3. int main(int argc, char *argv[]) { int number; int *pointer; number = atoi(argv[1]); pointer = number; print(number); return 0; } void print(int *x) { printf("The number supplied is %d", *x); }
4. $ gcc -o test test.c test.c: In function ‘main’: test.c:7:13: warning: assignment makes pointer from integer without a cast test.c: At top level: test.c:8:5: note: previous implicit declaration of ‘print’ was here test.c: In function ‘print’: test.c:15:5: warning: incompatible implicit declaration of built-in function ‘printf’ $ ./test Segmentation fault
5. $ gdb test Reading symbols from /home/user/test...(no debugging symbols found)...done. (gdb) run Starting program: /home/user/test Program received signal SIGSEGV, Segmentation fault. 0x00007ffff7a82b35 in ?? () from /lib/x86_64-linux-gnu/libc.so.6
6. (gdb) backtrace #0 0x00007ffff7a82b35 in ?? () from /lib/x86_64-linux-gnu/libc.so.6 #1 0x00007ffff7a7f900 in atoi () from /lib/x86_64-linux-gnu/libc.so.6 #2 0x000000000040056b in main ()
10. (gdb) info locals No symbol table info available. (gdb) info args No symbol table info available. (gdb) quit A debugging session is active. Inferior 1 [process 29043] will be killed. Quit anyway? (y or n) y
11. $ gcc -g -o test test.c $ gdb test Reading symbols from /home/ium/test...done. (gdb) list 1 int main(int argc, char *argv[]) 2 { 3 int number; 4 int *pointer; 5 6 number = atoi(argv[1]); 7 pointer = number; 8 print(number); 9 10 return 0;
12. (gdb) break 6 Breakpoint 1 at 0x400553: file test.c, line 6. (gdb) run Starting program: /home/ium/test Breakpoint 1, main (argc=1, argv=0x7fffffffe248) at test.c:6 6 number = atoi(argv[1]); (gdb) print argv[1] $1 = 0x0
13. (gdb) continue Continuing. Program received signal SIGSEGV, Segmentation fault. 0x00007ffff7a82b35 in ?? () from /lib/x86_64-linux-gnu/libc.so.6
14. (gdb) delete Delete all breakpoints? (y or n) y (gdb) run 255 The program being debugged has been started already. Start it from the beginning? (y or n) y Starting program: /home/user/test 255 Program received signal SIGSEGV, Segmentation fault. 0x000000000040059f in print (x=0xff) at test.c:15 15 printf("The number supplied is %d", *x);
15. (gdb) backtrace #0 0x000000000040059f in print (x=0xff) at test.c:15 #1 0x0000000000400588 in main (argc=2, argv=0x7fffffffe228) at test.c:8 (gdb) info args x = 0xff (gdb) frame 1 #1 0x0000000000400588 in main (argc=2, argv=0x7fffffffe228) at test.c:8 8 print(number);
16. (gdb) info locals number = 255 pointer = 0xff (gdb) frame 0 (gdb) x /5i $rip => 0x40059f <print+16>: mov (%rax),%eax 0x4005a1 <print+18>: mov %eax,%esi 0x4005a3 <print+20>: mov $0x4006ac,%edi 0x4005a8 <print+25>: mov $0x0,%eax 0x4005ad <print+30>: callq 0x400428 <print@plt> (gdb) x /s 0x4006ac 0x4006ac: "The number supplied is %d"
