.\" Copyright (c) 2008 Linux Foundation, written by Michael Kerrisk .\" <mtk.manpages@xxxxxxxxx> .\" .\" Permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" Permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" Since the Linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. The author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. The author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" Formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" .TH PTHREAD_ATTR_SETGUARDSIZE 3 2008-10-24 "Linux" "Linux Programmer's Manual" .SH NAME pthread_attr_setguardsize, pthread_attr_getguardsize \- set/get guard size attribute in thread attributes object .SH SYNOPSIS .nf .B #include <pthread.h> .BI "int pthread_attr_setguardsize(pthread_attr_t *" attr \ ", size_t " guardsize ); .BI "int pthread_attr_getguardsize(pthread_attr_t *" attr \ ", size_t *" guardsize ); .sp Compile and link with \fI\-pthread\fP. .SH DESCRIPTION The .BR pthread_attr_setguardsize () function sets the guard size attribute of the thread attributes object referred to by .I attr to the value specified in .IR guardsize . If .I guardsize is greater than 0, then for each new thread created using .I attr the system allocates an additional region of at least .I guardsize bytes at the end of the thread's stack to act as the guard area for the stack (but see BUGS). If .I guardsize is 0, then new threads created with .I 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 .I attr (using .BR pthread_attr_setstack (3) or .BR 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 .BR mprotect (2) to manually define a guard area at the end of the stack that it has allocated). The .BR pthread_attr_getguardsize () function returns the guard size attribute of the thread attributes object referred to by .I attr in the buffer pointed to by .IR guardsize . .SH RETURN VALUE On success, these functions return 0; on error, they return a non-zero error number. .SH ERRORS POSIX.1-2001 documents an .B EINVAL error if .I attr or .I guardsize is invalid. On Linux these functions always succeed (but portable and future-proof applications should nevertheless handle a possible error return). .SH VERSIONS These functions are provided by glibc since version 2.1. .SH CONFORMING TO POSIX.1-2001. .SH 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 .B 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, .BR pthread_attr_getguardsize () returns the guard size that was set by .BR 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. .SH 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 .B EINVAL error from .BR 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. .\" glibc includes the guardsize within the allocated stack size, .\" which looks pretty clearly to be in violation of POSIX. .\" .\" Filed bug, 22 Oct 2008: .\" http://sources.redhat.com/bugzilla/show_bug.cgi?id=6973 .\" .\" Older reports: .\" https//bugzilla.redhat.com/show_bug.cgi?id=435337 .\" Reportedly, LinuxThreads did the right thing, allocating .\" extra space at the end of the stack: .\" http://sourceware.org/ml/libc-alpha/2008-05/msg00086.html .SH EXAMPLE See .BR pthread_getattr_np (3). .SH SEE ALSO .BR mmap (2), .BR mprotect (2), .BR pthread_attr_init (3), .BR pthread_create (3), .BR pthread_attr_setstack (3), .BR pthread_attr_setstacksize (3), .BR pthreads (7) -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
