detect the highest used memory address, and only allocate pages above it

1 files changed, 12 insertions, 3 deletions

diff --git a/src/kernel/mem.c b/src/kernel/mem.c
index d002050..b455b25 100644
--- a/src/kernel/mem.c
+++ b/src/kernel/mem.c
@@ -1,11 +1,20 @@
 #include <arch/generic.h>
 #include <kernel/mem.h>
+#include <stdint.h>
 
-extern void *_bss_end;
 static void *highest_page;
 
-void mem_init() {
-	highest_page = &_bss_end;
+void mem_init(struct kmain_info *info) {
+	// finds the highest used page, and starts allocating pages above it
+	extern char _bss_end;
+	void *highest = &_bss_end;
+	size_t page_mask = PAGE_SIZE - 1;
+
+	if (highest < info->init.at + info->init.size)
+		highest = info->init.at + info->init.size;
+
+	// align up to PAGE_SIZE
+	highest_page = (void*)(((uintptr_t)highest + page_mask) & ~page_mask);
 }
 
 void *page_alloc(size_t pages) {