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 <stdio.h>
  22 #include "defs.h"
  23
  24 #ifdef HAVE_MMAP
  25
  26 #include <fcntl.h>
  27 #include <sys/mman.h>
  28
  29 #ifdef i386
  30 #define MMAP_BASE ((caddr_t) 0x81000000)
  31 #define MMAP_PGSZ 0x00002000  /* Must be multiple of real page size */
  32 #else
  33 #define MMAP_BASE ((caddr_t) 0xC2000000)
  34 #define MMAP_PGSZ 0x00002000  /* Must be multiple of real page size */
  35 #endif
  36
  37 #define PAGE_ALIGN(addr) (caddr_t) (((long)(addr) + MMAP_PGSZ - 1) & \
  38                                     ~(MMAP_PGSZ - 1))
  39
  40 static caddr_t mbase = MMAP_BASE;       /* Current base of mmap'd region */
  41 static caddr_t mbreak = MMAP_BASE;      /* Current "break" address */
  42 static caddr_t mtop = MMAP_BASE;        /* Current top of mmap'd region */
  43
  44 static int fd = -1;                     /* Open fd for /dev/zero */
  45
  46
  47 /*  Provide a utility routine for other modules to obtain compatible
  48     page alignment. */
  49
  50 PTR
  51 mmap_page_align (addr)
  52      PTR addr;
  53 {
  54   return (PAGE_ALIGN (addr));
  55 }
  56
  57 /*  Return the base address of the start of the mmap'd region.  Note that
  58     we can find the end of the region at anytime by calling mmap_sbrk(0) */
  59
  60 PTR
  61 mmap_base ()
  62 {
  63   return (mbase);
  64 }
  65
  66 /*  Works like sbrk(), but uses mmap to add to or subtract from a
  67     memory region. */
  68
  69 PTR
  70 mmap_sbrk (size)
  71      int size;
  72 {
  73   PTR result = NULL;
  74   int minc;
  75   caddr_t moveto;
  76
  77   if (size == 0)
  78     {
  79       /* Just return the current "break" value. */
  80       result = mbreak;
  81     }
  82   else if (size < 0)
  83     {
  84       /* We are deallocating memory.  If the amount requested would cause
  85          us to try to deallocate back past the base of the mmap'd region
  86          then do nothing, and return NULL.  Otherwise, deallocate the
  87          memory and return the old break value. */
  88       if (mbreak + size >= mbase)
  89         {
  90           result = (PTR) mbreak;
  91           mbreak += size;
  92           moveto = PAGE_ALIGN (mbreak);
  93           munmap (moveto, (size_t) (mtop - moveto));
  94           mtop = moveto;
  95         }
  96     }
  97   else
  98     {
  99       /* We are allocating memory.  Make sure we have an open file
 100          descriptor and then go on to get the memory. */
 101       if ((fd == -1) && (fd = open ("/dev/zero", O_RDONLY)) < 0)
 102         {
 103           result = NULL;
 104         }
 105       else if (mbreak + size > mtop)
 106         {
 107           /* The request would move us past the end of the currently
 108              mapped memory, so map in enough more memory to satisfy
 109              the request. */
 110           moveto = PAGE_ALIGN (mbreak + size);
 111           if (mmap (mtop, moveto - mtop, PROT_READ | PROT_WRITE,
 112                     MAP_PRIVATE | MAP_FIXED, fd, 0) == mtop)
 113             {
 114               mtop = moveto;
 115               result = (PTR) mbreak;
 116               mbreak += size;
 117             }
 118         }
 119       else
 120         {
 121           result = (PTR) mbreak;
 122           mbreak += size;
 123         }
 124     }
 125   return (result);
 126 }
 127
 128 PTR
 129 mmap_remap (base, mapsize, fd, foffset)
 130      PTR base;
 131      long mapsize;
 132      int fd;
 133      long foffset;
 134 {
 135   /* FIXME:  Quick hack, needs error checking and other attention. */
 136   munmap (mbase, (size_t) (mtop - mbase));
 137   mbase = base;
 138   mtop = mbase + mapsize;
 139   base = mmap (base, mapsize, PROT_READ | PROT_WRITE,
 140                MAP_PRIVATE | MAP_FIXED, dup (fd), foffset);
 141   return (base);
 142 }
 143
 144
 145 #endif  /* HAVE_MMAP */