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1 /*
2  * Find out the size of kernel's sigset_t.
3  *
4  * Copyright (c) 2016-2017 Dmitry V. Levin <ldv@altlinux.org>
5  * All rights reserved.
6  *
7  * Redistribution and use in source and binary forms, with or without
8  * modification, are permitted provided that the following conditions
9  * are met:
10  * 1. Redistributions of source code must retain the above copyright
11  *    notice, this list of conditions and the following disclaimer.
12  * 2. Redistributions in binary form must reproduce the above copyright
13  *    notice, this list of conditions and the following disclaimer in the
14  *    documentation and/or other materials provided with the distribution.
15  * 3. The name of the author may not be used to endorse or promote products
16  *    derived from this software without specific prior written permission.
17  *
18  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
19  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
20  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
21  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
22  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
23  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
24  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
25  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
26  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
27  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
28  */
29 
30 #include "tests.h"
31 #include <signal.h>
32 #include <unistd.h>
33 #include <asm/unistd.h>
34 
35 /*
36  * If the sigset size specified to rt_sigprocmask is not equal to the size
37  * of kernel's sigset_t, the kernel does not look at anything else and fails
38  * with EINVAL.
39  *
40  * Otherwise, if both pointers specified to rt_sigprocmask are NULL,
41  * the kernel just returns 0.
42  *
43  * This vaguely documented kernel feature can be used to probe
44  * the kernel and find out the size of kernel's sigset_t.
45  */
46 
47 unsigned int
get_sigset_size(void)48 get_sigset_size(void)
49 {
50 	static unsigned int set_size;
51 
52 	if (!set_size) {
53 		static const unsigned int big_size = 1024 / 8;
54 
55 		for (set_size = big_size; set_size; set_size >>= 1) {
56 			if (!syscall(__NR_rt_sigprocmask, SIG_SETMASK,
57 				     NULL, NULL, set_size))
58 				break;
59 		}
60 
61 		if (!set_size)
62 			perror_msg_and_fail("rt_sigprocmask");
63 	}
64 
65 	return set_size;
66 }
67