diff --git a/src/arch/x86_64.rs b/src/arch/x86_64.rs
index 3f96e2af0d..6ba5121bf5 100644
--- a/src/arch/x86_64.rs
+++ b/src/arch/x86_64.rs
@@ -109,7 +109,8 @@ pub struct FloatRegisters {
     pub mxcsr: u32,
     pub mxcsr_mask: u32,
     pub st_space: [u128; 8],
-    pub xmm_space: [u128; 16]
+    pub xmm_space: [u128; 16],
+    // TODO: YMM/ZMM
 }
 
 impl Deref for FloatRegisters {
@@ -128,3 +129,26 @@ impl DerefMut for FloatRegisters {
         }
     }
 }
+#[derive(Clone, Copy, Debug, Default)]
+#[repr(packed)]
+pub struct EnvRegisters {
+    pub fsbase: u64,
+    pub gsbase: u64,
+    // TODO: PKRU?
+}
+impl Deref for EnvRegisters {
+    type Target = [u8];
+    fn deref(&self) -> &[u8] {
+        unsafe {
+            slice::from_raw_parts(self as *const EnvRegisters as *const u8, mem::size_of::<EnvRegisters>())
+        }
+    }
+}
+
+impl DerefMut for EnvRegisters {
+    fn deref_mut(&mut self) -> &mut [u8] {
+        unsafe {
+            slice::from_raw_parts_mut(self as *mut EnvRegisters as *mut u8, mem::size_of::<EnvRegisters>())
+        }
+    }
+}
diff --git a/src/flag.rs b/src/flag.rs
index 30629b4a8d..9788884afa 100644
--- a/src/flag.rs
+++ b/src/flag.rs
@@ -295,6 +295,8 @@ bitflags! {
 // Auxiliery vector types
 pub const AT_NULL: usize = 0;
 pub const AT_PHDR: usize = 3;
+pub const AT_PHENT: usize = 4;
+pub const AT_PHNUM: usize = 5;
 pub const AT_ENTRY: usize = 9;
 
 bitflags! {