pthread_attr_setguardsize(3) — Linux manual page

pthread_...guardsize(3) Library Functions Manual pthread_...guardsize(3)

NAME

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

LIBRARY

       POSIX threads library (libpthread, -lpthread)

SYNOPSIS

       #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);

DESCRIPTION

       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.

RETURN VALUE

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

ERRORS

       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).

ATTRIBUTES

       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()         │               │         │
       └─────────────────────────────────────┴───────────────┴─────────┘

STANDARDS

       POSIX.1-2008.

HISTORY

       glibc 2.1.  POSIX.1-2001.

NOTES

       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.

BUGS

       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.

EXAMPLES

       See pthread_getattr_np(3).

SEE ALSO

       mmap(2), mprotect(2), pthread_attr_init(3),
       pthread_attr_setstack(3), pthread_attr_setstacksize(3),
       pthread_create(3), pthreads(7)

COLOPHON

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Linux man-pages 6.9.1          2024-05-02        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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