在debug二進制程序的時候，偶爾會用到反彙編，有時候也想反彙編指定的函數，那麼以下有兩種方法可以試試：用objdump的-d參數或者gdb的disassemble命令：
一、用objdump的-d參數，但不能指定函數名，objdump還有另外兩個參數--start-address和--stop-address，我們只要指定反彙編的起始地址和結束地址那應該就可以了，那怎麼得到函數的起止地址呢，這就需要nm工具了，整合成shell腳本如下：
#!/bin/sh
#file: /usr/bin/dis
#disassemble a function
#author: [email protected]
routine=$1
func=$2
if [ -z "$routine" ]; then
exit
fi
start=$(nm -n $routine | grep "\w\s$func" | awk '{print "0x"$1;exit}')
end=$(nm -n $routine | grep -A1 "\w\s$func" | awk '{getline; print "0x"$1;exit}')
if [ -z "$func" ]; then
objdump -d $routine
else
echo "start-address: $start, end-address: $end"
objdump -d $routine --start-address=$start --stop-address=$end
firoot@jusse:~/work/#dis ./nginx ngx_array_init
start-address: 0x0000000000404404, end-address: 0x000000000040448a
nginx: file format elf64-x86-64
Disassembly of section .text:
0000000000404404 <ngx_array_init>:
404404: 55 push %rbp
404405: 48 89 e5 mov %rsp,%rbp
404408: 48 83 ec 20 sub $0x20,%rsp
40440c: 48 89 7d f8 mov %rdi,-0x8(%rbp)
404410: 48 89 75 f0 mov %rsi,-0x10(%rbp)
404414: 48 89 55 e8 mov %rdx,-0x18(%rbp)
404418: 48 89 4d e0 mov %rcx,-0x20(%rbp)
40441c: 48 8b 45 f8 mov -0x8(%rbp),%rax
404420: 48 c7 40 08 00 00 00 movq $0x0,0x8(%rax)
404427: 00
404428: 48 8b 45 f8 mov -0x8(%rbp),%rax
40442c: 48 8b 55 e0 mov -0x20(%rbp),%rdx
404430: 48 89 50 10 mov %rdx,0x10(%rax)
404434: 48 8b 45 f8 mov -0x8(%rbp),%rax
404438: 48 8b 55 e8 mov -0x18(%rbp),%rdx
40443c: 48 89 50 18 mov %rdx,0x18(%rax)
404440: 48 8b 45 f8 mov -0x8(%rbp),%rax
404444: 48 8b 55 f0 mov -0x10(%rbp),%rdx
404448: 48 89 50 20 mov %rdx,0x20(%rax)
40444c: 48 8b 45 e8 mov -0x18(%rbp),%rax
404450: 48 89 c2 mov %rax,%rdx
404453: 48 0f af 55 e0 imul -0x20(%rbp),%rdx
404458: 48 8b 45 f0 mov -0x10(%rbp),%rax
40445c: 48 89 d6 mov %rdx,%rsi
40445f: 48 89 c7 mov %rax,%rdi
404462: e8 4e 37 00 00 callq 407bb5 <ngx_palloc>
404467: 48 8b 55 f8 mov -0x8(%rbp),%rdx
40446b: 48 89 02 mov %rax,(%rdx)
40446e: 48 8b 45 f8 mov -0x8(%rbp),%rax
404472: 48 8b 00 mov (%rax),%rax
404475: 48 85 c0 test %rax,%rax
404478: 75 09 jne 404483 <ngx_array_init+0x7f>
40447a: 48 c7 c0 ff ff ff ff mov $0xffffffffffffffff,%rax
404481: eb 05 jmp 404488 <ngx_array_init+0x84>
404483: b8 00 00 00 00 mov $0x0,%eax
404488: c9 leaveq
404489: c3 retq 二、用gdb的disassemble命令：
root@jusse:~/work/#gdb -q ./nginx
Reading symbols from /home/wangzuxi/work/svn/l7waf_build/install_dir/sbin/nginx...done.
(gdb) disassemble ngx_array_init
Dump of assembler code for function ngx_array_init:
0x00000000004cb21c <+0>: push %rbp
0x00000000004cb21d <+1>: mov %rsp,%rbp
0x00000000004cb220 <+4>: sub $0x20,%rsp
0x00000000004cb224 <+8>: mov %rdi,-0x8(%rbp)
0x00000000004cb228 <+12>: mov %rsi,-0x10(%rbp)
0x00000000004cb22c <+16>: mov %rdx,-0x18(%rbp)
0x00000000004cb230 <+20>: mov %rcx,-0x20(%rbp)
0x00000000004cb234 <+24>: mov -0x8(%rbp),%rax
0x00000000004cb238 <+28>: movq $0x0,0x8(%rax)
0x00000000004cb240 <+36>: mov -0x8(%rbp),%rax
0x00000000004cb244 <+40>: mov -0x20(%rbp),%rdx
0x00000000004cb248 <+44>: mov %rdx,0x10(%rax)
0x00000000004cb24c <+48>: mov -0x8(%rbp),%rax
0x00000000004cb250 <+52>: mov -0x18(%rbp),%rdx
0x00000000004cb254 <+56>: mov %rdx,0x18(%rax)
0x00000000004cb258 <+60>: mov -0x8(%rbp),%rax
0x00000000004cb25c <+64>: mov -0x10(%rbp),%rdx
0x00000000004cb260 <+68>: mov %rdx,0x20(%rax)
0x00000000004cb264 <+72>: mov -0x18(%rbp),%rax
0x00000000004cb268 <+76>: mov %rax,%rdx
0x00000000004cb26b <+79>: imul -0x20(%rbp),%rdx
0x00000000004cb270 <+84>: mov -0x10(%rbp),%rax
0x00000000004cb274 <+88>: mov %rdx,%rsi
0x00000000004cb277 <+91>: mov %rax,%rdi
0x00000000004cb27a <+94>: callq 0x407bb5 <ngx_palloc>
0x00000000004cb27f <+99>: mov -0x8(%rbp),%rdx
0x00000000004cb283 <+103>: mov %rax,(%rdx)
0x00000000004cb286 <+106>: mov -0x8(%rbp),%rax
0x00000000004cb28a <+110>: mov (%rax),%rax
0x00000000004cb28d <+113>: test %rax,%rax
0x00000000004cb290 <+116>: jne 0x4cb29b <ngx_array_init+127>
0x00000000004cb292 <+118>: mov $0xffffffffffffffff,%rax
0x00000000004cb299 <+125>: jmp 0x4cb2a0 <ngx_array_init+132>
0x00000000004cb29b <+127>: mov $0x0,%eax
0x00000000004cb2a0 <+132>: leaveq
0x00000000004cb2a1 <+133>: retq
End of assembler dump.
(gdb) q可以看出反彙編代碼與第一種方法的結果是一樣的，但這麼用gdb有點費勁了，還可以像下面這麼玩：
#!/bin/sh
#file: /usr/bin/gdbdis
#disassemble a function use gdb
#author: [email protected]
if test $# -ne 2; then
echo "Usage: `basename $0 .sh` file function" 1>&2
echo "For exampl: `basename $0 .sh` xxx func" 1>&2
exit 1
fi
result=""
GDB=${GDB:-/usr/bin/gdb}
# Run GDB, strip out unwanted noise.
result=`$GDB -quiet $1 <<EOF
disassemble $2
EOF`
echo "$result" | egrep -A 1000 -e "^\(gdb\)" | egrep -B 1000 -e "^\(gdb\)"同樣反彙編nginx的ngx_array_init函數的結果是一樣的：
./gdbdis ./nginx ngx_array_init
(gdb) Dump of assembler code for function ngx_array_init:
0x00000000004cb21c <+0>: push %rbp
0x00000000004cb21d <+1>: mov %rsp,%rbp
0x00000000004cb220 <+4>: sub $0x20,%rsp
0x00000000004cb224 <+8>: mov %rdi,-0x8(%rbp)
0x00000000004cb228 <+12>: mov %rsi,-0x10(%rbp)
0x00000000004cb22c <+16>: mov %rdx,-0x18(%rbp)
0x00000000004cb230 <+20>: mov %rcx,-0x20(%rbp)
0x00000000004cb234 <+24>: mov -0x8(%rbp),%rax
0x00000000004cb238 <+28>: movq $0x0,0x8(%rax)
0x00000000004cb240 <+36>: mov -0x8(%rbp),%rax
0x00000000004cb244 <+40>: mov -0x20(%rbp),%rdx
0x00000000004cb248 <+44>: mov %rdx,0x10(%rax)
0x00000000004cb24c <+48>: mov -0x8(%rbp),%rax
0x00000000004cb250 <+52>: mov -0x18(%rbp),%rdx
0x00000000004cb254 <+56>: mov %rdx,0x18(%rax)
0x00000000004cb258 <+60>: mov -0x8(%rbp),%rax
0x00000000004cb25c <+64>: mov -0x10(%rbp),%rdx
0x00000000004cb260 <+68>: mov %rdx,0x20(%rax)
0x00000000004cb264 <+72>: mov -0x18(%rbp),%rax
0x00000000004cb268 <+76>: mov %rax,%rdx
0x00000000004cb26b <+79>: imul -0x20(%rbp),%rdx
0x00000000004cb270 <+84>: mov -0x10(%rbp),%rax
0x00000000004cb274 <+88>: mov %rdx,%rsi
0x00000000004cb277 <+91>: mov %rax,%rdi
0x00000000004cb27a <+94>: callq 0x407bb5 <ngx_palloc>
0x00000000004cb27f <+99>: mov -0x8(%rbp),%rdx
0x00000000004cb283 <+103>: mov %rax,(%rdx)
0x00000000004cb286 <+106>: mov -0x8(%rbp),%rax
0x00000000004cb28a <+110>: mov (%rax),%rax
0x00000000004cb28d <+113>: test %rax,%rax
0x00000000004cb290 <+116>: jne 0x4cb29b <ngx_array_init+127>
0x00000000004cb292 <+118>: mov $0xffffffffffffffff,%rax
0x00000000004cb299 <+125>: jmp 0x4cb2a0 <ngx_array_init+132>
0x00000000004cb29b <+127>: mov $0x0,%eax
0x00000000004cb2a0 <+132>: leaveq
0x00000000004cb2a1 <+133>: retq
End of assembler dump.
(gdb) quit
