lib/immutable.c

   1 /* Immutable data.
   2
   3    Copyright (C) 2021-2024 Free Software Foundation, Inc.
   4
   5    This file is free software: you can redistribute it and/or modify
   6    it under the terms of the GNU Lesser General Public License as
   7    published by the Free Software Foundation; either version 2.1 of the
   8    License, or (at your option) any later version.
   9
  10    This file is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13    GNU Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public License
  16    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  17
  18 /* Written by Bruno Haible <bruno@clisp.org>, 2021.  */
  19
  20 #include <config.h>
  21
  22 /* Specification.  */
  23 #include "immutable.h"
  24
  25 #include <errno.h>
  26 #include <stdlib.h>
  27 #include <string.h>
  28
  29 #if IMMUTABLE_EFFECTIVE
  30 /* Real implementation.  */
  31
  32 /* Get CHAR_BIT.  */
  33 # include <limits.h>
  34
  35 /* Get intptr_t, uintptr_t.  */
  36 # include <stdint.h>
  37
  38 # include <stdio.h>
  39
  40 # if defined _WIN32 && !defined __CYGWIN__
  41
  42 /* Declare VirtualAlloc(), GetSystemInfo.  */
  43 #  define WIN32_LEAN_AND_MEAN
  44 #  define WIN32_EXTRA_LEAN
  45 #  include <windows.h>
  46
  47 /* Don't assume that UNICODE is not defined.  */
  48 #  undef CreateFileMapping
  49 #  define CreateFileMapping CreateFileMappingA
  50
  51 # else
  52
  53 /* Declare getpagesize().  */
  54 #  include <unistd.h>
  55 /* On HP-UX, getpagesize exists, but it is not declared in <unistd.h> even if
  56    the compiler options -D_HPUX_SOURCE -D_XOPEN_SOURCE=600 are used.  */
  57 #  ifdef __hpux
  58 extern
  59 #   ifdef __cplusplus
  60        "C"
  61 #   endif
  62        int getpagesize (void);
  63 #  endif
  64
  65 /* Declare mmap(), mprotect().  */
  66 #  include <sys/types.h>
  67 #  include <sys/mman.h>
  68
  69 /* Declare open().  */
  70 #  include <unistd.h>
  71 #  include <fcntl.h>
  72
  73 /* Get PATH_MAX.  */
  74 #  include "pathmax.h"
  75 #  ifndef PATH_MAX
  76 #   define PATH_MAX 4096
  77 #  endif
  78
  79 #  include "glthread/once.h"
  80
  81 # endif
  82
  83
  84 /* ================= Back end of the malloc implementation ================= */
  85
  86 /* The memory page size.
  87    Once it is initialized, a power of 2.  Typically 4096 or 8192.  */
  88 static uintptr_t pagesize;
  89
  90 /* Initializes pagesize.  */
  91 static void
  92 init_pagesize (void)
  93 {
  94   /* Simultaneous execution of this initialization in multiple threads is OK. */
  95 # if defined _WIN32 && !defined __CYGWIN__
  96   /* GetSystemInfo
  97      <https://msdn.microsoft.com/en-us/library/ms724381.aspx>
  98      <https://msdn.microsoft.com/en-us/library/ms724958.aspx>  */
  99   SYSTEM_INFO info;
 100   GetSystemInfo (&info);
 101   pagesize = info.dwPageSize;
 102 # else
 103   pagesize = getpagesize ();
 104 # endif
 105 }
 106
 107
 108 # if defined _WIN32 && !defined __CYGWIN__
 109
 110 static inline void
 111 init_mmap_file (void)
 112 {
 113 }
 114
 115 # else
 116
 117 /* Variables needed for obtaining memory pages via mmap().  */
 118 static int file_fd;
 119 static long file_length;
 120
 121 /* Initialization of these variables. */
 122 static void
 123 do_init_mmap_file (void)
 124 {
 125   /* Use TMPDIR, except if it is too long.  */
 126   const char *tmpdir = getenv ("TMPDIR");
 127   if (tmpdir == NULL || strlen (tmpdir) > PATH_MAX)
 128     tmpdir = "/tmp";
 129   /* Now strlen (tmpdir) <= PATH_MAX.  */
 130
 131   char filename[PATH_MAX + 1 + 41 + 1];
 132   sprintf (filename, "%s/glimmdata-%d-%ld", tmpdir, getpid (), random ());
 133
 134   file_fd = open (filename, O_CREAT | O_TRUNC | O_RDWR | O_CLOEXEC, 0700);
 135   if (file_fd < 0)
 136     {
 137       fprintf (stderr, "glimm: Cannot open %s!\n", filename);
 138       abort ();
 139     }
 140
 141   /* Remove the file from the file system as soon as possible, to make
 142      sure there is no leftover after this process terminates or crashes.  */
 143   unlink (filename);
 144
 145   file_length = 0;
 146 }
 147
 148 /* Once-only initializer for these variables.  */
 149 gl_once_define (static, for_mmap_once)
 150
 151 static inline void
 152 init_mmap_file (void)
 153 {
 154   /* Use a once-only initializer here, since simultaneous execution of
 155      do_init_mmap_file() in multiple threads must be avoided.  */
 156   gl_once (for_mmap_once, do_init_mmap_file);
 157 }
 158
 159 # endif
 160
 161
 162 /* Size of the (page-aligned) header that links the writable mapping
 163    and the read-only mapping together.  */
 164 # define SHARED_LINK_HEADER_SIZE \
 165     (INTPTR_WIDTH / CHAR_BIT)   /* = sizeof (void *) */
 166
 167 /* Allocates a contiguous set of pages of memory.
 168    size > 0, must be a multiple of pagesize.
 169    Returns a multiple of PAGESIZE, or 0 upon failure.  */
 170 static uintptr_t
 171 alloc_pages (size_t size)
 172 {
 173 # if defined _WIN32 && !defined __CYGWIN__
 174   /* Allocate pages from the system paging file.
 175      CreateFileMapping
 176      <https://docs.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-createfilemappinga>  */
 177   HANDLE h =
 178     CreateFileMapping (INVALID_HANDLE_VALUE, NULL, PAGE_READWRITE | SEC_COMMIT,
 179                        size >> 16 >> 16, size & 0xFFFFFFFFU, NULL);
 180   if (h == NULL)
 181     {
 182       fprintf (stderr,
 183                "glimm: Cannot allocate file mapping. GetLastError() = 0x%08X\n",
 184                (unsigned int) GetLastError ());
 185       return 0;
 186     }
 187   /* MapViewOfFile
 188      <https://docs.microsoft.com/en-us/windows/win32/api/memoryapi/nf-memoryapi-mapviewoffile>  */
 189   char *mem_w = (char *) MapViewOfFile (h, FILE_MAP_WRITE, 0, 0, size);
 190   char *mem_r = (char *) MapViewOfFile (h, FILE_MAP_READ,  0, 0, size);
 191   if (mem_w == NULL || mem_r == NULL)
 192     {
 193       /* UnmapViewOfFile
 194          <https://docs.microsoft.com/en-us/windows/win32/api/memoryapi/nf-memoryapi-unmapviewoffile>  */
 195       if (mem_w != NULL)
 196         UnmapViewOfFile (mem_w);
 197       if (mem_r != NULL)
 198         UnmapViewOfFile (mem_r);
 199       return 0;
 200     }
 201   /* It is OK to call CloseHandle before UnmapViewOfFile.  The file mapping
 202      object gets really closed only once all its views are unmapped.  */
 203   if (!CloseHandle (h))
 204     {
 205       UnmapViewOfFile (mem_w);
 206       UnmapViewOfFile (mem_r);
 207       CloseHandle (h);
 208       return 0;
 209     }
 210 # else
 211   /* Extend the file by size/pagesize pages.  */
 212   long new_file_length = file_length + size;
 213   if (ftruncate (file_fd, new_file_length) < 0)
 214     {
 215       fprintf (stderr, "glimm: Cannot extend backing file!\n");
 216       return 0;
 217     }
 218   /* Create separate writable mapping and read-only mapping.  */
 219   char *mem_w = (char *) mmap (NULL, size, PROT_READ | PROT_WRITE,
 220                                MAP_SHARED, file_fd, file_length);
 221   char *mem_r = (char *) mmap (NULL, size, PROT_READ,
 222                                MAP_SHARED, file_fd, file_length);
 223   if (mem_w == (char *)(-1) || mem_r == (char *)(-1))
 224     {
 225       if (mem_w != (char *)(-1))
 226         munmap (mem_w, size);
 227       if (mem_r != (char *)(-1))
 228         munmap (mem_r, size);
 229       return 0;
 230     }
 231   file_length = new_file_length;
 232 # endif
 233
 234   /* Link the two memory areas together.  */
 235   ((intptr_t *) mem_w)[0] = mem_r - mem_w;
 236   return (uintptr_t) mem_w;
 237 }
 238
 239 /* Frees a contiguous set of pages of memory, returned by alloc_pages.
 240    size > 0, must be a multiple of pagesize.  */
 241 static void
 242 free_pages (uintptr_t pages, size_t size)
 243 {
 244   pages -= SHARED_LINK_HEADER_SIZE;
 245   if ((pages & (pagesize - 1)) != 0)
 246     abort ();
 247   char *mem_w = (char *) pages;
 248   char *mem_r = mem_w + ((intptr_t *) mem_w)[0];
 249 # if defined _WIN32 && !defined __CYGWIN__
 250   if (!UnmapViewOfFile (mem_w))
 251     abort ();
 252   if (!UnmapViewOfFile (mem_r))
 253     abort ();
 254 # else
 255   if (munmap (mem_w, size) < 0)
 256     abort ();
 257   if (munmap (mem_r, size) < 0)
 258     abort ();
 259 # endif
 260 }
 261
 262 /* Cygwin defines PAGESIZE in <limits.h>.  */
 263 # undef PAGESIZE
 264
 265 /* ======================= Instantiate the front end ======================= */
 266
 267 # define PAGESIZE pagesize
 268 /* On Cygwin and Linux/PowerPC, PAGESIZE is 65536.  On macOS 11, it is 16384.
 269    On all other platforms, it is either 4096 or 8192.  */
 270 # if defined __CYGWIN__ || (defined __linux__ && defined __powerpc__)
 271 #  define PAGESIZE_MAX 65536
 272 # else
 273 #  define PAGESIZE_MAX 16384
 274 # endif
 275
 276 # define ALLOC_PAGES alloc_pages
 277 # define FREE_PAGES free_pages
 278 # define ALIGNMENT sizeof (void *)
 279 # define PAGE_RESERVED_HEADER_SIZE SHARED_LINK_HEADER_SIZE
 280
 281 # include "ssfmalloc.h"
 282
 283
 284 void *
 285 immmalloc (size_t size)
 286 {
 287   /* Initializations.  */
 288   if (!pagesize)
 289     {
 290       init_mmap_file ();
 291       init_pagesize ();
 292     }
 293
 294   void *writable_pointer = (void *) allocate_block (size);
 295   if (writable_pointer == NULL)
 296     errno = ENOMEM;
 297   return writable_pointer;
 298 }
 299
 300 const void *
 301 immfreeze (void *writable_pointer)
 302 {
 303   uintptr_t mem_w = (uintptr_t) writable_pointer & -(intptr_t)pagesize;
 304   return (void *) ((uintptr_t) writable_pointer + ((intptr_t *) mem_w)[0]);
 305 }
 306
 307 void
 308 immfree (const void *readonly_pointer)
 309 {
 310   uintptr_t mem_r = (uintptr_t) readonly_pointer & -(intptr_t)pagesize;
 311   free_block ((uintptr_t) readonly_pointer - ((intptr_t *) mem_r)[0]);
 312 }
 313
 314 #else
 315 /* Dummy implementation.  */
 316
 317 void *
 318 immmalloc (size_t size)
 319 {
 320   void *p = malloc (size);
 321   if (p == NULL)
 322     errno = ENOMEM;
 323   return p;
 324 }
 325
 326 const void *
 327 immfreeze (void *writable_pointer)
 328 {
 329   return writable_pointer;
 330 }
 331
 332 void
 333 immfree (const void *readonly_pointer)
 334 {
 335   void *writable_pointer = (void *) readonly_pointer;
 336   free (writable_pointer);
 337 }
 338
 339 #endif
 340
 341
 342 const char *
 343 immstrdup (const char *string)
 344 {
 345   size_t size = strlen (string) + 1;
 346   void *wp = immmalloc (size);
 347   if (wp == NULL)
 348     return NULL;
 349   memcpy (wp, string, size);
 350   return (const char *) immfreeze (wp);
 351 }