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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | ATTRIBUTES | CONFORMING TO | NOTES | BUGS | EXAMPLE | SEE ALSO | COLOPHON |
PTHREAD_ATTR_SETGUARDSIZE(3)nux Programmer's ManualREAD_ATTR_SETGUARDSIZE(3)
pthread_attr_setguardsize, pthread_attr_getguardsize - set/get guard
size attribute in thread attributes object
#include <pthread.h>
int pthread_attr_setguardsize(pthread_attr_t *attr, size_t guardsize);
int pthread_attr_getguardsize(const pthread_attr_t *attr, size_t *guardsize);
Compile and link with -pthread.
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).
These functions are provided by glibc since version 2.1.
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.1-2001, POSIX.1-2008.
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 release 4.12 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
Linux 2015-08-08 PTHREAD_ATTR_SETGUARDSIZE(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)