.\" $OpenBSD: ksyms.4,v 1.14 2019/01/25 00:19:26 millert Exp $
.\"
.\" Copyright (c) 1998 Todd C. Miller <millert@openbsd.org>
.\"
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.Dd $Mdocdate: January 25 2019 $
.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.