1pthread_attr_setguardsize(3)Library Functions Manualpthread_attr_setguardsize(3)
2
6 pthread_attr_setguardsize, pthread_attr_getguardsize - set/get guard
7 size attribute in thread attributes object
8
10 POSIX threads library (libpthread, -lpthread)
11
13 #include <pthread.h>
14 int pthread_attr_setguardsize(pthread_attr_t *attr, size_t guardsize);
16 int pthread_attr_getguardsize(const pthread_attr_t *restrict attr,
17 size_t *restrict guardsize);
18
20 The pthread_attr_setguardsize() function sets the guard size attribute
21 of the thread attributes object referred to by attr to the value speci‐
22 fied in guardsize.
23 If guardsize is greater than 0, then for each new thread created using
25 attr the system allocates an additional region of at least guardsize
26 bytes at the end of the thread's stack to act as the guard area for the
27 stack (but see BUGS).
28 If guardsize is 0, then new threads created with attr will not have a
30 guard area.
31 The default guard size is the same as the system page size.
33 If the stack address attribute has been set in attr (using
35 pthread_attr_setstack(3) or pthread_attr_setstackaddr(3)), meaning that
36 the caller is allocating the thread's stack, then the guard size attri‐
37 bute is ignored (i.e., no guard area is created by the system): it is
38 the application's responsibility to handle stack overflow (perhaps by
39 using mprotect(2) to manually define a guard area at the end of the
40 stack that it has allocated).
41 The pthread_attr_getguardsize() function returns the guard size attri‐
43 bute of the thread attributes object referred to by attr in the buffer
44 pointed to by guardsize.
45
47 On success, these functions return 0; on error, they return a nonzero
48 error number.
49
51 POSIX.1 documents an EINVAL error if attr or guardsize is invalid. On
52 Linux these functions always succeed (but portable and future-proof ap‐
53 plications should nevertheless handle a possible error return).
54
56 For an explanation of the terms used in this section, see at‐
57 tributes(7).
58 ┌────────────────────────────────────────────┬───────────────┬─────────┐
60 │Interface │ Attribute │ Value │
61 ├────────────────────────────────────────────┼───────────────┼─────────┤
62 │pthread_attr_setguardsize(), │ Thread safety │ MT-Safe │
63 │pthread_attr_getguardsize() │ │ │
64 └────────────────────────────────────────────┴───────────────┴─────────┘
65
67 POSIX.1-2008.
68
70 glibc 2.1. POSIX.1-2001.
71
73 A guard area consists of virtual memory pages that are protected to
74 prevent read and write access. If a thread overflows its stack into
75 the guard area, then, on most hard architectures, it receives a SIGSEGV
76 signal, thus notifying it of the overflow. Guard areas start on page
77 boundaries, and the guard size is internally rounded up to the system
78 page size when creating a thread. (Nevertheless, pthread_attr_get‐
79 guardsize() returns the guard size that was set by pthread_attr_set‐
80 guardsize().)
81 Setting a guard size of 0 may be useful to save memory in an applica‐
83 tion that creates many threads and knows that stack overflow can never
84 occur.
85 Choosing a guard size larger than the default size may be necessary for
87 detecting stack overflows if a thread allocates large data structures
88 on the stack.
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91 As at glibc 2.8, the NPTL threading implementation includes the guard
92 area within the stack size allocation, rather than allocating extra
93 space at the end of the stack, as POSIX.1 requires. (This can result
94 in an EINVAL error from pthread_create(3) if the guard size value is
95 too large, leaving no space for the actual stack.)
96 The obsolete LinuxThreads implementation did the right thing, allocat‐
98 ing extra space at the end of the stack for the guard area.
99
101 See pthread_getattr_np(3).
102
104 mmap(2), mprotect(2), pthread_attr_init(3), pthread_attr_setstack(3),
105 pthread_attr_setstacksize(3), pthread_create(3), pthreads(7)
106Linux man-pages 6.04 2023-03-30 pthread_attr_setguardsize(3)