---
tags: Development Note
---
[TOC]
# [DN-03]GDB 使用紀錄
開始試著用 GDB 來檢查追蹤程式流程和記憶體分配，跟著 GDB 來學習...
透過 GDB 來觀察 merge_soft 程式 [https://github.com/Lukechin/mergesort_doubly_linked_list/blob/master/mergesort.c ](https://)

### **編譯可以 debug 的輸出檔**
首先使用 GDB 蹤程式前，需要在編譯階段增加 ”-g” 參數來產生 debugging info
我們先編譯 merge_soft.c 並產生含有 debugging info 的執行檔 ”merge_soft”

$ gcc -g -o merge_soft merge_soft.c

### **編譯時產生preprocesser**

$ gcc -E -P

### **透過 GDB 來追蹤程式**

$ gdb merge_soft


### 常用命令
+ `b <line_number>` - setting breakpoint at <line_number>
+ `info b` - print breakpoints information
+ `disable b <break_number>` - disable target breakpoint

+ `continue` - run after code...
+ `Next` - run next instruct (no entry sub function)
+ `Step` - run next instruct (entry sub funxtion)
+ `List` - list the source code and each execution’s corresponding line number
+ `Backtrace` - show trace of all function calls in stack
+ `Info frame` - List address, language, address of arguments/local variables and which registers were saved in frame.
+ This will show where the return address is saved
+ Return address is in Register EIP
+ Calling stack pointer is in Register EBP

+ `x &variable` - show the address and value of a local variable (in hex format)
+ `x address` - print binary representation of 4 bytes of memory pointed to by address.

### 參考資料
+ [Buffer Overflow : Example of Using GDB to Check Stack Memory](http://www.cs.ucf.edu/~czou/CAP6135-12/bufferOverFlow-gdb-example.ppt)