Add rdfsbase, rdgsbase, wrfsbase, wrgsbase (#172)

Author: haraldh

src/asm/asm.s

@@ -233,3 +233,27 @@ _x86_64_asm_wrmsr:
 _x86_64_asm_hlt:
     hlt
     retq
+
+.global _x86_64_asm_rdfsbase
+.p2align 4
+_x86_64_asm_rdfsbase:
+    rdfsbase %rax
+    retq
+
+.global _x86_64_asm_wrfsbase
+.p2align 4
+_x86_64_asm_wrfsbase:
+    wrfsbase %rdi
+    retq
+
+.global _x86_64_asm_rdgsbase
+.p2align 4
+_x86_64_asm_rdgsbase:
+    rdgsbase %rax
+    retq
+
+.global _x86_64_asm_wrgsbase
+.p2align 4
+_x86_64_asm_wrgsbase:
+    wrgsbase %rdi
+    retq

src/asm/mod.rs

@@ -203,4 +203,28 @@ extern "C" {
         link_name = "_x86_64_asm_write_rflags"
     )]
     pub(crate) fn x86_64_asm_write_rflags(val: u64);
+
+    #[cfg_attr(
+        any(target_env = "gnu", target_env = "musl"),
+        link_name = "_x86_64_asm_rdfsbase"
+    )]
+    pub(crate) fn x86_64_asm_rdfsbase() -> u64;
+
+    #[cfg_attr(
+        any(target_env = "gnu", target_env = "musl"),
+        link_name = "_x86_64_asm_wrfsbase"
+    )]
+    pub(crate) fn x86_64_asm_wrfsbase(val: u64);
+
+    #[cfg_attr(
+        any(target_env = "gnu", target_env = "musl"),
+        link_name = "_x86_64_asm_rdgsbase"
+    )]
+    pub(crate) fn x86_64_asm_rdgsbase() -> u64;
+
+    #[cfg_attr(
+        any(target_env = "gnu", target_env = "musl"),
+        link_name = "_x86_64_asm_wrgsbase"
+    )]
+    pub(crate) fn x86_64_asm_wrgsbase(val: u64);
 }

src/registers/mod.rs

@@ -18,3 +18,102 @@ pub fn read_rip() -> u64 {
     }
     rip
 }
+
+/// Writes the FS segment base address
+///
+/// ## Safety
+///
+/// If `CR4.FSGSBASE` is not set, this instruction will throw an `#UD`.
+///
+/// The caller must ensure that this write operation has no unsafe side
+/// effects, as the FS segment base address is often used for thread
+/// local storage.
+#[inline]
+pub unsafe fn wrfsbase(val: u64) {
+    #[cfg(feature = "inline_asm")]
+    #[inline(always)]
+    unsafe fn inner(val: u64) {
+        llvm_asm!("wrfsbase $0" :: "r"(val) :: "volatile")
+    }
+
+    #[cfg(not(feature = "inline_asm"))]
+    #[inline(always)]
+    unsafe fn inner(val: u64) {
+        crate::asm::x86_64_asm_wrfsbase(val)
+    }
+
+    inner(val)
+}
+
+/// Reads the FS segment base address
+///
+/// ## Safety
+///
+/// If `CR4.FSGSBASE` is not set, this instruction will throw an `#UD`.
+#[inline]
+pub unsafe fn rdfsbase() -> u64 {
+    #[cfg(feature = "inline_asm")]
+    #[inline(always)]
+    unsafe fn inner() -> u64 {
+        let val: u64;
+        llvm_asm!("rdfsbase $0" : "=r" (val) ::: "volatile");
+        val
+    }
+
+    #[cfg(not(feature = "inline_asm"))]
+    #[inline(always)]
+    unsafe fn inner() -> u64 {
+        crate::asm::x86_64_asm_rdfsbase()
+    }
+
+    inner()
+}
+
+/// Writes the GS segment base address
+///
+/// ## Safety
+///
+/// If `CR4.FSGSBASE` is not set, this instruction will throw an `#UD`.
+///
+/// The caller must ensure that this write operation has no unsafe side
+/// effects, as the GS segment base address might be in use.
+#[inline]
+pub unsafe fn wrgsbase(val: u64) {
+    #[cfg(feature = "inline_asm")]
+    #[inline(always)]
+    unsafe fn inner(val: u64) {
+        llvm_asm!("wrgsbase $0" :: "r"(val) :: "volatile")
+    }
+
+    #[cfg(not(feature = "inline_asm"))]
+    #[inline(always)]
+    unsafe fn inner(val: u64) {
+        crate::asm::x86_64_asm_wrgsbase(val)
+    }
+
+    inner(val)
+}
+
+/// Reads the GS segment base address
+///
+/// ## Safety
+///
+/// If `CR4.FSGSBASE` is not set, this instruction will throw an `#UD`.
+#[inline]
+pub unsafe fn rdgsbase() -> u64 {
+    #[cfg(feature = "inline_asm")]
+    #[inline(always)]
+    unsafe fn inner() -> u64 {
+        let val: u64;
+        llvm_asm!("rdgsbase $0" : "=r" (val) ::: "volatile");
+        val
+    }
+
+    #[cfg(not(feature = "inline_asm"))]
+    #[inline(always)]
+    unsafe fn inner() -> u64 {
+        crate::asm::x86_64_asm_rdgsbase()
+    }
+
+    inner()
+}