Generate and debug core files in Linux

First, let's see what machine I use:

$ Uname-
Linux Dev 2.4.21-9.30 axsmp #1 SMP Wed May 26 23:37:09 EDT 2004 i686 i686 i386 GNU/Linux

Take a look at some default parameters. Note that the core file size is 0, and the core file will not be generated when a program error occurs.

$ Ulimit-
Core File size (blocks,-C) 0
Data seg size (Kbytes,-d) Unlimited
File size (blocks,-f) Unlimited
Max locked memory (Kbytes,-l) 4
Max memory size (Kbytes,-m) Unlimited
Open File (-N) 2048
Pipe size (512 bytes,-p) 8
Stack size (Kbytes,-S) 10240
CPU time (seconds,-T) Unlimited
Max user processes (-u) 7168
Virtual Memory (Kbytes,-v) Unlimited

Write a simple program to see if the core file is generated.

$ More Foo. c

# Include <stdio. h>

Static void sub (void );

Int main (void)
{
Sub ();
Return 0;
}

Static void sub (void)
{
Int * P = NULL;

/* Derefernce a null pointer, exact CT core dump .*/
Printf ("% d", * P );
}

$ Gcc-wall-G Foo. c
$./A. Out
Segmentation fault

$ LS-L core .*
Ls: core. *: no such file or directory

The core file is not found. Modify the ulimit settings to generate the file. 1024 is random. If the core file contains more than 1024 blocks, it cannot be generated.

$ Ulimit-C 1024

$ Ulimit-
Core File size (blocks,-C) 1024
Data seg size (Kbytes,-d) Unlimited
File size (blocks,-f) Unlimited
Max locked memory (Kbytes,-l) 4
Max memory size (Kbytes,-m) Unlimited
Open File (-N) 2048
Pipe size (512 bytes,-p) 8
Stack size (Kbytes,-S) 10240
CPU time (seconds,-T) Unlimited
Max user processes (-u) 7168
Virtual Memory (Kbytes,-v) Unlimited

$./A. Out
Segmentation fault (core dumped)
$ LS-L core .*
-RW ------- 1 uniware 53248 Jun 30 core.9128

Note that multiple (core dumped) are added to the output ). A core file is generated, and 9128 is the PID of the process. Let's use GDB to look at this core.

$ GDB -- core = core.9128
Gnu gdb Asianux (6.0post-0.20040223.17.1ax)
Copyright 2004 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-asianux-linux-gnu ".
Core was generated by './A. out '.
Program terminated with signal 11, segmentation fault.
#0 0x08048373 in ?? ()
(GDB) BT
#0 0x08048373 in ?? ()
#1 0xbfffd8f8 in ?? ()
#2 0x0804839e in ?? ()
#3 0xb74cc6b3 in ?? ()
#4 0x00000000 in ?? ()

At this time, you can't see backtrace with BT, that is, the call stack. It turns out that GDB does not know where the symbol information is. Let's tell it:

(GDB) file./A. Out
Reading symbols from./A. Out... done.
Using host libthread_db library "/lib/tls/libthread_db.so.1 ".
(GDB) BT
#0 0x08048373 in sub () at Foo. C: 17
#1 0x08048359 in main () at Foo. C: 8

Now the backtrace is available.

(GDB) L
8 sub ();
9 return 0;
10}
11
12 static void sub (void)
13 {
14 int * P = NULL;
15
16/* derefernce a null pointer, exact CT core dump .*/
17 printf ("% d", * P );
(GDB)

 

When a program unexpectedly exits, the kernel will generate a core file (a memory image with debugging information added) in the current working directory ). You can use GDB to view the core file and indicate the file and number of lines of code that cause program errors.

1. Core File generation switch and size limit
---------------------------------
1) Use the ulimit-C command to view the core file generation switch. If the result is 0, this function is disabled and core files are not generated.
2) use the ulimit-C filesize command to limit the size of the core file (The unit of filesize is Kbyte ). If ulimit-C unlimited is used, the size of the core file is not limited. If the generated information exceeds this size, it will be cropped to generate an incomplete core file. When debugging this core file, GDB will prompt an error.

2. Name and path of the Core File
----------------------------
Core File generation path:
Enter the same path for the executable file to run the command.
If the core file generated by the system does not contain any extension name, it is all named core. The new core file will overwrite the original core file.

1)/proc/sys/kernel/core_uses_pid can control whether PID is added to the file name of the core file as an extension. If the file content is 1, the PID is added as the extension, and the generated core file format is core. xxxx. If it is 0, the generated core file is named core.
Run the following command to modify the file:
Echo "1">/proc/sys/kernel/core_uses_pid

2) proc/sys/kernel/core_pattern can control the core file storage location and file name format.
Run the following command to modify the file:
Echo "/corefile/Core-% E-% P-% t"> core_pattern, which can generate core files in the/corefile directory, the generated file name is core-command name-PID-timestamp.
The following is a list of parameters:
% P-insert PID into filename add PID
% U-insert current uid into filename add current uid
% G-insert current GID into filename add current GID
% S-insert signal that caused the coredump into the filename added to generate core Signal
% T-insert UNIX time that the coredump occurred into filename UNIX time when the core file is generated
% H-insert hostname where the coredump happened into filename Add the Host Name
% E-insert coredumping executable name into filename add command name

3. view the Core File
-----------------
Use GDB to view the core file.
GDB./A. Out
Core-file core. xxxx
Use the BT command to see where the program went wrong.
The following two command methods have the same effect, but they do not take effect in some environments. Therefore, we recommend that you use the preceding command.
1) GDB-core = core. xxxx
File./A. Out
BT
2) GDB-C Core. xxxx
File./A. Out
BT

4. Use the core file for debugging ON THE DEVELOPMENT BOARD
-----------------------------
If the operating system of the Development Board is also Linux, the core debugging method is still applicable. If GDB is not supported on the Development Board, you can copy the Development Board environment (dependent libraries), executable files, and core files to Linux on the PC.
To debug the core file generated on the Development Board on a PC, you must use the gdb that comes with the cross compiler, in addition, you must specify the solib-absolute-prefix and solib-search-PATH variables in GDB to ensure that GDB can find the dependent library path of the executable program. There is a way to create a configuration file. You do not need to configure the above variables every time you start GDB, that is, create. gdbinit in the path to be run GDB.
Configuration File Content:
Set solib-absolute-Prefix your_cross_compile_path
Set solib-search-path your_cross_compile_path
Set solib-search-path your_developer_tools_lib_path
Handle sig32 nostop noprint pass

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