kernelは2.6.xがだめぽいので、2.4.xにしてbuildして立ち上げてみたら起動しました。相変わらずuserlandはなしなのでinitでこけますが。

+**Warning** FLASH configuration checksum error or invalid key
Use 'fconfig -i' to [re]initialize database
DP83902A - eeprom ESA: 00:02:cb:01:eb:1a
... waiting for BOOTP information
Ethernet eth0: MAC address 00:02:cb:01:eb:1a
IP: 192.168.1.16/255.255.255.0, Gateway: 192.168.1.1
Default server: 0.0.0.0

RedBoot(tm) bootstrap and debug environment [ROM]
Non-certified release, version UNKNOWN - built 21:28:57, Apr 11 2004

Platform: Akizuki H8/3068 Network micom (H8/300H)
Copyright (C) 2000, 2001, 2002, Red Hat, Inc.

RAM: 0x00400000-0x005f4000, [0x00400000-0x005e1000] available
FLASH: 0x00000000 - 0x00080000, 8 blocks of 0x00010000 bytes each.
RedBoot> ip_address -h 192.168.1.17
IP: 192.168.1.16/255.255.255.0, Gateway: 192.168.1.1
Default server: 192.168.1.17
RedBoot> load -r -b 0x400000 aki3068net-image.bin
Using default protocol (TFTP)
Raw file loaded 0x00400000-0x004bd4e7, assumed entry at 0x00400000
RedBoot> exec -c "console=ttySC1,38400" 0x400000
Now booting linux kernel:
Entry Address 0x00400000
Cmdline : console=ttySC1,38400
Linux version 2.4.31-uc0 (root@KURO-BOXHG) (gcc version 3.3.6) #4 Thu Jan 12 02:21:56 JST 2006

uClinux H8/300H
Target Hardware: AE-3068
H8/300 series support by Yoshinori Sato <ysato@users.sourceforge.jp>
Flat model support (C) 1998,1999 Kenneth Albanowski, D. Jeff Dionne
On node 0 totalpages: 1536
zone(0): 0 pages.
zone(1): 1536 pages.
zone(2): 0 pages.
Kernel command line: console=ttySC1,38400
virtual vector at 0x00fffd20
Calibrating delay loop... 3.25 BogoMIPS
Memory available: 1092k/1184k RAM, 0k/0k ROM (681k kernel code, 175k data)
Dentry cache hash table entries: 1024 (order: 1, 8192 bytes)
Inode cache hash table entries: 512 (order: 0, 4096 bytes)
Mount cache hash table entries: 512 (order: 0, 4096 bytes)
Buffer cache hash table entries: 1024 (order: 0, 4096 bytes)
Page-cache hash table entries: 2048 (order: 1, 8192 bytes)
POSIX conformance testing by UNIFIX
Linux NET4.0 for Linux 2.4
Based upon Swansea University Computer Society NET3.039
Initializing RT netlink socket
Starting kswapd
SuperH SCI(F) driver initialized
ttySC0 at 0x00ffffb0 is a SCI
ttySC1 at 0x00ffffb8 is a SCI
ttySC2 at 0x00ffffc0 is a SCI
ne.c:v1.10 9/23/94 Donald Becker (becker@scyld.com)
Last modified Nov 1, 2000 by Paul Gortmaker
NE*000 ethercard probe at 0x200000:<4>eth0: interrupt from stopped card
00 02 cb 01 eb 1a
eth0: NE1000 found at 0x200000, using IRQ 17.
Blkmem copyright 1998,1999 D. Jeff Dionne
Blkmem copyright 1998 Kenneth Albanowski
Blkmem 1 disk images:
0: 4D7E7C-4DAA7B [VIRTUAL 4D7E7C-4DAA7B] (RO) <ROMFS>
NET4: Linux TCP/IP 1.0 for NET4.0
IP Protocols: ICMP, UDP, TCP
IP: routing cache hash table of 512 buckets, 4Kbytes
TCP: Hash tables configured (established 512 bind 1024)
VFS: Mounted root (romfs filesystem) readonly.
Freeing unused kernel memory: 24k freed (0x4b4000 - 0x4b9000)
Kernel panic: No init found. Try passing init= option to kernel.

さっき良く見たらuClinux-h8のメーリングリストでしっかり昨年PowerPC用のcross tool chainのバイナリ一式が公開されてるではないですが、一生懸命release fileの方しかみてなくて知らなかった。でもまあパッチとかがしっかり反映されているおかげで自前でもこしらえることができましたが。uClinuxのビルドではそれ以外にcross環境ではまることがあって...それは後日明らかに