pthread_attr_setguardsize(3)

1PTHREAD_ATTR_SETGUARDSIZE(3)Linux Programmer's ManuaPlTHREAD_ATTR_SETGUARDSIZE(3)
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NAME

6       pthread_attr_setguardsize,  pthread_attr_getguardsize  -  set/get guard
7       size attribute in thread attributes object
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SYNOPSIS

10       #include <pthread.h>
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12       int pthread_attr_setguardsize(pthread_attr_t *attr, size_t guardsize);
13       int pthread_attr_getguardsize(const pthread_attr_t *attr, size_t *guardsize);
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15       Compile and link with -pthread.
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DESCRIPTION

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.
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22       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).
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27       If  guardsize  is 0, then new threads created with attr will not have a
28       guard area.
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30       The default guard size is the same as the system page size.
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32       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).
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40       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.
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RETURN VALUE

45       On success, these functions return 0; on error, they return  a  nonzero
46       error number.
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ERRORS

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).
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VERSIONS

54       These functions are provided by glibc since version 2.1.
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ATTRIBUTES

57       For   an   explanation   of   the  terms  used  in  this  section,  see
58       attributes(7).
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60       ┌─────────────────────────────┬───────────────┬─────────┐
61       │Interface                    │ Attribute     │ Value   │
62       ├─────────────────────────────┼───────────────┼─────────┤
63       │pthread_attr_setguardsize(), │ Thread safety │ MT-Safe │
64       │pthread_attr_getguardsize()  │               │         │
65       └─────────────────────────────┴───────────────┴─────────┘

CONFORMING TO

67       POSIX.1-2001, POSIX.1-2008.
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NOTES

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().)
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79       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.
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83       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.
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BUGS

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.)
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94       The obsolete LinuxThreads implementation did the right thing,  allocat‐
95       ing extra space at the end of the stack for the guard area.
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EXAMPLE

98       See pthread_getattr_np(3).
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COLOPHON

105       This page is part of release 5.04 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/.
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112Linux                             2017-09-15      PTHREAD_ATTR_SETGUARDSIZE(3)