Add PMM

Author: BrainStackOverFlow

kernel/kernel.c

@@ -1,5 +1,5 @@
-
 #include "libc/stdio.h"
+#include "pmm.h"
 #include "printf/printf_support.h"
 #include "terminal/terminal.h"
 #include <limine.h>
@@ -15,6 +15,12 @@ static volatile struct limine_entry_point_request entry_request = {
     .entry = entry,
 };
 
+struct limine_memmap_request limine_memmap_request = {
+    .id = LIMINE_MEMMAP_REQUEST,
+    .revision = 0,
+    .response = NULL,
+};
+
 static void hcf(void)
 {
     asm("cli");
@@ -43,6 +49,9 @@ void entry(void)
 
     printf("Hello Kernel Mode!\n");
 
+    pmm_t pmm;
+    pmm_init(&pmm, limine_memmap_request.response);
+
 cleanup:
     hcf();
 }

kernel/pmm.c

@@ -0,0 +1,66 @@
+#include "pmm.h"
+
+#include "utility/macro.h"
+
+void pmm_init(pmm_t* pmm, struct limine_memmap_response* limine_memmap) {
+    pmm_node_t* current = NULL;
+
+    for (size_t i = 0; i < limine_memmap->entry_count; i++) {
+        struct limine_memmap_entry* entry = limine_memmap->entries[i];
+        if (LIMINE_MEMMAP_USABLE == entry->type) {
+            pmm_node_t node = {.next = NULL,
+                               .prev = current,
+                               .base = (void*)(entry->base + PAGE_SIZE),
+                               .no_pages = (entry->length / PAGE_SIZE) - 1,
+                               .kind = PMM_NOT_ALLOCATED};
+            pmm_node_t* node_ptr = (void*)entry->base;
+            *node_ptr = node;
+
+            if (NULL == current) {
+                pmm->first_node = node_ptr;
+            } else {
+                current->next = node_ptr;
+            }
+            current = node_ptr;
+        }
+    }
+}
+
+void* pmm_alloc_pages(pmm_t* pmm, size_t no_pages) {
+    pmm_node_t* current = pmm->first_node;
+
+    while (NULL != current) {
+        if ((PMM_NOT_ALLOCATED == current->kind) &&
+            (current->no_pages <= no_pages)) {
+            break;
+        }
+
+        current = current->next;
+    }
+
+    if (NULL == current) {
+        return NULL;
+    }
+
+    size_t leftover_pages = current->no_pages - no_pages;
+
+    if (0 == leftover_pages) {
+        current->kind = PMM_ALLOCATED;
+        return current->base;
+    }
+
+    pmm_node_t* new_node = // may has bug
+        add_pointer(pmm_node_t*, current->base, no_pages * PAGE_SIZE);
+
+    new_node->next = current->next;
+    new_node->prev = current;
+    new_node->base = add_pointer(void*, new_node->base, PAGE_SIZE);
+    new_node->no_pages = leftover_pages - 1;
+    new_node->kind = PMM_NOT_ALLOCATED;
+
+    current->next = new_node;
+    current->no_pages = no_pages;
+    current->kind = PMM_ALLOCATED;
+
+    return current->base;
+}

kernel/pmm.h

@@ -0,0 +1,24 @@
+#include <limine.h>
+#include <stddef.h>
+
+#define PAGE_SIZE ((size_t)0x1000)
+
+typedef enum {
+    PMM_NOT_ALLOCATED,
+    PMM_ALLOCATED,
+} pmm_node_kind_t;
+
+typedef struct pmm_node_t {
+    struct pmm_node_t* next;
+    struct pmm_node_t* prev;
+    void* base;
+    size_t no_pages;
+    pmm_node_kind_t kind;
+} pmm_node_t;
+
+typedef struct {
+    pmm_node_t* first_node;
+} pmm_t;
+
+void pmm_init(pmm_t* pmm, struct limine_memmap_response* limine_memmap);
+void* pmm_alloc_pages(pmm_t* pmm, size_t no_pages);