sysdeps/mach/hurd/brk.c

   1 /* Copyright (C) 1991-2019 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <https://www.gnu.org/licenses/>.  */
  17
  18 #include <errno.h>
  19 #include <hurd.h>
  20 #include <hurd/resource.h>
  21 #include <cthreads.h>           /* For `struct mutex'.  */
  22
  23
  24 /* Initial maximum size of the data segment (this is arbitrary).  */
  25 #define DATA_SIZE       (128 * 1024 * 1024)
  26
  27 /* Up to the page including this address is allocated from the kernel.
  28    This address is the data resource limit.  */
  29 vm_address_t _hurd_data_end;
  30
  31 /* Up to this address is actually available to the user.
  32    Pages beyond the one containing this address allow no access.  */
  33 vm_address_t _hurd_brk = 0;
  34
  35 /* This name is used by the Linux crtbeginS.o for reasons you don't even
  36    want to think about it.  It's just easier to provide some definition for
  37    it than even to explain the braindamage involved.  */
  38 weak_alias (_hurd_brk, ___brk_addr)
  39
  40 struct mutex _hurd_brk_lock;
  41
  42 extern int __data_start, _end;
  43 weak_extern (__data_start)
  44 static vm_address_t static_data_start;
  45
  46
  47 /* Set the end of the process's data space to INADDR.
  48    Return 0 if successful, -1 if not.  */
  49 int
  50 __brk (void *inaddr)
  51 {
  52   int ret;
  53   HURD_CRITICAL_BEGIN;
  54   __mutex_lock (&_hurd_brk_lock);
  55   ret = _hurd_set_brk ((vm_address_t) inaddr);
  56   __mutex_unlock (&_hurd_brk_lock);
  57   HURD_CRITICAL_END;
  58   return ret;
  59 }
  60 weak_alias (__brk, brk)
  61
  62
  63 int
  64 _hurd_set_brk (vm_address_t addr)
  65 {
  66   error_t err = 0;
  67   vm_address_t pagend = round_page (addr);
  68   vm_address_t pagebrk = round_page (_hurd_brk);
  69   long int rlimit;
  70
  71   if (pagend <= pagebrk)
  72     {
  73       if (pagend < pagebrk)
  74         {
  75           /* XXX wish this were atomic... */
  76           /* First deallocate the memory to release its backing space.  */
  77           __vm_deallocate (__mach_task_self (), pagend, pagebrk - pagend);
  78           /* Now reallocate it with no access allowed.  */
  79           err = __vm_map (__mach_task_self (),
  80                           &pagend, pagebrk - pagend,
  81                           0, 0, MACH_PORT_NULL, 0, 0,
  82                           0, VM_PROT_READ|VM_PROT_WRITE|VM_PROT_EXECUTE,
  83                           VM_INHERIT_COPY);
  84           /* XXX what if error? */
  85         }
  86       _hurd_brk = addr;
  87       return 0;
  88     }
  89
  90   __mutex_lock (&_hurd_rlimit_lock);
  91   rlimit = _hurd_rlimits[RLIMIT_DATA].rlim_cur;
  92   __mutex_unlock (&_hurd_rlimit_lock);
  93
  94   if (addr - static_data_start > rlimit)
  95     {
  96       /* Need to increase the resource limit.  */
  97       errno = ENOMEM;
  98       return -1;
  99     }
 100
 101   if (pagend > _hurd_data_end)
 102     {
 103       vm_address_t alloc_start = _hurd_data_end;
 104
 105       /* We didn't allocate enough space!  Hopefully we can get some more!  */
 106
 107       if (_hurd_data_end > pagebrk)
 108         /* First finish allocation.  */
 109         err = __vm_protect (__mach_task_self (), pagebrk,
 110                             alloc_start - pagebrk, 0,
 111                             VM_PROT_READ|VM_PROT_WRITE|VM_PROT_EXECUTE);
 112       if (! err)
 113         _hurd_brk = alloc_start;
 114
 115       if (! err)
 116         err = __vm_allocate (__mach_task_self (), &alloc_start,
 117                              pagend - alloc_start, 0);
 118
 119       if (! err)
 120         _hurd_data_end = pagend;
 121     }
 122   else
 123     /* Make the memory accessible.  */
 124     err = __vm_protect (__mach_task_self (), pagebrk, pagend - pagebrk,
 125                         0, VM_PROT_READ|VM_PROT_WRITE|VM_PROT_EXECUTE);
 126
 127   if (err)
 128     return __hurd_fail (err);
 129
 130   _hurd_brk = addr;
 131   return 0;
 132 }
 133
 134 static void
 135 init_brk (void)
 136 {
 137   vm_address_t pagend;
 138
 139   __mutex_init (&_hurd_brk_lock);
 140
 141   static_data_start = (vm_address_t) (&__data_start ?: &_end);
 142
 143   /* If _hurd_brk is already set, don't change it.  The assumption is that
 144      it was set in a previous run before something like Emacs's unexec was
 145      called and dumped all the data up to the break at that point.  */
 146   if (_hurd_brk == 0)
 147     _hurd_brk = (vm_address_t) &_end;
 148
 149   pagend = round_page (_hurd_brk);
 150
 151   _hurd_data_end = round_page (static_data_start + DATA_SIZE);
 152
 153   if (pagend < _hurd_data_end)
 154     {
 155       /* We use vm_map to allocate and change permissions atomically.  */
 156       if (__vm_map (__mach_task_self (), &pagend, _hurd_data_end - pagend,
 157                     0, 0, MACH_PORT_NULL, 0, 0,
 158                     0, VM_PROT_READ|VM_PROT_WRITE|VM_PROT_EXECUTE,
 159                     VM_INHERIT_COPY))
 160         /* Couldn't allocate the memory.  The break will be very short.  */
 161         _hurd_data_end = pagend;
 162     }
 163
 164   (void) &init_brk;             /* Avoid ``defined but not used'' warning.  */
 165 }
 166 text_set_element (_hurd_preinit_hook, init_brk);