gdb/mmap-sbrk.c

   1 /* GDB support for an sbrk-like function that uses mmap.
   2    Copyright 1992 Free Software Foundation, Inc.
   3    Contributed by Cygnus Support, using pieces from other GDB modules.
   4
   5 This file is part of GDB.
   6
   7 This program is free software; you can redistribute it and/or modify
   8 it under the terms of the GNU General Public License as published by
   9 the Free Software Foundation; either version 2 of the License, or
  10 (at your option) any later version.
  11
  12 This program is distributed in the hope that it will be useful,
  13 but WITHOUT ANY WARRANTY; without even the implied warranty of
  14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15 GNU General Public License for more details.
  16
  17 You should have received a copy of the GNU General Public License
  18 along with this program; if not, write to the Free Software
  19 Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.  */
  20
  21 #include "defs.h"
  22
  23 #ifdef HAVE_MMAP
  24
  25 #include <fcntl.h>
  26 #include <sys/mman.h>
  27
  28 #ifdef i386
  29 #define MMAP_BASE ((caddr_t) 0x81000000)
  30 #define MMAP_PGSZ 0x00002000  /* Must be multiple of real page size */
  31 #else
  32 #define MMAP_BASE ((caddr_t) 0xC2000000)
  33 #define MMAP_PGSZ 0x00002000  /* Must be multiple of real page size */
  34 #endif
  35
  36 #define PAGE_ALIGN(addr) (caddr_t) (((long)(addr) + MMAP_PGSZ - 1) & \
  37                                     ~(MMAP_PGSZ - 1))
  38
  39 static caddr_t mbase = MMAP_BASE;       /* Current base of mmap'd region */
  40 static caddr_t mbreak = MMAP_BASE;      /* Current "break" address */
  41 static caddr_t mtop = MMAP_BASE;        /* Current top of mmap'd region */
  42
  43 static int fd = -1;                     /* Open fd for /dev/zero */
  44
  45
  46 /*  Provide a utility routine for other modules to obtain compatible
  47     page alignment. */
  48
  49 PTR
  50 mmap_page_align (addr)
  51      PTR addr;
  52 {
  53   return (PAGE_ALIGN (addr));
  54 }
  55
  56 /*  Return the base address of the start of the mmap'd region.  Note that
  57     we can find the end of the region at anytime by calling mmap_sbrk(0) */
  58
  59 PTR
  60 mmap_base ()
  61 {
  62   return (mbase);
  63 }
  64
  65 /*  Works like sbrk(), but uses mmap to add to or subtract from a
  66     memory region. */
  67
  68 PTR
  69 mmap_sbrk (size)
  70      int size;
  71 {
  72   PTR result = NULL;
  73   int minc;
  74   caddr_t moveto;
  75
  76   if (size == 0)
  77     {
  78       /* Just return the current "break" value. */
  79       result = mbreak;
  80     }
  81   else if (size < 0)
  82     {
  83       /* We are deallocating memory.  If the amount requested would cause
  84          us to try to deallocate back past the base of the mmap'd region
  85          then do nothing, and return NULL.  Otherwise, deallocate the
  86          memory and return the old break value. */
  87       if (mbreak + size >= mbase)
  88         {
  89           result = (PTR) mbreak;
  90           mbreak += size;
  91           moveto = PAGE_ALIGN (mbreak);
  92           munmap (moveto, (size_t) (mtop - moveto));
  93           mtop = moveto;
  94         }
  95     }
  96   else
  97     {
  98       /* We are allocating memory.  Make sure we have an open file
  99          descriptor and then go on to get the memory. */
 100       if ((fd == -1) && (fd = open ("/dev/zero", O_RDONLY)) < 0)
 101         {
 102           result = NULL;
 103         }
 104       else if (mbreak + size > mtop)
 105         {
 106           /* The request would move us past the end of the currently
 107              mapped memory, so map in enough more memory to satisfy
 108              the request. */
 109           moveto = PAGE_ALIGN (mbreak + size);
 110           if (mmap (mtop, moveto - mtop, PROT_READ | PROT_WRITE,
 111                     MAP_PRIVATE | MAP_FIXED, fd, 0) == mtop)
 112             {
 113               mtop = moveto;
 114               result = (PTR) mbreak;
 115               mbreak += size;
 116             }
 117         }
 118       else
 119         {
 120           result = (PTR) mbreak;
 121           mbreak += size;
 122         }
 123     }
 124   return (result);
 125 }
 126
 127 PTR
 128 mmap_remap (base, mapsize, fd, foffset)
 129      PTR base;
 130      long mapsize;
 131      int fd;
 132      long foffset;
 133 {
 134   /* FIXME:  Quick hack, needs error checking and other attention. */
 135   munmap (mbase, (size_t) (mtop - mbase));
 136   mbase = base;
 137   mtop = mbase + mapsize;
 138   base = mmap (base, mapsize, PROT_READ | PROT_WRITE,
 139                MAP_PRIVATE | MAP_FIXED, dup (fd), foffset);
 140   return (base);
 141 }
 142
 143
 144 #endif  /* HAVE_MMAP */