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.\" $FreeBSD: release/9.1.0/usr.sbin/kgzip/kgzip.8 140442 2005-01-18 20:02:45Z ru $
.\"
.Dd July 19, 1999
.Dt KGZIP 8
.Os
.Sh NAME
.Nm kgzip
.Nd compress a kernel
.Sh SYNOPSIS
.Nm
.Op Fl cv
.Op Fl f Ar format
.Op Fl l Ar loader
.Op Fl o Ar output
.Ar file
.Sh DESCRIPTION
The
.Nm
utility compresses a kernel or some other bootable binary.
Operation
is in two phases as follows:
.Bl -enum
.It
A load image of the executable file is built which omits all but
the
.Sq text
and
.Sq data
segments.
This image is compressed using
.Xr gzip 1
and output as data in relocatable object format.
.It
The object file is linked with a special self-hosting loader, producing
an executable suitable for booting with either the second- or
third-level bootstraps.
.El
.Pp
Supported object formats are 32-bit ELF and a.out ZMAGIC.
.Pp
If the
.Ar file
operand has a
.Sq .o
suffix, input is assumed to be for the link phase, and the first phase
is omitted.
.Pp
The options are:
.Bl -tag -width Fl
.It Fl c
Omit the link phase.
.It Fl v
Display object file information.
.It Fl f Ar format
Use
.Ar format
as the output format, where
.Ar format
is
.Sq aout
or
.Sq elf .
The default format is ELF.
.It Fl l Ar loader
Link
.Ar loader
as the loader.
.It Fl o Ar output
Name the output file
.Ar output .
The default is to use the input name with the suffix
.Sq .o
(for relocatables) or
.Sq .kgz
(for executables).
.El
.Sh NOTES
Global variables equivalent to the following are defined in the output:
.Bd -literal
struct kgz_hdr {
    char	ident[4];	/* identification: "KGZ" */
    uint32_t	dload;		/* decoded image load address */
    uint32_t	dsize;		/* decoded image size */
    uint32_t	isize;		/* image size in memory */
    uint32_t	entry;		/* entry point */
    uint32_t	nsize;		/* encoded image size */
} kgz;

uint8_t kgz_ndata[];		/* encoded data */
.Ed
.Pp
The encoded data is simply
.Xr gzip 1
output: a header (with no optional fields); compressed data; and 32-bit
CRC and size values.
.Sh FILES
.Bl -tag -width /usr/lib/kgzldr.o -compact
.It Pa /usr/lib/kgzldr.o
The default loader
.El
.Sh EXIT STATUS
.Ex -std
.Sh SEE ALSO
.Xr gzip 1 ,
.Xr ld 1 ,
.Xr a.out 5 ,
.Xr elf 5 ,
.Xr boot 8 ,
.Xr loader 8
.Sh AUTHORS
.An Robert Nordier Aq rnordier@FreeBSD.org .
.Sh BUGS
As symbols are lost, the usefulness of this utility for compressing
kernels is limited to situations where
.Xr loader 8
cannot be used; otherwise the preferred method of compressing a kernel
is simply to
.Xr gzip 1
it.