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#include "textoutput.hpp"
#include <array>
#include <cstdint>
struct PageDirectory
{
static constexpr std::uint32_t NotPresent = 0x2;
PageDirectory(): value(NotPresent) {}
PageDirectory(void *addr): value(reinterpret_cast<std::uint32_t>(addr) | 3) {}
std::uint32_t value;
};
static_assert(sizeof(PageDirectory) == sizeof(std::uint32_t));
extern std::uint32_t lowerMem;
extern std::uint32_t upperMem;
extern TextOutput& term;
static std::uintptr_t lowerFree = 0x400;
static std::uintptr_t upperFree = 0x100000;
alignas(4096)
static std::array<PageDirectory, 1024> pageDirectory;
alignas(4096)
static std::array<std::uint32_t, 1024> pageTable;
void memory_initialize()
{
lowerMem -= 1024;
const auto totalKb = (lowerMem + upperMem) / 1024u;
term.write("Claiming ");
term.write(totalKb);
term.write(" kB for allocations...\n");
std::uint32_t addr = 0;
for (auto& p : pageTable) {
p = addr | 3; // supervisor, r/w, present
addr += 0x1000;
}
pageDirectory[0] = PageDirectory(pageTable.data());
asm volatile(R"(
mov %%eax, %%cr3
mov %%cr0, %%eax
or $0x80000000, %%eax
mov %%eax, %%cr0
)" :: "a"(pageDirectory.data()));
term.write("Paging enabled.\n");
}
static void *memory_alloc(std::size_t size)
{
void *ret = nullptr;
if (lowerMem > size) {
ret = reinterpret_cast<void *>(lowerFree);
lowerFree += size;
lowerMem -= size;
} else if (upperMem > size) {
ret = reinterpret_cast<void *>(upperFree);
upperFree += size;
upperMem -= size;
} else {
// Uh oh!
term.write("!!! Kernel allocation failed !!!");
}
return ret;
}
void *operator new(std::size_t size)
{
return memory_alloc(size);
}
void *operator new[](std::size_t size)
{
return memory_alloc(size);
}
void operator delete(void *ptr)
{
}
void operator delete[](void *ptr)
{
}
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