1.\" Copyright (c) 1992, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" This code is derived from software developed by the Computer Systems 5.\" Engineering group at Lawrence Berkeley Laboratory under DARPA contract 6.\" BG 91-66 and contributed to Berkeley. 7.\" 8.\" Redistribution and use in source and binary forms, with or without 9.\" modification, are permitted provided that the following conditions 10.\" are met: 11.\" 1. Redistributions of source code must retain the above copyright 12.\" notice, this list of conditions and the following disclaimer. 13.\" 2. Redistributions in binary form must reproduce the above copyright 14.\" notice, this list of conditions and the following disclaimer in the 15.\" documentation and/or other materials provided with the distribution. 16.\" 3. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" @(#)kvm.3 8.1 (Berkeley) 6/4/93 33.\" $FreeBSD$ 34.\" 35.Dd April 30, 2016 36.Dt KVM 3 37.Os 38.Sh NAME 39.Nm kvm 40.Nd kernel memory interface 41.Sh LIBRARY 42.Lb libkvm 43.Sh DESCRIPTION 44The 45.Nm 46library provides a uniform interface for accessing kernel virtual memory 47images, including live systems and crash dumps. 48Access to live systems is via 49.Xr sysctl 3 50for some functions, and 51.Xr mem 4 52and 53.Xr kmem 4 54for other functions, 55while crash dumps can be examined via the core file generated by 56.Xr savecore 8 . 57The interface behaves similarly in both cases. 58Memory can be read and written, kernel symbol addresses can be 59looked up efficiently, and information about user processes can 60be gathered. 61.Pp 62The 63.Fn kvm_open 64function is first called to obtain a descriptor for all subsequent calls. 65.Sh COMPATIBILITY 66The kvm interface was first introduced in SunOS. 67A considerable 68number of programs have been developed that use this interface, 69making backward compatibility highly desirable. 70In most respects, the Sun kvm interface is consistent and clean. 71Accordingly, the generic portion of the interface (i.e., 72.Fn kvm_open , 73.Fn kvm_close , 74.Fn kvm_read , 75.Fn kvm_write , 76and 77.Fn kvm_nlist ) 78has been incorporated into the 79.Bx 80interface. 81Indeed, many kvm 82applications (i.e., debuggers and statistical monitors) use only 83this subset of the interface. 84.Pp 85The process interface was not kept. 86This is not a portability 87issue since any code that manipulates processes is inherently 88machine dependent. 89.Pp 90Finally, the Sun kvm error reporting semantics are poorly defined. 91The library can be configured either to print errors to 92.Dv stderr 93automatically, 94or to print no error messages at all. 95In the latter case, the nature of the error cannot be determined. 96To overcome this, the 97.Bx 98interface includes a 99routine, 100.Xr kvm_geterr 3 , 101to return (not print out) the error message 102corresponding to the most recent error condition on the 103given descriptor. 104.Sh CROSS DEBUGGING 105The 106.Nm 107library supports inspection of crash dumps from non-native kernels. 108Only a limited subset of the kvm interface is supported for these dumps. 109To inspect a crash dump of a non-native kernel, 110the caller must provide a 111.Fa resolver 112function when opening a descriptor via 113.Fn kvm_open2 . 114In addition, 115the kvm interface defines an integer type 116.Pq Vt kvaddr_t 117that is large enough to hold all valid addresses of all supported 118architectures. 119The interface also defines a new namelist structure type 120.Pq Vt "struct kvm_nlist" 121for use with 122.Fn kvm_nlist2 . 123To avoid address truncation issues, 124the caller should use 125.Fn kvm_nlist2 126and 127.Fn kvm_read2 128in place of 129.Fn kvm_nlist 130and 131.Fn kvm_read , 132respectively. 133Finally, only a limited subset of operations are supported for non-native 134crash dumps: 135.Fn kvm_close , 136.Fn kvm_geterr 137.Fn kvm_open2 , 138.Fn kvm_native , 139.Fn kvm_nlist2 , 140and 141.Fn kvm_read2 . 142.Sh SEE ALSO 143.Xr kvm_close 3 , 144.Xr kvm_getargv 3 , 145.Xr kvm_getenvv 3 , 146.Xr kvm_geterr 3 , 147.Xr kvm_getloadavg 3 , 148.Xr kvm_getprocs 3 , 149.Xr kvm_getswapinfo 3 , 150.Xr kvm_native 3 , 151.Xr kvm_nlist 3 , 152.Xr kvm_nlist2 3 , 153.Xr kvm_open 3 , 154.Xr kvm_open2 3 , 155.Xr kvm_openfiles 3 , 156.Xr kvm_read 3 , 157.Xr kvm_read2 3 , 158.Xr kvm_write 3 , 159.Xr sysctl 3 , 160.Xr kmem 4 , 161.Xr mem 4 162