How to debug core files in Linux

How to debug core files in Linux

 

 

When a program unexpectedly exits, the kernel may map the current memory of the program to the core file. The kernel will generate a core file in the current working directory (when a program crashes, copies the stored image of the process in the core file of the current working directory of the process. The core file is only a memory image (with debugging information added) and is mainly used for debugging ). 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

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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-cfilesize command to limit the size of the core file (The unit of filesize is Kbyte ). If ulimit-cunlimited 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

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If the core file generated by the system does not contain any other extension names, 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

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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

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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 (header files, libraries), executable files, and core files to Linux on the PC and run relevant commands.

Note: The executable file to be debugged must be added to-g during compilation so that the core file can display error information normally!