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.\" 34.Dd February 5, 2020 35.Dt KVM 3 36.Os 37.Sh NAME 38.Nm kvm 39.Nd kernel memory interface 40.Sh LIBRARY 41.Lb libkvm 42.Sh DESCRIPTION 43The 44.Nm 45library provides a uniform interface for accessing kernel virtual memory 46images, including live systems and crash dumps. 47Access to live systems is via 48.Xr sysctl 3 49for some functions, and 50.Xr mem 4 51and 52.Xr kmem 4 53for other functions, 54while crash dumps can be examined via the core file generated by 55.Xr savecore 8 . 56The interface behaves similarly in both cases. 57Memory can be read and written, kernel symbol addresses can be 58looked up efficiently, and information about user processes can 59be gathered. 60.Pp 61The 62.Fn kvm_open 63function is first called to obtain a descriptor for all subsequent calls. 64.Sh COMPATIBILITY 65The kvm interface was first introduced in SunOS. 66A considerable 67number of programs have been developed that use this interface, 68making backward compatibility highly desirable. 69In most respects, the Sun kvm interface is consistent and clean. 70Accordingly, the generic portion of the interface (i.e., 71.Fn kvm_open , 72.Fn kvm_close , 73.Fn kvm_read , 74.Fn kvm_write , 75and 76.Fn kvm_nlist ) 77has been incorporated into the 78.Bx 79interface. 80Indeed, many kvm 81applications (i.e., debuggers and statistical monitors) use only 82this subset of the interface. 83.Pp 84The process interface was not kept. 85This is not a portability 86issue since any code that manipulates processes is inherently 87machine dependent. 88.Pp 89Finally, the Sun kvm error reporting semantics are poorly defined. 90The library can be configured either to print errors to 91.Dv stderr 92automatically, 93or to print no error messages at all. 94In the latter case, the nature of the error cannot be determined. 95To overcome this, the 96.Bx 97interface includes a 98routine, 99.Xr kvm_geterr 3 , 100to return (not print out) the error message 101corresponding to the most recent error condition on the 102given descriptor. 103.Sh CROSS DEBUGGING 104The 105.Nm 106library supports inspection of crash dumps from non-native kernels. 107Only a limited subset of the kvm interface is supported for these dumps. 108To inspect a crash dump of a non-native kernel, 109the caller must provide a 110.Fa resolver 111function when opening a descriptor via 112.Fn kvm_open2 . 113In addition, 114the kvm interface defines an integer type 115.Pq Vt kvaddr_t 116that is large enough to hold all valid addresses of all supported 117architectures. 118The interface also defines a new namelist structure type 119.Pq Vt "struct kvm_nlist" 120for use with 121.Fn kvm_nlist2 . 122To avoid address truncation issues, 123the caller should use 124.Fn kvm_nlist2 125and 126.Fn kvm_read2 127in place of 128.Fn kvm_nlist 129and 130.Fn kvm_read , 131respectively. 132Finally, only a limited subset of operations are supported for non-native 133crash dumps: 134.Fn kvm_close , 135.Fn kvm_geterr , 136.Fn kvm_kerndisp , 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_kerndisp 3 , 151.Xr kvm_native 3 , 152.Xr kvm_nlist 3 , 153.Xr kvm_nlist2 3 , 154.Xr kvm_open 3 , 155.Xr kvm_open2 3 , 156.Xr kvm_openfiles 3 , 157.Xr kvm_read 3 , 158.Xr kvm_read2 3 , 159.Xr kvm_write 3 , 160.Xr sysctl 3 , 161.Xr kmem 4 , 162.Xr mem 4 163.Sh HISTORY 164The 165.Fn kvm_native , 166.Fn kvm_nlist2 , 167.Fn kvm_open2 , 168and 169.Fn kvm_read2 170functions first appeared in 171.Fx 11.0 . 172