f14fb60209
* Updating common/lib * Updating lib/csu * Updating lib/libc * Updating libexec/ld.elf_so * Corrected test on __minix in featuretest to actually follow the meaning of the comment. * Cleaned up _REENTRANT-related defintions. * Disabled -D_REENTRANT for libfetch * Removing some unneeded __NBSD_LIBC defines and tests Change-Id: Ic1394baef74d11b9f86b312f5ff4bbc3cbf72ce2
102 lines
3.1 KiB
Groff
102 lines
3.1 KiB
Groff
.\" $NetBSD: __builtin_object_size.3,v 1.10 2012/07/19 06:44:12 wiz Exp $
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.\"
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.\" Copyright (c) 2007 The NetBSD Foundation, Inc.
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.\" All rights reserved.
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.\"
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.\" This code is derived from software contributed to The NetBSD Foundation
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.\" by Christos Zoulas.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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.\" POSSIBILITY OF SUCH DAMAGE.
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.\"
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.\"
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.Dd July 18, 2012
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.Dt __BUILTIN_OBJECT_SIZE 3
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.Os
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.Sh NAME
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.Nm __builtin_object_size
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.Nd return the size of the given object
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.Sh SYNOPSIS
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.Ft size_t
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.Fn __builtin_object_size "void *ptr" "int type"
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.Sh DESCRIPTION
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The
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.Fn __builtin_object_size
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function is a
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.Xr gcc 1
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built-in function that returns the size of the
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.Fa ptr
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object if known at compile time and the object does not have any side
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effects.
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.Sh RETURN VALUES
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If the size of the object is not known or it has side effects the
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.Fn __builtin_object_size
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function returns:
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.Bl -tag -width (size_t)\-1 -offset indent
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.It Dv (size_t)\-1
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for
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.Fa type
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.Dv 0
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and
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.Dv 1 .
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.It Dv (size_t)0
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for
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.Fa type
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.Dv 2
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and
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.Dv 3 .
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.El
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.Pp
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If the size of the object is known, then the
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.Fn __builtin_object_size
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function returns the maximum size of all the objects that the compiler
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knows that they can be pointed to by
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.Fa ptr
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when
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.Fa type
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.Dv \*[Am] 2 == 0 ,
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and the minimum size when
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.Fa type
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.Dv \*[Am] 2 != 0 .
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.Sh SEE ALSO
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.Xr gcc 1 ,
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.Xr __builtin_return_address 3 ,
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.Xr attribute 3 ,
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.Xr ssp 3
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.Sh HISTORY
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The
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.Fn __builtin_object_size
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appeared in
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.Tn GCC 4.1 .
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.Sh CAVEATS
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This is a non-standard, compiler-specific extension.
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.Pp
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Note that currently the object size calculation pass is only done at -O1
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or above, meaning that this function always returns \-1 when the optimizer
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is off.
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.Pp
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There are some discussions about always doing the object size pass, but
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the issue is that without the optimization pass data sizes are not going
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to be correct.
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.Pp
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For that reason currently code fortification (size-checked replacement
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functions) is disabled when optimization is off.
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