[Solved] Read access privilage of last 5 elements

Question

I am assuming your arr is a POD (plain old data) array. You could make it in C++ a class and overload the operator[] to do runtime index checking.

You usually cannot do what you want, and if you could, it would be strongly implementation and operating system dependent.

On Linux, access permission to data is related to virtual memory mapping. This is related to the mmap(2) and munmap(2) with mprotect(2) system call. These calls work at a page-level granularity (a page is usually 4Kbytes, and 4Kbytes aligned).

You could make naughty tricks like mmap-ing a large region, mprotect its last page, and do unportable pointer arithmetic to compute the arr pointer. This is disgusting, so don’t do that. And catching SIGSEGV with dirty mmap-based tricks like this is not very portable and probably not very efficient. And a signal handler cannot throw C++ exceptions.

Accepted Answer

I am assuming your arr is a POD (plain old data) array. You could make it in C++ a class and overload the operator[] to do runtime index checking.

You usually cannot do what you want, and if you could, it would be strongly implementation and operating system dependent.

On Linux, access permission to data is related to virtual memory mapping. This is related to the mmap(2) and munmap(2) with mprotect(2) system call. These calls work at a page-level granularity (a page is usually 4Kbytes, and 4Kbytes aligned).

You could make naughty tricks like mmap-ing a large region, mprotect its last page, and do unportable pointer arithmetic to compute the arr pointer. This is disgusting, so don’t do that. And catching SIGSEGV with dirty mmap-based tricks like this is not very portable and probably not very efficient. And a signal handler cannot throw C++ exceptions.