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Creation-Date: 2012-12-25T22:10:21+08:00

====== gdb demo ======
Created Tuesday 25 December 2012

[geekard@geekard elf]$ **cat demo.c**
#include <stdio.h>
#include <stdlib.h>

int  globalVar = 1;
int  globalVarUninit;

static int  globalVarStatic = 3;

extern int externVar;
extern int add(int, int);
  
void greeting(char *name, int age, char** friends)
{

  int a = 23;
  char *nm = "zhangjun";
  char *fr[] = {"Tom", "John", "Pi", NULL};  //fr为__数组名称__，它指向一块内存单元，但是本身不咱用内存单元。
  char **fr = {"Tom", "John", "Pi", NULL};   //fr为__指针变量，指向一个保存有4个字符指针的内存单元(位于greeting的栈中)。__

  if (name == NULL)
     name = nm;
  if (age == 0)
     age = a;
  if (friends == NULL)
     friends = fr;

  printf("In greeting:\n");
  printf("\tHello, %s:\n", name);
  printf("\tYourt age is:%d.\n", age);
  printf("\tYourt friends are:\n");
  while (*friends != NULL) {
    printf("\t\t%s\n", *friends);
    friends += 1;
  }

 printf("Goodbye from greeting.\n");
}

int main(int argc, char *argv[]) 
{
  int autoVar = globalVar;
  static int staticVar = 2;
  int i = externVar;

  char *name = "geekard";
  int age = 23;
  char *friends[] = {"Tom", "John", "Pi", NULL};
  
  printf("In main:\n");
  printf("\tThe globalVarStatic is:%d\n",globalVarStatic);
  greeting(name, age, friends);
  add(2, 3);
}
[geekard@geekard elf]$ **cat foo.c** 
int externVar = 1;
int static staticVarStatic  = 2;

int add(int a, int b)
{ 
  return a + b;
}
[geekard@geekard elf]$ **gcc -g demo.c foo.c -o demo**
demo.c: In function ‘greeting’:
demo.c:18:3: warning: initialization from incompatible pointer type [enabled by default]
demo.c:18:3: warning: (near initialization for ‘fr’) [enabled by default]
demo.c:18:3: warning: excess elements in scalar initializer [enabled by default]
demo.c:18:3: warning: (near initialization for ‘fr’) [enabled by default]
demo.c:18:3: warning: excess elements in scalar initializer [enabled by default]
demo.c:18:3: warning: (near initialization for ‘fr’) [enabled by default]
demo.c:18:3: warning: excess elements in scalar initializer [enabled by default]
demo.c:18:3: warning: (near initialization for ‘fr’) [enabled by default]
[geekard@geekard elf]$ **gdb demo**
GNU gdb (GDB) 7.5.1
Copyright (C) 2012 Free Software Foundation, Inc.
。。。。。。
**(gdb) info source**
Current source file is demo.c
Compilation directory is /home/geekard/Code/elf
Located in /home/geekard/Code/elf/demo.c
Contains 53 lines.
Source language is c.
Compiled with DWARF 2 debugging format.
Does not include preprocessor macro info.
**(gdb) info sources**
Source files for which symbols have been read in:

/home/geekard/Code/elf/demo.c

Source files for which symbols will be read in on demand:

/home/geekard/Code/elf/foo.c

**(gdb) set args -a aa --bb=bbb ccc ** //设置dmo程序的默认命令行参数，执行run命令时会传入该参数。
**(gdb) show args  **//查看demo程序的命令行参数
Argument list to give program being debugged when it is started is "-a aa --bb=bbb ccc".
**(gdb) info args ** //查看当前stack frame对应函数的参数列表信息。
No frame selected.
(gdb) show env
XDG_VTNR=1
。。。。。
**(gdb) shell clear ** //执行shell命令，这里为clear。
**(gdb) info address greeting**  //在symbol table中查找greeting函数的入口地址
Symbol "greeting" is a function at address 0x804842c.
**(gdb) b 0x804842c  //在某个地址处设置断点时，地址前应该加星号，否则gdb认为它为函数名称。**
Function "0x804842c" not defined.
Make breakpoint pending on future shared library load? (y or [n]) n
**(gdb) b *0x804842c  **
Breakpoint 1 at 0x804842c: file demo.c, line 13.
**(gdb) b *greeting**  
Note: breakpoint 1 also set at pc 0x804842c.
Breakpoint 2 at 0x804842c: file demo.c, line 13.
**(gdb) b greeting**   //在greeting函数入口处设一个断点
Breakpoint 3 at 0x8048432: file demo.c, line 15.
**(gdb) info b**
Num     Type           Disp Enb Address    What
1      breakpoint     keep y   0x0804842c in greeting at demo.c:13
2       breakpoint     keep y   0x0804842c in greeting at demo.c:13
3      breakpoint     keep y   0x08048432 in greeting at demo.c:15
**(gdb) delete 2 //删除编号为2的断点**
**(gdb) list 12,16 //查看当前文件的12至16行。**
12      void greeting(char *name, int age, char** friends)
13      {
14
15        int a = 23;
16        char *nm = "zhangjun";
**(gdb) r**
Starting program: /home/geekard/Code/elf/demo -a aa --bb=bbb ccc  //gdb将set args命令的参数传给demo。
Breakpoint 1, greeting (name=0x804868b "geekard", age=23, friends=0xbffff950) at demo.c:13
13      {
**(gdb) disassemble greeting**   //反汇编greeting函数。如果disassmble没有参数，则默认反汇编当前所执行的函数。
Dump of assembler code for function greeting:
=> 0x0804842c <+0>:     push   %ebp  //demo停止在greeting函数的入口处，函数的prologue指令还没有执行。
   0x0804842d <+1>:     mov    %esp,%ebp
   0x0804842f <+3>:     sub    $0x28,%esp
(gdb) c  //继续执行，直到下一个断点处。
Continuing.

Breakpoint 3, greeting (name=0x804868b "geekard", age=23, friends=0xbffff950) at demo.c:15
15        int a = 23;
**(gdb) disassemble**  //反汇编当前执行的函数
Dump of assembler code for function greeting:
   0x0804842c <+0>:     push   %ebp
   0x0804842d <+1>:     mov    %esp,%ebp
   0x0804842f <+3>:     sub    $0x28,%esp
=> 0x08048432 <+6>:     movl   $0x17,-0xc(%ebp) //指令前的"=>"表示下一条**待执行**的指令位置。
//可见greeting的prologue指令已经执行，这意味着greeting的栈帧已经建立。但是greeting的auto variable初始化指令还没有执行。
   0x08048439 <+13>:    movl   $0x8048620,-0x10(%ebp)
   0x08048440 <+20>:    movl   $0x8048629,-0x14(%ebp)
   0x08048447 <+27>:    cmpl   $0x0,0x8(%ebp)
   0x0804844b <+31>:    jne    0x8048453 <greeting+39>
   0x0804844d <+33>:    mov    -0x10(%ebp),%eax
   0x08048450 <+36>:    mov    %eax,0x8(%ebp)
。。。。。
**(gdb) info args  //查看当前stack frame对应函数的参数列表。**
name = 0x804868b "geekard"
age = 23
friends = 0xbffff950  //传经来的时指针
**(gdb) info locals**   //greeting函数的auto variables还没有初始化，所以下列为无效值
a = -1209680176
nm = 0xbffff944 "\027"
fr = 0x80486a4  //
(gdb)