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.\" $OpenBSD: ksyms.4,v 1.15 2022/03/31 17:27:21 naddy Exp $
.\"
.\" Copyright (c) 1998 Todd C. Miller <millert@openbsd.org>
.\"
.\" Permission to use, copy, modify, and distribute this software for any
.\" purpose with or without fee is hereby granted, provided that the above
.\" copyright notice and this permission notice appear in all copies.
.\"
.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
.\"
.Dd $Mdocdate: March 31 2022 $
.Dt KSYMS 4
.Os
.Sh NAME
.Nm ksyms
.Nd kernel symbol table device
.Sh SYNOPSIS
.Cd "pseudo-device ksyms" Op Ar count
.Sh DESCRIPTION
The
.Pa /dev/ksyms
device masquerades as an
.Ox
native executable with the symbols from the running kernel as its symbol segment.
Use of
.Pa /dev/ksyms
requires that the boot loader preserve the kernel symbols and place
them at the end of the kernel's address space.
.Pp
The
.Pa /dev/ksyms
device is used to look up the symbol table name list from the running
kernel.
Because it represents the running kernel, it is guaranteed
to always be up to date even if the kernel file has been changed (or
is even non-existent).
It is most useful when used in conjunction with
.Xr nlist 3
or the
.Xr kvm 3
routines (note that
.Xr kvm_open 3
and
.Xr kvm_openfiles 3
will try
.Pa /dev/ksyms
automatically if the first parameter to them is the
.Dv NULL
pointer).
.Sh FILES
.Bl -tag -width Pa -compact
.It Pa /dev/ksyms
.El
.Sh ERRORS
An open of
.Pa /dev/ksyms
will fail if:
.Bl -tag -width Er
.It Bq Er EPERM
An open was attempted with write permissions.
.It Bq Er ENXIO
No kernel symbols were saved by the boot loader (usually because
they were removed with
.Xr strip 1 ) ,
or the kernel has been compiled without a
.Dq pseudo-device ksyms
line.
.El
.Sh SEE ALSO
.Xr kvm 3 ,
.Xr nlist 3
.Sh HISTORY
The
.Pa /dev/ksyms
device appeared in
.Ox 2.4 .
.Sh BUGS
It is not possible to
.Xr mmap 2
.Pa /dev/ksyms
because the boot loader does not load the symbol table onto a page
boundary (so it is not page aligned).
If all the boot loaders were fixed,
.Xr mmap 2
support would be trivial.
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