osdep/mmap_anon.c

   1  /**
   2  * \file mmap_anon.c
   3  * \brief Provide a compatible anonymous space mapping function
   4  */
   5 #include "config.h"
   6
   7 #include <stdio.h>
   8 #include <unistd.h>
   9 #include <fcntl.h>
  10 #include <sys/mman.h>
  11
  12 #if defined(MAP_ANON) && !defined(MAP_ANONYMOUS)
  13 #define MAP_ANONYMOUS MAP_ANON
  14 #endif
  15
  16 /*
  17  * mmap() anonymous space, depending on the system's mmap() style. On systems
  18  * that use the /dev/zero mapping idiom, zerofd will be set to the file descriptor
  19  * of the opened /dev/zero.
  20  */
  21
  22  /**
  23  * \brief mmap() anonymous space, depending on the system's mmap() style. On systems
  24  * that use the /dev/zero mapping idiom, zerofd will be set to the file descriptor
  25  * of the opened /dev/zero.
  26  *
  27  * \param addr address to map at.
  28  * \param len number of bytes from addr to be mapped.
  29  * \param prot protections (region accessibility).
  30  * \param flags specifies the type of the mapped object.
  31  * \param offset start mapping at byte offset.
  32  * \param zerofd
  33  * \return a pointer to the mapped region upon successful completion, -1 otherwise.
  34  */
  35 void *mmap_anon(void *addr, size_t len, int prot, int flags, off_t offset)
  36 {
  37     void *result;
  38
  39      /* From loader/ext.c:
  40       * "Linux EINVAL's on us if we don't pass MAP_PRIVATE to an anon mmap"
  41       * Therefore we preserve the same behavior on all platforms, ie. no
  42       * shared mappings of anon space (if the concepts are supported). */
  43 #if defined(MAP_SHARED) && defined(MAP_PRIVATE)
  44      flags = (flags & ~MAP_SHARED) | MAP_PRIVATE;
  45 #endif /* defined(MAP_SHARED) && defined(MAP_PRIVATE) */
  46
  47 #ifdef MAP_ANONYMOUS
  48     /* BSD-style anonymous mapping */
  49     result = mmap(addr, len, prot, flags | MAP_ANONYMOUS, -1, offset);
  50 #else
  51     /* SysV-style anonymous mapping */
  52     int fd;
  53     fd = open("/dev/zero", O_RDWR);
  54     if(fd < 0){
  55         perror( "Cannot open /dev/zero for READ+WRITE. Check permissions! error: ");
  56         return NULL;
  57     }
  58
  59     result = mmap(addr, len, prot, flags, fd, offset);
  60     close(fd);
  61 #endif /* MAP_ANONYMOUS */
  62
  63     return result;
  64 }