src/unexelf.c

   1 /* Copyright (C) 1985-1988, 1990, 1992, 1999-2017 Free Software
   2    Foundation, Inc.
   3
   4 This file is part of GNU Emacs.
   5
   6 GNU Emacs is free software: you can redistribute it and/or modify
   7 it under the terms of the GNU General Public License as published by
   8 the Free Software Foundation, either version 3 of the License, or (at
   9 your option) any later version.
  10
  11 GNU Emacs is distributed in the hope that it will be useful,
  12 but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14 GNU General Public License for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.  */
  18
  19 /*
  20 In other words, you are welcome to use, share and improve this program.
  21 You are forbidden to forbid anyone else to use, share and improve
  22 what you give them.   Help stamp out software-hoarding!  */
  23
  24
  25 /*
  26  * unexec.c - Convert a running program into an a.out file.
  27  *
  28  * Author:      Spencer W. Thomas
  29  *              Computer Science Dept.
  30  *              University of Utah
  31  * Date:        Tue Mar  2 1982
  32  * Modified heavily since then.
  33  *
  34  * Synopsis:
  35  *      unexec (const char *new_name, const char *old_name);
  36  *
  37  * Takes a snapshot of the program and makes an a.out format file in the
  38  * file named by the string argument new_name.
  39  * If old_name is non-NULL, the symbol table will be taken from the given file.
  40  * On some machines, an existing old_name file is required.
  41  *
  42  */
  43 \f
  44 /* We do not use mmap because that fails with NFS.
  45    Instead we read the whole file, modify it, and write it out.  */
  46
  47 #include <config.h>
  48 #include "unexec.h"
  49 #include "lisp.h"
  50
  51 #include <errno.h>
  52 #include <fcntl.h>
  53 #include <limits.h>
  54 #include <memory.h>
  55 #include <stdint.h>
  56 #include <stdio.h>
  57 #include <sys/stat.h>
  58 #include <sys/types.h>
  59 #include <unistd.h>
  60
  61 #if !defined (__NetBSD__) && !defined (__OpenBSD__)
  62 #include <elf.h>
  63 #endif /* not __NetBSD__ and not __OpenBSD__ */
  64 #include <sys/mman.h>
  65 #if defined (_SYSTYPE_SYSV)
  66 #include <sys/elf_mips.h>
  67 #include <sym.h>
  68 #endif /* _SYSTYPE_SYSV */
  69
  70 #ifndef MAP_ANON
  71 #ifdef MAP_ANONYMOUS
  72 #define MAP_ANON MAP_ANONYMOUS
  73 #else
  74 #define MAP_ANON 0
  75 #endif
  76 #endif
  77
  78 #ifndef MAP_FAILED
  79 #define MAP_FAILED ((void *) -1)
  80 #endif
  81
  82 #if defined (__alpha__) && !defined (__NetBSD__) && !defined (__OpenBSD__)
  83 /* Declare COFF debugging symbol table.  This used to be in
  84    /usr/include/sym.h, but this file is no longer included in Red Hat
  85    5.0 and presumably in any other glibc 2.x based distribution.  */
  86 typedef struct {
  87         short magic;
  88         short vstamp;
  89         int ilineMax;
  90         int idnMax;
  91         int ipdMax;
  92         int isymMax;
  93         int ioptMax;
  94         int iauxMax;
  95         int issMax;
  96         int issExtMax;
  97         int ifdMax;
  98         int crfd;
  99         int iextMax;
 100         long cbLine;
 101         long cbLineOffset;
 102         long cbDnOffset;
 103         long cbPdOffset;
 104         long cbSymOffset;
 105         long cbOptOffset;
 106         long cbAuxOffset;
 107         long cbSsOffset;
 108         long cbSsExtOffset;
 109         long cbFdOffset;
 110         long cbRfdOffset;
 111         long cbExtOffset;
 112 } HDRR, *pHDRR;
 113 #define cbHDRR sizeof (HDRR)
 114 #define hdrNil ((pHDRR)0)
 115 #endif
 116
 117 #ifdef __NetBSD__
 118 /*
 119  * NetBSD does not have normal-looking user-land ELF support.
 120  */
 121 # if defined __alpha__ || defined __sparc_v9__ || defined _LP64
 122 #  define ELFSIZE       64
 123 # else
 124 #  define ELFSIZE       32
 125 # endif
 126 # include <sys/exec_elf.h>
 127
 128 # ifndef PT_LOAD
 129 #  define PT_LOAD       Elf_pt_load
 130 #  if 0                                         /* was in pkgsrc patches for 20.7 */
 131 #   define SHT_PROGBITS Elf_sht_progbits
 132 #  endif
 133 #  define SHT_SYMTAB    Elf_sht_symtab
 134 #  define SHT_DYNSYM    Elf_sht_dynsym
 135 #  define SHT_NULL      Elf_sht_null
 136 #  define SHT_NOBITS    Elf_sht_nobits
 137 #  define SHT_REL       Elf_sht_rel
 138 #  define SHT_RELA      Elf_sht_rela
 139
 140 #  define SHN_UNDEF     Elf_eshn_undefined
 141 #  define SHN_ABS       Elf_eshn_absolute
 142 #  define SHN_COMMON    Elf_eshn_common
 143 # endif /* !PT_LOAD */
 144
 145 # ifdef __alpha__
 146 #  include <sys/exec_ecoff.h>
 147 #  define HDRR          struct ecoff_symhdr
 148 #  define pHDRR         HDRR *
 149 # endif /* __alpha__ */
 150
 151 #ifdef __mips__                 /* was in pkgsrc patches for 20.7 */
 152 # define SHT_MIPS_DEBUG DT_MIPS_FLAGS
 153 # define HDRR           struct Elf_Shdr
 154 #endif /* __mips__ */
 155 #endif /* __NetBSD__ */
 156
 157 #ifdef __OpenBSD__
 158 # include <sys/exec_elf.h>
 159 #endif
 160
 161 #if __GNU_LIBRARY__ - 0 >= 6
 162 # include <link.h>      /* get ElfW etc */
 163 #endif
 164
 165 #ifndef ElfW
 166 # define ElfBitsW(bits, type) Elf##bits##_##type
 167 # ifndef ELFSIZE
 168 #  ifdef _LP64
 169 #   define ELFSIZE 64
 170 #  else
 171 #   define ELFSIZE 32
 172 #  endif
 173 # endif
 174   /* This macro expands `bits' before invoking ElfBitsW.  */
 175 # define ElfExpandBitsW(bits, type) ElfBitsW (bits, type)
 176 # define ElfW(type) ElfExpandBitsW (ELFSIZE, type)
 177 #endif
 178
 179 /* The code often converts ElfW (Half) values like e_shentsize to ptrdiff_t;
 180    check that this doesn't lose information.  */
 181 #include <intprops.h>
 182 #include <verify.h>
 183 verify ((! TYPE_SIGNED (ElfW (Half))
 184          || PTRDIFF_MIN <= TYPE_MINIMUM (ElfW (Half)))
 185         && TYPE_MAXIMUM (ElfW (Half)) <= PTRDIFF_MAX);
 186
 187 #ifdef UNEXELF_DEBUG
 188 # define DEBUG_LOG(expr) fprintf (stderr, #expr " 0x%jx\n", (uintmax_t) (expr))
 189 #endif
 190
 191 /* Get the address of a particular section or program header entry,
 192  * accounting for the size of the entries.
 193  */
 194
 195 static void *
 196 entry_address (void *section_h, ptrdiff_t idx, ptrdiff_t entsize)
 197 {
 198   char *h = section_h;
 199   return h + idx * entsize;
 200 }
 201
 202 #define OLD_SECTION_H(n) \
 203   (*(ElfW (Shdr) *) entry_address (old_section_h, n, old_file_h->e_shentsize))
 204 #define NEW_SECTION_H(n) \
 205   (*(ElfW (Shdr) *) entry_address (new_section_h, n, new_file_h->e_shentsize))
 206 #define OLD_PROGRAM_H(n) \
 207   (*(ElfW (Phdr) *) entry_address (old_program_h, n, old_file_h->e_phentsize))
 208
 209 typedef unsigned char byte;
 210
 211 /* ****************************************************************
 212  * unexec
 213  *
 214  * driving logic.
 215  *
 216  * In ELF, this works by replacing the old bss SHT_NOBITS section with
 217  * a new, larger, SHT_PROGBITS section.
 218  *
 219  */
 220 void
 221 unexec (const char *new_name, const char *old_name)
 222 {
 223   int new_file, old_file;
 224   off_t new_file_size;
 225   void *new_break;
 226
 227   /* Pointers to the base of the image of the two files.  */
 228   caddr_t old_base, new_base;
 229
 230 #if MAP_ANON == 0
 231   int mmap_fd;
 232 #else
 233 # define mmap_fd -1
 234 #endif
 235
 236   /* Pointers to the file, program and section headers for the old and
 237      new files.  */
 238   ElfW (Ehdr) *old_file_h, *new_file_h;
 239   ElfW (Phdr) *old_program_h, *new_program_h;
 240   ElfW (Shdr) *old_section_h, *new_section_h;
 241
 242   /* Point to the section name table.  */
 243   char *old_section_names, *new_section_names;
 244
 245   ElfW (Phdr) *old_bss_seg, *new_bss_seg;
 246   ElfW (Addr) old_bss_addr, new_bss_addr;
 247   ElfW (Word) old_bss_size, bss_size_growth, new_data2_size;
 248   ElfW (Off) old_bss_offset, new_data2_offset;
 249
 250   ptrdiff_t n;
 251   ptrdiff_t old_bss_index;
 252   struct stat stat_buf;
 253   off_t old_file_size;
 254
 255   /* Open the old file, allocate a buffer of the right size, and read
 256      in the file contents.  */
 257
 258   old_file = emacs_open (old_name, O_RDONLY, 0);
 259
 260   if (old_file < 0)
 261     fatal ("Can't open %s for reading: %s", old_name, strerror (errno));
 262
 263   if (fstat (old_file, &stat_buf) != 0)
 264     fatal ("Can't fstat (%s): %s", old_name, strerror (errno));
 265
 266 #if MAP_ANON == 0
 267   mmap_fd = emacs_open ("/dev/zero", O_RDONLY, 0);
 268   if (mmap_fd < 0)
 269     fatal ("Can't open /dev/zero for reading: %s", strerror (errno));
 270 #endif
 271
 272   /* We cannot use malloc here because that may use sbrk.  If it does,
 273      we'd dump our temporary buffers with Emacs, and we'd have to be
 274      extra careful to use the correct value of sbrk(0) after
 275      allocating all buffers in the code below, which we aren't.  */
 276   old_file_size = stat_buf.st_size;
 277   if (! (0 <= old_file_size && old_file_size <= SIZE_MAX))
 278     fatal ("File size out of range");
 279   old_base = mmap (NULL, old_file_size, PROT_READ | PROT_WRITE,
 280                    MAP_ANON | MAP_PRIVATE, mmap_fd, 0);
 281   if (old_base == MAP_FAILED)
 282     fatal ("Can't allocate buffer for %s: %s", old_name, strerror (errno));
 283
 284   if (read (old_file, old_base, old_file_size) != old_file_size)
 285     fatal ("Didn't read all of %s: %s", old_name, strerror (errno));
 286
 287   /* Get pointers to headers & section names */
 288
 289   old_file_h = (ElfW (Ehdr) *) old_base;
 290   old_program_h = (ElfW (Phdr) *) ((byte *) old_base + old_file_h->e_phoff);
 291   old_section_h = (ElfW (Shdr) *) ((byte *) old_base + old_file_h->e_shoff);
 292   old_section_names = (char *) old_base
 293     + OLD_SECTION_H (old_file_h->e_shstrndx).sh_offset;
 294
 295   /* Find the PT_LOAD header covering the highest address.  This
 296      segment will be where bss sections are located, past p_filesz.  */
 297   old_bss_seg = 0;
 298   for (n = old_file_h->e_phnum; --n >= 0; )
 299     {
 300       ElfW (Phdr) *seg = &OLD_PROGRAM_H (n);
 301       if (seg->p_type == PT_LOAD
 302           && (old_bss_seg == 0
 303               || seg->p_vaddr > old_bss_seg->p_vaddr))
 304         old_bss_seg = seg;
 305     }
 306
 307   /* Note that old_bss_addr may be lower than the first bss section
 308      address, since the section may need aligning.  */
 309   old_bss_addr = old_bss_seg->p_vaddr + old_bss_seg->p_filesz;
 310   old_bss_offset = old_bss_seg->p_offset + old_bss_seg->p_filesz;
 311   old_bss_size = old_bss_seg->p_memsz - old_bss_seg->p_filesz;
 312
 313   /* Find the last bss style section in the bss segment range.  */
 314   old_bss_index = -1;
 315   for (n = old_file_h->e_shnum; --n > 0; )
 316     {
 317       ElfW (Shdr) *shdr = &OLD_SECTION_H (n);
 318       if (shdr->sh_type == SHT_NOBITS
 319           && shdr->sh_addr >= old_bss_addr
 320           && shdr->sh_addr + shdr->sh_size <= old_bss_addr + old_bss_size
 321           && (old_bss_index == -1
 322               || OLD_SECTION_H (old_bss_index).sh_addr < shdr->sh_addr))
 323         old_bss_index = n;
 324     }
 325
 326   if (old_bss_index == -1)
 327     fatal ("no bss section found");
 328
 329 #ifdef HAVE_SBRK
 330   new_break = sbrk (0);
 331 #else
 332   new_break = (byte *) old_bss_addr + old_bss_size;
 333 #endif
 334   new_bss_addr = (ElfW (Addr)) new_break;
 335   bss_size_growth = new_bss_addr - old_bss_addr;
 336   new_data2_size = bss_size_growth;
 337   new_data2_size += alignof (ElfW (Shdr)) - 1;
 338   new_data2_size -= new_data2_size % alignof (ElfW (Shdr));
 339
 340   new_data2_offset = old_bss_offset;
 341
 342 #ifdef UNEXELF_DEBUG
 343   fprintf (stderr, "old_bss_index %td\n", old_bss_index);
 344   DEBUG_LOG (old_bss_addr);
 345   DEBUG_LOG (old_bss_size);
 346   DEBUG_LOG (old_bss_offset);
 347   DEBUG_LOG (new_bss_addr);
 348   DEBUG_LOG (new_data2_size);
 349   DEBUG_LOG (new_data2_offset);
 350 #endif
 351
 352   if (new_bss_addr < old_bss_addr + old_bss_size)
 353     fatal (".bss shrank when undumping");
 354
 355   /* Set the output file to the right size.  Allocate a buffer to hold
 356      the image of the new file.  Set pointers to various interesting
 357      objects.  */
 358
 359   new_file = emacs_open (new_name, O_RDWR | O_CREAT, 0777);
 360   if (new_file < 0)
 361     fatal ("Can't creat (%s): %s", new_name, strerror (errno));
 362
 363   new_file_size = old_file_size + new_data2_size;
 364
 365   if (ftruncate (new_file, new_file_size))
 366     fatal ("Can't ftruncate (%s): %s", new_name, strerror (errno));
 367
 368   new_base = mmap (NULL, new_file_size, PROT_READ | PROT_WRITE,
 369                    MAP_ANON | MAP_PRIVATE, mmap_fd, 0);
 370   if (new_base == MAP_FAILED)
 371     fatal ("Can't allocate buffer for %s: %s", old_name, strerror (errno));
 372
 373   /* Make our new file, program and section headers as copies of the
 374      originals.  */
 375
 376   new_file_h = (ElfW (Ehdr) *) new_base;
 377   memcpy (new_file_h, old_file_h, old_file_h->e_ehsize);
 378
 379   /* Fix up file header.  Section header is further away now.  */
 380
 381   if (new_file_h->e_shoff >= old_bss_offset)
 382     new_file_h->e_shoff += new_data2_size;
 383
 384   new_program_h = (ElfW (Phdr) *) ((byte *) new_base + new_file_h->e_phoff);
 385   new_section_h = (ElfW (Shdr) *) ((byte *) new_base + new_file_h->e_shoff);
 386
 387   memcpy (new_program_h, old_program_h,
 388           old_file_h->e_phnum * old_file_h->e_phentsize);
 389   memcpy (new_section_h, old_section_h,
 390           old_file_h->e_shnum * old_file_h->e_shentsize);
 391
 392 #ifdef UNEXELF_DEBUG
 393   DEBUG_LOG (old_file_h->e_shoff);
 394   fprintf (stderr, "Old section count %td\n", (ptrdiff_t) old_file_h->e_shnum);
 395   DEBUG_LOG (new_file_h->e_shoff);
 396   fprintf (stderr, "New section count %td\n", (ptrdiff_t) new_file_h->e_shnum);
 397 #endif
 398
 399   /* Fix up program header.  Extend the writable data segment so
 400      that the bss area is covered too.  */
 401
 402   new_bss_seg = new_program_h + (old_bss_seg - old_program_h);
 403   new_bss_seg->p_filesz = new_bss_addr - new_bss_seg->p_vaddr;
 404   new_bss_seg->p_memsz = new_bss_seg->p_filesz;
 405
 406   /* Copy over what we have in memory now for the bss area. */
 407   memcpy (new_base + new_data2_offset, (caddr_t) old_bss_addr,
 408           bss_size_growth);
 409
 410   /* Walk through all section headers, copying data and updating.  */
 411   for (n = 1; n < old_file_h->e_shnum; n++)
 412     {
 413       caddr_t src;
 414       ElfW (Shdr) *old_shdr = &OLD_SECTION_H (n);
 415       ElfW (Shdr) *new_shdr = &NEW_SECTION_H (n);
 416
 417       if (new_shdr->sh_type == SHT_NOBITS
 418           && new_shdr->sh_addr >= old_bss_addr
 419           && (new_shdr->sh_addr + new_shdr->sh_size
 420               <= old_bss_addr + old_bss_size))
 421         {
 422           /* This section now has file backing.  */
 423           new_shdr->sh_type = SHT_PROGBITS;
 424
 425           /* SHT_NOBITS sections do not need a valid sh_offset, so it
 426              might be incorrect.  Write the correct value.  */
 427           new_shdr->sh_offset = (new_shdr->sh_addr - new_bss_seg->p_vaddr
 428                                  + new_bss_seg->p_offset);
 429
 430           /* If this is was a SHT_NOBITS .plt section, then it is
 431              probably a PowerPC PLT.  If it is PowerPC64 ELFv1 then
 432              glibc ld.so doesn't initialize the toc pointer word.  A
 433              non-zero toc pointer word can defeat Power7 thread safety
 434              during lazy update of a PLT entry.  This only matters if
 435              emacs becomes multi-threaded.  */
 436           if (strcmp (old_section_names + new_shdr->sh_name, ".plt") == 0)
 437             memset (new_shdr->sh_offset + new_base, 0, new_shdr->sh_size);
 438
 439           /* Extend the size of the last bss section to cover dumped
 440              data.  */
 441           if (n == old_bss_index)
 442             new_shdr->sh_size = new_bss_addr - new_shdr->sh_addr;
 443
 444           /* We have already copied this section from the current
 445              process.  */
 446           continue;
 447         }
 448
 449       /* Any section that was originally placed after the .bss
 450          section should now be offset by NEW_DATA2_SIZE.  */
 451       if (new_shdr->sh_offset >= old_bss_offset)
 452         new_shdr->sh_offset += new_data2_size;
 453
 454       /* Now, start to copy the content of sections.  */
 455       if (new_shdr->sh_type == SHT_NULL
 456           || new_shdr->sh_type == SHT_NOBITS)
 457         continue;
 458
 459       /* Some sections are copied from the current process instead of
 460          the old file.  */
 461       if (!strcmp (old_section_names + new_shdr->sh_name, ".data")
 462           || !strcmp (old_section_names + new_shdr->sh_name, ".sdata")
 463           || !strcmp (old_section_names + new_shdr->sh_name, ".lit4")
 464           || !strcmp (old_section_names + new_shdr->sh_name, ".lit8")
 465           || !strcmp (old_section_names + new_shdr->sh_name, ".sdata1")
 466           || !strcmp (old_section_names + new_shdr->sh_name, ".data1"))
 467         src = (caddr_t) old_shdr->sh_addr;
 468       else
 469         src = old_base + old_shdr->sh_offset;
 470
 471       memcpy (new_shdr->sh_offset + new_base, src, new_shdr->sh_size);
 472
 473 #if (defined __alpha__ && !defined __OpenBSD__) || defined _SYSTYPE_SYSV
 474       /* Update Alpha and MIPS COFF debug symbol table.  */
 475       if (strcmp (old_section_names + new_shdr->sh_name, ".mdebug") == 0
 476           && new_shdr->sh_offset - old_shdr->sh_offset != 0
 477 #if defined _SYSTYPE_SYSV
 478           && new_shdr->sh_type == SHT_MIPS_DEBUG
 479 #endif
 480           )
 481         {
 482           ptrdiff_t diff = new_shdr->sh_offset - old_shdr->sh_offset;
 483           HDRR *phdr = (HDRR *) (new_shdr->sh_offset + new_base);
 484
 485           phdr->cbLineOffset += diff;
 486           phdr->cbDnOffset += diff;
 487           phdr->cbPdOffset += diff;
 488           phdr->cbSymOffset += diff;
 489           phdr->cbOptOffset += diff;
 490           phdr->cbAuxOffset += diff;
 491           phdr->cbSsOffset += diff;
 492           phdr->cbSsExtOffset += diff;
 493           phdr->cbFdOffset += diff;
 494           phdr->cbRfdOffset += diff;
 495           phdr->cbExtOffset += diff;
 496         }
 497 #endif /* __alpha__ || _SYSTYPE_SYSV */
 498     }
 499
 500   /* Update the symbol values of _edata and _end.  */
 501   for (n = new_file_h->e_shnum; 0 < --n; )
 502     {
 503       byte *symnames;
 504       ElfW (Sym) *symp, *symendp;
 505       ElfW (Shdr) *sym_shdr = &NEW_SECTION_H (n);
 506
 507       if (sym_shdr->sh_type != SHT_DYNSYM
 508           && sym_shdr->sh_type != SHT_SYMTAB)
 509         continue;
 510
 511       symnames = ((byte *) new_base
 512                   + NEW_SECTION_H (sym_shdr->sh_link).sh_offset);
 513       symp = (ElfW (Sym) *) (sym_shdr->sh_offset + new_base);
 514       symendp = (ElfW (Sym) *) ((byte *) symp + sym_shdr->sh_size);
 515
 516       for (; symp < symendp; symp ++)
 517         {
 518           if (strcmp ((char *) (symnames + symp->st_name), "_end") == 0
 519               || strcmp ((char *) (symnames + symp->st_name), "end") == 0
 520               || strcmp ((char *) (symnames + symp->st_name), "_edata") == 0
 521               || strcmp ((char *) (symnames + symp->st_name), "edata") == 0)
 522             memcpy (&symp->st_value, &new_bss_addr, sizeof (new_bss_addr));
 523
 524           /* Strictly speaking, #ifdef below is not necessary.  But we
 525              keep it to indicate that this kind of change may also be
 526              necessary for other unexecs to support GNUstep.  */
 527 #ifdef NS_IMPL_GNUSTEP
 528           /* ObjC runtime modifies the values of some data structures
 529              such as classes and selectors in the .data section after
 530              loading.  As the dump process copies the .data section
 531              from the current process, that causes problems when the
 532              modified classes are reinitialized in the dumped
 533              executable.  We copy such data from the old file, not
 534              from the current process.  */
 535           if (strncmp ((char *) (symnames + symp->st_name),
 536                        "_OBJC_", sizeof ("_OBJC_") - 1) == 0)
 537             {
 538               ElfW (Shdr) *new_shdr = &NEW_SECTION_H (symp->st_shndx);
 539               if (new_shdr->sh_type != SHT_NOBITS)
 540                 {
 541                   ElfW (Shdr) *old_shdr = &OLD_SECTION_H (symp->st_shndx);
 542                   ptrdiff_t reladdr = symp->st_value - new_shdr->sh_addr;
 543                   ptrdiff_t newoff = reladdr + new_shdr->sh_offset;
 544
 545                   if (old_shdr->sh_type == SHT_NOBITS)
 546                     memset (new_base + newoff, 0, symp->st_size);
 547                   else
 548                     {
 549                       ptrdiff_t oldoff = reladdr + old_shdr->sh_offset;
 550                       memcpy (new_base + newoff, old_base + oldoff,
 551                               symp->st_size);
 552                     }
 553                 }
 554             }
 555 #endif
 556         }
 557     }
 558
 559   /* Modify the names of sections we changed from SHT_NOBITS to
 560      SHT_PROGBITS.  This is really just cosmetic, but some tools that
 561      (wrongly) operate on section names rather than types might be
 562      confused by a SHT_PROGBITS .bss section.  */
 563   new_section_names = ((char *) new_base
 564                        + NEW_SECTION_H (new_file_h->e_shstrndx).sh_offset);
 565   for (n = new_file_h->e_shnum; 0 < --n; )
 566     {
 567       ElfW (Shdr) *old_shdr = &OLD_SECTION_H (n);
 568       ElfW (Shdr) *new_shdr = &NEW_SECTION_H (n);
 569
 570       /* Replace the leading '.' with ','.  When .shstrtab is string
 571          merged this will rename both .bss and .rela.bss to ,bss and
 572          .rela,bss.  */
 573       if (old_shdr->sh_type == SHT_NOBITS
 574           && new_shdr->sh_type == SHT_PROGBITS)
 575         *(new_section_names + new_shdr->sh_name) = ',';
 576     }
 577
 578   /* This loop seeks out relocation sections for the data section, so
 579      that it can undo relocations performed by the runtime loader.
 580
 581      The following approach does not work on x86 platforms that use
 582      the GNU Gold linker, which can generate .rel.dyn relocation
 583      sections containing R_386_32 entries that the following code does
 584      not grok.  Emacs works around this problem by avoiding C
 585      constructs that generate such entries, which is horrible hack.
 586
 587      FIXME: Presumably more problems like this will crop up as linkers
 588      get fancier.  We really need to stop assuming that Emacs can grok
 589      arbitrary linker output.  See Bug#27248.  */
 590   for (n = new_file_h->e_shnum; 0 < --n; )
 591     {
 592       ElfW (Shdr) *rel_shdr = &NEW_SECTION_H (n);
 593       ElfW (Shdr) *shdr;
 594
 595       switch (rel_shdr->sh_type)
 596         {
 597         default:
 598           break;
 599         case SHT_REL:
 600         case SHT_RELA:
 601           /* This code handles two different size structs, but there should
 602              be no harm in that provided that r_offset is always the first
 603              member.  */
 604           shdr = &NEW_SECTION_H (rel_shdr->sh_info);
 605           if (!strcmp (old_section_names + shdr->sh_name, ".data")
 606               || !strcmp (old_section_names + shdr->sh_name, ".sdata")
 607               || !strcmp (old_section_names + shdr->sh_name, ".lit4")
 608               || !strcmp (old_section_names + shdr->sh_name, ".lit8")
 609               || !strcmp (old_section_names + shdr->sh_name, ".sdata1")
 610               || !strcmp (old_section_names + shdr->sh_name, ".data1"))
 611             {
 612               ElfW (Addr) offset = shdr->sh_addr - shdr->sh_offset;
 613               caddr_t reloc = old_base + rel_shdr->sh_offset, end;
 614               for (end = reloc + rel_shdr->sh_size;
 615                    reloc < end;
 616                    reloc += rel_shdr->sh_entsize)
 617                 {
 618                   ElfW (Addr) addr = ((ElfW (Rel) *) reloc)->r_offset - offset;
 619                   /* Ignore R_*_NONE relocs.  */
 620                   if (((ElfW (Rel) *) reloc)->r_offset == 0)
 621                     continue;
 622                   /* Assume reloc applies to a word.
 623                      ??? This is not always true, eg. TLS module/index
 624                      pair in .got which occupies two words.  */
 625                   memcpy (new_base + addr, old_base + addr,
 626                           sizeof (ElfW (Addr)));
 627                 }
 628             }
 629           break;
 630         }
 631     }
 632
 633   /* Write out new_file, and free the buffers.  */
 634
 635   if (write (new_file, new_base, new_file_size) != new_file_size)
 636     fatal ("Didn't write %lu bytes to %s: %s",
 637            (unsigned long) new_file_size, new_name, strerror (errno));
 638   munmap (old_base, old_file_size);
 639   munmap (new_base, new_file_size);
 640
 641   /* Close the files and make the new file executable.  */
 642
 643 #if MAP_ANON == 0
 644   emacs_close (mmap_fd);
 645 #endif
 646
 647   if (emacs_close (old_file) != 0)
 648     fatal ("Can't close (%s): %s", old_name, strerror (errno));
 649
 650   if (emacs_close (new_file) != 0)
 651     fatal ("Can't close (%s): %s", new_name, strerror (errno));
 652 }