[uml-user] kernel debugging with UML

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Hi there,

I've been playing around UML for some time. I finally got a working uml 
box but when I tried to debug a kernel module inside it, problems came 
along.

I found from the UML site that :

"In order to debug the kernel, you need build it from source. See this 
page <http://user-mode-linux.sourceforge.net/compile.html> for 
information on doing that. Make sure that you enable CONFIG_DEBUGSYM and 
CONFIG_PT_PROXY during the config. These will compile the kernel with 
-g, and enable the ptrace proxy so that gdb works with UML, respectively."

--I did this. 

You can have the kernel running under the control of gdb from the 
beginning by putting 'debug' on the command line.

-- I did "./linux debug".

Surprisingly, the uml just boot as usual. I didn't see any gdb info.

So  I tried " gdb ./linux", gdb starts and I keep type 'c' to get kernel 
boot. However,  there would be segmentation faults.

GNU gdb 5.3.92
Copyright 2003 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License, and you are
welcome to change it and/or distribute copies of it under certain 
conditions.
Type "show copying" to see the conditions.
There is absolutely no warranty for GDB.  Type "show warranty" for details.
This GDB was configured as "i586-suse-linux"...
(gdb) run
Starting program: /home/lei/uml/suse_rootfs/linux

Program received signal SIGTRAP, Trace/breakpoint trap.
0xa000c000 in _start () at proc_fs.h:154
154                     res->data=data;
(gdb) c
Continuing.
Checking for the skas3 patch in the host...found
Checking for /proc/mm...found

Program received signal SIGUSR1, User defined signal 1.
0xa0168741 in kill () at swab.h:160
160     {
(gdb) c
Continuing.
Checking for /dev/anon on the host...Not available (open failed with 
errno 2)
Linux version 2.4.26-3um (root@suzhou) (gcc version 3.3.1 (SuSE Linux)) 
#3 Thu Sep 30 15:53:55 CDT 2004
On node 0 totalpages: 8192
zone(0): 8192 pages.
zone(1): 0 pages.
zone(2): 0 pages.
Kernel command line: root=/dev/ubd0
Calibrating delay loop... 2549.35 BogoMIPS
Memory: 28828k available
Dentry cache hash table entries: 4096 (order: 3, 32768 bytes)
Inode cache hash table entries: 2048 (order: 2, 16384 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: 8192 (order: 3, 32768 bytes)
Checking for host processor cmov support...Yes
Checking for host processor xmm support...No
Checking that ptrace can change system call numbers...OK
Checking that host ptys support output SIGIO...Yes
Checking that host ptys support SIGIO on close...No, enabling workaround
POSIX conformance testing by UNIFIX

Program received signal SIGUSR1, User defined signal 1.
0xa0168741 in kill () at swab.h:160
160     {
(gdb) c
Continuing.
Linux NET4.0 for Linux 2.4
Based upon Swansea University Computer Society NET3.039
Initializing RT netlink socket

Program received signal SIGUSR1, User defined signal 1.
0xa0168741 in kill () at swab.h:160
160     {
(gdb) c
Continuing.

Program received signal SIGUSR1, User defined signal 1.
0xa0168741 in kill () at swab.h:160
160     {
(gdb) c
Continuing.
Starting kswapd

Program received signal SIGUSR1, User defined signal 1.
0xa0168741 in kill () at swab.h:160
160     {
(gdb) c
Continuing.

Program received signal SIGUSR1, User defined signal 1.
0xa0168741 in kill () at swab.h:160
160     {
(gdb) n

Program received signal SIGSEGV, Segmentation fault.
__libc_siglongjmp (env=0x1, val=0) at ../sysdeps/generic/longjmp.c:33
33      ../sysdeps/generic/longjmp.c: No such file or directory.
        in ../sysdeps/generic/longjmp.c
(gdb) c
Continuing.
Kernel panic: Segfault with no mm
 <6>SysRq : Show Regs

EIP: 0023:[<a0168741>] CPU: 0 Not tainted ESP: 002b:40001fb4 EFLAGS: 
00000206
    Not tainted
EAX: 00000000 EBX: 0000094e ECX: 00000013 EDX: 0000094e
ESI: 00000000 EDI: 00000000 EBP: 40001fd0 DS: 002b ES: 002b
Call Trace: [<a00ea447>] [<a01c82fb>] [<a01cb4ce>] [<a00ea3d6>] [<a00d498b>]
   [<a001e47a>] [<a0160dcc>] [<a01cfa2c>] [<a001144d>] [<a001142f>] 
[<a00d3e0d>]
   [<a01cada5>] [<a0168795>] [<a00d1d84>] [<a00d4269>] [<a0168741>] 
[<a00d415d>]
   [<a00da857>] [<a00da84e>] [<a00d42c1>] [<a01686a8>] [<a016841e>] 
[<a0168795>]
   [<a00d1d1f>] [<a016841e>] [<a0039186>] [<a00d9914>] [<a0039186>] 
[<a00d98fd>]
   [<a0039186>] [<a00d9e01>] [<a01686a8>] [<a0168741>]

Program received signal SIGSEGV, Segmentation fault.
0xa017f25d in __opendir (name=0xa2800000 "") at opendir.c:159
159     opendir.c: No such file or directory.
        in opendir.c
(gdb) c
Continuing.

Program exited with code 01.
(gdb)

***********************************************************************************

Any hints?

TIA
Lei