Add non inline_asm XCr0 implementation

Signed-off-by: Joe Richey <joerichey@google.com>

Author: josephlr

src/asm/asm.s

@@ -280,3 +280,21 @@ _x86_64_asm_rdgsbase:
 _x86_64_asm_wrgsbase:
     wrgsbase %rdi
     retq
+
+.global _x86_64_asm_xgetbv
+.p2align 4
+_x86_64_asm_xgetbv:
+    mov    %edi, %ecx    # First param is the XCR number
+    xgetbv
+    shl    $32,  %rdx    # shift edx to upper 32bit
+    mov    %eax, %eax    # clear upper 32bit of rax
+    or     %rdx, %rax    # or with rdx
+    retq
+
+.global _x86_64_asm_xsetbv
+.p2align 4
+_x86_64_asm_xsetbv:
+    movl  %edi, %ecx    # First param is the XCR number
+    movl  %esi, %eax    # Second param is the low 32-bits
+    xsetbv              # Third param (high 32-bits) is already in %edx
+    retq

src/asm/mod.rs

@@ -251,4 +251,16 @@ extern "C" {
         link_name = "_x86_64_asm_wrgsbase"
     )]
     pub(crate) fn x86_64_asm_wrgsbase(val: u64);
+
+    #[cfg_attr(
+        any(target_env = "gnu", target_env = "musl"),
+        link_name = "_x86_64_asm_xgetbv"
+    )]
+    pub(crate) fn x86_64_asm_xgetbv(xcr: u32) -> u64;
+
+    #[cfg_attr(
+        any(target_env = "gnu", target_env = "musl"),
+        link_name = "_x86_64_asm_xsetbv"
+    )]
+    pub(crate) fn x86_64_asm_xsetbv(xcr: u32, low: u32, high: u32);
 }

src/registers/xcontrol.rs

@@ -24,7 +24,7 @@ bitflags! {
     }
 }
 
-#[cfg(all(feature = "instructions", feature = "inline_asm"))]
+#[cfg(feature = "instructions")]
 mod x86_64 {
     use super::*;
     impl XCr0 {
@@ -37,16 +37,22 @@ mod x86_64 {
         /// Read the current raw XCR0 value.
         #[inline]
         pub fn read_raw() -> u64 {
-            let (low, high): (u32, u32);
+            #[cfg(feature = "inline_asm")]
             unsafe {
+                let (low, high): (u32, u32);
                 asm!(
                     "xgetbv",
                     in("ecx") 0,
                     out("rax") low, out("rdx") high,
                     options(nomem, nostack, preserves_flags),
                 );
+                (high as u64) << 32 | (low as u64)
+            }
+
+            #[cfg(not(feature = "inline_asm"))]
+            unsafe {
+                crate::asm::x86_64_asm_xgetbv(0)
             }
-            (high as u64) << 32 | (low as u64)
         }
 
         /// Write XCR0 flags.
@@ -78,12 +84,17 @@ mod x86_64 {
         pub unsafe fn write_raw(value: u64) {
             let low = value as u32;
             let high = (value >> 32) as u32;
+
+            #[cfg(feature = "inline_asm")]
             asm!(
                 "xsetbv",
                 in("ecx") 0,
                 in("rax") low, in("rdx") high,
                 options(nomem, nostack, preserves_flags),
             );
+
+            #[cfg(not(feature = "inline_asm"))]
+            crate::asm::x86_64_asm_xsetbv(0, low, high);
         }
     }
 }