Add a Cargo Feature for Enabling SSE

Cargo.toml

@@ -17,6 +17,7 @@ xmas-elf = { version = "0.6.2", optional = true }
 x86_64 = { version = "0.7.2", optional = true }
 usize_conversions = { version = "0.2.0", optional = true }
 fixedvec = { version = "0.2.4", optional = true }
+bit_field = "*"
 
 [dependencies.font8x8]
 version = "0.2.4"
@@ -34,6 +35,7 @@ binary = ["xmas-elf", "x86_64", "usize_conversions", "fixedvec", "llvm-tools", "
 vga_320x200 = ["font8x8"]
 recursive_page_table = []
 map_physical_memory = []
+sse = []
 
 [profile.dev]
 panic = "abort"

example-kernel/src/main.rs

@@ -11,7 +11,7 @@ pub extern "C" fn _start() -> ! {
     // named `_start` by default
 
     let vga_buffer = 0xb8000 as *mut u8;
-    
+
     // print `HELLO` to the screen (see
     // https://os.phil-opp.com/minimal-rust-kernel/#printing-to-screen)
     for (i, &byte) in HELLO.iter().enumerate() {

src/main.rs

@@ -87,6 +87,30 @@ extern "C" {
 
 #[no_mangle]
 pub unsafe extern "C" fn stage_4() -> ! {
+    #[cfg(feature = "sse")]
+    {
+        use bit_field::BitField;
+        use x86_64::registers::control::Cr0;
+        let mut flags = Cr0::read_raw();
+        flags.set_bit(2, false);
+        flags.set_bit(1, true);
+        flags.set_bit(9, true);
+        flags.set_bit(10, true);
+        unsafe {
+            Cr0::write_raw(flags);
+        }
+        // For now, we must use inline ASM here
+        let mut cr4: u64;
+        unsafe {
+            asm!("mov %cr4, $0" : "=r" (cr4));
+        }
+        cr4.set_bit(9, true);
+        cr4.set_bit(10, true);
+        unsafe {
+            asm!("mov $0, %cr4" :: "r" (cr4) : "memory");
+        }
+    }
+
     // Set stack segment
     asm!("mov bx, 0x0
           mov ss, bx" ::: "bx" : "intel");

src/stage_2.s

@@ -95,7 +95,6 @@ enter_protected_mode_again:
     mov eax, cr0
     or al, 1    # set protected mode bit
     mov cr0, eax
-
     push 0x8
     lea eax, [stage_3]
     push eax

test-kernel/Cargo.toml

@@ -6,3 +6,4 @@ edition = "2018"
 
 [dependencies]
 x86_64 = "0.3.4"
+bootloader = {path = "..", features=["sse"]}