虚拟内存、页表与 mmap

#include <array>
#include <cstddef>
#include <iostream>
#include <stdexcept>
std::size_t translate(std::size_t address) {
    constexpr std::size_t page=4096;
    constexpr std::array<std::size_t,3> frames{5,7,2};
    if(address/page>=frames.size()) throw std::out_of_range("unmapped");
    return frames[address/page]*page+address%page;
}
int main() {
    if(translate(0)!=20480 || translate(4095)!=24575 || translate(4099)!=28675)
        throw std::runtime_error("translation");
    bool rejected=false;
    try {
        const auto unexpected=translate(12288);
        std::cout<<"unexpected unmapped address="<<unexpected<<'\n';
        return 1;
    } catch(const std::out_of_range&) { rejected=true; }
    if(!rejected) throw std::runtime_error("missing bounds");
    std::cout<<"4099->"<<translate(4099)<<" / 8192->"<<translate(8192)<<'\n';
}

#include <sys/mman.h>
#include <unistd.h>
#include <cstddef>
#include <iostream>
#include <limits>
#include <stdexcept>
int main() {
    const long queried=::sysconf(_SC_PAGESIZE);
    if(queried<=0) throw std::runtime_error("page size");
    const auto page=static_cast<std::size_t>(queried);
    if(page>std::numeric_limits<std::size_t>::max()/2) throw std::runtime_error("size");
    void* region=::mmap(nullptr,page*2,PROT_READ|PROT_WRITE,MAP_PRIVATE|MAP_ANON,-1,0);
    if(region==MAP_FAILED) throw std::runtime_error("mmap");
    auto* bytes=static_cast<unsigned char*>(region);
    bytes[page-1]=7; bytes[page]=9;
    const int first=bytes[page-1],second=bytes[page];
    if(::munmap(region,page*2)!=0) throw std::runtime_error("munmap");
    if(first!=7 || second!=9) throw std::runtime_error("boundary");
    std::cout<<"boundary="<<first<<','<<second<<'\n';
}