PTHREAD_ATTR_SETGUARDSIZE(3) Linux Programmer's Manual PTHREAD_ATTR_SETGUARDSIZE(3)
pthread_attr_setguardsize, pthread_attr_getguardsize - set/get guard size attribute in
thread attributes object
int pthread_attr_setguardsize(pthread_attr_t *attr, size_t guardsize);
int pthread_attr_getguardsize(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 mpro-
tect(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.1-2001 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.
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 architec-
tures, 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.
mmap(2), mprotect(2), pthread_attr_init(3), pthread_attr_setstack(3), pthread_attr_set-
stacksize(3), pthread_create(3), pthreads(7)
This page is part of release 3.55 of the Linux man-pages project. A description of the
project, and information about reporting bugs, can be found at
Linux 2008-10-24 PTHREAD_ATTR_SETGUARDSIZE(3)