sysdeps/mach/hurd/brk.c

   1 /* Copyright (C) 1991-2024 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 <lock-intern.h>        /* For `struct mutex'.  */
  22 #include <vm_param.h>
  23
  24 #include "set-hooks.h"
  25
  26
  27 /* Initial maximum size of the data segment (this is arbitrary).  */
  28 #define DATA_SIZE       (128 * 1024 * 1024)
  29
  30 /* Up to the page including this address is allocated from the kernel.
  31    This address is the data resource limit.  */
  32 vm_address_t _hurd_data_end;
  33
  34 /* Up to this address is actually available to the user.
  35    Pages beyond the one containing this address allow no access.  */
  36 vm_address_t _hurd_brk = 0;
  37
  38 /* This name is used by the Linux crtbeginS.o for reasons you don't even
  39    want to think about it.  It's just easier to provide some definition for
  40    it than even to explain the braindamage involved.  */
  41 weak_alias (_hurd_brk, ___brk_addr)
  42
  43 struct mutex _hurd_brk_lock;
  44
  45 static vm_address_t brk_start;
  46
  47
  48 /* Set the end of the process's data space to INADDR.
  49    Return 0 if successful, -1 if not.  */
  50 int
  51 __brk (void *inaddr)
  52 {
  53   int ret;
  54   HURD_CRITICAL_BEGIN;
  55   __mutex_lock (&_hurd_brk_lock);
  56   ret = _hurd_set_brk ((vm_address_t) inaddr);
  57   __mutex_unlock (&_hurd_brk_lock);
  58   HURD_CRITICAL_END;
  59   return ret;
  60 }
  61 weak_alias (__brk, brk)
  62
  63
  64 int
  65 _hurd_set_brk (vm_address_t addr)
  66 {
  67   error_t err = 0;
  68   vm_address_t pagend = round_page (addr);
  69   vm_address_t pagebrk = round_page (_hurd_brk);
  70   long int rlimit;
  71
  72   if (pagend <= pagebrk)
  73     {
  74       if (pagend < pagebrk)
  75         {
  76           /* XXX wish this were atomic... */
  77           /* First deallocate the memory to release its backing space.  */
  78           __vm_deallocate (__mach_task_self (), pagend, pagebrk - pagend);
  79           /* Now reallocate it with no access allowed.  */
  80           err = __vm_map (__mach_task_self (),
  81                           &pagend, pagebrk - pagend,
  82                           0, 0, MACH_PORT_NULL, 0, 0,
  83                           0, VM_PROT_READ|VM_PROT_WRITE|VM_PROT_EXECUTE,
  84                           VM_INHERIT_COPY);
  85           /* XXX what if error? */
  86         }
  87       _hurd_brk = addr;
  88       return 0;
  89     }
  90
  91   __mutex_lock (&_hurd_rlimit_lock);
  92   rlimit = _hurd_rlimits[RLIMIT_DATA].rlim_cur;
  93   __mutex_unlock (&_hurd_rlimit_lock);
  94
  95   if (addr - brk_start > rlimit)
  96     /* Need to increase the resource limit.  */
  97     return __hurd_fail (ENOMEM);
  98
  99   if (pagend > _hurd_data_end)
 100     {
 101       vm_address_t alloc_start = _hurd_data_end;
 102
 103       /* We didn't allocate enough space!  Hopefully we can get some more!  */
 104
 105       if (_hurd_data_end > pagebrk)
 106         /* First finish allocation.  */
 107         err = __vm_protect (__mach_task_self (), pagebrk,
 108                             alloc_start - pagebrk, 0,
 109                             VM_PROT_READ|VM_PROT_WRITE);
 110       if (! err)
 111         _hurd_brk = alloc_start;
 112
 113       if (! err)
 114         err = __vm_allocate (__mach_task_self (), &alloc_start,
 115                              pagend - alloc_start, 0);
 116
 117       if (! err)
 118         _hurd_data_end = pagend;
 119     }
 120   else
 121     /* Make the memory accessible.  */
 122     err = __vm_protect (__mach_task_self (), pagebrk, pagend - pagebrk,
 123                         0, VM_PROT_READ|VM_PROT_WRITE);
 124
 125   if (err)
 126     return __hurd_fail (err);
 127
 128   _hurd_brk = addr;
 129   return 0;
 130 }
 131
 132 static void attribute_used_retain
 133 init_brk (void)
 134 {
 135   vm_address_t pagend;
 136
 137   __mutex_init (&_hurd_brk_lock);
 138
 139   brk_start = (vm_address_t) BRK_START;
 140
 141   /* If _hurd_brk is already set, don't change it.  The assumption is that
 142      it was set in a previous run before something like Emacs's unexec was
 143      called and dumped all the data up to the break at that point.  */
 144   if (_hurd_brk == 0) {
 145     _hurd_brk = (vm_address_t) BRK_START;
 146   }
 147
 148   pagend = round_page (_hurd_brk);
 149
 150   _hurd_data_end = round_page (brk_start + DATA_SIZE);
 151
 152   if (pagend < _hurd_data_end)
 153     {
 154       /* We use vm_map to allocate and change permissions atomically.  */
 155       if (__vm_map (__mach_task_self (), &pagend, _hurd_data_end - pagend,
 156                     0, 0, MACH_PORT_NULL, 0, 0,
 157                     0, VM_PROT_READ|VM_PROT_WRITE|VM_PROT_EXECUTE,
 158                     VM_INHERIT_COPY))
 159         /* Couldn't allocate the memory.  The break will be very short.  */
 160         _hurd_data_end = pagend;
 161     }
 162 }
 163 SET_RELHOOK (_hurd_preinit_hook, init_brk);