1/* Copyright (C) 1991-2022 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. */
32vm_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. */
36vm_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. */
41weak_alias (_hurd_brk, ___brk_addr)
42
43struct mutex _hurd_brk_lock;
44
45static 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. */
50int
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}
61weak_alias (__brk, brk)
62
63
64int
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 {
97 /* Need to increase the resource limit. */
98 errno = ENOMEM;
99 return -1;
100 }
101
102 if (pagend > _hurd_data_end)
103 {
104 vm_address_t alloc_start = _hurd_data_end;
105
106 /* We didn't allocate enough space! Hopefully we can get some more! */
107
108 if (_hurd_data_end > pagebrk)
109 /* First finish allocation. */
110 err = __vm_protect (__mach_task_self (), pagebrk,
111 alloc_start - pagebrk, 0,
112 VM_PROT_READ|VM_PROT_WRITE|VM_PROT_EXECUTE);
113 if (! err)
114 _hurd_brk = alloc_start;
115
116 if (! err)
117 err = __vm_allocate (__mach_task_self (), &alloc_start,
118 pagend - alloc_start, 0);
119
120 if (! err)
121 _hurd_data_end = pagend;
122 }
123 else
124 /* Make the memory accessible. */
125 err = __vm_protect (__mach_task_self (), pagebrk, pagend - pagebrk,
126 0, VM_PROT_READ|VM_PROT_WRITE|VM_PROT_EXECUTE);
127
128 if (err)
129 return __hurd_fail (err);
130
131 _hurd_brk = addr;
132 return 0;
133}
134
135static void attribute_used_retain
136init_brk (void)
137{
138 vm_address_t pagend;
139
140 __mutex_init (&_hurd_brk_lock);
141
142 brk_start = (vm_address_t) BRK_START;
143
144 /* If _hurd_brk is already set, don't change it. The assumption is that
145 it was set in a previous run before something like Emacs's unexec was
146 called and dumped all the data up to the break at that point. */
147 if (_hurd_brk == 0) {
148 _hurd_brk = (vm_address_t) BRK_START;
149 }
150
151 pagend = round_page (_hurd_brk);
152
153 _hurd_data_end = round_page (brk_start + DATA_SIZE);
154
155 if (pagend < _hurd_data_end)
156 {
157 /* We use vm_map to allocate and change permissions atomically. */
158 if (__vm_map (__mach_task_self (), &pagend, _hurd_data_end - pagend,
159 0, 0, MACH_PORT_NULL, 0, 0,
160 0, VM_PROT_READ|VM_PROT_WRITE|VM_PROT_EXECUTE,
161 VM_INHERIT_COPY))
162 /* Couldn't allocate the memory. The break will be very short. */
163 _hurd_data_end = pagend;
164 }
165}
166SET_RELHOOK (_hurd_preinit_hook, init_brk);
167

source code of glibc/sysdeps/mach/hurd/brk.c