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[alert7@redhat62 alert7]$ gcc -fomit-frame-pointer -o test test.c<br>
[alert7@redhat62 alert7]$ wc -c test<br>
11773 test<br>
[alert7@redhat62 alert7]$ gdb -q test<br>
(gdb) disass main<br>
Dump of assembler code for function main:<br>
0x80483e0 : call 0x80483d0<br>
0x80483e5 : xor %eax,%eax<br>
0x80483e7 : jmp 0x80483f0<br>
0x80483e9 : lea 0x0(%esi,1),%esi<br>
0x80483f0 : ret<br>
....<br>
End of assembler dump.<br>
(gdb) disass hi<br>
Dump of assembler code for function hi:<br>
0x80483d0 : push $0x8048450<br>
0x80483d5 : call 0x8048308<br>
0x80483da : add $0x4,%esp<br>
0x80483dd : ret<br>
0x80483de : mov %esi,%esi<br>
End of assembler dump.<br>
在main()和hi()中都去掉了以下指令<br>
push %ebp<br>
mov %esp,%ebp//这两条指令安装<br>
leave//这条指令恢复<br>
来看看部分的内存映象<br>
(内存高址)<br>
+--------+<br>
|bffffbc4| argv的地址(即argv[0]的地址)<br>
0xbffffb84 +--------+<br>
|00000001| argc的值<br>
0xbffffb80 +--------+<br>
|400309cb|main的返回地址<br>
0xbffffb7c +--------+<br>
|080483e5| hi()的返回地址<br>
0xbffffb78 +--------+<br>
|08048450| "hi"字符串的地址<br>
0xbffffb74 +--------+<br>
| ...... |<br>
(内存低址)<br>
没有保存上层执行环境的ebp.<br>
<br>
<br>
<br>
[目录]<br>
<br>
--------------------------------------------------------------------------------<br>
<br>
<br>
-fomit-frame-pointer && -O2<br>
<br>
★ -fomit-frame-pointer && -O2<br>
-fomit-frame-pointer编译选项去掉了<br>
push %ebp<br>
mov %esp,%ebp//这两条指令安装<br>
leave//这条指令恢复<br>
-O2编译选项去掉了<br>
add $0x4,%esp<br>
两个加起来会不会这四条指令一起去掉，从而使stack不平衡呢？<br>
[alert7@redhat62 alert7]$ gcc -fomit-frame-pointer -O2 -o test test.c<br>
[alert7@redhat62 alert7]$ wc -c test<br>
11741 test<br>
[alert7@redhat62 alert7]$ gdb -q test<br>
(gdb) disass main<br>
Dump of assembler code for function main:<br>
0x80483d8 : call 0x80483c8<br>
0x80483dd : xor %eax,%eax<br>
0x80483df : ret<br>
End of assembler dump.<br>
(gdb) disass hi<br>
Dump of assembler code for function hi:<br>
0x80483c8 : push $0x8048430<br>
0x80483cd : call 0x8048308<br>
0x80483d2 : add $0x4,%esp<br>
0x80483d5 : ret<br>
0x80483d6 : mov %esi,%esi<br>
End of assembler dump.<br>
来看看部分的内存映象<br>
(内存高址)<br>
+--------+<br>
|bffffbc4| argv的地址(即argv[0]的地址)<br>
0xbffffb84 +--------+<br>
|00000001| argc的值<br>
0xbffffb80 +--------+<br>
|400309cb|main的返回地址<br>
0xbffffb7c +--------+<br>
|080483dd| hi()的返回地址<br>
0xbffffb78 +--------+<br>
|08048430| "hi"字符串的地址<br>
0xbffffb74 +--------+<br>
| ...... |<br>
(内存低址)<br>
此时就没有把add $0x4,%esp优化掉，如果优化掉的话，整个stack就<br>
会变的不平衡，从而会导致程序出错。<br>
<br>
<br>
[目录]<br>
<br>
--------------------------------------------------------------------------------<br>
<br>
<br>
-fPIC 编译选项<br>
<br>
★ -fPIC 编译选项<br>
-fPIC If supported for the target machine, emit position-independent<br>
code, suitable for dynamic linking,even if branches need large<br>
displacements.<br>
产生位置无关代码（PIC），一般创建共享库时用到。<br>
在x86上，PIC的代码的符号引用都是通过ebx进行操作的。<br>
<br>
[alert7@redhat62 alert7]$ gcc -fPIC -o test test.c<br>
[alert7@redhat62 alert7]$ wc -c test<br>
11805 test<br>
[alert7@redhat62 alert7]$ gdb -q test<br>
(gdb) disass main<br>
Dump of assembler code for function main:<br>
0x80483f8 : push %ebp<br>
0x80483f9 : mov %esp,%ebp<br>
0x80483fb : push %ebx<br>
0x80483fc : call 0x8048401<br>
0x8048401 : pop %ebx//取得该指令的地址<br>
0x8048402 : add $0x1093,%ebx//此时ebx里面存放着是GOT表的地址<br>
0x8048408 : call 0x80483d0<br>
0x804840d : xor %eax,%eax<br>
0x804840f : jmp 0x8048411<br>
0x8048411 : mov 0xfffffffc(%ebp),%ebx<br>
0x8048414 : leave<br>
0x8048415 : ret<br>
...<br>
End of assembler dump.<br>
(gdb) disass hi<br>
Dump of assembler code for function hi:<br>
0x80483d0 : push %ebp<br>
0x80483d1 : mov %esp,%ebp<br>
0x80483d3 : push %ebx<br>
0x80483d4 : call 0x80483d9<br>
0x80483d9 : pop %ebx<br>
0x80483da : add $0x10bb,%ebx<br>
0x80483e0 : lea 0xffffefdc(%ebx),%edx<br>
0x80483e6 : mov %edx,%eax<br>
0x80483e8 : push %eax<br>
0x80483e9 : call 0x8048308<br>
0x80483ee : add $0x4,%esp<br>
0x80483f1 : mov 0xfffffffc(%ebp),%ebx<br>
0x80483f4 : leave<br>
0x80483f5 : ret<br>
0x80483f6 : mov %esi,%esi<br>
End of assembler dump.<br>
来看看部分的内存映象<br>
<br>
(内存高址)<br>
+--------+<br>
|bffffbc4| argv的地址(即argv[0]的地址)<br>
0xbffffb84 +--------+<br>
|00000001| argc的值<br>
0xbffffb80 +--------+<br>
|400309cb|main的返回地址<br>
0xbffffb7c +--------+ <-- 调用main函数前的esp<br>
|bffffb98| 调用main函数前的ebp<br>
0xbffffb78 +--------+ <-- main函数的ebp<br>
|401081ec| 保存的ebx<br>
0xbffffb74 +--------+<br>
|0804840d| （存放过call 0x8048401的下一条指令地址）<br>
0xbffffb70 +--------+<br>
|bffffb78| 调用hi()前的esp<br>
0xbffffb6c +--------+<br>
|08049494| GOT表地址<br>
0xbffffb68 +--------+<br>
|08048470|（存放过call 0x80483d9的下一条指令地址）<br>
0xbffffb64 +--------+<br>
| ...... |<br>
(内存低址)<br>
<br>
<br>
<br>
[目录]<br>
<br>
--------------------------------------------------------------------------------<br>
<br>
<br>
-static 编译选项<br>
<br>
★ -static 编译选项<br>
-static<br>
On systems that support dynamic linking, this prevents<br>
linking with the shared libraries. On other systems,<br>
this option has no effect.<br>
把一些函数都静态的编译到程序中，而无需动态链接了。<br>
[alert7@redhat62 alert7]$ gcc -o test -static test.c<br>
[alert7@redhat62 alert7]$ wc -c test<br>
962808 test<br>
[alert7@redhat62 alert7]$ gdb -q test<br>
(gdb) disass main<br>
Dump of assembler code for function main:<br>
0x80481b4 : push %ebp<br>
0x80481b5 : mov %esp,%ebp<br>
0x80481b7 : call 0x80481a0<br>
0x80481bc : xor %eax,%eax<br>
0x80481be : jmp 0x80481c0<br>
0x80481c0 : leave<br>
0x80481c1 : ret<br>
...<br>
End of assembler dump.<br>
(gdb) disass hi<br>
Dump of assembler code for function hi:<br>
0x80481a0 : push %ebp<br>
0x80481a1 : mov %esp,%ebp<br>
0x80481a3 : push $0x8071528<br>
0x80481a8 : call 0x804865c<br>
0x80481ad : add $0x4,%esp<br>
0x80481b0 : leave<br>
0x80481b1 : ret<br>
0x80481b2 : mov %esi,%esi<br>
End of assembler dump.<br>
[alert7@redhat62 alert7]$ ldd test<br>
not a dynamic executable<br>
-static出来的代码已经没有PLT了，GOT虽然有，已经全部为0了。<br>
<br>
<br>
<br>
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