1PTHREAD_ATTR_SETGUARDSIZE(3)Linux Programmer's ManuaPlTHREAD_ATTR_SETGUARDSIZE(3)
2
6 pthread_attr_setguardsize, pthread_attr_getguardsize - set/get guard
7 size attribute in thread attributes object
8
10 #include <pthread.h>
11 int pthread_attr_setguardsize(pthread_attr_t *attr, size_t guardsize);
13 int pthread_attr_getguardsize(const pthread_attr_t *attr, size_t *guardsize);
14 Compile and link with -pthread.
16
18 The pthread_attr_setguardsize() function sets the guard size attribute
19 of the thread attributes object referred to by attr to the value speci‐
20 fied in guardsize.
21 If guardsize is greater than 0, then for each new thread created using
23 attr the system allocates an additional region of at least guardsize
24 bytes at the end of the thread's stack to act as the guard area for the
25 stack (but see BUGS).
26 If guardsize is 0, then new threads created with attr will not have a
28 guard area.
29 The default guard size is the same as the system page size.
31 If the stack address attribute has been set in attr (using
33 pthread_attr_setstack(3) or pthread_attr_setstackaddr(3)), meaning that
34 the caller is allocating the thread's stack, then the guard size
35 attribute is ignored (i.e., no guard area is created by the system): it
36 is the application's responsibility to handle stack overflow (perhaps
37 by using mprotect(2) to manually define a guard area at the end of the
38 stack that it has allocated).
39 The pthread_attr_getguardsize() function returns the guard size
41 attribute of the thread attributes object referred to by attr in the
42 buffer pointed to by guardsize.
43
45 On success, these functions return 0; on error, they return a nonzero
46 error number.
47
49 POSIX.1 documents an EINVAL error if attr or guardsize is invalid. On
50 Linux these functions always succeed (but portable and future-proof
51 applications should nevertheless handle a possible error return).
52
54 These functions are provided by glibc since version 2.1.
55
57 For an explanation of the terms used in this section, see
58 attributes(7).
59 ┌─────────────────────────────┬───────────────┬─────────┐
61 │Interface │ Attribute │ Value │
62 ├─────────────────────────────┼───────────────┼─────────┤
63 │pthread_attr_setguardsize(), │ Thread safety │ MT-Safe │
64 │pthread_attr_getguardsize() │ │ │
65 └─────────────────────────────┴───────────────┴─────────┘
67 POSIX.1-2001, POSIX.1-2008.
68
70 A guard area consists of virtual memory pages that are protected to
71 prevent read and write access. If a thread overflows its stack into
72 the guard area, then, on most hard architectures, it receives a SIGSEGV
73 signal, thus notifying it of the overflow. Guard areas start on page
74 boundaries, and the guard size is internally rounded up to the system
75 page size when creating a thread. (Nevertheless, pthread_attr_get‐
76 guardsize() returns the guard size that was set by pthread_attr_set‐
77 guardsize().)
78 Setting a guard size of 0 may be useful to save memory in an applica‐
80 tion that creates many threads and knows that stack overflow can never
81 occur.
82 Choosing a guard size larger than the default size may be necessary for
84 detecting stack overflows if a thread allocates large data structures
85 on the stack.
86
88 As at glibc 2.8, the NPTL threading implementation includes the guard
89 area within the stack size allocation, rather than allocating extra
90 space at the end of the stack, as POSIX.1 requires. (This can result
91 in an EINVAL error from pthread_create(3) if the guard size value is
92 too large, leaving no space for the actual stack.)
93 The obsolete LinuxThreads implementation did the right thing, allocat‐
95 ing extra space at the end of the stack for the guard area.
96
98 See pthread_getattr_np(3).
99
101 mmap(2), mprotect(2), pthread_attr_init(3), pthread_attr_setstack(3),
102 pthread_attr_setstacksize(3), pthread_create(3), pthreads(7)
103
105 This page is part of release 5.07 of the Linux man-pages project. A
106 description of the project, information about reporting bugs, and the
107 latest version of this page, can be found at
108 https://www.kernel.org/doc/man-pages/.
109Linux 2020-06-09 PTHREAD_ATTR_SETGUARDSIZE(3)