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To: Michael Richardson <mcr@sandelman.ottawa.on.ca>
Cc: user-mode-linux-devel@lists.sourceforge.net
From: Jeff Dike <jdike@karaya.com>
Subject: [uml-devel] Re: stack trace
Date: Mon, 16 Sep 2002 22:36:06 -0500
mcr@sandelman.ottawa.on.ca said:
> Can you post (on list or web site) a "script" output of you trying to
> get the right stack out of a stuck uml (tracing myself)...?
Yup. Here we go...
Here, I attach to the tracing thread and get the stack of the current thread,
which happens to be the idle thread.
um 1013: gdb linux 14936
GNU gdb 5.0rh-5 Red Hat Linux 7.1
Copyright 2001 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 "i386-redhat-linux"...
/home/jdike/linux/2.4/um/14936: No such file or directory.
Attaching to program: /home/jdike/linux/2.4/um/linux, process 14936
0xa014efe9 in __wait4 ()
# This is how you get the current task in the tracing thread - get_current()
# only works in a kernel thread.
(gdb) p (struct task_struct *)cpu_tasks[0].task
$2 = (struct task_struct *) 0xa01c0000
# Get the host pid of that task.
(gdb) p $2.thread.extern_pid
$3 = 14939
# Get the current ip and sp.
(gdb) shell cat /proc/14939/stat
14939 (linux) T 14936 14936 883 34816 14936 64 5 3 806 7 62 12 0 0 9 0 0 2
588043 142770176 5008 4294967295 2684358656 2686348640 3221223520 2686205764
sp ^^^^^^^^^^
2685727185 73728 201392128 167776768 268444672 3222308129 0 0 17 0
ip ^^^^^^^^^^
# the sp and ip are items 4 and 5 after the 4294967295 (on 2.2 hosts, that's
2^31 - 1 rather than 2^32 - 1).
(gdb) p/x 2686205764
$4 = 0xa01c3f44
(gdb) p/x 2685727185
$5 = 0xa014f1d1
# Where's the ip?
(gdb) i sym 0xa014f1d1
nanosleep + 17 in section .text
# look at the stack around the sp
(gdb) x/32x 0xa01c3f30
0xa01c3f30 : 0x00000000 0x00000000 0xa01c3f60 0xa00020a8
0xa01c3f40 : 0x00000004 0xa012e891 0xa01c3f58 0xa01c3f58
0xa01c3f50 : 0xa01c3f70 0xa0023667 0x00000009 0x3b023380
0xa01c3f60 : 0xa01c3fa0 0xa012a21d 0x0000000a 0xa01c0000
0xa01c3f70 : 0xa01c3fa0 0xa012a213 0x00000003 0x00000024
0xa01c3f80 : 0xa01c3fa0 0xa0011bc4 0xa012b25c 0x00000000
0xa01c3f90 : 0xa01c3fb0 0x00000000 0xa01c3ffc 0x0000000d
0xa01c3fa0 : 0xa01c3fb0 0xa000c50e 0xa01812e0 0xa01c3ffc
# The trick here is to locate a frame near the current sp. You're looking
# for a consecutive pair of longwords (fp, ip) having the properties that:
# fp is on the current kernel stack and points further up it
# ip is a text address (if you can't recognize a UML text address by
# sight, print out &_stext and &_etext)
#
# Starting at 0xa01c3f44, the first pair of works satisfying these requirements
# is at 0xa01c3f50.
# So, print that pair out as hex.
(gdb) p/x *((int (*)[2])0xa01c3f50)
$9 = {0xa01c3f70, 0xa0023667}
# Now, we start climbing the stack.
(gdb) p/x *((int (*)[2])$[0])
$10 = {0xa01c3fa0, 0xa012a213}
(gdb)
$11 = {0xa01c3fb0, 0xa000c50e}
(gdb)
$12 = {0xa01c3fc0, 0xa000356d}
(gdb)
$13 = {0xa01c3fd0, 0xa013082f}
(gdb)
$14 = {0xa01c3ff0, 0xa012fbdd}
# Stop when you see a NULL frame pointer or gdb bitches at you.
(gdb)
$15 = {0x0, 0xa01513aa}
# Now we get the symbolic version of the stack with 'i sym' of the second item
# in each pair.
(gdb) i sym 0xa0023667
check_pgt_cache + 23 in section .text
(gdb) i sym 0xa012a213
cpu_idle + 123 in section .text
(gdb) i sym 0xa000c50e
rest_init + 46 in section .text
(gdb) i sym 0xa000356d
start_kernel + 361 in section .text.init
(gdb) i sym 0xa013082f
start_kernel_proc + 63 in section .text
(gdb) i sym 0xa012fbdd
signal_tramp + 209 in section .text
(gdb) i sym 0xa01513aa
thread_start + 4 in section .text
# You can also get line number information with 'i line'.
(gdb) i line *0xa012a213
Line 488 of "process_kern.c" starts at address 0xa012a213 <cpu_idle+123>
and ends at 0xa012a21d <cpu_idle+133>.
(gdb)
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