paging in c

2 files changed, 47 insertions, 0 deletions

diff --git a/kernel/src/mem/paging.c b/kernel/src/mem/paging.c
new file mode 100644
index 0000000..aa7f91e
--- /dev/null
+++ b/kernel/src/mem/paging.c
@@ -0,0 +1,35 @@
+#include <stdint.h>
+#include <paging.h>
+
+void load_pt_lvl4(uint64_t*);
+
+__attribute__((aligned(4096))) uint64_t page_table_lvl4[512];
+__attribute__((aligned(4096))) uint64_t page_table_lvl3[512];
+__attribute__((aligned(4096))) uint64_t page_table_lvl2_kernel[512];
+__attribute__((aligned(4096))) uint64_t page_table_lvl2_fb[512];
+
+#define PAGE_SIZE 0x00200000
+#define FLAG_PRESENT 0x1
+#define FLAG_WRITABLE 0x2
+#define FLAG_HUGE 0x80
+
+void init_paging(void)
+{
+	page_table_lvl4[0] = (uint64_t)page_table_lvl3 + FLAG_PRESENT + FLAG_WRITABLE;
+	page_table_lvl3[0] = (uint64_t)page_table_lvl2_kernel + FLAG_PRESENT + FLAG_WRITABLE;
+	page_table_lvl3[3] = (uint64_t)page_table_lvl2_fb + FLAG_PRESENT + FLAG_WRITABLE;
+
+	// 0x00000000 - 0x00400000 : 0x00000000 - 0x00400000
+	for (uint64_t i = 0; i < 2; i++) {
+		page_table_lvl2_kernel[i] = i * PAGE_SIZE + FLAG_PRESENT + FLAG_WRITABLE + FLAG_HUGE;
+	}
+
+	// TODO: remove initial mapping for fb and instead page on demand
+
+	// 0xe0000000 - 0xffffffff : 0xe0000000 - 0xffffffff
+	for (uint64_t i = 0; i < 512; i++) {
+		page_table_lvl2_fb[i] = i * PAGE_SIZE + 0xc0000000 + FLAG_PRESENT + FLAG_WRITABLE + FLAG_HUGE;
+	}
+
+	load_pt_lvl4(page_table_lvl4);
+}
diff --git a/kernel/src/mem/paging_asm.S b/kernel/src/mem/paging_asm.S
new file mode 100644
index 0000000..5a1dcf7
--- /dev/null
+++ b/kernel/src/mem/paging_asm.S
@@ -0,0 +1,12 @@
+.section .text
+
+.global load_pt_lvl4
+load_pt_lvl4:
+    push %rbp
+    mov %rsp, %rbp
+
+    mov %rdi, %cr3
+
+    mov %rbp, %rsp
+    pop %rbp
+    ret