page allocation

linker.ld

@@ -30,4 +30,7 @@ SECTIONS
     PROVIDE(_stack_bottom = .);
     . += 4096; 
     PROVIDE(stack_top = .);
+
+   . = ALIGN(4K);
+   _heap_start =.;
 }

src/kernel/kernel.c

@@ -10,5 +10,14 @@ void kmain() {
     kputs("-------------------");
     knewline();
     page_init();
+
+    kprint("Stress testing memory...\n");
+    while(1) {
+        void *p = page_alloc();
+        if (p == NULL) {
+            kpanic("Expected OOM reached!");
+        }
+    }
+
     poweroff();
 }

src/kernel/memory.c

@@ -2,6 +2,7 @@
 #include <stddef.h>
 #include "drivers/uart.h"
 #include "memory.h"
+#include "panic.h"
 
 #define PAGE_SIZE 4096
 
@@ -9,13 +10,19 @@ struct Page {
 	struct Page *next;
 };
 
-static struct Page *free_list;
+struct HeapHeader {
+	size_t size;
+	int is_free;
+	struct HeapHeader *next;
+};
 
-extern uint8_t _bss_end[]; // named in the linker script
+static struct Page *free_list = NULL;
+
+extern uint8_t _heap_start[]; // named in the linker script
 
 void page_init() {
 	kprint("Initialising page allocator.\n");
-	uintptr_t start = ((uintptr_t)_bss_end + PAGE_SIZE - 1) & ~(PAGE_SIZE - 1);
+	uintptr_t start = ((uintptr_t)_heap_start + PAGE_SIZE - 1) & ~(PAGE_SIZE - 1);
 	uintptr_t end = 0x88000000; // Default QEMU RAM limit
 
 	for (uintptr_t addr = start; addr + PAGE_SIZE <= end; addr += PAGE_SIZE) {
@@ -31,3 +38,19 @@ void page_free(void *addr) {
 	p->next = free_list;
 	free_list = p;
 }
+
+void *page_alloc() { {
+	if (free_list == NULL) {
+		kpanic("No free pages!");
+	}
+	struct Page *p = free_list;
+	free_list = free_list->next;
+
+	//zero out the page
+	for (int i = 0; i < (PAGE_SIZE/8); i++) {
+		((uint8_t *)p)[i] = 0;
+	}
+
+	return (void *)p;
+}
+}

src/kernel/memory.h

@@ -3,5 +3,6 @@
 
 void page_init();
 void page_free(void *addr);
+void *page_alloc();
 
 #endif

src/kernel/panic.c

@@ -4,6 +4,7 @@
 #include <syscon/syscon.h>
 
 void kpanic(const char *reason){
+    kprint("\n!!! PANIC!!!\n");
 	kprint(reason);
 	poweroff();
 }