1.\" $NetBSD: return_address.9,v 1.7 2014/03/18 18:20:40 riastradh Exp $ 2.\" 3.\" Copyright (c) 2009 The NetBSD Foundation, Inc. 4.\" All rights reserved. 5.\" 6.\" This code is derived from software contributed to The NetBSD Foundation 7.\" by David Young. 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.Dd May 5, 2010 31.Dt RETURN_ADDRESS 9 i386 32.Os 33.Sh NAME 34.Nm return_address 35.Nd return address from call stack 36.Sh SYNOPSIS 37.In i386/return.h 38.Ft void * 39.Fn return_address "unsigned int level" 40.Sh DESCRIPTION 41The 42.Fn return_address 43function evaluates to the first return address on the call stack 44if 45.Fa level 46equals 0, or else 47to the return address for the stack frame 48.Fa level 49frames down. 50.Pp 51This function is intended to be called by diagnostic code to record 52the call stack. 53.Pp 54A special fault handler stops 55.Fn return_address 56from crashing the kernel by examining a non-existent or corrupt stack 57frame. 58.Pp 59Kernel compilation options affect both the ability of 60.Fn return_address 61to locate return addresses on the stack, and the programmer's 62ability to interpret the addresses. 63The compiler may optimize away the stack frame pointers that 64.Fn return_address 65depends on. 66.Pp 67To use 68.Fn return_address 69effecively, try a kernel configuration option such as 70.Bd -literal 71makeoptions DEBUG="-g -fno-omit-frame-pointer \e 72 -fno-optimize-sibling-calls -O0" 73.Ed 74.Sh RETURN VALUES 75The 76.Fn return_address 77function returns the requested return address, or 78.Dv NULL 79if it cannot dissect the call stack. 80.Sh CODE REFERENCES 81.Pa sys/arch/i386/i386/copy.S , 82.Pa sys/arch/i386/include/return.h 83.Sh REFERENCES 84.Xr config 5 85.Sh HISTORY 86The 87.Fn return_address 88function first appeared in 89.Nx 6.0 . 90.Sh AUTHORS 91.An "David Young" Aq Mt dyoung@NetBSD.org 92