// memory manager. shares pages across many basic blocks.

#include <vector>

using std::vector;

// Provides blocks

class MM {

public:

    MM() {

        PAGE_SIZE_ = getpagesize();

    }

    // alloc into a page aligned buffer or fail.

    void alloc(void** output, int bytes) {

        if (page_capacity_ < bytes) {

            new_page(bytes);

        }

        (*output) = (void*)page_offset_;

        page_offset_ += bytes;

        page_capacity_ -= bytes;

    }

private:

    void new_page(int requested) {

        int bytes = requested < PAGE_SIZE_ ? PAGE_SIZE_ : requested;

        if (posix_memalign((void**)&page_, PAGE_SIZE_, bytes) != 0) {

            puts("memalign failed");

            exit(1);

        }

        if (page_ < 0) {

            perror("memalign fail: ");

            exit(1);

        }

        // NOTE: not w^x friendly, pages are both

        // writable and executable.

        if (mprotect((void*)page_, bytes, PROT_EXEC | PROT_READ | PROT_WRITE) < 0) {

            perror("failed to mprotect");

            exit(1);

        }

        page_capacity_ = bytes;

        page_offset_ = page_;

    }

    int PAGE_SIZE_;

    char* page_ = nullptr;

    char* page_offset_ = nullptr;

    int page_capacity_ = 0;

};