.\"
.\" SPDX-License-Identifier: BSD-3-Clause
.\"
.\" Copyright (c) 2025	Juniper Networks, Inc.
.\"
.Dd October 29, 2025
.Dt KEXEC_LOAD 2
.Os
.Sh NAME
.Nm kexec_load
.Nd prepare new kernel to reboot into
.Sh SYNOPSIS
.Lb libc
.In sys/kexec.h
.Ft int
.Fn kexec_load "uint64_t entry" "unsigned long count" \
 "struct kexec_segment *segments" "unsigned long flags"
.Sh DESCRIPTION
The
.Fn kexec_load
system call loads a new kernel that can be executed later by
.Xr reboot 2 .
Subsequent calls will replace previously loaded images.
.Pp
The
.Fa flags
argument is a bitmask of flags that control the operation of the call.
This argument is present for compatibility with Linux, although it is currently
unused and must be 0.
.Pp
The
.Fa entry
argument is the physical address of the entry point of the new kernel image.
.Pp
The
.Fa count
argument is the number of segments in the image, currently limited to 16.
A value of 0 will unload the currently staged image, if one exists, without
staging a new image.
.Pp
The
.Fa segments
argument is an array of
.Fa count
members of the following structure:
.Bd -literal -offset indent
struct  kexec_segment {
    void *buf;
    size_t bufsz;
    vm_paddr_t mem;
    vm_size_t memsz;
};
.Ed
.Pp
The
.Va buf
and
.Va bufsz
members specify a memory region in the caller's address space containing the
source of the segment.
The
.Va mem
and
.Va memsz
members specify the target physical region of the segment.
.Va bufsz
must be less than or equal to
.Va memsz ,
and
.Va mem
and
.Va memsz
must be page aligned.
The region covered by
.Va mem
must be in the list covered by the
.Va vm.phys_segs
sysctl.
.Pp
The
.Fn kexec_load
system call stages the kernel image in safe memory along with all
machine-dependent image data until
.Xr reboot 2
is called with the
.Va RB_KEXEC
flag to load the image and execute the new kernel.
.Sh RETURN VALUES
The
.Fn kexec_load
system call returns 0 on success.
On failure, -1 is returned, and
.Va errno
is set to indicate the error.
On success any previously loaded image is unloaded and replaced with the new
image.
On failure, the previously loaded image is unchanged.
.Sh ERRORS
The following errors may be returned:
.Bl -tag -width Er
.It Bq Er EINVAL
Too many segments in image.
.It Bq Er EINVAL
The value of
.Va bufsz
is larger than
.Va memsz
in one or more segments.
.It Bq Er EINVAL
Machine-dependent load error.
.It Bq Er EBUSY
Another
.Fn kexec_load
call is in progress.
.Sh HISTORY
The
.Nm
system call appeared in
.Fx 16.0 .