.\"	$NetBSD: return_address.9,v 1.7 2014/03/18 18:20:40 riastradh Exp $
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.\" Copyright (c) 2009 The NetBSD Foundation, Inc.
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.\" This code is derived from software contributed to The NetBSD Foundation
.\" by David Young.
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.Dd May 5, 2010
.Dt RETURN_ADDRESS 9 i386
.Os
.Sh NAME
.Nm return_address
.Nd return address from call stack
.Sh SYNOPSIS
.In i386/return.h
.Ft void *
.Fn return_address "unsigned int level"
.Sh DESCRIPTION
The
.Fn return_address
function evaluates to the first return address on the call stack
if
.Fa level
equals 0, or else
to the return address for the stack frame
.Fa level
frames down.
.Pp
This function is intended to be called by diagnostic code to record
the call stack.
.Pp
A special fault handler stops
.Fn return_address
from crashing the kernel by examining a non-existent or corrupt stack
frame.
.Pp
Kernel compilation options affect both the ability of
.Fn return_address
to locate return addresses on the stack, and the programmer's
ability to interpret the addresses.
The compiler may optimize away the stack frame pointers that
.Fn return_address
depends on.
.Pp
To use
.Fn return_address
effecively, try a kernel configuration option such as
.Bd -literal
makeoptions     DEBUG="-g -fno-omit-frame-pointer \e
		       -fno-optimize-sibling-calls -O0"
.Ed
.Sh RETURN VALUES
The
.Fn return_address
function returns the requested return address, or
.Dv NULL
if it cannot dissect the call stack.
.Sh CODE REFERENCES
.Pa sys/arch/i386/i386/copy.S ,
.Pa sys/arch/i386/include/return.h
.Sh REFERENCES
.Xr config 5
.Sh HISTORY
The
.Fn return_address
function first appeared in
.Nx 6.0 .
.Sh AUTHORS
.An "David Young" Aq Mt dyoung@NetBSD.org