164 lines
5.1 KiB
Groff
164 lines
5.1 KiB
Groff
.\" Copyright (c) 2008-2009 Stacey Son <sson@FreeBSD.org>
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd April 5, 2009
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.Dt KSYMS 4
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.Os
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.Sh NAME
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.Nm ksyms
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.Nd kernel symbol table interface
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.Sh SYNOPSIS
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.Cd "device ksyms"
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.Sh DESCRIPTION
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The
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.Pa /dev/ksyms
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character device provides a read-only interface to a snapshot of the kernel
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symbol table.
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The in-kernel symbol manager is designed to be able to handle
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many types of symbols tables, however, only
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.Xr elf 5
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symbol tables are supported by this device.
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The ELF format image contains two
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sections: a symbol table and a corresponding string table.
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.Bl -tag -width indent -offset indent
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.It Dv Symbol Table
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The SYMTAB section contains the symbol table entries present in the current
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running kernel, including the symbol table entries of any loaded modules.
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The symbols are ordered by the kernel module load time starting with kernel file
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symbols first, followed by the first loaded module's symbols and so on.
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.It Dv String Table
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The STRTAB section contains the symbol name strings from the kernel and any
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loaded modules that the symbol table entries reference.
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.El
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.Pp
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Elf formatted symbol table data read from the
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.Pa /dev/ksyms
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file represents the state of the kernel at the time when the device is opened.
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Since
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.Pa /dev/ksyms
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has no text or data, most of the fields are initialized to NULL.
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The
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.Nm
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driver does not block the loading or unloading of modules into the kernel
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while the
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.Pa /dev/ksyms
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file is open but may contain stale data.
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.Sh IOCTLS
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The
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.Xr ioctl 2
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command codes below are defined in
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.Aq Pa sys/ksyms.h .
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.Pp
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The (third) argument to the
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.Xr ioctl 2
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should be a pointer to the type indicated.
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.Bl -tag -width indent -offset indent
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.It Dv KIOCGSIZE (size_t)
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Returns the total size of the current symbol table.
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This can be used when allocating a buffer to make a copy of
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the kernel symbol table.
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.It Dv KIOCGADDR (void *)
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Returns the address of the kernel symbol table mapped in
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the process memory.
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.El
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.Sh FILES
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.Bl -tag -width /dev/ksymsX
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.It Pa /dev/ksyms
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.El
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.Sh ERRORS
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An
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.Xr open 2
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of
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.Pa /dev/ksyms
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will fail if:
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.Bl -tag -width Er
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.It Bq Er EBUSY
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The device is already open.
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A process must close
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.Pa /dev/ksyms
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before it can be opened again.
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.It Bq Er ENOMEM
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There is a resource shortage in the kernel.
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.It Bq Er ENXIO
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The driver was unsuccessful in creating a snapshot of the kernel symbol
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table.
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This may occur if the kernel was in the process of loading or
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unloading a module.
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.El
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.Sh SEE ALSO
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.Xr ioctl 2 ,
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.Xr nlist 3 ,
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.Xr elf 5 ,
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.Xr kldload 8
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.Sh HISTORY
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A
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.Nm
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device exists in many different operating systems.
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This implementation is similar in function to the Solaris and NetBSD
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.Nm
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driver.
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.Pp
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The
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.Nm
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driver first appeared in
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.Fx 8.0
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to support
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.Xr lockstat 1 .
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.Sh AUTHORS
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The
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.Nm
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driver was written by
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.An Stacey Son Aq Mt sson@FreeBSD.org .
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.Sh BUGS
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Because files can be dynamically linked into the kernel at any time the symbol
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information can vary.
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When you open the
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.Pa /dev/ksyms
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file, you have access to an ELF image which represents a snapshot of the state
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of the kernel symbol information at that instant in time.
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Keeping the device open does not block the loading or unloading of kernel
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modules.
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To get a new snapshot you must close and re-open the device.
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.Pp
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A process is only allowed to open the
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.Pa /dev/ksyms
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file once at a time.
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The process must close the
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.Pa /dev/ksyms
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before it is allowed to open it again.
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.Pp
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The
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.Nm
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driver uses the calling process' memory address space to store the snapshot.
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.Xr ioctl 2
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can be used to get the memory address where the symbol table is stored to
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save kernel memory.
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.Xr mmap 2
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may also be used but it will map it to another address.
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