                                         progname, filename, sizeof(X)); \
 134                         exit(EXIT_FAILURE); \
 135                 } \
 136                 __res; \
 137         }))
 138
 139 /* Set a value 'Y' in the elf header to 'X', compensating for endianness.
 140  */
 141 #define ESET(Y,X) \
 142                 do if (!do_reverse_endian) { \
 143                         Y = (X); \
 144                 } else if (sizeof(Y) == 1) { \
 145                         Y = (X); \
 146                 } else if (sizeof(Y) == 2) { \
 147                         Y = bswap_16((uint16_t)(X)); \
 148                 } else if (sizeof(Y) == 4) { \
 149                         Y = bswap_32((uint32_t)(X)); \
 150                 } else if (sizeof(Y) == 8) { \
 151                         Y = bswap_64((uint64_t)(X)); \
 152                 } else { \
 153                         fprintf(stderr, "%s: %s: ESET failed for size %d\n", \
 154                                         progname, filename, sizeof(Y)); \
 155                         exit(EXIT_FAILURE); \
 156                 } while (0)
 157
 158
 159 /* A macro for I/O errors: The given error message is used only when
 160  * errno is not set.
 161  */
 162 #define ferr(msg)       (err(errno ? strerror(errno) : (msg)))
 163
 164
 165
 166 #define HEADER_FUNCTIONS(CLASS) \
 167  \
 168 /* readelfheader() reads the ELF header into our global variable, and \
 169  * checks to make sure that this is in fact a file that we should be \
 170  * munging. \
 171  */ \
 172 static int readelfheader ## CLASS (int fd, Elf ## CLASS ## _Ehdr *ehdr) \
 173 { \
 174          if (read(fd, ((char *)ehdr)+EI_NIDENT, sizeof(*ehdr) - EI_NIDENT) \
 175                 != sizeof(*ehdr) - EI_NIDENT) \
 176                 return ferr("missing or incomplete ELF header."); \
 177  \
 178         /* Verify the sizes of the ELF header and the program segment \
 179          * header table entries. \
 180          */ \
 181         if (EGET(ehdr->e_ehsize) != sizeof(Elf ## CLASS ## _Ehdr)) \
 182                 return err("unrecognized ELF header size."); \
 183         if (EGET(ehdr->e_phentsize) != sizeof(Elf ## CLASS ## _Phdr)) \
 184                 return err("unrecognized program segment header size."); \
 185  \
 186         /* Finally, check the file type. \
 187          */ \
 188         if (EGET(ehdr->e_type) != ET_EXEC && EGET(ehdr->e_type) != ET_DYN) \
 189                 return err("not an executable or shared-object library."); \
 190  \
 191         return TRUE; \
 192 } \
 193  \
 194 /* readphdrtable() loads the program segment header table into memory. \
 195  */ \
 196 static int readphdrtable ## CLASS (int fd, Elf ## CLASS ## _Ehdr const *ehdr, \
 197                                                                    Elf ## CLASS ## _Phdr **phdrs) \
 198 { \
 199         size_t  size; \
 200  \
 201         if (!EGET(ehdr->e_phoff) || !EGET(ehdr->e_phnum) \
 202 )               return err("ELF file has no program header table."); \
 203  \
 204         size = EGET(ehdr->e_phnum) * sizeof **phdrs; \
 205         if (!(*phdrs = malloc(size))) \
 206                 return err("Out of memory!"); \
 207  \
 208         errno = 0; \
 209         if (read(fd, *phdrs, size) != (ssize_t)size) \
 210                 return ferr("missing or incomplete program segment header table."); \
 211  \
 212         return TRUE; \
 213 } \
 214  \
 215 /* getmemorysize() determines the offset of the last byte of the file \
 216  * that is referenced by an entry in the program segment header table. \
 217  * (Anything in the file after that point is not used when the program \
 218  * is executing, and thus can be safely discarded.) \
 219  */ \
 220 static int getmemorysize ## CLASS (Elf ## CLASS ## _Ehdr const *ehdr, \
 221                                                                    Elf ## CLASS ## _Phdr const *phdrs, \
 222                                                  unsigned long *newsize) \
 223 { \
 224         Elf ## CLASS ## _Phdr const   *phdr; \
 225         unsigned long   size, n; \
 226         int                     i; \
 227  \
 228         /* Start by setting the size to include the ELF header and the \
 229          * complete program segment header table. \
 230          */ \
 231         size = EGET(ehdr->e_phoff) + EGET(ehdr->e_phnum) * sizeof *phdrs; \
 232         if (size < sizeof *ehdr) \
 233                 size = sizeof *ehdr; \
 234  \
 235         /* Then keep extending the size to include whatever data the \
 236          * program segment header table references. \
 237          */ \
 238         for (i = 0, phdr = phdrs ; i < EGET(ehdr->e_phnum) ; ++i, ++phdr) { \
 239                 if (EGET(phdr->p_type) != PT_NULL) { \
 240                         n = EGET(phdr->p_offset) + EGET(phdr->p_filesz); \
 241                         if (n > size) \
 242                                 size = n; \
 243                 } \
 244         } \
 245  \
 246         *newsize = size; \
 247         return TRUE; \
 248 } \
 249  \
 250 /* modifyheaders() removes references to the section header table if \
 251  * it was stripped, and reduces program header table entries that \
 252  * included truncated bytes at the end of the file. \
 253  */ \
 254 static int modifyheaders ## CLASS (Elf ## CLASS ## _Ehdr *ehdr, \
 255                                                                    Elf ## CLASS ## _Phdr *phdrs, \
 256                                                                    unsigned long newsize) \
 257 { \
 258         Elf ## CLASS ## _Phdr *phdr; \
 259         int             i; \
 260  \
 261         /* If the section header table is gone, then remove all references \
 262          * to it in the ELF header. \
 263          */ \
 264         if (EGET(ehdr->e_shoff) >= newsize) { \
 265                 ESET(ehdr->e_shoff,0); \
 266                 ESET(ehdr->e_shnum,0); \
 267                 ESET(ehdr->e_shentsize,0); \
 268                 ESET(ehdr->e_shstrndx,0); \
 269         } \
 270  \
 271         /* The program adjusts the file size of any segment that was \
 272          * truncated. The case of a segment being completely stripped out \
 273          * is handled separately. \
 274          */ \
 275         for (i = 0, phdr = phdrs ; i < EGET(ehdr->e_phnum) ; ++i, ++phdr) { \
 276                 if (EGET(phdr->p_offset) >= newsize) { \
 277                         ESET(phdr->p_offset,newsize); \
 278                         ESET(phdr->p_filesz,0); \
 279                 } else if (EGET(phdr->p_offset) + EGET(phdr->p_filesz) > newsize) { \
 280                         newsize -= EGET(phdr->p_offset); \
 281                         ESET(phdr->p_filesz, newsize); \
 282                 } \
 283         } \
 284  \
 285         return TRUE; \
 286 } \
 287  \
 288 /* commitchanges() writes the new headers back to the original file \
 289  * and sets the file to its new size. \
 290  */ \
 291 static int commitchanges ## CLASS (int fd, Elf ## CLASS ## _Ehdr const *ehdr, \
 292                                                                    Elf ## CLASS ## _Phdr *phdrs, \
 293                                                                    unsigned long newsize) \
 294 { \
 295         size_t  n; \
 296  \
 297         /* Save the changes to the ELF header, if any. \
 298          */ \
 299         if (lseek(fd, 0, SEEK_SET)) \
 300                 return ferr("could not rewind file"); \
 301         errno = 0; \
 302         if (write(fd, ehdr, sizeof *ehdr) != sizeof *ehdr) \
 303                 return err("could not modify file"); \
 304  \
 305         /* Save the changes to the program segment header table, if any. \
 306          */ \
 307         if (lseek(fd, EGET(ehdr->e_phoff), SEEK_SET) == (off_t)-1) { \
 308                 err("could not seek in file."); \
 309                 goto warning; \
 310         } \
 311         n = EGET(ehdr->e_phnum) * sizeof *phdrs; \
 312         if (write(fd, phdrs, n) != (ssize_t)n) { \
 313                 err("could not write to file"); \
 314                 goto warning; \
 315         } \
 316  \
 317         /* Eleventh-hour sanity check: don't truncate before the end of \
 318          * the program segment header table. \
 319          */ \
 320         if (newsize < EGET(ehdr->e_phoff) + n) \
 321                 newsize = EGET(ehdr->e_phoff) + n; \
 322  \
 323         /* Chop off the end of the file. \
 324          */ \
 325         if (ftruncate(fd, newsize)) { \
 326                 err("could not resize file"); \
 327                 goto warning; \
 328         } \
 329  \
 330         return TRUE; \
 331  \
 332  warning: \
 333         return err("ELF file may have been corrupted!"); \
 334 }
 335
 336
 337 /* First elements of Elf32_Ehdr and Elf64_Ehdr are common.
 338  */
 339 static int readelfheaderident(int fd, Elf32_Ehdr *ehdr)
 340 {
 341         errno = 0;
 342         if (read(fd, ehdr, EI_NIDENT) != EI_NIDENT)
 343                 return ferr("missing or incomplete ELF header.");
 344
 345         /* Check the ELF signature.
 346          */
 347         if (!(ehdr->e_ident[EI_MAG0] == ELFMAG0 &&
 348                   ehdr->e_ident[EI_MAG1] == ELFMAG1 &&
 349                   ehdr->e_ident[EI_MAG2] == ELFMAG2 &&
 350                   ehdr->e_ident[EI_MAG3] == ELFMAG3))
 351         {
 352                 err("missing ELF signature.");
 353                 return -1;
 354         }
 355
 356         /* Compare the file's class and endianness with the program's.
 357          */
 358 #if __BYTE_ORDER == __LITTLE_ENDIAN
 359         if (ehdr->e_ident[EI_DATA] == ELFDATA2LSB) {
 360                 do_reverse_endian = 0;
 361         } else if (ehdr->e_ident[EI_DATA] == ELFDATA2MSB) {
 362 /*              fprintf(stderr, "ELF file has different endianness.\n"); */
 363                 do_reverse_endian = 1;
 364         }
 365 #elif __BYTE_ORDER == __BIG_ENDIAN
 366         if (ehdr->e_ident[EI_DATA] == ELFDATA2LSB) {
 367 /*              fprintf(stderr, "ELF file has different endianness.\n"); */
 368                 do_reverse_endian = 1;
 369         } else if (ehdr->e_ident[EI_DATA] == ELFDATA2MSB) {
 370                 do_reverse_endian = 0;
 371         }
 372 #else
 373 #error unkown endianness
 374 #endif
 375         else {
 376                 err("Unsupported endianness");
 377                 return -1;
 378         }
 379
 380         /* Check the target architecture.
 381          */
 382 /*       if (EGET(ehdr->e_machine) != ELF_ARCH) { */
 383 /*              /\* return err("ELF file created for different architecture."); *\/ */
 384 /*              fprintf(stderr, "ELF file created for different architecture.\n"); */
 385 /*      } */
 386         return ehdr->e_ident[EI_CLASS];
 387 }
 388
 389
 390 HEADER_FUNCTIONS(32)
 391
 392 HEADER_FUNCTIONS(64)
 393
 394 /* truncatezeros() examines the bytes at the end of the file's
 395  * size-to-be, and reduces the size to exclude any trailing zero
 396  * bytes.
 397  */
 398 static int truncatezeros(int fd, unsigned long *newsize)
 399 {
 400         unsigned char   contents[1024];
 401         unsigned long   size, n;
 402
 403         size = *newsize;
 404         do {
 405                 n = sizeof contents;
 406                 if (n > size)
 407                         n = size;
 408                 if (lseek(fd, size - n, SEEK_SET) == (off_t)-1)
 409                         return ferr("cannot seek in file.");
 410                 if (read(fd, contents, n) != (ssize_t)n)
 411                         return ferr("cannot read file contents");
 412                 while (n && !contents[--n])
 413                         --size;
 414         } while (size && !n);
 415
 416         /* Sanity check.
 417          */
 418         if (!size)
 419                 return err("ELF file is completely blank!");
 420
 421         *newsize = size;
 422         return TRUE;
 423 }
 424
 425 /* main() loops over the cmdline arguments, leaving all the real work
 426  * to the other functions.
 427  */
 428 int main(int argc, char *argv[])
 429 {
 430         int                             fd;
 431         union {
 432                 Elf32_Ehdr      ehdr32;
 433                 Elf64_Ehdr      ehdr64;
 434         } e;
 435         union {
 436                 Elf32_Phdr      *phdrs32;
 437                 Elf64_Phdr      *phdrs64;
 438         } p;
 439         unsigned long   newsize;
 440         char                    **arg;
 441         int                             failures = 0;
 442
 443         if (argc < 2 || argv[1][0] == '-') {
 444                 printf("Usage: sstrip FILE...\n"
 445                            "sstrip discards all nonessential bytes from an executable.\n\n"
 446                            "Version 2.0-X Copyright (C) 2000,2001 Brian Raiter.\n"
 447                            "Cross-devel hacks Copyright (C) 2004 Manuel Novoa III.\n"
 448                            "This program is free software, licensed under the GNU\n"
 449                            "General Public License. There is absolutely no warranty.\n");
 450                 return EXIT_SUCCESS;
 451         }
 452
 453         progname = argv[0];
 454
 455         for (arg = argv + 1 ; *arg != NULL ; ++arg) {
 456                 filename = *arg;
 457
 458                 fd = open(*arg, O_RDWR);
 459                 if (fd < 0) {
 460                         ferr("can't open");
 461                         ++failures;
 462                         continue;
 463                 }
 464
 465                 switch (readelfheaderident(fd, &e.ehdr32)) {
 466                         case ELFCLASS32:
 467                                 if (!(readelfheader32(fd, &e.ehdr32)                                    &&
 468                                           readphdrtable32(fd, &e.ehdr32, &p.phdrs32)            &&
 469                                           getmemorysize32(&e.ehdr32, p.phdrs32, &newsize)       &&
 470                                           truncatezeros(fd, &newsize)                                           &&
 471                                           modifyheaders32(&e.ehdr32, p.phdrs32, newsize)        &&
 472                                           commitchanges32(fd, &e.ehdr32, p.phdrs32, newsize)))
 473                                         ++failures;
 474                                 break;
 475                         case ELFCLASS64:
 476                                 if (!(readelfheader64(fd, &e.ehdr64)                                    &&
 477                                           readphdrtable64(fd, &e.ehdr64, &p.phdrs64)            &&
 478                                           getmemorysize64(&e.ehdr64, p.phdrs64, &newsize)       &&
 479                                           truncatezeros(fd, &newsize)                                           &&
 480                                           modifyheaders64(&e.ehdr64, p.phdrs64, newsize)        &&
 481                                           commitchanges64(fd, &e.ehdr64, p.phdrs64, newsize)))
 482                                         ++failures;
 483                                 break;
 484                         default:
 485                                 ++failures;
 486                                 break;
 487                 }
 488                 close(fd);
 489         }
 490
 491         return failures ? EXIT_FAILURE : EXIT_SUCCESS;
 492 }