cf3059747a
- Added bitmap-based physical memory manager (PMM) that parses the Multiboot2 memory map to discover available RAM regions. - Supports two allocation zones: PMM_ZONE_DMA (below 16MB) and PMM_ZONE_NORMAL (above 16MB), with automatic fallback from NORMAL to DMA when the preferred zone is exhausted. - Marks kernel memory region and multiboot info structure as reserved using _kernel_start/_kernel_end linker symbols. - Page 0 is always marked as used to prevent returning NULL as a valid address. - Added linker script symbols (_kernel_start, _kernel_end) to track kernel memory boundaries for the allocator. - Kernel now initializes PMM after PIC and performs test allocations to verify the subsystem works.