Print assembler hex in one pass

最新推荐文章于 2021-07-06 16:00:39 发布

转载最新推荐文章于 2021-07-06 16:00:39 发布 · 1.1k 阅读

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#hex #compiler #optimization #microsoft #byte #blog

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本文介绍了一种使用C++实现的批量打印汇编代码的方法。通过一个具体的示例展示了如何利用裸汇编指令进行特定操作，并提供了一个简单的主函数来逐字节输出汇编代码。为了确保代码的有效性和紧凑性，特别提到了在编译时启用最小化大小优化选项的重要性。

Jason Geffner posted a piece of code to demonstrate how to print out a bulk of assembler hex in one pass,
http://blogs.msdn.com/geffner/archive/2006/02/10/529320.aspx, i managed to work out another way to
accomplish the same work:

#include "stdafx.h"

typedef unsigned char __u8;

void __declspec(naked) shellcode(void)
{
__asm {
        mov eax, 0x15db
        rol eax, 0x13
        xor eax, 0xdeadbeef
        shr eax, 0x10
        mov ebx, eax
        shl eax, 0x2
        add eax, ebx
        add eax, ebx
        add eax, ebx
        add eax, 0x4
}
}

void __declspec(naked) stub(void)
{
}

int __cdecl main(int argc, char* argv[])
{
    int i;
    for (i = 0; i < (__u8 *)stub - (__u8 *)shellcode; i++)
    {
        printf ("//x%02x", ((__u8*)shellcode)[i]);
    }
    printf("/n");
    return 0;
}

don't forget to turn on Minimize Size optimization option in Visual C++ compiler, missing this option will make the compiler align the machine code with 4 bytes, so for the sample code, there're 2 byte nop instruction in tail.
Jason is a Virus Analyst of Microsoft Anti Malware team, his blog is worth of a reading.