GDB Usage

From Richliu's wiki

目錄 1 設定 2 參數 3 基本指令 4 Setting breakpoints 4.1 Setting Catch point 4.2 Delete breakpoint 4.3 Breakpoint Commands 4.4 Signal 4.5 Stopping and starting multi-thread programs 5 Debugging programs with multiple threads 6 Examining Source Files 6.1 Searching Source files 6.2 Source and Machine Code 7 Examining Data 7.1 Examining Memory 7.2 Automatic Display 7.3 Print settings 7.4 Register 7.5 Memory Region Attributes 8 操作 9 Reference

設定

• ex: set width 70

參數

• gdb program core : 有 Core File 的時候用
• gdb program 1234 : will assign this program to pid 1234

基本指令

• break 設中斷點: ex: break m4_changequote
• run 設行程式: ex: run
• n next
  • n [count]
• s step(會進 subfunction)
  • s [count]

• p 列出參數: ex: p rqueue
  • p file:variable
  • p function:variable

• l 列出 source code ex: l
• quit 離開
• info breakpoint 看 breakpoint 的 state
• b 設定中斷點
• f show frame
• bt backtrace : 向後追
  • bt [n] backtrace 追幾個
  • info frame/ info f
  • info locals : print the local variables of the selected frame 可以列出 frame 內的 local 變數

Setting breakpoints

• break function
• break +offset
• break -offset
• break linenum
• break filename:linenum
• break fllename:function
• break *address 給沒有 debug information 用
• break Without any arguments, break sets a breakpoint at the next instruction.
• break .... if cond
• rbreak regex 用 Regular expression 去 break 所有的 function
• info breakpoints [n]
• info break [n]
• info watchpoints [n]
• watch expr 寫入 expr 時中斷
• rwatch expr 讀出 expr 時中斷
• awatch expr 讀寫 expr 時中斷

Setting Catch point

• catch event
  • throw : The throw of a C++ exception
  • catch : The catching of a C++ exception

Delete breakpoint

• clear  : Delete any breakpoints
• clear function
• clear filename:functin
• clear filename:linenum
• delete [breakpoints] [range...] 刪除所有的 breakpoint, watchpoints or catchpoints
• disable [breakpoints] [range...]
• enable [breakpoints] [range...]
• delete [breakpoints] once range...
• delete [breakpoints] delete range...

Breakpoint Commands

ex:

break foo if x>0
commands
silent
printf "x is %d\n",x
cont
end

Signal

• info signals
• info handle print table of all the kinds of signals and how GDB has been told to handle each one.
• handle signal keywords.
  • keywords
    • nostop 當 signal 發生時不會停
    • stop 當 signal 發生時會停止
    • print 當 signal 發生時會印出訊息
    • noprint 和 nostop 一樣
    • pass/noignore 讓程式看到 signal 並且 handle it
    • nopass/ignore 不謞程式看到/handle signal

Stopping and starting multi-thread programs

• break linespac thead threano
• break linespaec thread thradno if ...

 ex: break frik.c:13 thread 28 if bartab > lim

Debugging programs with multiple threads

GDB provodes there facilities for debugging multi-thread programs:

• automatic notification of new threads
• 'thread threadno', a comand to switch among threads
• 'info threads', a command to inquire about existing threads
• 'thread apply [theadno] [all] args', a command to apply a command to a list of threads.
• thread-specific breakpoints

Examining Source Files

• list linenum
• list function
• list - # Print lines just before the lines last printed
• set listsize count
• set listsize

• list first,last # first, 和 last 可拿掉其中一個, 要保留 ,

Searching Source files

• forward-search regexp
• search regexp
• reverse-search regexp

Source and Machine Code

• set disassembly-flavor instruction-set
  • intel : intel style assembly
  • att : AT&T style assembly

• step 1

(gdb) info line 9
Line 9 of "test.c" starts at address 0x804839e <main+42>
and ends at 0x80483b1 <main+61>.

• step 2

(gdb) info line *0x804839e
Line 9 of "test.c" starts at address 0x804839e <main+42>
and ends at 0x80483b1 <main+61>.

• step 3

(gdb) disas  0x804839e 0x80483b1
Dump of assembler code from 0x804839e to 0x80483b1:
0x0804839e <main+42>:   mov    0xfffffffc(%ebp),%eax
0x080483a1 <main+45>:   mov    %eax,0x4(%esp)
0x080483a5 <main+49>:   movl   $0x80484c8,(%esp)
0x080483ac <main+56>:   call   0x80482a8 <_init+56>
End of assembler dump.

Examining Data

Examining Memory

• x/nfu addr
• x addr
• x

• • n, 重複次數
  • f, 顯示格式, 和 printf 一樣
  • u, 單位格式
    • b Bytes.
    • h Halfwords (Two Bytes)
    • w Words (four bytes). Default
    • g Giant words ( eight bytes)
  • addr 開始顯示位置, 可以用 info btrakpoints , info line , print 找出來

Automatic Display

每一個 Step 都顯示 Variables

• display expr
• display /fmt expr
• display /fmt addr
• delete display [dnum]
• disable display [dnum]
• enable display [dnum]
• info display

Print settings

• set print address/ set print address on # default

(gdb) s
evalaa (a=0xbffffa04, b=0xbffffa00) at test.c:4
4          return *a+*b;
(gdb) x 0xbffffa04
0xbffffa04:     0x00000001
(gdb) x 0xbffffa00
0xbffffa00:     0x00000002
(gdb) f
#0  evalaa (a=0xbffffa04, b=0xbffffa00) at test.c:4
4          return *a+*b;

• set print address off

(gdb) f
#0  evalaa (a=, b=) at test.c:4
4          return *a+*b;

Register

• info register 列出常用的 Register
• info all-registers 列出所有的 Register, ex: mmx
• info registers regname

也可以用這種方式看 register

p/x $PC
x/i $PC

如果要改變 stack

set $sp +=4

• info float 查看浮點運算器

Memory Region Attributes

• mem address1 address2 attributes
• delete mem nums
• disable mem nums
• enable mem nums
• info mem
  • Attributes
    • ro
    • wo
    • rw
    • 8 use 8 bit memory accesses
    • 16
    • 32
    • 64
    • cache : Enable GDB to cache target memory
    • nocache : Disable GDB from caching target memory.

操作

• C+d 離開

Reference

Debugging with GDB the GNU Source-Level Debugger for GDB version 5.1.1 ISBN 1-882114-88-4