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 = { version = "0.10.0", optional = true }
 
 [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 = ["bit_field"]
 
 [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

@@ -54,6 +54,8 @@ mod frame_allocator;
 mod level4_entries;
 mod page_table;
 mod printer;
+#[cfg(feature = "sse")]
+mod sse;
 
 pub struct IdentityMappedAddr(PhysAddr);
 
@@ -142,6 +144,10 @@ fn load_elf(
     // Extract required information from the ELF file.
     let mut preallocated_space = alloc_stack!([ProgramHeader64; 32]);
     let mut segments = FixedVec::new(&mut preallocated_space);
+    #[cfg(feature = "sse")]
+    {
+        sse::enable_sse();
+    }
     let entry_point;
     {
         let kernel_start_ptr = usize_from(kernel_start.as_u64()) as *const u8;

src/sse.rs

@@ -0,0 +1,24 @@
+/// Enables Streaming SIMD Extensions (SSE) support for loaded kernels.
+#[cfg(feature = "sse")]
+pub fn enable_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");
+    }
+}

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