0cd475f86b
Document that the 7f911abe "Add support to libkvm for reading vmcores
from other architectures." added functions appeared first in FreeBSD 11.0.
173 lines
5.1 KiB
Groff
173 lines
5.1 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.3 8.1 (Berkeley) 6/4/93
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.\" $FreeBSD$
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.\"
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.Dd February 5, 2020
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.Dt KVM 3
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.Os
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.Sh NAME
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.Nm kvm
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.Nd kernel memory interface
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.Sh LIBRARY
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.Lb libkvm
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.Sh DESCRIPTION
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The
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.Nm
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library provides a uniform interface for accessing kernel virtual memory
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images, including live systems and crash dumps.
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Access to live systems is via
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.Xr sysctl 3
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for some functions, and
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.Xr mem 4
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and
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.Xr kmem 4
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for other functions,
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while crash dumps can be examined via the core file generated by
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.Xr savecore 8 .
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The interface behaves similarly in both cases.
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Memory can be read and written, kernel symbol addresses can be
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looked up efficiently, and information about user processes can
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be gathered.
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.Pp
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The
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.Fn kvm_open
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function is first called to obtain a descriptor for all subsequent calls.
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.Sh COMPATIBILITY
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The kvm interface was first introduced in SunOS.
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A considerable
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number of programs have been developed that use this interface,
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making backward compatibility highly desirable.
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In most respects, the Sun kvm interface is consistent and clean.
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Accordingly, the generic portion of the interface (i.e.,
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.Fn kvm_open ,
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.Fn kvm_close ,
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.Fn kvm_read ,
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.Fn kvm_write ,
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and
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.Fn kvm_nlist )
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has been incorporated into the
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.Bx
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interface.
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Indeed, many kvm
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applications (i.e., debuggers and statistical monitors) use only
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this subset of the interface.
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.Pp
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The process interface was not kept.
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This is not a portability
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issue since any code that manipulates processes is inherently
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machine dependent.
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.Pp
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Finally, the Sun kvm error reporting semantics are poorly defined.
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The library can be configured either to print errors to
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.Dv stderr
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automatically,
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or to print no error messages at all.
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In the latter case, the nature of the error cannot be determined.
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To overcome this, the
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.Bx
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interface includes a
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routine,
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.Xr kvm_geterr 3 ,
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to return (not print out) the error message
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corresponding to the most recent error condition on the
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given descriptor.
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.Sh CROSS DEBUGGING
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The
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.Nm
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library supports inspection of crash dumps from non-native kernels.
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Only a limited subset of the kvm interface is supported for these dumps.
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To inspect a crash dump of a non-native kernel,
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the caller must provide a
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.Fa resolver
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function when opening a descriptor via
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.Fn kvm_open2 .
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In addition,
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the kvm interface defines an integer type
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.Pq Vt kvaddr_t
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that is large enough to hold all valid addresses of all supported
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architectures.
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The interface also defines a new namelist structure type
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.Pq Vt "struct kvm_nlist"
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for use with
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.Fn kvm_nlist2 .
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To avoid address truncation issues,
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the caller should use
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.Fn kvm_nlist2
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and
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.Fn kvm_read2
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in place of
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.Fn kvm_nlist
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and
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.Fn kvm_read ,
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respectively.
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Finally, only a limited subset of operations are supported for non-native
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crash dumps:
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.Fn kvm_close ,
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.Fn kvm_geterr ,
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.Fn kvm_kerndisp ,
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.Fn kvm_open2 ,
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.Fn kvm_native ,
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.Fn kvm_nlist2 ,
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and
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.Fn kvm_read2 .
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.Sh SEE ALSO
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.Xr kvm_close 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_getloadavg 3 ,
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.Xr kvm_getprocs 3 ,
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.Xr kvm_getswapinfo 3 ,
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.Xr kvm_kerndisp 3 ,
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.Xr kvm_native 3 ,
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.Xr kvm_nlist 3 ,
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.Xr kvm_nlist2 3 ,
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.Xr kvm_open 3 ,
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.Xr kvm_open2 3 ,
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.Xr kvm_openfiles 3 ,
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.Xr kvm_read 3 ,
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.Xr kvm_read2 3 ,
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.Xr kvm_write 3 ,
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.Xr sysctl 3 ,
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.Xr kmem 4 ,
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.Xr mem 4
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.Sh HISTORY
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The
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.Fn kvm_native ,
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.Fn kvm_nlist2 ,
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.Fn kvm_open2 ,
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and
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.Fn kvm_read2
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functions first appeared in
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.Fx 11.0 .
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