Owen Hsu: Introduction to gdb https://www.slideshare.net/owenhsu/introduction-to-gdb-3790833

gdb_hello.log

user@pc:~$ gcc -Wall -g hello.c -o hello
user@pc:~$ gdb hello

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 hello...done.
(gdb) break main
Breakpoint 1 at 0x40055a: file hello.c, line 9.
(gdb) run 123 abc
Starting program: /home/user/hello 123 abc

Breakpoint 1, main (argc=3, argv=0x7fffffffe558) at hello.c:9
9   printf("\n%s\n\n", szHello);
(gdb) list
4 }
5 
6 const char *szHello = "Hello World";
7 int main(int argc, char *argv[])
8 {
9   printf("\n%s\n\n", szHello);
10    
11    int i;
12    for (i=0; i<argc; i++) {
13      printf("argv[%d]\n", i);
(gdb) break 14
Breakpoint 2 at 0x400590: file hello.c, line 14.
(gdb) continue
Continuing.

Hello World

argv[0]

Breakpoint 2, main (argc=3, argv=0x7fffffffe558) at hello.c:14
14      printf("- main: %s\n", argv[i]);
(gdb) next
- main: /home/user/hello
15      func(argv[i]);
(gdb) step
func (pMem=0x7fffffffe790 "/home/user/hello") at hello.c:3
3   printf("- func: %p\n\n", pMem);
(gdb) backtrace
#0  func (pMem=0x7fffffffe790 "/home/user/hello") at hello.c:3
#1  0x00000000004005d8 in main (argc=3, argv=0x7fffffffe558) at hello.c:15
(gdb) list
1 #include <stdio.h>
2 void func(char *pMem) {
3   printf("- func: %p\n\n", pMem);
4 }
5 
6 const char *szHello = "Hello World";
7 int main(int argc, char *argv[])
8 {
9   printf("\n%s\n\n", szHello);
10    
(gdb) print pMem
$1 = 0x7fffffffe790 "/home/user/hello"
(gdb) continue
Continuing.
- func: 0x7fffffffe790

argv[1]

Breakpoint 2, main (argc=3, argv=0x7fffffffe558) at hello.c:14
14      printf("- main: %s\n", argv[i]);
(gdb) next
- main: 123
15      func(argv[i]);
(gdb) step
func (pMem=0x7fffffffe7a7 "123") at hello.c:3
3   printf("- func: %p\n\n", pMem);
(gdb) print pMem
$2 = 0x7fffffffe7a7 "123"
(gdb) pinrt *pMem
Undefined command: "pinrt".  Try "help".
(gdb) print *pMem
$3 = 49 '1'
(gdb) continue
Continuing.
- func: 0x7fffffffe7a7

argv[2]

Breakpoint 2, main (argc=3, argv=0x7fffffffe558) at hello.c:14
14      printf("- main: %s\n", argv[i]);
(gdb) next
- main: abc
15      func(argv[i]);
(gdb) next
- func: 0x7fffffffe7ab

12    for (i=0; i<argc; i++) {
(gdb) continue
Continuing.
[Inferior 1 (process 15246) exited normally]

hello.c

#include <stdio.h>
void func(char *pMem) {
  printf("- func: %p\n\n", pMem);
}

const char *szHello = "Hello World";
int main(int argc, char *argv[])
{
  printf("\n%s\n\n", szHello);

  int i;
  for (i=0; i<argc; i++) {
    printf("argv[%d]\n", i);
    printf("- main: %s\n", argv[i]);
    func(argv[i]);
  }

  return 0;
}