我怎样才能防止strcpy（）被优化 [英] How can I prevent strcpy() being optimised

问题描述

我在黑客攻击：剥削的艺术一书中学习了一个例子，我得到了不同的结果。

似乎strcpy（）函数编译为如下指令：

  0x802384c5< main + 27> ;:调用0x80482C4< strcpy @ plt> 
  

然而，当我编译相同的程序时，它将删除对库的调用并用一系列mov指令：

  0x8048475< main + 25> ;: mov DWORD PTR [eax]，0x6c6c6548 
 0x804847b<主+ 31计算值：MOV DWORD PTR [EAX +为0x4]，0x6f57206f 
 0x8048482<主+ 38计算值：MOV DWORD PTR [EAX + 0x8中]，0x21646c72 
 0x8048489<主+ 45计算值：MOV WORD PTR [eax + 0xc]，0xa 
  

据我所知，编译器可以进行各种优化，虽然它是默认的，我甚至试着用-O0来编译它，以防止优化。

如何编译代码以便引用外部库？ / p>

自从uni以来，我还没有做过任何C或汇编程序，所以请对我轻轻一点：） 方案使用GCC，你可以使用 -fno-builtin （禁用所有内建函数）或 -fno-builtin-strcpy （只是禁用内置 strcpy ）。

I'm following an example in the book Hacking: The Art of Exploitation and I am getting different results to the book.

It seems that the strcpy() function in the example compiles to an instruction like:

0x802384c5 <main+27>: call 0x80482C4 <strcpy@plt>

whereas when I compile the same program it removes the call to the library and replaces it with a series of mov instructions:

0x8048475 <main+25>: mov    DWORD PTR [eax],0x6c6c6548
0x804847b <main+31>: mov    DWORD PTR [eax+0x4],0x6f57206f
0x8048482 <main+38>: mov    DWORD PTR [eax+0x8],0x21646c72
0x8048489 <main+45>: mov    WORD PTR [eax+0xc],0xa

I understand that the compiler can make various optimizations, but even though it's the default I've even tried compiling it with -O0 which is supposed to prevent optimisations.

How can I compile the code so it references the external library?

I've not done any C or assembly since uni, so be gentle with me :)

解决方案

With GCC, you can use the -fno-builtin (disable all builtins) or -fno-builtin-strcpy (just disable builtin strcpy).

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