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.\" $FreeBSD$ 29.\" 30.Dd August 2, 2017 31.Dt KSYMS 4 32.Os 33.Sh NAME 34.Nm ksyms 35.Nd kernel symbol table interface 36.Sh SYNOPSIS 37.Cd "device ksyms" 38.Sh DESCRIPTION 39The 40.Pa /dev/ksyms 41character device provides a read-only interface to a snapshot of the kernel 42symbol table. 43The in-kernel symbol manager is designed to be able to handle 44many types of symbols tables, however, only 45.Xr elf 5 46symbol tables are supported by this device. 47The ELF format image contains two 48sections: a symbol table and a corresponding string table. 49.Bl -tag -width indent -offset indent 50.It Dv Symbol Table 51The SYMTAB section contains the symbol table entries present in the current 52running kernel, including the symbol table entries of any loaded modules. 53The symbols are ordered by the kernel module load time starting with kernel file 54symbols first, followed by the first loaded module's symbols and so on. 55.It Dv String Table 56The STRTAB section contains the symbol name strings from the kernel and any 57loaded modules that the symbol table entries reference. 58.El 59.Pp 60Elf formatted symbol table data read from the 61.Pa /dev/ksyms 62file represents the state of the kernel at the time when the device is opened. 63Since 64.Pa /dev/ksyms 65has no text or data, most of the fields are initialized to NULL. 66The 67.Nm 68driver does not block the loading or unloading of modules into the kernel 69while the 70.Pa /dev/ksyms 71file is open but may contain stale data. 72.Sh FILES 73.Bl -tag -width /dev/ksymsX 74.It Pa /dev/ksyms 75.El 76.Sh ERRORS 77An 78.Xr open 2 79of 80.Pa /dev/ksyms 81will fail if: 82.Bl -tag -width Er 83.It Bq Er EBUSY 84The device is already open. 85A process must close 86.Pa /dev/ksyms 87before it can be opened again. 88.It Bq Er ENOMEM 89There is a resource shortage in the kernel. 90.It Bq Er ENXIO 91The driver was unsuccessful in creating a snapshot of the kernel symbol 92table. 93This may occur if the kernel was in the process of loading or 94unloading a module. 95.El 96.Sh SEE ALSO 97.Xr nlist 3 , 98.Xr elf 5 , 99.Xr kldload 8 100.Sh HISTORY 101A 102.Nm 103device exists in many different operating systems. 104This implementation is similar in function to the Solaris and NetBSD 105.Nm 106driver. 107.Pp 108The 109.Nm 110driver first appeared in 111.Fx 8.0 112to support 113.Xr lockstat 1 . 114.Sh AUTHORS 115The 116.Nm 117driver was written by 118.An Stacey Son Aq Mt sson@FreeBSD.org . 119.Sh BUGS 120Because files can be dynamically linked into the kernel at any time the symbol 121information can vary. 122When you open the 123.Pa /dev/ksyms 124file, you have access to an ELF image which represents a snapshot of the state 125of the kernel symbol information at that instant in time. 126Keeping the device open does not block the loading or unloading of kernel 127modules. 128To get a new snapshot you must close and re-open the device. 129.Pp 130A process is only allowed to open the 131.Pa /dev/ksyms 132file once at a time. 133The process must close the 134.Pa /dev/ksyms 135before it is allowed to open it again. 136