Init process not found when booting with ramdisk as rootfs - linux

Question

I'm trying to setup a ramdisk for a setup I have with AT91SAM9261 and 2.6.30 kernel.
I know you would say why don't I use initramfs? I will use also that one, as of now I would like to check if I can boot with a ramdisk as rootfs.
I have already a root fs running fine on this system in jffs2 format.
I used below tutorial:
http://www.ibm.com/developerworks/library/l-initrd/
So I created the ramdisk directly on the embedded target, with 4MB size.
I used "dd" and "mkefs" and the ramdisk image works fine if I mount it as loop when rootfs is my jffs2.
I can browse mount_point and do stuff inside.
The content was created according to the section "Manually building initial RAM disk" in the above link.
In /dev I placed null and console, in /bin I copied busybox and created the links.
I set the execute attribute to init script as well, which works fine when I run it here (as loop device with jffs2 as rootfs)
In my kernel config I enabled ramdisk support as follows:
CONFIG_BLK_DEV_INITRD=y
CONFIG_RD_GZIP=y
CONFIG_BLK_DEV_RAM=y
CONFIG_BLK_DEV_RAM_COUNT=16
CONFIG_BLK_DEV_RAM_SIZE=4096
Using tftp I download the ramdisk image to 0x21100000.
At 0x20008000 I have the kernel uncompressed and at 0x22000000 the zImage copied.
However, I'm not able to boot successfully the system as it hangs when checking init process.
As I mentioned, I checked several times that my init can be executed,
I also used in the bootargs init=/bin/busybox or other scripts/binaries to check if any can be used as init.
Command line I use now:
bootargs=64M console=ttyS0,115200 root=/dev/ram0 rw
initrd=0x21100000,4194304 init=/init
For some I set ownership to "nobody" just to check if it makes any difference.
As it can be seen in the log output the ramdisk is mounted, but init fails.
It gives a warning to check the ext2 image, which I did before copying it and I have no error reported.
The tftp server is on Windows7. I though I might have some incompatibility if I copy the ramdisk image from linux to Windows then do tftp from Windows server.
So I copied the image again from Windows to linux, mounted it and checked if the FS reports any error and scripts can be executed - everything looks normal.
So I do have all files in place, attributes set, ramdisk is reported as being mounted ok as rootfs, but init cannot be found.
Uncompressing Linux......................................................................................................... done, booting the kernel.
Linux version 2.6.30-olimex (mishu#KubuntuVM) (gcc version 4.3.3 (Sourcery G++ Lite 2009q1-203) ) #1 Mon Dec 29 13:53:54 CET 2014
CPU: ARM926EJ-S [41069265] revision 5 (ARMv5TEJ), cr=00053177
CPU: VIVT data cache, VIVT instruction cache
Machine: Olimex SAM9-L9261
Ignoring unrecognised tag 0x54410008
Memory policy: ECC disabled, Data cache writeback
Clocks: CPU 198 MHz, master 99 MHz, main 18.432 MHz
Built 1 zonelists in Zone order, mobility grouping on. Total pages: 16256
Kernel command line: 64M console=ttyS0,115200 root=/dev/ram0 rw initrd=0x21100000,4194304 init=/init
NR_IRQS:192
AT91: 96 gpio irqs in 3 banks
PID hash table entries: 256 (order: 8, 1024 bytes)
Console: colour dummy device 80x30
console [ttyS0] enabled
Dentry cache hash table entries: 8192 (order: 3, 32768 bytes)
Inode-cache hash table entries: 4096 (order: 2, 16384 bytes)
Memory: 64MB = 64MB total
Memory: 57384KB available (2924K code, 246K data, 132K init, 0K highmem)
Calibrating delay loop... 99.12 BogoMIPS (lpj=495616)
Mount-cache hash table entries: 512
CPU: Testing write buffer coherency: ok
net_namespace: 716 bytes
NET: Registered protocol family 16
AT91: Power Management
AT91: Starting after user reset
bio: create slab <bio-0> at 0
SCSI subsystem initialized
usbcore: registered new interface driver usbfs
usbcore: registered new interface driver hub
usbcore: registered new device driver usb
NET: Registered protocol family 2
IP route cache hash table entries: 1024 (order: 0, 4096 bytes)
TCP established hash table entries: 2048 (order: 2, 16384 bytes)
TCP bind hash table entries: 2048 (order: 1, 8192 bytes)
TCP: Hash tables configured (established 2048 bind 2048)
TCP reno registered
NET: Registered protocol family 1
Trying to unpack rootfs image as initramfs...
rootfs image is not initramfs (junk in compressed archive); looks like an initrd
Freeing initrd memory: 4096K
NetWinder Floating Point Emulator V0.97 (double precision)
JFFS2 version 2.2. (NAND) (SUMMARY) © 2001-2006 Red Hat, Inc.
msgmni has been set to 120
io scheduler noop registered
io scheduler anticipatory registered (default)
atmel_lcdfb atmel_lcdfb.0: backlight control is not available
atmel_lcdfb atmel_lcdfb.0: 225KiB frame buffer at 23140000 (mapped at ffc00000)
Console: switching to colour frame buffer device 40x30
atmel_lcdfb atmel_lcdfb.0: fb0: Atmel LCDC at 0x00600000 (mapped at c4866000), irq 21
atmel_usart.0: ttyS0 at MMIO 0xfefff200 (irq = 1) is a ATMEL_SERIAL
atmel_usart.1: ttyS1 at MMIO 0xfffb0000 (irq = 6) is a ATMEL_SERIAL
brd: module loaded
loop: module loaded
ssc ssc.1: Atmel SSC device at 0xc4878000 (irq 15)
Driver 'sd' needs updating - please use bus_type methods
dm9000 Ethernet Driver, V1.31
eth0 (dm9000): not using net_device_ops yet
eth0: dm9000e at c486a000,c486e044 IRQ 107 MAC: 3a:1f:34:08:54:64 (chip)
NAND device: Manufacturer ID: 0xec, Chip ID: 0xdc (Samsung NAND 512MiB 3,3V 8-bit)
Scanning device for bad blocks
Bad eraseblock 1478 at 0x00000b8c0000
Creating 2 MTD partitions on "atmel_nand":
0x000000000000-0x000000040000 : "Partition 1"
0x000000040000-0x000020000000 : "Partition 2"
atmel_spi atmel_spi.0: Atmel SPI Controller at 0xfffc8000 (irq 12)
ohci_hcd: USB 1.1 'Open' Host Controller (OHCI) Driver
at91_ohci at91_ohci: AT91 OHCI
at91_ohci at91_ohci: new USB bus registered, assigned bus number 1
at91_ohci at91_ohci: irq 20, io mem 0x00500000
usb usb1: New USB device found, idVendor=1d6b, idProduct=0001
usb usb1: New USB device strings: Mfr=3, Product=2, SerialNumber=1
usb usb1: Product: AT91 OHCI
usb usb1: Manufacturer: Linux 2.6.30-olimex ohci_hcd
usb usb1: SerialNumber: at91
usb usb1: configuration #1 chosen from 1 choice
hub 1-0:1.0: USB hub found
hub 1-0:1.0: 2 ports detected
Initializing USB Mass Storage driver...
usbcore: registered new interface driver usb-storage
USB Mass Storage support registered.
udc: at91_udc version 3 May 2006
g_serial gadget: Gadget Serial v2.4
g_serial gadget: g_serial ready
mice: PS/2 mouse device common for all mice
input: gpio-keys as /class/input/input0
ads7846 spi0.2: touchscreen, irq 29
input: ADS784x Touchscreen as /class/input/input1
rtc-at91sam9 at91_rtt.0: rtc core: registered at91_rtt as rtc0
IRQ 1/rtc0: IRQF_DISABLED is not guaranteed on shared IRQs
rtc-at91sam9 at91_rtt.0: rtc0: SET TIME!
i2c /dev entries driver
i2c-gpio: probe of i2c-gpio failed with error -16
Registered led device: led1
Registered led device: led2
Registered led device: led3
Advanced Linux Sound Architecture Driver Version 1.0.20.
at73c213 spi0.3: at73c213: supported bitrate is 48500 (64 divider)
usb 1-1: new full speed USB device using at91_ohci and address 2
usb 1-1: New USB device found, idVendor=0457, idProduct=0151
usb 1-1: New USB device strings: Mfr=0, Product=2, SerialNumber=3
usb 1-1: Product: USB Mass Storage Device
usb 1-1: SerialNumber: 8d54bd8186b42c
usb 1-1: configuration #1 chosen from 1 choice
scsi0 : SCSI emulation for USB Mass Storage devices
ALSA device list:
#0: SAM9-L9261 external DAC on irq 15
TCP cubic registered
NET: Registered protocol family 17
RPC: Registered udp transport module.
RPC: Registered tcp transport module.
rtc-at91sam9 at91_rtt.0: hctosys: unable to read the hardware clock
RAMDISK: ext2 filesystem found at block 0
RAMDISK: Loading 4096KiB [1 disk] into ram disk... done.
EXT2-fs warning: mounting unchecked fs, running e2fsck is recommended
VFS: Mounted root (ext2 filesystem) on device 1:0.
Freeing init memory: 132K
Failed to execute /init. Attempting defaults...
Kernel panic - not syncing: No init found. Try passing init= option to kernel.
[<c002f414>] (unwind_backtrace+0x0/0xdc) from [<c025bd34>] (panic+0x40/0x110)
[<c025bd34>] (panic+0x40/0x110) from [<c0029500>] (init_post+0xd0/0xf8)
[<c0029500>] (init_post+0xd0/0xf8) from [<c00085a0>] (kernel_init+0xbc/0xe4)
[<c00085a0>] (kernel_init+0xbc/0xe4) from [<c0041998>] (do_exit+0x0/0x5ac)
[<c0041998>] (do_exit+0x0/0x5ac) from [<00000001>] (0x1)
I plan to rebuild busybox and try again, but as my current ramdisk image works when I mount it as loop I don't have too much confidence it will change something.
I'm out of ideas. I've been trying the whole day to get this working.
Help is much appreciated.
Thanks.

Answer 1

Missing libraries were the root cause for the non-executable init placed on the ramdisk.
Using chroot turned out to be extremely useful. With this issue I learned how to use chroot and simulate a jail.
Another trick was to use user_debug=31 in the command line so that the kernel will output a message saying that the file is not found.
It looks like the "file not found" does not really point to a missing file, but to a failure to read the file system due to busybox not executing properly (missing libraries).
In parallel I have compiled dynamically the busybox 1.20.02 for my arm architecture and the ramdisk worked properly (without libs).
This user_debug=31 turned out to be again useful when I compiled and ran busybox, as it was also failing after mounting the ramdisk, but it thrown out an "undefined exception" which led me to a wrong "arch" value used for compiling busybox. After changing it everything was fine.