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 April 5, 2009 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 IOCTLS 73The 74.Xr ioctl 2 75command codes below are defined in 76.Aq Pa sys/ksyms.h . 77.Pp 78The (third) argument to the 79.Xr ioctl 2 80should be a pointer to the type indicated. 81.Bl -tag -width indent -offset indent 82.It Dv KIOCGSIZE (size_t) 83Returns the total size of the current symbol table. 84This can be used when allocating a buffer to make a copy of 85the kernel symbol table. 86.It Dv KIOCGADDR (void *) 87Returns the address of the kernel symbol table mapped in 88the process memory. 89.El 90.Sh FILES 91.Bl -tag -width /dev/ksymsX 92.It Pa /dev/ksyms 93.El 94.Sh ERRORS 95An 96.Xr open 2 97of 98.Pa /dev/ksyms 99will fail if: 100.Bl -tag -width Er 101.It Bq Er EBUSY 102The device is already open. 103A process must close 104.Pa /dev/ksyms 105before it can be opened again. 106.It Bq Er ENOMEM 107There is a resource shortage in the kernel. 108.It Bq Er ENXIO 109The driver was unsuccessful in creating a snapshot of the kernel symbol 110table. 111This may occur if the kernel was in the process of loading or 112unloading a module. 113.El 114.Sh SEE ALSO 115.Xr ioctl 2 , 116.Xr nlist 3 , 117.Xr elf 5 , 118.Xr kldload 8 119.Sh HISTORY 120A 121.Nm 122device exists in many different operating systems. 123This implementation is similar in function to the Solaris and NetBSD 124.Nm 125driver. 126.Pp 127The 128.Nm 129driver first appeared in 130.Fx 8.0 131to support 132.Xr lockstat 1 . 133.Sh AUTHORS 134The 135.Nm 136driver was written by 137.An Stacey Son Aq Mt sson@FreeBSD.org . 138.Sh BUGS 139Because files can be dynamically linked into the kernel at any time the symbol 140information can vary. 141When you open the 142.Pa /dev/ksyms 143file, you have access to an ELF image which represents a snapshot of the state 144of the kernel symbol information at that instant in time. 145Keeping the device open does not block the loading or unloading of kernel 146modules. 147To get a new snapshot you must close and re-open the device. 148.Pp 149A process is only allowed to open the 150.Pa /dev/ksyms 151file once at a time. 152The process must close the 153.Pa /dev/ksyms 154before it is allowed to open it again. 155.Pp 156The 157.Nm 158driver uses the calling process' memory address space to store the snapshot. 159.Xr ioctl 2 160can be used to get the memory address where the symbol table is stored to 161save kernel memory. 162.Xr mmap 2 163may also be used but it will map it to another address. 164