Script started on Fri 20 Apr 2018 07:49:27 PM PDT
kmwinst@klaatu:~/lecture11$ ./reverse
Please enter a string: foo
Segmentation fault
kmwinst@klaatu:~/lecture11\klaatu:~/lecture11$ gdb reverse
GNU gdb (GDB) Red Hat Enterprise Linux 7.11-67.el7
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-redhat-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 reverse...done.
(gdb) run
Starting program: /homes/mwinst/lecture11/reverse 
Missing separate debuginfos, use: debuginfo-install glibc-2.17-196.el7_4.2.x86_64
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".
Please enter a string: foo

Program received signal SIGSEGV, Segmentation fault.
0x00007ffff764f710 in __strcpy_sse2 () from /lib64/libc.so.6
Missing separate debuginfos, use: debuginfo-install libgcc-4.8.5-16.el7_4.2.x86_64 libstdc++-4.8.5-16.el7_4.2.x86_64 zlib-1.2.7-17.el7.x86_64
(gdb) backtrace
#0  0x00007ffff764f710 in __strcpy_sse2 () from /lib64/libc.so.6
#1  0x00000000004006bd in reverse (s=0x7fffffffdcb0 "foo\n") at reverse.c:19
#2  0x000000000040076b in main () at reverse.c:41
(gdb) bt
#0  0x00007ffff764f710 in __strcpy_sse2 () from /lib64/libc.so.6
#1  0x00000000004006bd in reverse (s=0x7fffffffdcb0 "foo\n") at reverse.c:19
#2  0x000000000040076b in main () at reverse.c:41
(gdb) up
#1  0x00000000004006bd in reverse (s=0x7fffffffdcb0 "foo\n") at reverse.c:19
19	  strcpy(result, s);
(gdb) list
14	  char * result = NULL;            /* the reversed string */
15	  int L, R;
16	  char ch;
17	
18	  /* copy original string then reverse and return the copy */
19	  strcpy(result, s);
20	
21	  L = 0;
22	  R = strlen(result);
23	  while (L < R) {
(gdb) up
#2  0x000000000040076b in main () at reverse.c:41
41	  rev_line = reverse(line);
(gdb) list
36	  char line[MAX_STR];    /* original input line */
37	  char * rev_line;       /* backwards copy from reverse function */
38	
39	  printf("Please enter a string: ");
40	  fgets(line, MAX_STR, stdin);
41	  rev_line = reverse(line);
42	  printf("The original string was:   >%s<\n", line);
43	  printf("Backwards, that string is: >%s<\n", rev_line);
44	  printf("Thank you for trying our program.\n");
45	  return EXIT_SUCCESS;
(gdb) print line
$1 = "foo\n\000\000\000\000\030\000\000\000\001", '\000' <repeats 35 times>, "\001\000\000\000\000\000\000\000\375\a@", '\000' <repeats 21 times>, "\260\a@\000\000\000\000\000\240\005@\000\000\000\000\000\000\336\377\377"
(gdb) p line
$2 = "foo\n\000\000\000\000\030\000\000\000\001", '\000' <repeats 35 times>, "\001\000\000\000\000\000\000\000\375\a@", '\000' <repeats 21 times>, "\260\a@\000\000\000\000\000\240\005@\000\000\000\000\000\000\336\377\377"
(gdb) down
#1  0x00000000004006bd in reverse (s=0x7fffffffdcb0 "foo\n") at reverse.c:19
19	  strcpy(result, s);
(gdb) p s
$3 = 0x7fffffffdcb0 "foo\n"
(gdb) p result
$4 = 0x0
(gdb) p L
$5 = 32767
(gdb) p R
$6 = -8928
(gdb) info locals
result = 0x0
L = 32767
R = -8928
ch = 0 '\000'
(gdb) quit
A debugging session is active.

	Inferior 1 [process 20734] will be killed.

Quit anyway? (y or n) y
kmwinst@klaatu:~/lecture11\klaatu:~/lecture11$ emacs reverse.c
kmwinst@klaatu:~/lecture11\klaatu:~/lecture11$ gcc -Wall -std=c11 -g -o reverse reverse.c
kmwinst@klaatu:~/lecture11\klaatu:~/lecture11$ ./reverse
Please enter a string: foo
The original string was:   >foo
<
Backwards, that string is: ><
Thank you for trying our program.
kmwinst@klaatu:~/lecture11\klaatu:~/lecture11$ gdb reverse
GNU gdb (GDB) Red Hat Enterprise Linux 7.11-67.el7
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-redhat-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 reverse...done.
(gdb) break reverse
Breakpoint 1 at 0x4006a6: file reverse.c, line 18.
(gdb) run
Starting program: /homes/mwinst/lecture11/reverse 
Missing separate debuginfos, use: debuginfo-install glibc-2.17-196.el7_4.2.x86_64
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".
Please enter a string: b foo

Breakpoint 1, reverse (s=0x7fffffffdcb0 "foo\n", result=0x7fffffffdc40 "") at reverse.c:18
18	  strcpy(result, s);
Missing separate debuginfos, use: debuginfo-install libgcc-4.8.5-16.el7_4.2.x86_64 libstdc++-4.8.5-16.el7_4.2.x86_64 zlib-1.2.7-17.el7.x86_64
(gdb) bt
#0  reverse (s=0x7fffffffdcb0 "foo\n", result=0x7fffffffdc40 "") at reverse.c:18
#1  0x0000000000400774 in main () at reverse.c:41
(gdb) list
13	char * reverse(char * s, char * result) {
14	  int L, R;
15	  char ch;
16	
17	  /* copy original string then reverse and return the copy */
18	  strcpy(result, s);
19	
20	  L = 0;
21	  R = strlen(result);
22	  while (L < R) {
(gdb) p s
$1 = 0x7fffffffdcb0 "foo\n"
(gdb) p strlen(s)
$2 = 4
(gdb) step
20	  L = 0;
(gdb) p result
$3 = 0x7fffffffdc40 "foo\n"
(gdb) step
21	  R = strlen(result);
(gdb) step
22	  while (L < R) {
(gdb) p L
$4 = 0
(gdb) p R
$5 = 4
(gdb) list
17	  /* copy original string then reverse and return the copy */
18	  strcpy(result, s);
19	
20	  L = 0;
21	  R = strlen(result);
22	  while (L < R) {
23	    ch = result[L];
24	    result[L] = result[R];
25	    result[R] = ch;
26	    L++; R--;
(gdb) step
23	    ch = result[L];
(gdb) step
24	    result[L] = result[R];
(gdb) p ch
$6 = 102 'f'
(gdb) p result[R]
$7 = 0 '\000'
(gdb) quit
A debugging session is active.

	Inferior 1 [process 20972] will be killed.

Quit anyway? (y or n) y
kmwinst@klaatu:~/lecture11\klaatu:~/lecture11$ emacs reverse.c
kmwinst@klaatu:~/lecture11\klaatu:~/lecture11$ gcc -Wall -std=c11 -g -o reverse reverse.c
kmwinst@klaatu:~/lecture11\klaatu:~/lecture11$ ./reverse
Please enter a string: foo
The original string was:   >foo
<
Backwards, that string is: >
oof<
Thank you for trying our program.
kmwinst@klaatu:~/lecture11\klaatu:~/lecture11$ exit

Script done on Fri 20 Apr 2018 07:54:12 PM PDT