Copy basic paging functions from MINIX 3

arch/Makefile

@@ -5,6 +5,7 @@ CC = $(CCPREFIX)gcc
 OBJS = start.s.o
 OBJS += init.c.o
 OBJS += multiboot.c.o
+OBJS += paging.c.o
 
 # Architecture-independent
 OBJS += info.c.o

arch/paging.c

@@ -0,0 +1,80 @@
+#include "paging.h"
+
+#include <kernelmq/stdlib.h>
+
+#define I386_VM_PT_ENTRIES 1024
+
+#define I386_PAGE_SIZE      4096
+#define I386_BIG_PAGE_SIZE  (I386_PAGE_SIZE * I386_VM_PT_ENTRIES)
+
+// i386 paging constants
+#define I386_VM_PRESENT 0x001   // Page is present
+#define I386_VM_WRITE   0x002   // Read/write access allowed
+#define I386_VM_READ    0x000   // Read access only
+#define I386_VM_USER    0x004   // User access allowed
+#define I386_VM_PWT 0x008   // Write through
+#define I386_VM_PCD 0x010   // Cache disable
+#define I386_VM_ACC 0x020   // Accessed
+#define I386_VM_ADDR_MASK 0xFFFFF000 // physical address
+#define I386_VM_ADDR_MASK_4MB 0xFFC00000 // physical address
+#define I386_VM_OFFSET_MASK_4MB 0x003FFFFF // physical address
+
+// Page directory specific flags.
+#define I386_VM_BIGPAGE 0x080 // 4MB page
+
+// TODO: implement this
+#define assert(n) if (n) {}
+#define panic()   if (1) {}
+
+static unsigned long pagedir[I386_VM_PT_ENTRIES] __attribute__((aligned(4096)));
+
+void paging_clear()
+{
+    kmemset(pagedir, 0, sizeof(pagedir));
+}
+
+void paging_identity(const struct KernelMQ_Info *const kinfo)
+{
+    assert(kinfo->mem_upper_base);
+
+    for (int i = 0; i < I386_VM_PT_ENTRIES; ++i) {
+        unsigned int flags = I386_VM_PRESENT |
+                             I386_VM_BIGPAGE |
+                             I386_VM_USER    |
+                             I386_VM_WRITE;
+
+        unsigned long phys = i * I386_BIG_PAGE_SIZE;
+
+        if ((kinfo->mem_upper_base & I386_VM_ADDR_MASK_4MB) <=
+            (phys & I386_VM_ADDR_MASK_4MB)
+        ) {
+            flags |= I386_VM_PWT | I386_VM_PCD;
+        }
+
+        pagedir[i] = phys | flags;
+    }
+}
+
+int paging_mapkernel(const struct KernelMQ_Info *const kinfo)
+{
+    assert(!(kinfo->kernel_phys_base % I386_BIG_PAGE_SIZE));
+    assert(!(kinfo->kernel_virt_base % I386_BIG_PAGE_SIZE));
+
+    int pde = kinfo->kernel_virt_base / I386_BIG_PAGE_SIZE;
+
+    unsigned long mapped = 0;
+    unsigned long kern_phys = kinfo->kernel_phys_base;
+
+    while (mapped < kinfo->kernel_size) {
+        pagedir[pde] = kern_phys | I386_VM_PRESENT |
+                                   I386_VM_BIGPAGE |
+                                   I386_VM_WRITE;
+
+        mapped += I386_BIG_PAGE_SIZE;
+        kern_phys += I386_BIG_PAGE_SIZE;
+
+        ++pde;
+    }
+
+    return pde;
+}

arch/paging.h

@@ -0,0 +1,10 @@
+#ifndef KERNELMQ_INCLUDED_PAGING
+#define KERNELMQ_INCLUDED_PAGING 1
+
+#include <kernelmq/info.h>
+
+void paging_clear();
+void paging_identity(const struct KernelMQ_Info *kinfo);
+int paging_mapkernel(const struct KernelMQ_Info *kinfo);
+
+#endif