problem debugging kernel module using kernel crash dump with kgdb

[Miki Magyari]

hi,

I'm new to kernel programming, working on a kernel module and trying
to debug a crash dump after a panic. Here is the backtrace:

(kgdb) bt
#0  doadump () at pcpu.h:246
#1  0xc089cb9e in boot (howto=260) at /usr/src/sys/kern/kern_shutdown.c:416
#2  0xc089ce72 in panic (fmt=Variable "fmt" is not available.
) at /usr/src/sys/kern/kern_shutdown.c:590
#3  0xc04d1ab7 in db_panic (addr=Could not find the frame base for "db_panic".
) at /usr/src/sys/ddb/db_command.c:478
#4  0xc04d20e1 in db_command (last_cmdp=0xc0dd2f5c, cmd_table=0x0,
dopager=1) at /usr/src/sys/ddb/db_command.c:445
#5  0xc04d223a in db_command_loop () at /usr/src/sys/ddb/db_command.c:498
#6  0xc04d40dd in db_trap (type=3, code=0) at /usr/src/sys/ddb/db_main.c:229
#7  0xc08cc4e6 in kdb_trap (type=3, code=0, tf=0xc8caa818) at
/usr/src/sys/kern/subr_kdb.c:535
#8  0xc0bd4a9b in trap (frame=0xc8caa818) at /usr/src/sys/i386/i386/trap.c:690
#9  0xc0bb5f7b in calltrap () at /usr/src/sys/i386/i386/exception.s:165
#10 0xc08cc66a in kdb_enter (why=0xc0cab4ec "panic", msg=0xc0cab4ec
"panic") at cpufunc.h:71
#11 0xc089ce56 in panic (fmt=0xc0ca9eb8 "mtx_lock() of spin mutex %s @
%s:%d") at /usr/src/sys/kern/kern_shutdown.c:573
#12 0xc088d4ea in _mtx_lock_flags (m=0xc2911904, opts=0,
file=0xc0cb66ca "/usr/src/sys/kern/vfs_bio.c", line=2545) at
/usr/src/sys/kern/kern_mutex.c:197
#13 0xc091a282 in getblk (vp=0xc2911810, blkno=2, size=512, slpflag=0,
slptimeo=0, flags=0) at /usr/src/sys/kern/vfs_bio.c:2545
#14 0xc091ab24 in breadn (vp=0xc2911810, blkno=Unhandled dwarf
expression opcode 0x93
) at /usr/src/sys/kern/vfs_bio.c:800
#15 0xc091ac9c in bread (vp=0xc2911810, blkno=Unhandled dwarf
expression opcode 0x93
) at /usr/src/sys/kern/vfs_bio.c:748
#16 0xc286d5b4 in minixfs_mount (mp=0xc2492000) at
/usr/src/sys/modules/minixfs/../../fs/minixfs/minixfs_vfsops.c:149
#17 0xc09290a8 in vfs_donmount (td=0xc2817280, fsflags=0,
fsoptions=0xc2499780) at /usr/src/sys/kern/vfs_mount.c:988
#18 0xc092a7e5 in nmount (td=0xc2817280, uap=0xc8caacf8) at
/usr/src/sys/kern/vfs_mount.c:424
#19 0xc0bd4220 in syscall (frame=0xc8caad38) at
/usr/src/sys/i386/i386/trap.c:1111
#20 0xc0bb5fe0 in Xint0x80_syscall () at /usr/src/sys/i386/i386/exception.s:261

after using "f 16" I can use "list" command to see the source code and
the bread() call that causes the panic, but I'm unable to investigate
local variables for this code part using "i loc". It displays
variables for function minixfs_mount, but bread() is actually called
from minixfs_mountfs, called by minixfs_mount.

Any pointers why this subfunction not shown with "bt" and why I cannot
get local variables for it?

thanks in advance,
Miki