注：以下內容為學習筆記，多數是從書本、資料中得來，只為加深印象，及日後參考。然而本人表達能力較差，寫的不好。因非翻譯、非轉載，只好選原創，但多數乃摘抄，實為慚愧。但若能幫助一二訪客，幸甚！

除錯在程式設計中是不可缺少的，嘗試使用GDB 除錯一下昨晚的AT&T彙編程式碼：

[email protected]:~/program/asm/cpuid$ as -gstabs -o cpuid.o cpuid.s
[email protected]:~/program/asm/cpuid$ ls
cpuid.o  cpuid.s  cpuid.s~  makefile  makefile~
 
[email protected]:~/program/asm/cpuid$ ld -o cpuid cpuid.o
[email protected]:~/program/asm/cpuid$ gdb cpuid 
GNU gdb (GDB) 7.1-ubuntu
Copyright (C) 2010 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 "i486-linux-gnu".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from /home/liury/program/asm/cpuid/cpuid...done.
(gdb) l
1	# cpuid.s Sample program to extract the processor Vendor ID
2	.section .data
3	output:
4		.ascii "The processor Vendor ID is 'XXXXXXXXXXXX'\n"
5	
6	.section .text
7	.global _start
8	
9	_start:
10		movl	$0,	%eax		# The CPUID output option(the Vendor ID string)	
(gdb) break *_start
Breakpoint 1 at 0x8048074: file cpuid.s, line 10.
(gdb) r
Starting program: /home/liury/program/asm/cpuid/cpuid 
The processor Vendor ID is 'GenuineIntel'

Program exited normally.
(gdb) q
 

發現斷點處沒有停，後來得知此乃GDB的一個BUG...而必須在_start後面的第一個指令碼元素的位置包含一條偽指令。
需要在_start後面加一條NOP指令：

_start:
	nop
	movl	$0,	%eax
	cpuid

[email protected]:~/program/asm/cpuid$ gdb cpuid
GNU gdb (GDB) 7.1-ubuntu
Copyright (C) 2010 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 "i486-linux-gnu".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from /home/liury/program/asm/cpuid/cpuid...done.
(gdb) l
1	# cpuid.s Sample program to extract the processor Vendor ID
2	.section .data
3	output:
4		.ascii "The processor Vendor ID is 'XXXXXXXXXXXX'\n"
5	
6	.section .text
7	.global _start
8	
9	_start:
10		nop
(gdb) break *_start+1
Breakpoint 1 at 0x8048075: file cpuid.s, line 11.
(gdb) r
Starting program: /home/liury/program/asm/cpuid/cpuid 

Breakpoint 1, _start () at cpuid.s:11
11		movl	$0,	%eax		# The CPUID output option(the Vendor ID string)	
(gdb) next
12		cpuid
(gdb) info registers
eax            0x0	0
ecx            0x0	0
edx            0x0	0
ebx            0x0	0
esp            0xbffff0a0	0xbffff0a0
ebp            0x0	0x0
esi            0x0	0
edi            0x0	0
eip            0x804807a	0x804807a <_start+6>
eflags         0x212	[ AF IF ]
cs             0x73	115
ss             0x7b	123
ds             0x7b	123
es             0x7b	123
fs             0x0	0
gs             0x0	0
(gdb) n
13		movl	$output,%edi
(gdb) info registers
eax            0xa	10
ecx            0x6c65746e	1818588270
edx            0x49656e69	1231384169
ebx            0x756e6547	1970169159
esp            0xbffff0a0	0xbffff0a0
ebp            0x0	0x0
esi            0x0	0
edi            0x0	0
eip            0x804807c	0x804807c <_start+8>
eflags         0x212	[ AF IF ]
cs             0x73	115
ss             0x7b	123
ds             0x7b	123
es             0x7b	123
fs             0x0	0
gs             0x0	0
(gdb) print /x $ecx
$1 = 0x6c65746e
(gdb) x /42cb &output
0x80490ac <output>:	84 'T'	104 'h'	101 'e'	32 ' '	112 'p'	114 'r'	111 'o'	99 'c'
0x80490b4 <output+8>:	101 'e'	115 's'	115 's'	111 'o'	114 'r'	32 ' '	86 'V'	101 'e'
0x80490bc <output+16>:	110 'n'	100 'd'	111 'o'	114 'r'	32 ' '	73 'I'	68 'D'	32 ' '
0x80490c4 <output+24>:	105 'i'	115 's'	32 ' '	39 '\''	88 'X'	88 'X'	88 'X'	88 'X'
0x80490cc <output+32>:	88 'X'	88 'X'	88 'X'	88 'X'	88 'X'	88 'X'	88 'X'	88 'X'
0x80490d4 <output+40>:	39 '\''	10 '\n'
(gdb) c
Continuing.
The processor Vendor ID is 'GenuineIntel'

Program exited normally.
(gdb) q
 

break 加斷點

run 執行

next 單步執行

info registers 顯示所有暫存器的值

print 顯示特定暫存器的值

print /d 顯示十進位制的值

print /t 顯示二進位制的值

print /x 顯示十六進位制的值

x 顯示特定記憶體地址的內容

x /nyz

n是要顯示的欄位數，y是輸出格式：

c 用於字元

d 十進位制

x 十六進位制
z是要顯示的欄位長度

b 位元組8位

h 16位

w 32位字

q 退出gdb