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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | STANDARDS | HISTORY | NOTES | BUGS | EXAMPLES | SEE ALSO | COLOPHON |
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pthread_...guardsize(3) Library Functions Manual pthread_...guardsize(3)
pthread_attr_setguardsize, pthread_attr_getguardsize - set/get
guard size attribute in thread attributes object
POSIX threads library (libpthread, -lpthread)
#include <pthread.h>
int pthread_attr_setguardsize(pthread_attr_t *attr, size_t guardsize);
int pthread_attr_getguardsize(const pthread_attr_t *restrict attr,
size_t *restrict guardsize);
The pthread_attr_setguardsize() function sets the guard size
attribute of the thread attributes object referred to by attr to
the value specified in guardsize.
If guardsize is greater than 0, then for each new thread created
using attr the system allocates an additional region of at least
guardsize bytes at the end of the thread's stack to act as the
guard area for the stack (but see BUGS).
If guardsize is 0, then new threads created with attr will not
have a guard area.
The default guard size is the same as the system page size.
If the stack address attribute has been set in attr (using
pthread_attr_setstack(3) or pthread_attr_setstackaddr(3)), meaning
that the caller is allocating the thread's stack, then the guard
size attribute is ignored (i.e., no guard area is created by the
system): it is the application's responsibility to handle stack
overflow (perhaps by using mprotect(2) to manually define a guard
area at the end of the stack that it has allocated).
The pthread_attr_getguardsize() function returns the guard size
attribute of the thread attributes object referred to by attr in
the buffer pointed to by guardsize.
On success, these functions return 0; on error, they return a
nonzero error number.
POSIX.1 documents an EINVAL error if attr or guardsize is invalid.
On Linux these functions always succeed (but portable and future-
proof applications should nevertheless handle a possible error
return).
For an explanation of the terms used in this section, see
attributes(7).
┌──────────────────────────────────────┬───────────────┬─────────┐
│ Interface │ Attribute │ Value │
├──────────────────────────────────────┼───────────────┼─────────┤
│ pthread_attr_setguardsize(), │ Thread safety │ MT-Safe │
│ pthread_attr_getguardsize() │ │ │
└──────────────────────────────────────┴───────────────┴─────────┘
POSIX.1-2008.
glibc 2.1. POSIX.1-2001.
A guard area consists of virtual memory pages that are protected
to prevent read and write access. If a thread overflows its stack
into the guard area, then, on most hard architectures, it receives
a SIGSEGV signal, thus notifying it of the overflow. Guard areas
start on page boundaries, and the guard size is internally rounded
up to the system page size when creating a thread. (Nevertheless,
pthread_attr_getguardsize() returns the guard size that was set by
pthread_attr_setguardsize().)
Setting a guard size of 0 may be useful to save memory in an
application that creates many threads and knows that stack
overflow can never occur.
Choosing a guard size larger than the default size may be
necessary for detecting stack overflows if a thread allocates
large data structures on the stack.
As at glibc 2.8, the NPTL threading implementation includes the
guard area within the stack size allocation, rather than
allocating extra space at the end of the stack, as POSIX.1
requires. (This can result in an EINVAL error from
pthread_create(3) if the guard size value is too large, leaving no
space for the actual stack.)
The obsolete LinuxThreads implementation did the right thing,
allocating extra space at the end of the stack for the guard area.
See pthread_getattr_np(3).
mmap(2), mprotect(2), pthread_attr_init(3),
pthread_attr_setstack(3), pthread_attr_setstacksize(3),
pthread_create(3), pthreads(7)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.15.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-08-11. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
man-pages@man7.org
Linux man-pages 6.15 2025-05-17 pthread_...guardsize(3)
Pages that refer to this page: pthread_attr_init(3), pthread_attr_setstack(3), pthread_attr_setstacksize(3), pthread_getattr_default_np(3), pthread_getattr_np(3)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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