Makefile

@@ -1,4 +1,4 @@
-SOURCES = src/string/string.c src/io/kbd/ps2.c src/io/serial/serial.c src/io/term/printf.c src/io/term/term.c src/idt/idt.c src/mem/gdt/gdt.c src/mem/misc/utils.c src/time/timer.c src/kmain.c
+SOURCES = src/mem/paging/pmm.c src/string/string.c src/io/kbd/ps2.c src/io/serial/serial.c src/io/term/printf.c src/io/term/term.c src/idt/idt.c src/mem/gdt/gdt.c src/mem/misc/utils.c src/time/timer.c src/kmain.c
 
 build:
 	rm -f *.o

src/kernel.h

@@ -13,7 +13,7 @@ enum ErrorCodes
 #include "io/serial/serial.h"
 #include "io/term/printf.h"
 
-#define DEBUG(log, ...) fctprintf((void*)&skputc, 0, "debug: [%s]: " log "\n", __FILE__, ##__VA_ARGS__)
+#define DEBUG(log, ...) fctprintf((void*)&skputc, 0, "debug: [%s]: " log "\r\n", __FILE__, ##__VA_ARGS__)
 
 // printf("debug: [%s]: " log "\n", __FILE__, ##__VA_ARGS__);
 #endif

src/kmain.c

@@ -10,6 +10,7 @@
 #include "kernel.h"
 #include "time/timer.h"
 #include "io/kbd/ps2.h"
+#include "mem/paging/pmm.h"
 
 // Limine version used
 __attribute__((used, section(".limine_requests")))
@@ -29,6 +30,13 @@ static volatile struct limine_memmap_request memmap_request = {
 	.revision = 0
 };
 
+// Higher Half Direct Map
+__attribute__((used, section(".limine_requests")))
+static volatile struct limine_hhdm_request hhdm_request = {
+	.id = LIMINE_HHDM_REQUEST,
+	.revision = 0
+};
+
 __attribute__((used, section(".limine_requests_start")))
 static volatile LIMINE_REQUESTS_START_MARKER;
 
@@ -61,13 +69,18 @@ void kmain()
 	if (memmap_request.response == NULL) hcf();
 	memmap_display(memmap_request.response);
 
+	if (hhdm_request.response == NULL) hcf();
+	hhdm_display(hhdm_request.response);
+
+	pmm_init(memmap_request.response, hhdm_request.response);
+
 	CLEAR_INTERRUPTS;
 	gdt_init();
 	idt_init();
 	timer_init();
 	SET_INTERRUPTS;
 
-	//keyboard_init(FR);
+	keyboard_init(FR);
 
 	// Draw something
 	printf("%s, %s!\n", "Hello", "world");

src/mem/misc/utils.c

@@ -111,6 +111,12 @@ void memmap_display(struct limine_memmap_response* response)
 				strcpy(type, "UNKNOWN");
 				break;
 		}
-		DEBUG("entry %u: [%016x | %u bytes] - %s", i, entry->base, entry->length, type);
+		DEBUG("entry %02u: [0x%016x | %016u bytes] - %s", i, entry->base, entry->length, type);
 	}
+}
+
+// Display the HHDM
+void hhdm_display(struct limine_hhdm_response* hhdm)
+{
+	DEBUG("Got HHDM revision=%u offset=0x%p", hhdm->revision, hhdm->offset);
 }

src/mem/misc/utils.h

@@ -9,5 +9,6 @@ void* memmove(void *dest, const void* src, size_t n);
 int memcmp(const void* s1, const void* s2, size_t n);
 
 void memmap_display(struct limine_memmap_response* response);
+void hhdm_display(struct limine_hhdm_response* hhdm);
 
 #endif

src/mem/paging/pmm.c

@@ -8,10 +8,68 @@ to see which pages are used by kernel/bootloader/mmio/fb etc.
 */
 
 #include "paging.h"
+#include <limine.h>
+#include <stddef.h>
+#include <kernel.h>
+#include "../misc/utils.h"
 
 /*
 First we'll have to discover the physical memory layout,
 and for that we can use a Limine request.
 */
 
-uint64_t pages_bitmap[];
+/*
+We will look for the biggest usable physical memory region
+and use this for the bitmap. The reserved memory will be ignored.
+*/
+
+struct usable_memory* usable_mem;
+struct limine_memmap_entry* biggest_entry;
+
+uint64_t* bitmap;
+
+static void pmm_allocate_bitmap(struct limine_hhdm_response* hhdm)
+{
+    uint64_t pages = biggest_entry->length / PAGE_SIZE;
+    DEBUG("we need %u pages (bits) that will fit in %u uint64_t", pages, pages/64);
+
+    bitmap = (uint64_t*)(biggest_entry->base + hhdm->offset);
+    DEBUG("bitmap will live at 0x%p", bitmap);
+
+    // All pages are marked free since we're in a USABLE region
+    memset(bitmap, 0x00, pages/64);
+}
+
+static void pmm_find_biggest_usable_region(struct limine_memmap_response* memmap, struct limine_hhdm_response* hhdm)
+{
+    // Max length of a usable memory region
+    uint64_t length_max = 0;
+    uint64_t offset = hhdm->offset;
+
+    DEBUG("Usable Memory:");
+    for (size_t i=0; i<memmap->entry_count; i++)
+    {
+        struct limine_memmap_entry* entry = memmap->entries[i];
+
+        if (entry->type == LIMINE_MEMMAP_USABLE)
+        {
+            DEBUG("0x%p-0x%p mapped at 0x%p-0x%p", entry->base, entry->base+entry->length,
+                        entry->base+offset, entry->base+entry->length+offset);
+            if (entry->length > length_max)
+            {
+                length_max = entry->length;
+                biggest_entry = entry;
+            }
+        }
+    }
+
+    DEBUG("Biggest usable memory region:");
+    DEBUG("0x%p-0x%p mapped at 0x%p-0x%p", biggest_entry->base, biggest_entry->base + biggest_entry->length,
+            biggest_entry->base+offset, biggest_entry->base+biggest_entry->length+offset);
+}
+
+void pmm_init(struct limine_memmap_response* memmap, struct limine_hhdm_response* hhdm)
+{
+    pmm_find_biggest_usable_region(memmap, hhdm);
+    pmm_allocate_bitmap(hhdm);
+}

src/mem/paging/pmm.h

@@ -0,0 +1,16 @@
+#ifndef PAGING_PMM_H
+#define PAGING_PMM_H
+
+#include <limine.h>
+
+void pmm_init(struct limine_memmap_response* memmap, struct limine_hhdm_response* hhdm);
+
+// Might be upgraded to a freelist later.
+// For now, we can take the biggest usable region and we will be fine.
+struct usable_memory
+{
+    uint64_t base; // physical
+    uint64_t length;
+};
+
+#endif