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97 lines
1.9 KiB
C++
97 lines
1.9 KiB
C++
#include "textoutput.hpp"
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#include <array>
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#include <cstdint>
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struct PageDirectory
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{
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static constexpr std::uint32_t NotPresent = 0x2;
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PageDirectory(): value(NotPresent) {}
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PageDirectory(void *addr): value(reinterpret_cast<std::uint32_t>(addr) | 7) {}
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std::uint32_t value;
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};
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static_assert(sizeof(PageDirectory) == sizeof(std::uint32_t));
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extern std::uint32_t lowerMem;
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extern std::uint32_t upperMem;
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extern TextOutput& term;
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static std::uintptr_t lowerFree = 0x400;
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static std::uintptr_t upperFree = 0x100000;
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alignas(4096)
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static std::array<PageDirectory, 1024> pageDirectory;
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alignas(4096)
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static std::array<std::uint32_t, 1024> pageTable;
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void memory_initialize()
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{
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lowerMem -= 1024;
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const auto totalKb = (lowerMem + upperMem) / 1024u;
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term.write("Claiming ");
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term.write(totalKb);
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term.write(" kB for allocations...\n");
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std::uint32_t addr = 0;
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for (auto& p : pageTable) {
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p = addr | 7; // supervisor, r/w, present
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addr += 0x1000;
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}
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pageDirectory[0] = PageDirectory(pageTable.data());
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asm volatile(R"(
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mov %%eax, %%cr3
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mov %%cr0, %%eax
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or $0x80000000, %%eax
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mov %%eax, %%cr0
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)" :: "a"(pageDirectory.data()));
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term.write("Paging enabled.\n");
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}
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static void *memory_alloc(std::size_t size)
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{
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void *ret = nullptr;
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if (lowerMem > size) {
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ret = reinterpret_cast<void *>(lowerFree);
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lowerFree += size;
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lowerMem -= size;
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} else if (upperMem > size) {
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ret = reinterpret_cast<void *>(upperFree);
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upperFree += size;
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upperMem -= size;
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} else {
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// Uh oh!
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term.write("!!! Kernel allocation failed !!!");
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}
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return ret;
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}
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void *operator new(std::size_t size)
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{
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return memory_alloc(size);
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}
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void *operator new[](std::size_t size)
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{
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return memory_alloc(size);
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}
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void operator delete(void *ptr)
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{
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}
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void operator delete[](void *ptr)
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{
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}
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