Android的自修改code - NDK [英] Android Self-modifying code - NDK

问题描述

我试图做一个自我修改code库，我已经scowered遍，我有后续code：

I am trying to make a self-modifying code library and I have scowered all over and I have the follow code:

typedef int (*FUNC) (void);
int test();

JNIEXPORT int Java_com_example_untitled_MyActivity_decrypt( JNIEnv* env, jobject thiz)
{
    void *code = mmap(NULL, 4, PROT_WRITE | PROT_EXEC, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);

    if (code != MAP_FAILED) {
        memcpy(code, test, 4);

        return ( (FUNC)code)();
    }

    return 0;
}

int test()
{
    return 100;
}

请帮忙...我用原住民自我修改$ C $在Androidç的作为我的出发点和他们说了一些有关与-marm和拇指位...

Please help...I used Native self-modifying code on Android as my starting point and they said something about compiling with "-marm" and thumb bit...

我的问题我有是，它只是崩溃。我已经使用cacheflush功能，似乎没有帮助试过。我很茫然。

My issue I'm having is, it's just crashing. I have tried using the cacheflush function, didn't seem to help. I am at a loss.

推荐答案

在ARM，则需要刷新CPU高速缓存，以确保在执行前，他们刚刚复制的指令是可见的CPU。一个简单的方法来做到这一点是：

On ARM, you need to flush the CPU caches in order to ensure that the instructions you just copied are visible to the CPU before they are executed. A simple way to do this is:

#include <unistd.h>  // for cacheflush()

...

// Copy the instructions to the destination address.
memcpy(dest, original_intructions, size_of_instructions);

// Clear the CPU cache
cacheflush((uintptr_t)dest, (uintptr_t)dest + size_of_instructions, 0);

// Run them.
return ((FUNC)dest)();

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