Document that the 7f911abe
"Add support to libkvm for reading vmcores
from other architectures." added functions appeared first in FreeBSD 11.0.
277 lines
6.8 KiB
Groff
277 lines
6.8 KiB
Groff
.\" Copyright (c) 1992, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" This code is derived from software developed by the Computer Systems
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.\" Engineering group at Lawrence Berkeley Laboratory under DARPA contract
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.\" BG 91-66 and contributed to Berkeley.
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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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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)kvm_open.3 8.3 (Berkeley) 4/19/94
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.\" $FreeBSD$
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.\"
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.Dd March 20, 2017
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.Dt KVM_OPEN 3
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.Os
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.Sh NAME
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.Nm kvm_open ,
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.Nm kvm_open2 ,
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.Nm kvm_openfiles ,
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.Nm kvm_close
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.Nd initialize kernel virtual memory access
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.Sh LIBRARY
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.Lb libkvm
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.Sh SYNOPSIS
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.In fcntl.h
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.In kvm.h
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.Ft kvm_t *
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.Fn kvm_open "const char *execfile" "const char *corefile" "const char *swapfile" "int flags" "const char *errstr"
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.Ft kvm_t *
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.Fo kvm_open2
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.Fa "const char *execfile"
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.Fa "const char *corefile"
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.Fa "int flags"
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.Fa "char *errbuf"
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.Fa "int (*resolver)(const char *name, kvaddr_t *addr)"
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.Fc
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.Ft kvm_t *
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.Fn kvm_openfiles "const char *execfile" "const char *corefile" "const char *swapfile" "int flags" "char *errbuf"
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.Ft int
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.Fn kvm_close "kvm_t *kd"
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.Sh DESCRIPTION
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The functions
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.Fn kvm_open ,
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.Fn kvm_open2 ,
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and
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.Fn kvm_openfiles
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return a descriptor used to access kernel virtual memory
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via the
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.Xr kvm 3
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library routines.
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Both active kernels and crash dumps are accessible
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through this interface.
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.Pp
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The
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.Fa execfile
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argument is the executable image of the kernel being examined.
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This file must contain a symbol table.
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If this argument is
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.Dv NULL ,
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the currently running system is assumed,
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as determined from
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.Xr getbootfile 3 .
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.Pp
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The
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.Fa corefile
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argument is the kernel memory device file.
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It can be either
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.Pa /dev/mem
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or a crash dump core generated by
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.Xr savecore 8 .
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If
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.Fa corefile
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is
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.Dv NULL ,
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the default indicated by
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.Dv _PATH_MEM
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from
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.In paths.h
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is used.
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It can also be set to a special value
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.Pa /dev/null
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by utilities like
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.Xr ps 1
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that do not directly access kernel memory.
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.Pp
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The
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.Fa swapfile
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argument is currently unused.
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.Pp
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The
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.Fa flags
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argument indicates read/write access as in
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.Xr open 2
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and applies only to the core file.
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Only
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.Dv O_RDONLY ,
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.Dv O_WRONLY ,
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and
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.Dv O_RDWR
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are permitted.
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.Pp
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The
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.Nm kvm
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library provides two different error reporting mechanisms.
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One provides backward compatibility with the SunOS kvm library, while the
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other provides an improved error reporting framework.
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The mechanism used by a descriptor is determined by the function used to
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open the descriptor.
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.Pp
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The
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.Fn kvm_open
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function is the Sun kvm compatible open call.
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Here, the
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.Fa errstr
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argument indicates how errors should be handled.
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If it is
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.Dv NULL ,
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no errors are reported and the application cannot know the
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specific nature of the failed kvm call.
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If it is not
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.Dv NULL ,
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errors are printed to
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.Dv stderr
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with
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.Fa errstr
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prepended to the message, as in
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.Xr perror 3 .
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Normally, the name of the program is used here.
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The string is assumed to persist at least until the corresponding
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.Fn kvm_close
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call.
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.Pp
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The
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.Fn kvm_open2
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and
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.Fn kvm_openfiles
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functions provide
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.Bx
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style error reporting.
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Here, error messages are not printed out by the library.
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Instead, the application obtains the error message
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corresponding to the most recent kvm library call using
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.Fn kvm_geterr
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(see
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.Xr kvm_geterr 3 ) .
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The results are undefined if the most recent kvm call did not produce
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an error.
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Since
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.Fn kvm_geterr
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requires a kvm descriptor, but the open routines return
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.Dv NULL
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on failure,
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.Fn kvm_geterr
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cannot be used to get the error message if open fails.
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Thus,
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.Fn kvm_open2
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and
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.Fn kvm_openfiles
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will place any error message in the
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.Fa errbuf
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argument.
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This buffer should be _POSIX2_LINE_MAX characters large (from
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<limits.h>).
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.Pp
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The
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.Fa resolver
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argument points to a function used by the
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.Nm kvm
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library to map symbol names to kernel virtual addresses.
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When the
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.Fa resolver
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function is called,
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.Fa name
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specifies the requested symbol name.
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If the function is able to resolve the name to an address,
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the address should be set in
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.Fa addr
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and the function should return zero.
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If the function is not able to resolve the name to an address,
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it should return a non-zero value.
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When opening a native kernel image,
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.Fa resolver
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may be set to
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.Dv NULL
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to use an internal function to resolve symbol names.
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Non-native kernel images
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.Pq such as when cross-debugging a crash dump
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require a valid
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.Fa resolver .
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.Sh RETURN VALUES
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The
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.Fn kvm_open ,
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.Fn kvm_open2 ,
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and
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.Fn kvm_openfiles
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functions return a descriptor to be used
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in all subsequent kvm library calls.
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The library is fully re-entrant.
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On failure,
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.Dv NULL
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is returned, in which case
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.Fn kvm_open2
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and
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.Fn kvm_openfiles
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write the error message into
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.Fa errbuf .
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.Pp
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.Rv -std kvm_close
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.Sh ERRORS
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The
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.Fn kvm_close
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function may fail and set the global variable
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.Va errno
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for any of the errors specified for
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.Xr close 2 .
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.Pp
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The
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.Fn kvm_close
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function may also fail and set
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.Va errno
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if:
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.Bl -tag -width Er
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.It Bq Er EINVAL
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The value passed via
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.Fa kd
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was
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.Dv NULL .
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.El
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.Sh SEE ALSO
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.Xr close 2 ,
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.Xr open 2 ,
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.Xr kvm 3 ,
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.Xr kvm_getargv 3 ,
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.Xr kvm_getenvv 3 ,
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.Xr kvm_geterr 3 ,
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.Xr kvm_getprocs 3 ,
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.Xr kvm_native 3 ,
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.Xr kvm_nlist 3 ,
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.Xr kvm_read 3 ,
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.Xr kvm_write 3 ,
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.Xr kmem 4 ,
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.Xr mem 4
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.Sh BUGS
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There should not be three open calls.
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The ill-defined error semantics
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of the Sun library and the desire to have a backward-compatible library
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for
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.Bx
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left little choice.
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.Sh HISTORY
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The
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.Fn kvm_open2
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function first appeared in
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.Fx 11.0 .
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