.\" $OpenBSD: ksyms.4,v 1.1 1998/08/25 02:50:56 millert Exp $
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.\" Copyright (c) 1998 Todd C. Miller <Todd.Miller@courtesan.com>
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.Dd August 24, 1998
.Dt KSYMS 4
.Os OpenBSD
.Sh NAME
.Nm ksyms
.Nd kernel symbol table device
.Sh SYNOPSIS
.Sy pseudo-device Nm ksyms 1
.Sh DESCRIPTION
The
.Nm ksyms
device masquerades as an
.Em a.out
executable with the symbols from the running kernel as its
symbol segment.  Use of
.Nm
requires that the boot loader preserve the kernel symbols and place
them at the end of the kernel's address space.  Any port that is capable
of using the
.Em DDB
debugger does this, even if
.Em DDB
is not configured into the kernel.
.Pp
The
.Nm
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 conjuction with
.Xr nlist 3
or the
.Xr kvm 3
routines (note that
.Xr kvm_open 3
and
.Xr kvm_openfiles 3
will try
.Nm
automatically if the first parameter to them is the
.Dv NULL
pointer).
.Sh ERRORS
device will 
An open of
.Nm
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).
.El
.Sh SEE ALSO
.Xr kvm 3 ,
.Xr nlist 3
.Sh HISTORY
The
.Nm
device appeared in
.Ox 2.4 .
.Sh BUGS
It is not possible to
.Xr mmap 2
.Nm
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.