1.\" $NetBSD: __builtin_object_size.3,v 1.8 2010/12/19 09:33:52 jruoho Exp $ 2.\" 3.\" Copyright (c) 2007 The NetBSD Foundation, Inc. 4.\" All rights reserved. 5.\" 6.\" This code is derived from software contributed to The NetBSD Foundation 7.\" by Christos Zoulas. 8.\" 9.\" Redistribution and use in source and binary forms, with or without 10.\" modification, are permitted provided that the following conditions 11.\" are met: 12.\" 1. Redistributions of source code must retain the above copyright 13.\" notice, this list of conditions and the following disclaimer. 14.\" 2. Redistributions in binary form must reproduce the above copyright 15.\" notice, this list of conditions and the following disclaimer in the 16.\" documentation and/or other materials provided with the distribution. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 19.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 20.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 21.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 22.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 23.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 24.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 25.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 26.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 27.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 28.\" POSSIBILITY OF SUCH DAMAGE. 29.\" 30.\" 31.Dd December 19, 2010 32.Dt __BUILTIN_OBJECT_SIZE 3 33.Os 34.Sh NAME 35.Nm __builtin_object_size 36.Nd return the size of the given object 37.Sh SYNOPSIS 38.Ft size_t 39.Fn __builtin_object_size "void *ptr" "int type" 40.Sh DESCRIPTION 41The 42.Fn __builtin_object_size 43function is a 44.Xr gcc 1 45built-in function that returns the size of the 46.Fa ptr 47object if known at compile time and the object does not have any side 48effects. 49.Sh RETURN VALUES 50If the size of the object is not known or it has side effects the 51.Fn __builtin_object_size 52function returns: 53.Bl -tag -width (size_t)-1 -offset indent 54.It Dv (size_t)-1 55for 56.Fa type 57.Dv 0 58and 59.Dv 1 . 60.It Dv (size_t)0 61for 62.Fa type 63.Dv 2 64and 65.Dv 3 . 66.El 67.Pp 68If the size of the object is known, then the 69.Fn __builtin_object_size 70function returns the maximum size of all the objects that the compiler 71knows that they can be pointed to by 72.Fa ptr 73when 74.Fa type 75.Dv \*[Am] 2 == 0 , 76and the minimum size when 77.Fa type 78.Dv \*[Am] 2 != 0 . 79.Sh SEE ALSO 80.Xr gcc 1 , 81.Xr __builtin_return_address 3 , 82.Xr attribute 3 , 83.Xr ssp 3 84.Sh HISTORY 85The 86.Fn __builtin_object_size 87appeared in 88.Tn GCC 4.1 . 89.Sh CAVEATS 90This is a non-standard, compiler-specific extension. 91