#include <pthread.h>
int pthread_attr_getguardsize(const pthread_attr_t *restrict attr,
size_t *restrict guardsize);
int pthread_attr_setguardsize(pthread_attr_t *attr,
size_t guardsize);
The pthread_attr_setguardsize() function shall set the guardsize attribute in the attr object. The new value of this attribute shall be obtained from the guardsize parameter. If guardsize is zero, a guard area shall not be provided for threads created with attr. If guardsize is greater than zero, a guard area of at least size guardsize bytes shall be provided for each thread created with attr.
The guardsize attribute controls the size of the guard area for the created thread's stack. The guardsize attribute provides protection against overflow of the stack pointer. If a thread's stack is created with guard protection, the implementation allocates extra memory at the overflow end of the stack as a buffer against stack overflow of the stack pointer. If an application overflows into this buffer an error shall result (possibly in a SIGSEGV signal being delivered to the thread).
A conforming implementation may round up the value contained in guardsize to a multiple of the configurable system variable {PAGESIZE} (see <sys/mman.h>). If an implementation rounds up the value of guardsize to a multiple of {PAGESIZE}, a call to pthread_attr_getguardsize() specifying attr shall store in the guardsize parameter the guard size specified by the previous pthread_attr_setguardsize() function call.
The default value of the guardsize attribute is implementation-defined.
If the stackaddr attribute has been set (that is, the caller is allocating and managing its own thread stacks), the guardsize attribute shall be ignored and no protection shall be provided by the implementation. It is the responsibility of the application to manage stack overflow along with stack allocation and management in this case.
The behavior is undefined if the value specified by the attr argument to pthread_attr_getguardsize() or pthread_attr_setguardsize() does not refer to an initialized thread attributes object.
These functions shall not return an error code of [EINTR].
The following sections are informative.
This example shows how to obtain the guardsize attribute of a thread attribute object.
#include <pthread.h>
pthread_attr_t thread_attr;
size_t guardsize;
int rc;
/* code initializing thread_attr */
...
rc = pthread_attr_getguardsize (&thread_attr, &guardsize);
if (rc != 0) {
/* handle error */
...
}
else {
if (guardsize > 0) {
/* a guard area of at least guardsize bytes is provided */
...
}
else {
/* no guard area provided */
...
}
}
The default size of the guard area is left implementation-defined since on systems supporting very large page sizes, the overhead might be substantial if at least one guard page is required by default.
If an implementation detects that the value specified by the attr argument to pthread_attr_getguardsize() or pthread_attr_setguardsize() does not refer to an initialized thread attributes object, it is recommended that the function should fail and report an [EINVAL] error.
Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .