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get a quick snapshot of the kernel's symbol table including the symbols from any loaded modules (the symbols are all merged into one symbol table). Unlike like other implementations, this ksyms driver maps memory in the process memory space to store the snapshot at the time /dev/ksyms is opened. It also checks to see if the process has already a snapshot open and won't allow it to open /dev/ksyms it again until it closes first. This prevents kernel and process memory from being exhausted. Note that /dev/ksyms is used by the lockstat(1) command. Reviewed by: gallatin kib (freebsd-arch) Approved by: gnn (mentor)
159 lines
5.4 KiB
Groff
159 lines
5.4 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. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. 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. 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. 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. The
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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 formated 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. 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. 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 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. 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 of the kernel symbol information at that instant in time. Keeping the device open does not block the loading or unloading of kernel modules. 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. 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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.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
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.Aq sson@freebsd.org .
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