1 /* Copyright (C) 1991-2023 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);