[uml-user] Building UML with busybox as root file system

[Tamil M. <rf....@gm...>]

Hi ,
I downloaded the latest version of linux-3.11.8 ,configured it as UML and
got the statically compiled binary (linux).

Then i downloaded the latest busybox 1.21.1 and compiled with default
configuration. Then i converted the busybox binary into a  ext4 filesystem.

while running linux as UML,

./linux ubda=./busybox mem=128M

i'm getting the following error

 EXT4-fs (ubda): mounted filesystem with ordered data mode. Opts: (null)
[    1.170000] VFS: Mounted root (ext4 filesystem) readonly on device 98:0.
[    1.170000] Kernel panic - not syncing: No init found.  Try passing
init= option to kernel. See Linux Documentation/init.txt for guidance.
[    1.170000] CPU: 0 PID: 1 Comm: swapper Not tainted 3.11.8 #6
[    1.170000] 67c3fe78 67c3feb0 60058699 6004c888 60600531 00000000
00000000 67c3fec0
[    1.170000]        604f6fe3 67c3ffc0 604f1e3b 00000000 3000000008
67c3ffd0 67c3fef0 657fe900
[    1.170000]        6004c888 00000f76 6004c888 00000003 67c3fe40 60600529
fffffffe 67c3ffa0
[    1.170000] Call Trace:
[    1.170000] 67c3fe88:  [<60058699>] dump_stack_print_info+0xa5/0xae
[    1.170000] 67c3fe90:  [<6004c888>] put_cred_rcu+0x0/0xa4
[    1.170000] 67c3feb8:  [<604f6fe3>] dump_stack+0x17/0x19
[    1.170000] 67c3fec8:  [<604f1e3b>] panic+0xf7/0x1ee
[    1.170000] 67c3fef8:  [<6004c888>] put_cred_rcu+0x0/0xa4
[    1.170000] 67c3ff08:  [<6004c888>] put_cred_rcu+0x0/0xa4
[    1.170000] 67c3ff38:  [<600ac7ce>] do_execve_common+0x49b/0x4f0
[    1.170000] 67c3ff48:  [<6004d600>]
async_synchronize_cookie_domain+0x56/0x112
[    1.170000] 67c3ffc8:  [<604f0c88>] kernel_init+0xb6/0xba
[    1.170000] 67c3ffd8:  [<6001c374>] new_thread_handler+0x7a/0x95
[    1.170000]
[    1.170000]
[    1.170000] Modules linked in:
[    1.170000] Pid: 1, comm: swapper Not tainted 3.11.8
[    1.170000] RIP: 0033:[<000000006048c0a7>]
[    1.170000] RSP: 00007fff11356248  EFLAGS: 00000246
[    1.170000] RAX: 0000000000000000 RBX: 00000000000048ec RCX:
ffffffffffffffff
[    1.170000] RDX: 0000000000000000 RSI: 0000000000000013 RDI:
00000000000048ec
[    1.170000] RBP: 00007fff11356270 R08: 0000000000000000 R09:
00007fff11356270
[    1.170000] R10: 0000000000000000 R11: 0000000000000246 R12:
00000000000048e8
[    1.170000] R13: 00007fff11356458 R14: 00007fff11356e3a R15:
0000000000000007
[    1.170000] Call Trace:
[    1.170000] 67c3fe38:  [<6001d2f6>] show_trace+0x8e/0x95
[    1.170000] 67c3fe48:  [<6001e808>] panic_exit+0x2b/0x41
[    1.170000] 67c3fe68:  [<6004c298>] notifier_call_chain+0x32/0x5c
[    1.170000] 67c3fea8:  [<6004c2cb>] __atomic_notifier_call_chain+0x9/0xb
[    1.170000] 67c3feb8:  [<6004c2dc>] atomic_notifier_call_chain+0xf/0x11
[    1.170000] 67c3fec8:  [<604f1e56>] panic+0x112/0x1ee
[    1.170000] 67c3fef8:  [<6004c888>] put_cred_rcu+0x0/0xa4
[    1.170000] 67c3ff08:  [<6004c888>] put_cred_rcu+0x0/0xa4
[    1.170000] 67c3ff38:  [<600ac7ce>] do_execve_common+0x49b/0x4f0
[    1.170000] 67c3ff48:  [<6004d600>]
async_synchronize_cookie_domain+0x56/0x112
[    1.170000] 67c3ffc8:  [<604f0c88>] kernel_init+0xb6/0xba
[    1.170000] 67c3ffd8:  [<6001c374>] new_thread_handler+0x7a/0x95
[    1.170000]
Aborted

To summarize,i'm getting a kernel panic due to the missing of init. Please
help me in fixing the problem

Thanks & regards,
Tamil