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joyhuang9473/bar.c

Last active September 18, 2018 06:50
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bar.c
#include <stdlib.h>
void bar(int *val) {
*val = 11;
val = NULL;
*val = 17;
}
Raw
bar.h
void bar(int*);
Raw
foo.c
#include "bar.h"
int foo = 3;
int main()
{
foo = 8;
bar(&foo);
return 0;
}
Raw
gdb_foobar.log
user@pc:~$ gcc -Wall -g -fPIC -shared bar.c -o libbar.so
user@pc:~$ gcc -Wall -g foo.c ./libbar.so -o foobar
user@pc:~$ gdb foobar
GNU gdb (Ubuntu 7.11.1-0ubuntu1~16.5) 7.11.1
Copyright (C) 2016 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:
<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 foobar...done.
(gdb) break main
Breakpoint 1 at 0x40068a: file foo.c, line 5.
(gdb) display foo
1: foo = 3
(gdb) run
Starting program: /home/user/foobar
Breakpoint 1, main () at foo.c:5
5 foo = 8;
1: foo = 3
(gdb) info shared
From To Syms Read Shared Object Library
0x00007ffff7dd7ac0 0x00007ffff7df5850 Yes /lib64/ld-linux-x86-64.so.2
0x00007ffff7bd5550 0x00007ffff7bd5677 Yes ./libbar.so
0x00007ffff782a8b0 0x00007ffff797db04 Yes /lib/x86_64-linux-gnu/libc.so.6
(gdb) next
6 bar(&foo);
1: foo = 8
(gdb) step
bar (val=0x601038 <foo>) at bar.c:3
3 *val = 11;
1: foo = 8
(gdb) info stack
#0 bar (val=0x601038 <foo>) at bar.c:3
#1 0x000000000040069e in main () at foo.c:6
(gdb) list
1 #include <stdlib.h>
2 void bar(int *val) {
3 *val = 11;
4 val = NULL;
5 *val = 17;
6 }
(gdb) display val
2: val = (int *) 0x601038 <foo>
(gdb) print val
$1 = (int *) 0x601038 <foo>
(gdb) step
4 val = NULL;
1: foo = 11
2: val = (int *) 0x601038 <foo>
(gdb) step
5 *val = 17;
1: foo = 11
2: val = (int *) 0x0
(gdb) step
Program received signal SIGSEGV, Segmentation fault.
0x00007ffff7bd566e in bar (val=0x0) at bar.c:5
5 *val = 17;
1: foo = 11
2: val = (int *) 0x0
(gdb) break bar
Breakpoint 2 at 0x7ffff7bd5658: file bar.c, line 3.
(gdb) info breakpoints
Num Type Disp Enb Address What
1 breakpoint keep y 0x000000000040068a in main at foo.c:5
breakpoint already hit 1 time
2 breakpoint keep y 0x00007ffff7bd5658 in bar at bar.c:3
(gdb) delete 1
(gdb) run
The program being debugged has been started already.
Start it from the beginning? (y or n) y
Starting program: /home/user/foobar
Breakpoint 2, bar (val=0x601038 <foo>) at bar.c:3
3 *val = 11;
1: foo = 8
2: val = (int *) 0x601038 <foo>
(gdb) step
4 val = NULL;
1: foo = 11
2: val = (int *) 0x601038 <foo>
(gdb) shell vim bar.c
(gdb) shell gcc -Wall -g -fPIC -shared bar.c -o libbar.so
(gdb) run
The program being debugged has been started already.
Start it from the beginning? (y or n) y
Starting program: /home/user/foobar
Breakpoint 2, bar (val=0x601038 <foo>) at bar.c:3
3 *val = 11;
1: foo = 8
2: val = (int *) 0x601038 <foo>
(gdb) c
Continuing.
[Inferior 1 (process 15540) exited normally]
(gdb)
Raw
gdb_foobar_2.log
user@pc:~$ gcc -Wall -fPIC -shared bar.c -o libbar.so
user@pc:~$ gcc -Wall -g foo.c ./libbar.so -o foobar
user@pc:~$ gdb foobar
GNU gdb (Ubuntu 7.11.1-0ubuntu1~16.5) 7.11.1
Copyright (C) 2016 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:
<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 foobar...done.
(gdb) watch foo
Hardware watchpoint 1: foo
(gdb) run
Starting program: /home/user/foobar
Hardware watchpoint 1: foo
Old value = 3
New value = 8
main () at foo.c:6
6 bar(&foo);
(gdb) stepi
0x0000000000400699 6 bar(&foo);
(gdb) stepi
0x0000000000400560 in bar@plt ()
(gdb) info stack
#0 0x0000000000400560 in bar@plt ()
#1 0x000000000040069e in main () at foo.c:6
(gdb) info frame
Stack level 0, frame at 0x7fffffffe480:
rip = 0x400560 in bar@plt; saved rip = 0x40069e
called by frame at 0x7fffffffe490
Arglist at 0x7fffffffe470, args:
Locals at 0x7fffffffe470, Previous frame's sp is 0x7fffffffe480
Saved registers:
rip at 0x7fffffffe478
(gdb) step
Single stepping until exit from function bar@plt,
which has no line number information.
0x00007ffff7bd5650 in bar () from ./libbar.so
(gdb) info stack
#0 0x00007ffff7bd5650 in bar () from ./libbar.so
#1 0x000000000040069e in main () at foo.c:6
(gdb) infor frame
Undefined command: "infor". Try "help".
(gdb) info frame
Stack level 0, frame at 0x7fffffffe480:
rip = 0x7ffff7bd5650 in bar; saved rip = 0x40069e
called by frame at 0x7fffffffe490
Arglist at 0x7fffffffe470, args:
Locals at 0x7fffffffe470, Previous frame's sp is 0x7fffffffe480
Saved registers:
rip at 0x7fffffffe478
(gdb) stepi
0x00007ffff7bd5651 in bar () from ./libbar.so
(gdb) stepi
0x00007ffff7bd5654 in bar () from ./libbar.so
(gdb) stepi
0x00007ffff7bd5658 in bar () from ./libbar.so
(gdb) stepi
0x00007ffff7bd565c in bar () from ./libbar.so
(gdb) stepi
Hardware watchpoint 1: foo
Old value = 8
New value = 11
0x00007ffff7bd5662 in bar () from ./libbar.so
(gdb) stepi
0x00007ffff7bd566a in bar () from ./libbar.so
(gdb) stepi
0x00007ffff7bd566e in bar () from ./libbar.so
(gdb) stepi
Program received signal SIGSEGV, Segmentation fault.
0x00007ffff7bd566e in bar () from ./libbar.so
(gdb) disassemble 0x00007ffff7bd566e
Dump of assembler code for function bar:
0x00007ffff7bd5650 <+0>: push %rbp
0x00007ffff7bd5651 <+1>: mov %rsp,%rbp
0x00007ffff7bd5654 <+4>: mov %rdi,-0x8(%rbp)
0x00007ffff7bd5658 <+8>: mov -0x8(%rbp),%rax
0x00007ffff7bd565c <+12>: movl $0xb,(%rax)
0x00007ffff7bd5662 <+18>: movq $0x0,-0x8(%rbp)
0x00007ffff7bd566a <+26>: mov -0x8(%rbp),%rax
=> 0x00007ffff7bd566e <+30>: movl $0x11,(%rax)
0x00007ffff7bd5674 <+36>: nop
0x00007ffff7bd5675 <+37>: pop %rbp
0x00007ffff7bd5676 <+38>: retq
End of assembler dump.
(gdb) run
The program being debugged has been started already.
Start it from the beginning? (y or n) y
Starting program: /home/user/foobar
Hardware watchpoint 1: foo
Old value = 3
New value = 8
main () at foo.c:6
6 bar(&foo);
(gdb) step
Hardware watchpoint 1: foo
Old value = 8
New value = 11
0x00007ffff7bd5662 in bar () from ./libbar.so
(gdb) stepi
0x00007ffff7bd566a in bar () from ./libbar.so
(gdb) stepi
0x00007ffff7bd566e in bar () from ./libbar.so
(gdb) stepi
Program received signal SIGSEGV, Segmentation fault.
0x00007ffff7bd566e in bar () from ./libbar.so
(gdb) disassemble 0x00007ffff7bd566e
Dump of assembler code for function bar:
0x00007ffff7bd5650 <+0>: push %rbp
0x00007ffff7bd5651 <+1>: mov %rsp,%rbp
0x00007ffff7bd5654 <+4>: mov %rdi,-0x8(%rbp)
0x00007ffff7bd5658 <+8>: mov -0x8(%rbp),%rax
0x00007ffff7bd565c <+12>: movl $0xb,(%rax)
0x00007ffff7bd5662 <+18>: movq $0x0,-0x8(%rbp)
0x00007ffff7bd566a <+26>: mov -0x8(%rbp),%rax
=> 0x00007ffff7bd566e <+30>: movl $0x11,(%rax)
0x00007ffff7bd5674 <+36>: nop
0x00007ffff7bd5675 <+37>: pop %rbp
0x00007ffff7bd5676 <+38>: retq
End of assembler dump.
(gdb) shell objdump -d libbar.so | less
(gdb) shell vim libbar.so
(gdb) run
The program being debugged has been started already.
Start it from the beginning? (y or n) y
Starting program: /home/user/foobar
Hardware watchpoint 1: foo
Old value = 3
New value = 8
main () at foo.c:6
6 bar(&foo);
(gdb) step
Hardware watchpoint 1: foo
Old value = 8
New value = 11
0x00007ffff7bd5662 in bar () from ./libbar.so
(gdb) step
Single stepping until exit from function bar,
which has no line number information.
main () at foo.c:8
8 return 0;
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