1.\" Copyright (c) 2008-2009 Stacey Son <sson@FreeBSD.org> 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. Neither the name of the University nor the names of its contributors 13.\" may be used to endorse or promote products derived from this software 14.\" without specific prior written permission. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 28.Dd August 2, 2017 29.Dt KSYMS 4 30.Os 31.Sh NAME 32.Nm ksyms 33.Nd kernel symbol table interface 34.Sh SYNOPSIS 35.Cd "device ksyms" 36.Sh DESCRIPTION 37The 38.Pa /dev/ksyms 39character device provides a read-only interface to a snapshot of the kernel 40symbol table. 41The in-kernel symbol manager is designed to be able to handle 42many types of symbols tables, however, only 43.Xr elf 5 44symbol tables are supported by this device. 45The ELF format image contains two 46sections: a symbol table and a corresponding string table. 47.Bl -tag -width indent -offset indent 48.It Dv Symbol Table 49The SYMTAB section contains the symbol table entries present in the current 50running kernel, including the symbol table entries of any loaded modules. 51The symbols are ordered by the kernel module load time starting with kernel file 52symbols first, followed by the first loaded module's symbols and so on. 53.It Dv String Table 54The STRTAB section contains the symbol name strings from the kernel and any 55loaded modules that the symbol table entries reference. 56.El 57.Pp 58Elf formatted symbol table data read from the 59.Pa /dev/ksyms 60file represents the state of the kernel at the time when the device is opened. 61Since 62.Pa /dev/ksyms 63has no text or data, most of the fields are initialized to NULL. 64The 65.Nm 66driver does not block the loading or unloading of modules into the kernel 67while the 68.Pa /dev/ksyms 69file is open but may contain stale data. 70.Sh FILES 71.Bl -tag -width /dev/ksymsX 72.It Pa /dev/ksyms 73.El 74.Sh ERRORS 75An 76.Xr open 2 77of 78.Pa /dev/ksyms 79will fail if: 80.Bl -tag -width Er 81.It Bq Er EBUSY 82The device is already open. 83A process must close 84.Pa /dev/ksyms 85before it can be opened again. 86.It Bq Er ENOMEM 87There is a resource shortage in the kernel. 88.It Bq Er ENXIO 89The driver was unsuccessful in creating a snapshot of the kernel symbol 90table. 91This may occur if the kernel was in the process of loading or 92unloading a module. 93.El 94.Sh SEE ALSO 95.Xr nlist 3 , 96.Xr elf 5 , 97.Xr kldload 8 98.Sh HISTORY 99A 100.Nm 101device exists in many different operating systems. 102This implementation is similar in function to the Solaris and NetBSD 103.Nm 104driver. 105.Pp 106The 107.Nm 108driver first appeared in 109.Fx 8.0 110to support 111.Xr lockstat 1 . 112.Sh AUTHORS 113The 114.Nm 115driver was written by 116.An Stacey Son Aq Mt sson@FreeBSD.org . 117.Sh BUGS 118Because files can be dynamically linked into the kernel at any time the symbol 119information can vary. 120When you open the 121.Pa /dev/ksyms 122file, you have access to an ELF image which represents a snapshot of the state 123of the kernel symbol information at that instant in time. 124Keeping the device open does not block the loading or unloading of kernel 125modules. 126To get a new snapshot you must close and re-open the device. 127.Pp 128A process is only allowed to open the 129.Pa /dev/ksyms 130file once at a time. 131The process must close the 132.Pa /dev/ksyms 133before it is allowed to open it again. 134