Android NDK堆分配问题

Question

I'm currently trying to figure out exactly how the Android Native heap works: I'm allocating some memory on the heap via new, then printing the address of the pointer to see where the memory was allocated. However, it seems that the address of the memory allocation doesn't follow a simple pattern, for example when I try:

//native-lib.cpp (in in Android App)

int *pInt1 = new int();
int *pInt2 = new int ();
int *pInt3 = new int ();
int *pInt4 = new int ();
int *pInt5 = new int ();
int *pInt6 = new int ();
int *pInt7 = new int ();
int *pInt8 = new int [100000];
int *pInt9 = new int [99999999];
int *pInt10 = new int ();

__android_log_print(ANDROID_LOG_ERROR, "ADDRESS INT 1:", "%p\n", pInt1);
__android_log_print(ANDROID_LOG_ERROR, "ADDRESS INT 2:", "%p\n", pInt2);
__android_log_print(ANDROID_LOG_ERROR, "ADDRESS INT 3:", "%p\n", pInt3);
__android_log_print(ANDROID_LOG_ERROR, "ADDRESS INT 4:", "%p\n", pInt4);
__android_log_print(ANDROID_LOG_ERROR, "ADDRESS INT 5:", "%p\n", pInt5);
__android_log_print(ANDROID_LOG_ERROR, "ADDRESS INT 6:", "%p\n", pInt6);
__android_log_print(ANDROID_LOG_ERROR, "ADDRESS INT 7:", "%p\n", pInt7);
__android_log_print(ANDROID_LOG_ERROR, "ADDRESS INT 8:", "%p\n", pInt8);
__android_log_print(ANDROID_LOG_ERROR, "ADDRESS INT 9:", "%p\n", pInt9);
__android_log_print(ANDROID_LOG_ERROR, "ADDRESS INT 10:", "%p\n", pInt10);

The result I get from the logs is:

E/ADDRESS INT 1:: 0xacb78ac0
E/ADDRESS INT 2:: 0xacb78b10
E/ADDRESS INT 3:: 0xacb78ab8
E/ADDRESS INT 4:: 0xacb78a00
E/ADDRESS INT 5:: 0xacb78a10
E/ADDRESS INT 6:: 0xacb78a18
E/ADDRESS INT 7:: 0xacb78a88
E/ADDRESS INT 8:: 0xb3900000
E/ADDRESS INT 9:: 0x89c00000
E/ADDRESS INT 10:: 0xacb78a90

Which doesn't make any sense to me, because the address of pInt2 is larger than the address of pInt1, but pInt3 is less than both pInt1 and pInt2, and so on. When I allocate memory for a large array of integers (pInt8 and pInt9), it seems the location of where the memory was allocated on the heap will change as well, and it looks arbitrary to me.

Can anyone explain this? Or how exactly the Android NDK heap works? I expect the heap to grow in just one direction and I also expect to be fully contiguous, which clearly it's not from my experiment, so I don't really know what's going on.

Answer 1

new返回的地址是一个虚拟地址，系统要花更多的精力来随机化这些地址，从而使某些黑客攻击更加困难。