[x86] implement __read/write eflags

Author: gnzlbg

src/x86/ia32.rs

@@ -0,0 +1,50 @@
+//! `i386/ia32` intrinsics
+
+/// Reads EFLAGS.
+#[cfg(target_arch = "x86")]
+#[inline(always)]
+pub unsafe fn __readeflags() -> u32 {
+    let eflags: u32;
+    asm!("pushfd; popl $0" : "=r"(eflags) : : : "volatile");
+    eflags
+}
+
+/// Reads EFLAGS.
+#[cfg(target_arch = "x86_64")]
+#[inline(always)]
+pub unsafe fn __readeflags() -> u64 {
+    let eflags: u64;
+    asm!("pushfq; popq $0" : "=r"(eflags) : : : "volatile");
+    eflags
+}
+
+/// Write EFLAGS.
+#[cfg(target_arch = "x86")]
+#[inline(always)]
+pub unsafe fn __writeeflags(eflags: u32) {
+    asm!("pushl $0; popfd" : : "r"(eflags) : "cc", "flags" : "volatile");
+}
+
+/// Write EFLAGS.
+#[cfg(target_arch = "x86_64")]
+#[inline(always)]
+pub unsafe fn __writeeflags(eflags: u64) {
+    asm!("pushq $0; popfq" : : "r"(eflags) : "cc", "flags" : "volatile");
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_eflags() {
+        unsafe {
+            // reads eflags, writes them back, reads them again,
+            // and compare for equality:
+            let v = __readeflags();
+            __writeeflags(v);
+            let u = __readeflags();
+            assert_eq!(v, u);
+        }
+    }
+}

src/x86/mod.rs

@@ -1,5 +1,6 @@
 //! `x86` and `x86_64` intrinsics.
 
+pub use self::ia32::*;
 pub use self::xsave::*;
 
 pub use self::sse::*;
@@ -31,6 +32,7 @@ mod macros;
 mod runtime;
 
 mod xsave;
+mod ia32;
 
 mod sse;
 mod sse2;