Debugging paging problem on VirtualBox (VT-x)

1 files changed, 60 insertions, 4 deletions

diff --git a/kernel/x86.c b/kernel/x86.c
index 94f4f89..c1113bf 100644
--- a/kernel/x86.c
+++ b/kernel/x86.c
@@ -1,5 +1,45 @@
 #include "x86.h"
 
+// get control registers (cr0-cr4)
+
+uint32_t x86_get_cr0()
+{
+    uint32_t cr;
+    asm volatile("mov %%cr0, %0": "=b"(cr));
+    return cr;
+}
+
+uint32_t x86_get_cr1()
+{
+    uint32_t cr=0;
+    
+    // reading the reserved cr1 register results in crash.
+    // (at least on emulators)
+    // asm volatile("mov %%cr1, %0": "=b"(cr));
+    
+    return cr;
+}
+
+uint32_t x86_get_cr2()
+{
+    uint32_t cr;
+    asm volatile("mov %%cr2, %0": "=b"(cr));
+    return cr;
+}
+
+uint32_t x86_get_cr3()
+{
+    uint32_t cr=0;
+    asm volatile("mov %%cr3, %0": "=b"(cr));
+    return cr;
+}
+
+uint32_t x86_get_cr4()
+{
+    uint32_t cr;
+    asm volatile("mov %%cr4, %0": "=b"(cr));
+    return cr;
+}
 void x86_outb(int port, uint8_t data)
 {
     __asm __volatile("outb %0,%w1" : : "a" (data), "d" (port));
@@ -43,15 +83,31 @@ void x86_set_pdbr(uint32_t addr)
 
 }
 
+// enable PT bit in CR0
 void x86_paging_enable()
 {
-    unsigned int cr0;
-    asm volatile("mov %%cr0, %0": "=b"(cr0));
-    cr0 |= 0x80000000;
+    uint32_t cr0=x86_get_cr0();
+    cr0 |= 0x80000000; // enable paging 
+
+//    cr0 |= 0x40000000; // cahce disable
+//    cr0 |= 0x20000000; // not-write-through
+//    cr0 |= 0x10000; // write to read-only pages
+
+    asm volatile("mov %0, %%cr0":: "b"(cr0));
+}
+
+
+// disable PT bit in CR0
+void x86_paging_disable()
+{
+    uint32_t cr0=x86_get_cr0();
+    cr0 &= ~0x80000000;
     asm volatile("mov %0, %%cr0":: "b"(cr0));
 }
 
-x86_flush_tlb(uint32_t addr)
+void x86_flush_tlb(uint32_t addr)
 {
 	asm volatile("invlpg (%0)" ::"r" (addr) : "memory");
 }
+
+