Got BIOS downcalls from Prot32 working

src/bios.S

@@ -87,6 +87,9 @@ bios_func:  push        %ebp
             // To support any interrupt number, we use self-modifying code.
             mov         %al, _bf_int+1
 
+            PROT16
+            REAL
+
             mov          0(%edi), %eax
             mov          4(%edi), %ecx
             mov          8(%edi), %edx
@@ -95,17 +98,11 @@ bios_func:  push        %ebp
             mov         20(%edi), %esi
             mov         24(%edi), %edi
 
-            PROT16
-            REAL
-
             // This instruction will get written at runtime
 _bf_int:    .byte       0xCD, 0 // INT imm8
             push        $0
             pushf
 
-            PROT
-            PROT32
-
             push        %edi
             mov         8+4(%ebp), %edi
             mov         %eax,  0(%edi)
@@ -117,6 +114,9 @@ _bf_int:    .byte       0xCD, 0 // INT imm8
             pop         %eax
             mov         %eax, 24(%edi)
 
+            PROT
+            PROT32
+
             pop         %eax
 
             pop         %esi

src/main.c

@@ -51,6 +51,28 @@ struct vesa_info {
 
 extern uint16_t bios_func(uint8_t inum, uint32_t reg[]);
 
+#define PG_PRESENT 0x001
+#define PG_WRITE   0x002
+#define PG_USER    0x004
+#define PG_SIZE    0x080
+#define PG_GLOBAL  0x100
+
+__attribute__((aligned(4096))) uint64_t pml4[512];
+__attribute__((aligned(4096))) uint64_t pdp[512];
+__attribute__((aligned(4096))) uint64_t pd[512];
+
+uint64_t
+pg_setup()
+{
+	pml4[0] = (uint64_t)(uint32_t)pdp | PG_WRITE | PG_PRESENT;
+	pdp[0] = (uint64_t)(uint32_t)pd | PG_WRITE | PG_PRESENT;
+	for (unsigned i = 0; i < 512; i++) {
+		pd[i] = (i * (uint64_t)0x200000) | PG_WRITE | PG_PRESENT | PG_SIZE;
+	}
+	uint64_t cr3 = (uint64_t)(uint32_t)pml4;
+	return cr3;
+}
+
 void
 main()
 {
@@ -72,6 +94,8 @@ main()
 		bios_write(buf);
 	}
 
+	pg_setup();
+
 #if 0
 	char foo[24];
 
@@ -109,6 +133,8 @@ main()
 	reg[6] = 0;
 	bios_func(0x10, reg);
 
+	bios_write("what?\r\n");
+
 	for (;;) {
 		__asm__ ("hlt");
 	}