Re: Strange vkernel crash

[Dave Hayes <dave@xxxxxxxxxxx>]

Matthew Dillon <dillon@apollo.backplane.com> writes:
>     Maybe something in your /etc/ttys (the vkernel's /etc/ttys, that is)
>     is causing init to blow up the vkernel.  Try messing with that.  Be
>     sure to save the original in case that turns out to be the cause.

Well I've been bangin the ol head against the screen on this
crash. Since I really need to make progress here, it's like walking
through a forest with sunglasses on:

In /home/dave/gdbthis
 set args -m 64m -r /var/vkernel/rootimg.1.8.1
 break start_init
 run
 break vm_map_find
 continue

# gdb -x /home/dave/gdbthis ./kernel.debug
GNU gdb 6.2.1
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GDB is free software, covered by the GNU General Public License, and you are
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Type "show copying" to see the conditions.
There is absolutely no warranty for GDB.  Type "show warranty" for details.
This GDB was configured as "i386-dragonfly"...
Breakpoint 1 at 0x809170a: file thread.h, line 83.
Using memory file: /var/vkernel/memimg.000000
Copyright (c) 2003, 2004, 2005, 2006, 2007 The DragonFly Project.
Copyright (c) 1992-2003 The FreeBSD Project.
Copyright (c) 1979, 1980, 1983, 1986, 1988, 1989, 1991, 1992, 1993, 1994
        The Regents of the University of California. All rights reserved.
DragonFly 1.8.1-RELEASE #0: Wed Apr  4 19:52:02 PDT 2007
    dave@dfdev.jetcafe.org:/usr/altsrc/src.1.8.1/sys/compile/VKERNEL
real memory = 67108864 (65536K bytes)
avail memory = 62545920 (61080K bytes)
md0: Malloc disk
initclocks
IP packet filtering initialized, divert disabled, rule-based forwarding 
enabled, default to accept, logging disabled
DUMMYNET initialized (011031)
IPsec: Initialized Security Association Processing.
Mounting root from ufs:vkd0a

Breakpoint 1, start_init (dummy=0x0) at thread.h:83
83          __asm ("movl %%fs:globaldata,%0" : "=r" (gd) : 
"m"(__mycpu__dummy));
Breakpoint 2 at 0x81d98fc: file ../../vm/vm_map.c, line 996.

Breakpoint 2, vm_map_find (map=0x58772f00, object=0x7, offset=Unhandled dwarf 
expression opcode 0x93
) at ../../vm/vm_map.c:996
996             start = *addr;
(gdb) break subyte 
Breakpoint 3 at 0x81f840c: file ../../platform/vkernel/platform/copyio.c, line 
209.
(gdb) c
Continuing.

Breakpoint 3, subyte (base=0x1, byte=1) at ../../platform/vkernel/platform/copy
io.c:209
209             unsigned char c = byte;
(gdb) bt 
#0  subyte (base=0x1, byte=1) at ../../platform/vkernel/platform/copyio.c:209
#1  0x08091994 in start_init (dummy=0x0) at ../../kern/init_main.c:530
#2  0x081f6796 in fork_trampoline () at ../../platform/vkernel/i386/fork_tramp.
s:78
(gdb) c
Continuing.

Program received signal SIGSEGV, Segmentation fault.
0x081fa76f in pmap_enter (pmap=0x58772f84, va=3217027072, m=0x548f7140, prot=7 
'\a', wired=0)
    at ../../platform/vkernel/platform/pmap.c:1734
1734            origpte = *pte;
(gdb) bt
#0  0x081fa76f in pmap_enter (pmap=0x58772f84, va=3217027072, m=0x548f7140, 
prot=7 '\a', wired=0)
    at ../../platform/vkernel/platform/pmap.c:1734
#1  0x081d5b76 in vm_fault_page (map=0x58772f00, vaddr=3217027072, 
fault_type=3 '\003',
    fault_flags=1227878396, errorp=0x5877ac94) at ../../vm/vm_fault.c:579
#2  0x081f8351 in copyout (kaddr=0x5877acbb, udaddr=0xbfbfffff, len=1)
    at ../../platform/vkernel/platform/copyio.c:169
#3  0x081f842c in subyte (base=0x548f7140, byte=1418686784) at 
. ./../platform/vkernel/platform/copyio.c:212
#4  0x08091994 in start_init (dummy=0x0) at ../../kern/init_main.c:530
#5  0x081f6796 in fork_trampoline () at ../../platform/vkernel/i386/fork_tramp.
s:78
(gdb) up 4
#4  0x08091994 in start_init (dummy=0x0) at ../../kern/init_main.c:530
530                     (void)subyte(--ucp, 0);         /* trailing zero */

It seems when it gets to the "subyte" call the first time, something
has trashed the stack.

What is the quickest way to find this problem and solve it? 
------
Dave Hayes - Consultant - Altadena CA, USA - dave@jetcafe.org 
>>> The opinions expressed above are entirely my own <<<

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