Reference Links
Step by step guide
Compile following code.
#include <stdio.h>
int main() {
int* ptr = NULL;
*ptr = 10;
return 0;
}
$ gcc -g -o cd_test core_dump_test.c
$ ll
total 32
drwxr-xr-x 8 josh josh 4096 Aug 25 14:39 ./
drwxr-xr-x 9 josh josh 4096 Aug 25 14:16 ../
-rwxr-xr-x 1 josh josh 16912 Aug 25 14:39 cd_test*
-rwxrwxrwx 1 josh josh 84 Aug 25 14:38 core_dump_test.c*
Run the binary and check the SegFault.
$ ./cd_test
Segmentation fault
$ ll
total 32
drwxr-xr-x 8 josh josh 4096 Aug 25 14:39 ./
drwxr-xr-x 9 josh josh 4096 Aug 25 14:16 ../
-rwxr-xr-x 1 josh josh 16912 Aug 25 14:39 cd_test*
-rwxrwxrwx 1 josh josh 84 Aug 25 14:38 core_dump_test.c*
Make the file size of the core unlimited.
$ ulimit -a
real-time non-blocking time (microseconds, -R) unlimited
core file size (blocks, -c) 0
data seg size (kbytes, -d) unlimited
scheduling priority (-e) 0
file size (blocks, -f) unlimited
pending signals (-i) 31178
max locked memory (kbytes, -l) 64
max memory size (kbytes, -m) unlimited
open files (-n) 1048576
pipe size (512 bytes, -p) 8
POSIX message queues (bytes, -q) 819200
real-time priority (-r) 0
stack size (kbytes, -s) 8192
cpu time (seconds, -t) unlimited
max user processes (-u) 31178
virtual memory (kbytes, -v) unlimited
file locks (-x) unlimited
$ ulimit -c unlimited
$ ulimit -a
real-time non-blocking time (microseconds, -R) unlimited
core file size (blocks, -c) unlimited
data seg size (kbytes, -d) unlimited
scheduling priority (-e) 0
file size (blocks, -f) unlimited
pending signals (-i) 31178
max locked memory (kbytes, -l) 64
max memory size (kbytes, -m) unlimited
open files (-n) 1048576
pipe size (512 bytes, -p) 8
POSIX message queues (bytes, -q) 819200
real-time priority (-r) 0
stack size (kbytes, -s) 8192
cpu time (seconds, -t) unlimited
max user processes (-u) 31178
virtual memory (kbytes, -v) unlimited
file locks (-x) unlimited
Run again and check the message with the core dump file.
$ ./cd_test
Segmentation fault (core dumped)
$ ll
total 148
drwxr-xr-x 2 josh josh 4096 Aug 25 14:44 ./
drwxr-xr-x 9 josh josh 4096 Aug 25 14:41 ../
-rwxr-xr-x 1 josh josh 16912 Aug 25 14:39 cd_test*
-rw------- 1 josh josh 294912 Aug 25 14:44 core
-rwxrwxrwx 1 josh josh 84 Aug 25 14:38 core_dump_test.c*
Debug with the core dump using GDB
$ gdb cd_test core
GNU gdb (Ubuntu 12.1-0ubuntu1~22.04) 12.1
Copyright (C) 2022 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 "x86_64-linux-gnu".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<https://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"...
--Type <RET> for more, q to quit, c to continue without paging--
Reading symbols from cd_test...
[New LWP 10011]
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
Core was generated by `./cd_test'.
Program terminated with signal SIGSEGV, Segmentation fault.
#0 0x0000562ee5dec13d in main () at core_dump_test.c:5
5 *ptr = 10;
(gdb)
Simple GDB commands
(gdb) print ptr
$1 = (int *) 0x0
(gdb) info locals
ptr = 0x0
(gdb) info args
No arguments.
(gdb) info reg
rax 0x0 0
rbx 0x0 0
rcx 0x562ee5deedf8 94759425076728
rdx 0x7ffc889cb388 140722600457096
rsi 0x7ffc889cb378 140722600457080
rdi 0x1 1
rbp 0x7ffc889cb260 0x7ffc889cb260
rsp 0x7ffc889cb260 0x7ffc889cb260
r8 0x7f8068441f10 140189481836304
r9 0x7f806845c040 140189481943104
r10 0x7f8068456908 140189481920776
r11 0x7f8068471680 140189482030720
r12 0x7ffc889cb378 140722600457080
r13 0x562ee5dec129 94759425065257
r14 0x562ee5deedf8 94759425076728
r15 0x7f8068490040 140189482156096
rip 0x562ee5dec13d 0x562ee5dec13d <main+20>
eflags 0x10246 [ PF ZF IF RF ]
cs 0x33 51
ss 0x2b 43
ds 0x0 0
es 0x0 0
fs 0x0 0
gs 0x0 0
(gdb) backtrace
#0 0x0000562ee5dec13d in main () at core_dump_test.c:5
(gdb) disas main
Dump of assembler code for function main:
0x0000562ee5dec129 <+0>: endbr64
0x0000562ee5dec12d <+4>: push %rbp
0x0000562ee5dec12e <+5>: mov %rsp,%rbp
0x0000562ee5dec131 <+8>: movq $0x0,-0x8(%rbp)
0x0000562ee5dec139 <+16>: mov -0x8(%rbp),%rax
=> 0x0000562ee5dec13d <+20>: movl $0xa,(%rax)
0x0000562ee5dec143 <+26>: mov $0x0,%eax
0x0000562ee5dec148 <+31>: pop %rbp
0x0000562ee5dec149 <+32>: ret
End of assembler dump.
(gdb) i proc m
Mapped address spaces:
Start Addr End Addr Size Offset objfile
0x562ee5deb000 0x562ee5dec000 0x1000 0x0 /home/josh/workspace/Workspace/Sandbox/CoreDump/cd_test
0x562ee5dec000 0x562ee5ded000 0x1000 0x1000 /home/josh/workspace/Workspace/Sandbox/CoreDump/cd_test
0x562ee5ded000 0x562ee5dee000 0x1000 0x2000 /home/josh/workspace/Workspace/Sandbox/CoreDump/cd_test
0x562ee5dee000 0x562ee5def000 0x1000 0x2000 /home/josh/workspace/Workspace/Sandbox/CoreDump/cd_test
0x562ee5def000 0x562ee5df0000 0x1000 0x3000 /home/josh/workspace/Workspace/Sandbox/CoreDump/cd_test
0x7f8068227000 0x7f806824f000 0x28000 0x0 /usr/lib/x86_64-linux-gnu/libc.so.6
0x7f806824f000 0x7f80683e4000 0x195000 0x28000 /usr/lib/x86_64-linux-gnu/libc.so.6
0x7f80683e4000 0x7f806843c000 0x58000 0x1bd000 /usr/lib/x86_64-linux-gnu/libc.so.6
0x7f806843c000 0x7f8068440000 0x4000 0x214000 /usr/lib/x86_64-linux-gnu/libc.so.6
0x7f8068440000 0x7f8068442000 0x2000 0x218000 /usr/lib/x86_64-linux-gnu/libc.so.6
0x7f8068456000 0x7f8068458000 0x2000 0x0 /usr/lib/x86_64-linux-gnu/ld-linux-x86-64.so.2
0x7f8068458000 0x7f8068482000 0x2a000 0x2000 /usr/lib/x86_64-linux-gnu/ld-linux-x86-64.so.2
0x7f8068482000 0x7f806848d000 0xb000 0x2c000 /usr/lib/x86_64-linux-gnu/ld-linux-x86-64.so.2
0x7f806848e000 0x7f8068490000 0x2000 0x37000 /usr/lib/x86_64-linux-gnu/ld-linux-x86-64.so.2
0x7f8068490000 0x7f8068492000 0x2000 0x39000 /usr/lib/x86_64-linux-gnu/ld-linux-x86-64.so.2
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