i386: stand: Tiny clean up for `start_pxeboot.o`, NFC

i386: stand: Retire its own nfs.c, and switch to libsa/nfs.c. NFC

branches: 1.28.26;
Incrase pxeboot code size limit from 64k to 128k. Fixes PR kern/54560.
The start_pxe.S part was suggested by mlelstv.

Consistently use ${RELEASEDIR}/${RELEASEMACHINE} instead of
${RELEASEDIR}/${MACHINE} (Paul Ripke)

Add multiboot 2 support to x86 bootloaders

multiboot 2 is required to boot Xen on an EFI system.
This also require a kernel patch for properly discovering
the ACPI RSDP, which is available after 20190912, in
src/sys/arch/x86/acpi/acpi_machdep.c 1.26-1.28

There are a few missing bit in this multiboot 2 implementation
(which are unused by Xen):
- Header tags Address, Freambuffer, and Relocatable are ignored
- Tags APM and Network are not provided
- Tags ACPI old and ACP new are only provided for ACPI boot
- Tag boot device does not provides the subpart (BSD disklabel partition)

Notes:
- multiboot2 is disabled in dosboot, otherwise the binary
gets too big and build fails.
- in src/sys/arch/i386/stand/efiboot, consinit() is renamed
as efi_consinit() to avoid prototype conflicts in src/sys/sys/systm.h

branches: 1.25.2; 1.25.6;
- Disable MKSANITIZER
- Redo using NOPIE
- Add NORELRO

branches: 1.24.10; 1.24.16;
We'll define the kernel types for standalone code.

Define _KERNTYPES for things that need it.

branches: 1.22.6;
Reduce amount of -no-integrated-as on x86 as .code16 is now supported by
LLVM.

branches: 1.21.4; 1.21.14; 1.21.18;
Disable integrated assembler for files that use .code16 or .code32 for
now. Disable Clang completely for bootxx and netboot for now until the
size issue has been sorted out.

branches: 1.20.4; 1.20.6;
fix tyop in default flag definition

Invert the flag bits to control module loading: rename
LOADMODULES->NOMODULES and READBOOTCONF->NOBOOTCONF.
This way, the default value (0) wired into old bootxx_* and installed
to file systems remains valid and we avoid problems on partial updates.

On i386/amd64, define two flag bits in the boot parameters which control
whether modules are loaded and whether boot.cfg is evaluated, and
set both to "off" per default in the PXE bootloader.
Extend "installboot" to toggle the bits.
This way, pxeboot works with existing dhcp server setups (and as
described in the manpage) out of the box. Also, boot.cfg reading
involves a stat() call which is horribly inefficient with the
TFTP pseudo file system.

Remove extra trailing slash in ${S} path.

Convert more MACHINE tests to MACHINE_ARCH

branches: 1.15.2; 1.15.8;
disable PIE for boot code.

branches: 1.14.40; 1.14.44; 1.14.50;
Install pxeboot_ia32.bin as part of a "make release" on i386 and amd64.

branches: 1.13.2; 1.13.4;
Fix ypo. (hi abs!)

Noticed at #NetBSD-code.

Enable EPIA_HACK here too - http://mail-index.netbsd.org/port-i386/2006/08/18/0002.html

branches: 1.11.4; 1.11.6;
Use LDFLAGS (with $(CC) syntax) instead of appending to LD.

branches: 1.10.4;
- -mcpu=i386 is gone in GCC4
- we need -Wno-attributes (to avoid __packed__ warnings)
- use -Wno-pointer-sign
- remove some redundancy from pxeboot/Makefile

branches: 1.9.6; 1.9.8; 1.9.10; 1.9.14;
Take the console (etc) parameters from the patchable header, instead of
hard-coded constants.
Now the updated installboot can be used to modify the console and baud rate.

copy some settings from ../boot/Makefile.boot that let us try to load
64-bit kernels on amd64.

branches: 1.7.10; 1.7.12;
fix several related bugs that cause sysctl machdep.diskinfo to
lose when booted from pxeboot.
. make sure that i386_alldisks gets initialized even if
bios geometry information is not available in the bootinfo
. if i386_alldisks is not initialized, have sysctl return EOPNOTSUPP
. compile pxeboot with -DPASS_BIOSGEOM and I386_INCLUDE_DISK=yes
this may increase the size of pxeboot which is required to run
in 64k. However, it seems to be working ok on my system

branches: 1.6.2; 1.6.4;
Add -DSLOW to reduce the size of libz a bit.

use our own NFS fs implementation, which is smaller, does a better job
in error reporting and coexists with the TFTP fs

use NOMAN instead of MKMAN=no. noted by David Bonnafous on port-i386@

branches: 1.3.2; 1.3.4; 1.3.16;
* Rename the pxeboot binary from "pxeboot" to "pxeboot_ia32", since
there are other architectures (e.g. IA64) which also use PXE.
* Get the console right in pxeboot, from Andreas Gustafsson.
* Add a "com0" version of pxeboot, to address the same issue that
biosboot_com0 addresses.

Cleanup of i386 bootloader building:
* Add separate directories for the individual netboot ROMs and
always build them.
* Each bootloader Makefile explicitly specifies the start file
and link address it wishes to use.
* genprom becomes a proper host program.
* Make sure all generated files get cleaned up.
* Set BINDIR in Makefile.inc
* Add compressed image support to pxeboot.
* Make pxeboot use the default serial console speed (9600).

Add a PXE boot loader. PXE interface code is derived by code
written by Alfred Perlstein, Paul Saab, John Baldwin for FreeBSD.

Still needs some work, but this will load a kernel on a Soekris net4501.

Many thanks to Frank van der Linden and his simulator wizardry for
helping me debug the low-level startup code.

merge ktrace-lwp.

#include <lib/libsa/stand.h> rather than <stand.h> or "stand.h"

Use FS_OPS() macro.

branches: 1.2.2;
kick out mi libsa/netif.c references

branches: 1.1.2; 1.1.4; 1.1.16;
Add a PXE boot loader. PXE interface code is derived by code
written by Alfred Perlstein, Paul Saab, John Baldwin for FreeBSD.

Still needs some work, but this will load a kernel on a Soekris net4501.

Many thanks to Frank van der Linden and his simulator wizardry for
helping me debug the low-level startup code.

Retire varargs.h support. Move machine/stdarg.h logic into MI
sys/stdarg.h and expect compiler to provide proper builtins, defaulting
to the GCC interface. lint still has a special fallback.
Reduce abuse of _BSD_VA_LIST_ by defining __va_list by default and
derive va_list as required by standards.

Shut down the PXE network stack when we are done with it.

This fixes an issue where a CK804 nfe(4) would have a
byte-reversed MAC address after pxeboot(8).

Change about 4500 of the K&R function definitions to ANSI ones.
There are still about 1600 left, but they have ',' or /* ... */
in the actual variable definitions - which my awk script doesn't handle.
There are also many that need () -> (void).
(The script does handle misordered arguments.)

Remove all the __P() from sys (excluding sys/dist)
Diff checked with grep and MK1 eyeball.
i386 and amd64 GENERIC and sys still build.

branches: 1.7.6; 1.7.12;
Add support to pxeboot to allow the loading of modules. Changes to main.c
are taken from boot/boot2.c.

This allows an install to be started by running:
load tftp:miniroot.kmod
boot tftp:netbsd-GENERIC

Note that the change to dev_net.c to comment out the network shutdown,
suggests we need to hook the network shutdown in the the common exec code.
If the network is shutdown, it fails to reinitialise and so fails to load
the module.

branches: 1.6.2;
Remove clause 3 and 4 from TNF licenses

branches: 1.5.104; 1.5.106; 1.5.108;
-use our own netif layer
-call the pxe unload function only on close(), not on open() errors,
so we have a chance to retry
-remove some remaining references to NFS

cleanup:
-update comments
-remove remaining references to "bootparam"
-don't try to interpret extra arguments to net_open() - we
get only passed a NULL anyway (see devopen.c)

kick out RARP/bootparam - PXE uses BOOTP anyway

use our own NFS fs implementation, which is smaller, does a better job
in error reporting and coexists with the TFTP fs

branches: 1.1.2; 1.1.4; 1.1.16;
Need private copies of these files for now.

Remove all the __P() from sys (excluding sys/dist)
Diff checked with grep and MK1 eyeball.
i386 and amd64 GENERIC and sys still build.

branches: 1.1.2; 1.1.4; 1.1.16; 1.1.128; 1.1.136; 1.1.142;
Need private copies of these files for now.

kill extra whitespaces
reviewed by tsutsui@

bcopy -> memcpy

branches: 1.7.78; 1.7.86; 1.7.92;
merge ktrace-lwp.

#include <lib/libsa/stand.h> rather than <stand.h> or "stand.h"

Uhm - the last change broke everything but very simple setups.
(it only allowed to boot an nfs /netbsd automatically)
To make it work for people who can't tell the DHCP server to pass
the right kernel file to pxeboot, without losing flexibility for
people who can, do the following:
Use the filename given by the DHCP server if it contains a ":". A ":"
was already used to seperate filesystem and filename, so we don't
lose anything. Otoh, a path to pxeboot usually doesn't contain a ":",
so it should still work if we got the old pxeboot filename again.

So, on other platforms we use the BOOTP/DHCP file name for the boot program
and use a default file name of "netbsd" for the kernel. Do the same thing
here, as it hardly makes sense any other way.

branches: 1.3.2;
If we get passed a filename (from the command line or default "netbsd"),
pass it to the BOOTP server in the "filename" field.
(as the "netboot" bootROMs already did)
So the user can easily switch between different kernels/configurations.

branches: 1.2.2; 1.2.4; 1.2.16;
Pay attention to the file name provided by the DHCP server, using
it rather than the default of "netbsd" if it's in the reply.

Add a PXE boot loader. PXE interface code is derived by code
written by Alfred Perlstein, Paul Saab, John Baldwin for FreeBSD.

Still needs some work, but this will load a kernel on a Soekris net4501.

Many thanks to Frank van der Linden and his simulator wizardry for
helping me debug the low-level startup code.

Allow the dev= command when processing /boot.cfg file. This
addresses kern/59207

i386/pxeboot: Nix trailing whitespace.

No functional change intended.

Support baudrate in consdev command.

branches: 1.32.10;
Remove banner printing code from bootloaders, add it to libsa.

This harmonizes efiboot and the various x86 bootloaders to use shared
code for printing the banner. By friendly coincidence, it also adds
support for specifying 'banner=' in arm efiboot's boot.cfg, as on x86.

patch posted to tech-kern@ 2014/06/25 for review with minor changes
resulting from feedback.

move multiple copies of code for parsing boot.cfg file from sparc, i386
and zaurus into libsa/bootcfg.{h,c}. largely retained i386 parsing logic
in addition to keeping sparc dispatch function while remaining consistent
with boot.cfg(5).

previous sparc64 file format has been obsoleted but only used by boot
CDs distrib/sparc64/bootfs/boot.cfg has been updated to compensate.

exported names have been prefixed with either BOOTCFG_ or bootcfg_ as per
feedback from christos@

tested on amd64 & sparc64 but not zaurus.

branches: 1.30.10;
update help

branches: 1.29.4; 1.29.14;
Support userconf(4) command in boot(8)/boot.cfg(5) on i386/amd64.

From jmmv@, no objections seen in the proposed thread:

http://mail-index.netbsd.org/tech-kern/2009/01/22/msg004081.html

Honor bp_timeout even when X86_BP_FLAGS_NOBOOTCONF is set.
Or, in other words, bring back the 5 second countdown in pxeboot(8).

branches: 1.27.2;
MI libsa provides panic() and exit() functions, no need to provide our own.
As MI libsa exit() calls panic() with a "exit" message, don't use it if we
print our own farewell or have already panic()ed.

Bring the help command output from boot and pxeboot on par with their
code.

Add multiboot command. This lets us netboot the xen+dom0 kernel combo.

branches: 1.24.2; 1.24.4;
Invert the flag bits to control module loading: rename
LOADMODULES->NOMODULES and READBOOTCONF->NOBOOTCONF.
This way, the default value (0) wired into old bootxx_* and installed
to file systems remains valid and we avoid problems on partial updates.

On i386/amd64, define two flag bits in the boot parameters which control
whether modules are loaded and whether boot.cfg is evaluated, and
set both to "off" per default in the PXE bootloader.
Extend "installboot" to toggle the bits.
This way, pxeboot works with existing dhcp server setups (and as
described in the manpage) out of the box. Also, boot.cfg reading
involves a stat() call which is horribly inefficient with the
TFTP pseudo file system.

Shut down the PXE network stack when we are done with it.

This fixes an issue where a CK804 nfe(4) would have a
byte-reversed MAC address after pxeboot(8).

Don't commit the selected VBE mode until the loader is past the point of
no return; need to stick in text mode as long as possible since libsa does
not include a rasops library. While here, add the 'vesa' command to pxeboot
to mirror biosboot behaviour.

Fix 'boot -z' bogons.

Remove all the __P() from sys (excluding sys/dist)
Diff checked with grep and MK1 eyeball.
i386 and amd64 GENERIC and sys still build.

branches: 1.18.2;
don't clear the screen unconditionally. Now controlled by an option.
Thanks enami

add a boot.cfg option to clear the screen; default off. From Anon Ymous

Make pxeboot understand boot.cfg.

branches: 1.15.2;
The structure of our elf kernel is:

elf header/program headers/text/data/note/
section headers/symbol table/string table

We need to read the section headers first to find the offset of the note
and thus we requite backwards seek. The only reason we need to read the
note is to find the version of the kernel, and this seems not to be used
anywhere. We could potentially change the kernel ldscript to add the note
information in the program headers, but dealing with ldscripts is painful
and producing a more complex binary could break some dumb standalone loader.
So the simple solution is to just disable the note loading for floppies
which is what this patch does. If someone wants to fix it in a better way,
be my guest.

Change the x86 boot blocks so they don't include builder login and date.

For now, we include kernel revision as a way of allowing users to
notice that boot blocks have gotten very old, so the first line of the
printout looks like this (depending on the particular block):

>> NetBSD/x86 BIOS Boot, Revision 3.4 (from NetBSD 5.0)

This may be changed a bit pending feedback. (Some people think that
the kernel revision shouldn't be there at all, for example.)

Part of the project to assure that bit-identical sources produce
bit-identical release binaries.

branches: 1.13.2; 1.13.4;
Add support to pxeboot to allow the loading of modules. Changes to main.c
are taken from boot/boot2.c.

This allows an install to be started by running:
load tftp:miniroot.kmod
boot tftp:netbsd-GENERIC

Note that the change to dev_net.c to comment out the network shutdown,
suggests we need to hook the network shutdown in the the common exec code.
If the network is shutdown, it fails to reinitialise and so fails to load
the module.

branches: 1.12.6; 1.12.8; 1.12.10; 1.12.12;
Garbage collect the remaining parts of COMPAT_OLDBOOT. The boot loader
support has been removed at least 4 years ago and NetBSD 1.3 is ancient.

branches: 1.11.52; 1.11.58;
Pull the boot timeout for the boot_params header.
Allows it to be set to a very large number so the boot on Soekris systems
can be interrupted.

Take the console (etc) parameters from the patchable header, instead of
hard-coded constants.
Now the updated installboot can be used to modify the console and baud rate.

add "consdev" from ../boot.
make "quit" work like it does in ../boot
(ie. let us try again with a bootloader from a different device).

branches: 1.8.2;
De-__P().

Consistently pass 'int *' arguments to parsebootfile.

branches: 1.7.2; 1.7.16;
Backout previous, this file is not affected by kernel options.

Make sure to include opt_foo.h if a defflag option FOO is used.

kick out RARP/bootparam - PXE uses BOOTP anyway

branches: 1.4.2; 1.4.4; 1.4.16;
* Rename the pxeboot binary from "pxeboot" to "pxeboot_ia32", since
there are other architectures (e.g. IA64) which also use PXE.
* Get the console right in pxeboot, from Andreas Gustafsson.
* Add a "com0" version of pxeboot, to address the same issue that
biosboot_com0 addresses.

Pay attention to the file name provided by the DHCP server, using
it rather than the default of "netbsd" if it's in the reply.

* Remove a debug-breakpoint that is no longer needed.
* Move the pxe_init() call to when we open the virtual netif.
* Make sure to call pxe_fini() when we close the virtual netif.

Add a PXE boot loader. PXE interface code is derived by code
written by Alfred Perlstein, Paul Saab, John Baldwin for FreeBSD.

Still needs some work, but this will load a kernel on a Soekris net4501.

Many thanks to Frank van der Linden and his simulator wizardry for
helping me debug the low-level startup code.

Revert previous code move to accommodate relocation that does not fit.
Move pxe_command_buf declaration next to the code so
that it fits on the 16 bit relocation. It is in the text segment, but
it does not matter since it is mapped read-write.

branches: 1.17.12; 1.17.22; 1.17.26;
Shut down the PXE network stack when we are done with it.

This fixes an issue where a CK804 nfe(4) would have a
byte-reversed MAC address after pxeboot(8).

kill extra whitespaces
reviewed by tsutsui@

bcopy -> memcpy

Ansify function definitions w/o arguments. Generated with sed.

Change about 4500 of the K&R function definitions to ANSI ones.
There are still about 1600 left, but they have ',' or /* ... */
in the actual variable definitions - which my awk script doesn't handle.
There are also many that need () -> (void).
(The script does handle misordered arguments.)

branches: 1.12.2;
Replace time_t values in libsa sources with the following two types
to avoid unnecessary 64 bit ops which would make binaries larger:

satime_t (currently unsigned int):
numbers in seconds returned by the machine dependent getsecs() function
which are used to measure relative time

saseconds_t (currently int):
numbers in seconds used to specify timeout to network drivers

Per discussion on current-users.

merge christos-time_t

branches: 1.10.62; 1.10.64; 1.10.68; 1.10.76;
Remove a call, pxe_call(PXENV_UNLOAD_STACK), that causes Soekris
net45x1 boards to hang at boot---the call never returns. This
fixes PR/25174 for me.

branches: 1.9.4; 1.9.6; 1.9.8; 1.9.10; 1.9.12;
u_intN_t -> uintN_t

merge ktrace-lwp.

branches: 1.7.2;
Get rid off the ugly S_SIZE() macro which breaks the build now that
bcmp() is a macro, too.

branches: 1.6.2;
Kick out the netif layer from mi libsa and implement an own, smaller, one
(we really don't need to support multiple interfaces)
Also arrange things so that we are able to unload the PXE stacks only
when we are sure that we don't need them anymore. (To make this more
useful, a hook in exec() is needed.

Fix bug in readudp(): we have to return the correct length
of the received packet to the caller.
TFTP works now.

branches: 1.4.2; 1.4.8;
Change scan step from 16 to 2, when pxe_init() check the presence of PXE.
This change improve checking the presence of PXE.

branches: 1.3.4;
Don't ask bootp() to put a "PXEClient" Vendor Class Identifier option
in the DHCP request.

* Remove a debug-breakpoint that is no longer needed.
* Move the pxe_init() call to when we open the virtual netif.
* Make sure to call pxe_fini() when we close the virtual netif.

Add a PXE boot loader. PXE interface code is derived by code
written by Alfred Perlstein, Paul Saab, John Baldwin for FreeBSD.

Still needs some work, but this will load a kernel on a Soekris net4501.

Many thanks to Frank van der Linden and his simulator wizardry for
helping me debug the low-level startup code.

Fix typos in comments:
s/mulicast/multicast/
s/muticast/multicast/
s/muliplicator/multiplicator/
s/muti-precision/multi-precision/

branches: 1.8.32;
Fix typos.

s/recieve/receive/

branches: 1.6.60;
It just so happens we don't need -Wno-attributes if we
place __packed in the right place.

branches: 1.5.24; 1.5.32;
Convert many of the uses of __attribute__ to equivalent
__packed, __unused and __dead macros from cdefs.h

branches: 1.4.50; 1.4.56; 1.4.60; 1.4.64;
merge ktrace-lwp.

branches: 1.3.2;
Get rid off the ugly S_SIZE() macro which breaks the build now that
bcmp() is a macro, too.

Spell address with two d's. Inspired by similar changes in OpenBSD,
originating from Jonathon Gray and forwarded by jmc@openbsd.

branches: 1.1.2; 1.1.4; 1.1.16; 1.1.22;
Add a PXE boot loader. PXE interface code is derived by code
written by Alfred Perlstein, Paul Saab, John Baldwin for FreeBSD.

Still needs some work, but this will load a kernel on a Soekris net4501.

Many thanks to Frank van der Linden and his simulator wizardry for
helping me debug the low-level startup code.

Revert previous code move to accommodate relocation that does not fit.
Move pxe_command_buf declaration next to the code so
that it fits on the 16 bit relocation. It is in the text segment, but
it does not matter since it is mapped read-write.

Move an instruction above .code16 so that it produces an R_386_32 instead
of an R_386_16 relocation, which is truncated to fit. XXX: untested.

branches: 1.3.142; 1.3.152; 1.3.158;
Change all .S files to use .code16 and .code32
Support 32bit addresses >64k as valid on bios calls.
Move stack for dosboot and biosboot to >64 so stack doesn't hit data.
Use disk sector number passed by mbr code to select default partition
(the mbr code doesn't do this yet).
NB only biosboot and dosboot have been tested so far.
(changes approved by christos and fvdl)

branches: 1.2.2; 1.2.8;
Add (missing)pushl/popl for %edi in ENTRY(pxecall_pxenv).

branches: 1.1.4;
Add a PXE boot loader. PXE interface code is derived by code
written by Alfred Perlstein, Paul Saab, John Baldwin for FreeBSD.

Still needs some work, but this will load a kernel on a Soekris net4501.

Many thanks to Frank van der Linden and his simulator wizardry for
helping me debug the low-level startup code.

Shut down the PXE network stack when we are done with it.

This fixes an issue where a CK804 nfe(4) would have a
byte-reversed MAC address after pxeboot(8).

branches: 1.1.108; 1.1.122;
Kick out the netif layer from mi libsa and implement an own, smaller, one
(we really don't need to support multiple interfaces)
Also arrange things so that we are able to unload the PXE stacks only
when we are sure that we don't need them anymore. (To make this more
useful, a hook in exec() is needed.

branches: 1.1.2; 1.1.4; 1.1.16;
Add a PXE boot loader. PXE interface code is derived by code
written by Alfred Perlstein, Paul Saab, John Baldwin for FreeBSD.

Still needs some work, but this will load a kernel on a Soekris net4501.

Many thanks to Frank van der Linden and his simulator wizardry for
helping me debug the low-level startup code.

Incrase pxeboot code size limit from 64k to 128k. Fixes PR kern/54560.
The start_pxe.S part was suggested by mlelstv.

branches: 1.6.48; 1.6.56; 1.6.60;
Automatically adjust pxeboot(8) stack based on the end of .bss, like is already
done in biosboot.S for boot(8).
(The heap location will need to be adjusted if pxeboot expands much more.)

branches: 1.5.2;
MI libsa provides panic() and exit() functions, no need to provide our own.
As MI libsa exit() calls panic() with a "exit" message, don't use it if we
print our own farewell or have already panic()ed.

branches: 1.4.94; 1.4.102;
Take the console (etc) parameters from the patchable header, instead of
hard-coded constants.
Now the updated installboot can be used to modify the console and baud rate.

branches: 1.3.12;
Rename bootparams to boot_params for consistency.

branches: 1.2.4;
Use real_to_prot (etc) from stand/lib.
Add a patchable header for boot parameters (eg console type).

Move start_pxe.S to a more sensible place

i386/stand: Document NFSv3 support to {efi,pxe}boot/version

x86/boot: fill in a bunch of missed changes and bump some versions.

missed features included:
- support for partition labels
- recursive labels inside RAID partitions
- booting a directory with kernel and modules
- multiBoot 2
- "root" command that changes default root
- "vesa" command to control graphical modes
- bi-endian support in disklabel, RAID and UFS
- fixes for buggy ACPI implementations
- fix PXE device path type
- fixes for buggy ACPI implementations
- serial console support with raw I/O accessors
- ASCII art

XXX: perhaps we could pullup some of these as minor version to release
branches but it seems extreme for a largely cosmetic issue. the
version across releases has a different build ID, so you can
already tell the difference between versions that changed.

branches: 1.3.118;
Update the version numbers following commit, and make them all identical.

branches: 1.2.104; 1.2.108; 1.2.110; 1.2.112; 1.2.114;
Change all .S files to use .code16 and .code32
Support 32bit addresses >64k as valid on bios calls.
Move stack for dosboot and biosboot to >64 so stack doesn't hit data.
Use disk sector number passed by mbr code to select default partition
(the mbr code doesn't do this yet).
NB only biosboot and dosboot have been tested so far.
(changes approved by christos and fvdl)

branches: 1.1.2; 1.1.4; 1.1.16;
Add a PXE boot loader. PXE interface code is derived by code
written by Alfred Perlstein, Paul Saab, John Baldwin for FreeBSD.

Still needs some work, but this will load a kernel on a Soekris net4501.

Many thanks to Frank van der Linden and his simulator wizardry for
helping me debug the low-level startup code.