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.Dd February 5, 2020 33.Dt KVM 3 34.Os 35.Sh NAME 36.Nm kvm 37.Nd kernel memory interface 38.Sh LIBRARY 39.Lb libkvm 40.Sh DESCRIPTION 41The 42.Nm 43library provides a uniform interface for accessing kernel virtual memory 44images, including live systems and crash dumps. 45Access to live systems is via 46.Xr sysctl 3 47for some functions, and 48.Xr mem 4 49and 50.Xr kmem 4 51for other functions, 52while crash dumps can be examined via the core file generated by 53.Xr savecore 8 . 54The interface behaves similarly in both cases. 55Memory can be read and written, kernel symbol addresses can be 56looked up efficiently, and information about user processes can 57be gathered. 58.Pp 59The 60.Fn kvm_open 61function is first called to obtain a descriptor for all subsequent calls. 62.Sh COMPATIBILITY 63The kvm interface was first introduced in SunOS. 64A considerable 65number of programs have been developed that use this interface, 66making backward compatibility highly desirable. 67In most respects, the Sun kvm interface is consistent and clean. 68Accordingly, the generic portion of the interface (i.e., 69.Fn kvm_open , 70.Fn kvm_close , 71.Fn kvm_read , 72.Fn kvm_write , 73and 74.Fn kvm_nlist ) 75has been incorporated into the 76.Bx 77interface. 78Indeed, many kvm 79applications (i.e., debuggers and statistical monitors) use only 80this subset of the interface. 81.Pp 82The process interface was not kept. 83This is not a portability 84issue since any code that manipulates processes is inherently 85machine dependent. 86.Pp 87Finally, the Sun kvm error reporting semantics are poorly defined. 88The library can be configured either to print errors to 89.Dv stderr 90automatically, 91or to print no error messages at all. 92In the latter case, the nature of the error cannot be determined. 93To overcome this, the 94.Bx 95interface includes a 96routine, 97.Xr kvm_geterr 3 , 98to return (not print out) the error message 99corresponding to the most recent error condition on the 100given descriptor. 101.Sh CROSS DEBUGGING 102The 103.Nm 104library supports inspection of crash dumps from non-native kernels. 105Only a limited subset of the kvm interface is supported for these dumps. 106To inspect a crash dump of a non-native kernel, 107the caller must provide a 108.Fa resolver 109function when opening a descriptor via 110.Fn kvm_open2 . 111In addition, 112the kvm interface defines an integer type 113.Pq Vt kvaddr_t 114that is large enough to hold all valid addresses of all supported 115architectures. 116The interface also defines a new namelist structure type 117.Pq Vt "struct kvm_nlist" 118for use with 119.Fn kvm_nlist2 . 120To avoid address truncation issues, 121the caller should use 122.Fn kvm_nlist2 123and 124.Fn kvm_read2 125in place of 126.Fn kvm_nlist 127and 128.Fn kvm_read , 129respectively. 130Finally, only a limited subset of operations are supported for non-native 131crash dumps: 132.Fn kvm_close , 133.Fn kvm_geterr , 134.Fn kvm_kerndisp , 135.Fn kvm_open2 , 136.Fn kvm_native , 137.Fn kvm_nlist2 , 138and 139.Fn kvm_read2 . 140.Sh SEE ALSO 141.Xr kvm_close 3 , 142.Xr kvm_getargv 3 , 143.Xr kvm_getenvv 3 , 144.Xr kvm_geterr 3 , 145.Xr kvm_getloadavg 3 , 146.Xr kvm_getprocs 3 , 147.Xr kvm_getswapinfo 3 , 148.Xr kvm_kerndisp 3 , 149.Xr kvm_native 3 , 150.Xr kvm_nlist 3 , 151.Xr kvm_nlist2 3 , 152.Xr kvm_open 3 , 153.Xr kvm_open2 3 , 154.Xr kvm_openfiles 3 , 155.Xr kvm_read 3 , 156.Xr kvm_read2 3 , 157.Xr kvm_write 3 , 158.Xr sysctl 3 , 159.Xr kmem 4 , 160.Xr mem 4 161.Sh HISTORY 162The 163.Fn kvm_native , 164.Fn kvm_nlist2 , 165.Fn kvm_open2 , 166and 167.Fn kvm_read2 168functions first appeared in 169.Fx 11.0 . 170