[uml-user] Making a module for user-mode-linux and debugging it with gdb

[david j. <djh...@gm...>]

Hi,

I have been doing pretty hard since last few days to set up user-mode-linux
in my ubuntu-14.04 LTS host. I am a noob on this and want to debug
openvswitch kernel module by using user-mode-linux. Currently I am
following these links to up my uml:
    http://www.opensourceforu.com/2010/09/user-mode-linux-setup-and-debug/
    http://www.landley.net/code/UML.html
    https://help.ubuntu.com/community/UserModeLinux

but after I run this command linux-3.13/linux
rootfstype=linux-3.13/uml-root-trusty it is Aborted with the following
output:

Core dump limits :
    soft - 0
    hard - NONE
Checking that ptrace can change system call numbers...OK
Checking syscall emulation patch for ptrace...OK
Checking advanced syscall emulation patch for ptrace...OK
Checking for tmpfs mount on /dev/shm.../run/shm...OK
Checking PROT_EXEC mmap in /dev/shm/...OK
Checking for the skas3 patch in the host:
  - /proc/mm...not found: No such file or directory
  - PTRACE_FAULTINFO...not found
  - PTRACE_LDT...not found
UML running in SKAS0 mode
Adding 24801280 bytes to physical memory to account for exec-shield gap
Initialized stdio console driver
Using a channel type which is configured out of UML
setup_one_line failed for device 1 : Configuration failed
Using a channel type which is configured out of UML
setup_one_line failed for device 2 : Configuration failed
Using a channel type which is configured out of UML
setup_one_line failed for device 3 : Configuration failed
Using a channel type which is configured out of UML
setup_one_line failed for device 4 : Configuration failed
Using a channel type which is configured out of UML
setup_one_line failed for device 5 : Configuration failed
Using a channel type which is configured out of UML
setup_one_line failed for device 6 : Configuration failed
Using a channel type which is configured out of UML
setup_one_line failed for device 7 : Configuration failed
Using a channel type which is configured out of UML
setup_one_line failed for device 8 : Configuration failed
Using a channel type which is configured out of UML
setup_one_line failed for device 9 : Configuration failed
Using a channel type which is configured out of UML
setup_one_line failed for device 10 : Configuration failed
Using a channel type which is configured out of UML
setup_one_line failed for device 11 : Configuration failed
Using a channel type which is configured out of UML
setup_one_line failed for device 12 : Configuration failed
Using a channel type which is configured out of UML
setup_one_line failed for device 13 : Configuration failed
Using a channel type which is configured out of UML
setup_one_line failed for device 14 : Configuration failed
Using a channel type which is configured out of UML
setup_one_line failed for device 15 : Configuration failed
Console initialized on /dev/tty0
console [tty0] enabled
console [mc-1] enabled
VFS: Cannot open root device "98:0" or unknown-block(98,0): error -19
Please append a correct "root=" boot option; here are the available
partitions:
Kernel panic - not syncing: VFS: Unable to mount root fs on
unknown-block(98,0)
CPU: 0 PID: 1 Comm: swapper Not tainted 3.13.0 #1
Stack:
 63037d50 00000002 60238906 00000002
 60238947 60147ad0 601ad287 00008001
 600d8900 63172000 63037d60 601af835
Call Trace:
 [<60147ad0>] ? bust_spinlocks+0x0/0x60
 [<601ad287>] ? printk+0x0/0xa0
 [<600d8900>] ? SyS_mount+0x0/0x110
 [<601af835>] dump_stack+0x2a/0x2c
 [<601ac99c>] panic+0x137/0x286
 [<601ac865>] ? panic+0x0/0x286
 [<60024ac0>] ? unblock_signals+0x0/0xb0
 [<600d89e8>] ? SyS_mount+0xe8/0x110
 [<601ad287>] ? printk+0x0/0xa0
 [<600d8900>] ? SyS_mount+0x0/0x110
 [<6000211b>] mount_root+0x0/0x82
 [<60015290>] ? do_one_initcall+0x0/0x190
 [<60015290>] ? do_one_initcall+0x0/0x190
 [<601429d0>] ? strcpy+0x0/0x30
 [<60002199>] mount_root+0x7e/0x82
 [<6000211b>] ? mount_root+0x0/0x82
 [<60142ab0>] ? strncmp+0x0/0x60
 [<60002380>] prepare_namespace+0x1e3/0x22b
 [<60024ac0>] ? unblock_signals+0x0/0xb0
 [<600d3f60>] ? SyS_dup+0x0/0x70
 [<60015290>] ? do_one_initcall+0x0/0x190
 [<60001c8b>] kernel_init_freeable+0x27c/0x297
 [<600011b7>] ? repair_env_string+0x0/0xbd
 [<6005325d>] ? finish_task_switch.isra.71+0x2d/0x80
 [<601ac1f5>] kernel_init+0x15/0x1b0
 [<60016d61>] new_thread_handler+0x81/0xb0

Aborted (core dumped)

Secondly. I did also install user-mode-linux and other relavant utilities
with apt-get and when I run linux rootfstype=hostfs rw init=/bin/bash it
works but I am not understanding how to compile my required module and
debug it in this scenario.

I'll be really grateful for your help to get it fixed or your suggestions.
Thank you in advance!

kind Regards;
david