Run program on boot with initramfs

Question

I'm running uClinux on a SmartFusion2 as part of a University team building a small cube satellite. However, I'm not super experienced in Linux kernel, and this issue has had me stumped for a few days. I'm trying to get the SmartFusion to run a program on bootup. Currently, the only .uImage that does this is the test 'hello' file. I'm trying to recreate the process for another program, but am running into some difficulties.

in my hello directory I have the following files: hello.busybox, hello.kernel.M2S, help.txt, hello.uImage, Makefile, hello.initramfs, hello (directory)

in the hello subdirectory (projects/hello/hello):

hello (executable), hello.c, hello.gdb, hello.h, hello.o, Makefile

to try and get the uImage to boot and run a different program, I made a copy of my projects/hello/hello directory and renamed it 'goodbye', with a few minor changes int the .h and .c files for testing purposes. Now I'm trying to get the executable 'hello' in projects/hello/goodbye to run on boot.

My initramfs file originally looked like this:

# This is a very simple, default initramfs

dir /dev 0755 0 0
nod /dev/console 0600 0 0 c 5 1
nod /dev/tty 0666 0 0 c 5 0
nod /dev/null 0600 0 0 c 1 3
nod /dev/mem 0600 0 0 c 1 1
nod /dev/kmem 0600 0 0 c 1 2
nod /dev/zero 0600 0 0 c 1 5
nod /dev/random 0600 0 0 c 1 8
nod /dev/urandom 0600 0 0 c 1 9

dir /dev/pts 0755 0 0
nod /dev/ptmx 0666 0 0 c 5 2

nod /dev/ttyS0 0666 0 0 c 4 64
nod /dev/ttyS1 0666 0 0 c 4 65
nod /dev/ttyS2 0666 0 0 c 4 66
nod /dev/ttyS3 0666 0 0 c 4 67
nod /dev/ttyS4 0666 0 0 c 4 68
nod /dev/ttyS5 0666 0 0 c 4 69

dir /bin 755 0 0
dir /proc 755 0 0

file /bin/hello ${INSTALL_ROOT}/projects/${SAMPLE}/hello/hello 755 0 0
slink /bin/init hello 777 0 0
I changed the last two lines of the initramfs to read as follows:

file /bin/hello ${INSTALL_ROOT}/projects/${SAMPLE}/hello/goodbye 755 0 0
slink /bin/init hello 777 0 0

But when I try and boot the SmartFusion2 after remaking the uImage, I get this, witht the error at the bottom:

Starting kernel ...

Linux version 2.6.33-arm1 (ecenstudent@EE10308) (gcc version 4.4.1 (Sourcery G++ Lite 2010q1-189) ) #38 Thu May 25 09:09:08 MDT 2017
CPU: ARMv7-M Processor [412fc231] revision 1 (ARMv7M)
CPU: NO data cache, 8K instruction cache
Machine: Microsemi M2S
Built 1 zonelists in Zone order, mobility grouping on.  Total pages: 16256
Kernel command line: m2s_platform=m2s-fg484-som console=ttyS0,115200 panic=10 ip=10.2.118.102:10.2.118.101:192.168.0.1::m2s-fg484-som:eth0:off ethaddr=3C:FB:96:05:00:53
PID hash table entries: 256 (order: -2, 1024 bytes)
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: 64408k/64408k available, 1128k reserved, 0K highmem
Virtual kernel memory layout:
    vector  : 0x00000000 - 0x00001000   (   4 kB)
    fixmap  : 0xfff00000 - 0xfffe0000   ( 896 kB)
    vmalloc : 0x00000000 - 0xffffffff   (4095 MB)
    lowmem  : 0xa0000000 - 0xa4000000   (  64 MB)
    modules : 0xa0000000 - 0x01000000   (1552 MB)
      .init : 0xa0008000 - 0xa0012000   (  40 kB)
      .text : 0xa0074bc0 - 0xa0083000   (  58 kB)
      .data : 0xa0084000 - 0xa008cce0   (  36 kB)
Hierarchical RCU implementation.
NR_IRQS:83
Calibrating delay loop... 132.30 BogoMIPS (lpj=661504)
Mount-cache hash table entries: 512
Switching to clocksource mss_timer2
Serial: 8250/16550 driver, 2 ports, IRQ sharing disabled
serial8250.0: ttyS0 at MMIO 0x40000000 (irq = 10) is a 16550A
console [ttyS0] enabled
serial8250.1: ttyS1 at MMIO 0x40010000 (irq = 11) is a 16550A
Freeing init memory: 40K
Kernel panic - not syncing: No init found.  Try passing init= option to kernel.
Backtrace: no frame pointer
Rebooting in 10 seconds..

Can somebody help explain why this is happening and what I need to do to my initramfs to make it run the proper program on boot? Thanks!!

Answer 1

As it turns out, I was confused about how those two lines worked. When I finally figured it out, they looked like this:

file /bin/hello ${INSTALL_ROOT}/projects/${SAMPLE}/goodbye/hello 755 0 0
slink /bin/init hello 777 0 0

then it worked as desired, and I was able to implement it into other uImages.