x86_64: Use Rust to setup SSE2

Now that we are using the x86_64 crate, we don't need ASM to set the
flags on the CR0 and CR4 registers. This also makes the code much more
readable.

src/asm/ram64.s

@@ -8,17 +8,6 @@ ram64_start:
     movb $'L', %al
     outb %al, %dx
 
-    # Enable SSE2 for XMM registers (needed for EFI calling)
-    # Clear CR0.EM and Set CR0.MP
-    movq %cr0, %rax
-    andb $0b11111011, %al # Clear bit 2
-    orb  $0b00000010, %al # Set bit 1
-    movq %rax, %cr0
-    # Set CR4.OSFXSR and CR4.OSXMMEXCPT
-    movq %cr4, %rax
-    orb  $0b00000110, %ah # Set bits 9 and 10
-    movq %rax, %cr4
-
     # Setup the stack (at the end of our RAM region)
     movq $ram_max, %rsp
 

src/main.rs

@@ -20,7 +20,10 @@
 
 use core::panic::PanicInfo;
 
-use x86_64::instructions::hlt;
+use x86_64::{
+    instructions::hlt,
+    registers::control::{Cr0, Cr0Flags, Cr4, Cr4Flags},
+};
 
 #[macro_use]
 mod serial;
@@ -83,6 +86,18 @@ fn setup_pagetables() {
     log!("Page tables setup");
 }
 
+// Enable SSE2 for XMM registers (needed for EFI calling)
+fn enable_sse() {
+    let mut cr0 = Cr0::read();
+    cr0.remove(Cr0Flags::EMULATE_COPROCESSOR);
+    cr0.insert(Cr0Flags::MONITOR_COPROCESSOR);
+    unsafe { Cr0::write(cr0) };
+    let mut cr4 = Cr4::read();
+    cr4.insert(Cr4Flags::OSFXSR);
+    cr4.insert(Cr4Flags::OSXMMEXCPT_ENABLE);
+    unsafe { Cr4::write(cr4) };
+}
+
 const VIRTIO_PCI_VENDOR_ID: u16 = 0x1af4;
 const VIRTIO_PCI_BLOCK_DEVICE_ID: u16 = 0x1042;
 
@@ -166,6 +181,7 @@ fn boot_from_device(device: &mut block::VirtioBlockDevice) -> bool {
 #[cfg_attr(not(test), no_mangle)]
 pub extern "C" fn rust64_start() -> ! {
     log!("\nStarting..");
+    enable_sse();
     setup_pagetables();
 
     pci::print_bus();