core dump

Preface

Segment error （ The core has been dumped ）！！！

# ./test.out 
Segmentation fault (core dumped)

$ ./core.out 
 Segment error  ( The core has been dumped )

Run a program , It happened accidentally Segment error （ The core has been dumped ）, How sad . Fortunately we have core dump, It can help debug program crash problems . Let's have a chat today core dump.

summary

core dump The word comes from magnetic-core memory, This is the mainstream memory medium in the 1960s and 1970s .core Refers to memory, which is now memory .
The operating system terminates when a process receives a signal , Write the contents of the process address space and the related status information of the process to a disk file , This process is called core dump, The generated file is called core file .
core dump The scene of the crash was recorded . We can use gdb Yes core Document analysis , It's called live restore , You can see why the program crashed .

Prerequisite

a) It needs to be opened in advance core dump function , Use the following command

ulimit -c 1024

b) gcc The compiler needs to add -g Option to add debugging information .

Test environment

BananaPi M1（ stay ubuntu Cannot generate core file , Students who know the method can leave a message ）

The test program

test.c

#include <stdio.h>

int main(int argc, char argv) 
{
    
	int *p = NULL;

	*p = 0; 	//  Assign a value to the address pointed to by the null pointer , trigger core dump

	return 0;
}

compile

$ /home/liyongjun/project/board/buildroot/BPi-M1/host/bin/arm-buildroot-linux-uclibcgnueabihf-gcc -g test.c -o test.out

core dump

stay BananaPi M1 Up operation

# ./test.out 
Segmentation fault
# ulimit -c 1024
# ./test.out 
Segmentation fault (core dumped)
# ls
core   test.out

First run , It was found that core dump, It's because it's not enabled core dump function , Use ulimit -c 1024 After enabling , And that's what happened core dump,ls Can see core file .

gdb analysis

Upload to ubuntu Use gdb analysis

$ arm-linux-gnueabihf-gdb test.out core 
GNU gdb (Linaro_GDB-2017.08) 8.0.0.20170823-git
Copyright (C) 2017 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "--host=x86_64-unknown-linux-gnu --target=arm-linux-gnueabihf".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
<http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from test.out...done.
[New LWP 149]

warning: Could not load shared library symbols for 2 libraries, e.g. /lib/libc.so.0.
Use the "info sharedlibrary" command to see the complete listing.
Do you need "set solib-search-path" or "set sysroot"?
Core was generated by `./test.out'. Program terminated with signal SIGSEGV, Segmentation fault. #0 0x004e15a0 in main (argc=1, argv=116 't') at test.c:7
7		*p = 0; 	//  Assign a value to the address pointed to by the null pointer , trigger core dump
(gdb)

gdb Directly locate the crash point ： The first 7 That's ok ：*p = 0;.