1PTHREAD_ATTR_GETGUARDSIZE(3PP)OSIX Programmer's ManuPaTlHREAD_ATTR_GETGUARDSIZE(3P)
2
6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
10
12 pthread_attr_getguardsize, pthread_attr_setguardsize — get and set the
13 thread guardsize attribute
14
16 #include <pthread.h>
17 int pthread_attr_getguardsize(const pthread_attr_t *restrict attr,
19 size_t *restrict guardsize);
20 int pthread_attr_setguardsize(pthread_attr_t *attr,
21 size_t guardsize);
22
24 The pthread_attr_getguardsize() function shall get the guardsize
25 attribute in the attr object. This attribute shall be returned in the
26 guardsize parameter.
27 The pthread_attr_setguardsize() function shall set the guardsize
29 attribute in the attr object. The new value of this attribute shall be
30 obtained from the guardsize parameter. If guardsize is zero, a guard
31 area shall not be provided for threads created with attr. If guardsize
32 is greater than zero, a guard area of at least size guardsize bytes
33 shall be provided for each thread created with attr.
34 The guardsize attribute controls the size of the guard area for the
36 created thread's stack. The guardsize attribute provides protection
37 against overflow of the stack pointer. If a thread's stack is created
38 with guard protection, the implementation allocates extra memory at the
39 overflow end of the stack as a buffer against stack overflow of the
40 stack pointer. If an application overflows into this buffer an error
41 shall result (possibly in a SIGSEGV signal being delivered to the
42 thread).
43 A conforming implementation may round up the value contained in guard‐
45 size to a multiple of the configurable system variable {PAGESIZE} (see
46 <sys/mman.h>). If an implementation rounds up the value of guardsize
47 to a multiple of {PAGESIZE}, a call to pthread_attr_getguardsize()
48 specifying attr shall store in the guardsize parameter the guard size
49 specified by the previous pthread_attr_setguardsize() function call.
50 The default value of the guardsize attribute is implementation-defined.
52 If the stackaddr attribute has been set (that is, the caller is allo‐
54 cating and managing its own thread stacks), the guardsize attribute
55 shall be ignored and no protection shall be provided by the implementa‐
56 tion. It is the responsibility of the application to manage stack over‐
57 flow along with stack allocation and management in this case.
58 The behavior is undefined if the value specified by the attr argument
60 to pthread_attr_getguardsize() or pthread_attr_setguardsize() does not
61 refer to an initialized thread attributes object.
62
64 If successful, the pthread_attr_getguardsize() and pthread_attr_set‐
65 guardsize() functions shall return zero; otherwise, an error number
66 shall be returned to indicate the error.
67
69 These functions shall fail if:
70 EINVAL The parameter guardsize is invalid.
72 These functions shall not return an error code of [EINTR].
74 The following sections are informative.
76
78 Retrieving the guardsize Attribute
79 This example shows how to obtain the guardsize attribute of a thread
80 attribute object.
81 #include <pthread.h>
84 pthread_attr_t thread_attr;
86 size_t guardsize;
87 int rc;
88 /* code initializing thread_attr */
90 ...
91 rc = pthread_attr_getguardsize (&thread_attr, &guardsize);
93 if (rc != 0) {
94 /* handle error */
95 ...
96 }
97 else {
98 if (guardsize > 0) {
99 /* a guard area of at least guardsize bytes is provided */
100 ...
101 }
102 else {
103 /* no guard area provided */
104 ...
105 }
106 }
107
109 None.
110
112 The guardsize attribute is provided to the application for two reasons:
113 1. Overflow protection can potentially result in wasted system
115 resources. An application that creates a large number of threads,
116 and which knows its threads never overflow their stack, can save
117 system resources by turning off guard areas.
118 2. When threads allocate large data structures on the stack, large
120 guard areas may be needed to detect stack overflow.
121 The default size of the guard area is left implementation-defined since
123 on systems supporting very large page sizes, the overhead might be sub‐
124 stantial if at least one guard page is required by default.
125 If an implementation detects that the value specified by the attr argu‐
127 ment to pthread_attr_getguardsize() or pthread_attr_setguardsize() does
128 not refer to an initialized thread attributes object, it is recommended
129 that the function should fail and report an [EINVAL] error.
130
132 None.
133
135 The Base Definitions volume of POSIX.1‐2017, <pthread.h>, <sys_mman.h>
136
138 Portions of this text are reprinted and reproduced in electronic form
139 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
140 table Operating System Interface (POSIX), The Open Group Base Specifi‐
141 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
142 Electrical and Electronics Engineers, Inc and The Open Group. In the
143 event of any discrepancy between this version and the original IEEE and
144 The Open Group Standard, the original IEEE and The Open Group Standard
145 is the referee document. The original Standard can be obtained online
146 at http://www.opengroup.org/unix/online.html .
147 Any typographical or formatting errors that appear in this page are
149 most likely to have been introduced during the conversion of the source
150 files to man page format. To report such errors, see https://www.ker‐
151 nel.org/doc/man-pages/reporting_bugs.html .
152IEEE/The Open Group 2017 PTHREAD_ATTR_GETGUARDSIZE(3P)