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Full Discussion: How to do core dump analysis
Top Forums UNIX for Advanced & Expert Users How to do core dump analysis Post 75404 by question on Friday 17th of June 2005 03:53:47 PM
Old 06-17-2005
Cannot get backtrace command work "bt", cannot access memory?

Hi,
I think I have similar question, please bear me to put here.
I recently created a testing program containing only one thread to generate core file to analyze, but I couldn't use gdb to print stack trace, It says "cannot access memory ...".
Why? did I miss any command?
I did the test both on Linux and Solaris, same result.


tc11:/home/canzh/test> gcc -g devide.c

tc11:/home/canzh/test> ./a.out
Segmentation fault (core dumped)

tc11:/home/canzh/test> gdb a.out core
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"...
Core was generated by `./a.out'.
Program terminated with signal 11, Segmentation fault.
Cannot access memory at address 0x40016bec
#0 0x400a68d6 in ?? ()
(gdb) bt
#0 0x400a68d6 in ?? ()
Cannot access memory at address 0xbffff8a8
(gdb) where
#0 0x400a68d6 in ?? ()
Cannot access memory at address 0xbffff8a8
(gdb) quit
tc11:/home/canzh/test> uname -a
Linux tc11 2.4.2-2 #1 Sun Apr 8 20:41:30 EDT 2001 i686 unknown
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SAVECORE(8)						      System Manager's Manual						       SAVECORE(8)

NAME
savecore - save a core dump of the operating system SYNOPSIS
savecore dirname [ system ] DESCRIPTION
Savecore is meant to be called at the end of the /etc/rc file. Its function is to save the core dump of the system (if one was made) and to write a reboot message in the shutdown log. It saves the core image in the file dirname/core.n and its corresponding namelist in dirname/unix.n. The second argument is the namelist for the system which made the core image; the current system is always assumed to be /unix. The trailing ".n" in the pathnames is replaced by a number which grows every time savecore is run in that directory. Before savecore writes out a core image, it reads a number from the file dirname/minfree. If there are fewer free blocks on the file sys- tem which contains dirname than the number obtained from the minfree file, the core dump is not done. If the minfree file does not exist, savecore always writes out the core file (assuming that a core dump was taken). Savecore also writes a reboot message in the shut down log. If the system crashed as a result of a panic, savecore records the panic string in the shut down log too. If savecore detects that the system time is wrong because of a crash (the time in the core image is after the current time), it will reset the system time to its best estimate of the time, which is the time in the core image plus the elapsed time since the reboot. It announces the time that it set when this occurs. FILES
/usr/adm/shutdownlogshutdown log /unix current UNIX BUGS
The method used to determine whether a dump is present, and to prevent the same core image from being saved multiple times, is not elegant. This information should be passed to init by the system; however, this is difficult because the system may have to be rebooted a second time if the root filesystem is patched. 3rd Berkeley Distribution SAVECORE(8)
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