Use memoffset::offset_of rather than implementing it ourselves.

TEST=tools/dev_container tools/run_tests
TEST=tools/dev_container tools/run_tests --target=vm:aarch64

Change-Id: Iccdf0653001599d76c742db27349e274f7a4bb23
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/3497460
Reviewed-by: Daniel Verkamp <dverkamp@chromium.org>
Tested-by: kokoro <noreply+kokoro@google.com>
Commit-Queue: Andrew Walbran <qwandor@google.com>

aarch64/Cargo.toml

@@ -13,6 +13,7 @@ kernel_cmdline = { path = "../kernel_cmdline" }
 kvm = { path = "../kvm" }
 kvm_sys = { path = "../kvm_sys" }
 libc = "*"
+memoffset = "0.6.5"
 minijail = "*"
 remain = "*"
 resources = { path = "../resources" }

hypervisor/Cargo.toml

@@ -12,6 +12,7 @@ enumn = "0.1.0"
 kvm = { path = "../kvm" }
 kvm_sys = { path = "../kvm_sys" }
 libc = "*"
+memoffset = "0.6.5"
 serde = { version = "1", features = [ "derive" ] }
 sync = { path = "../common/sync" }
 base = { path = "../common/base" }

hypervisor/src/kvm/aarch64.rs

@@ -17,23 +17,6 @@ use crate::{
     VcpuExit, VcpuFeature, Vm, VmAArch64, VmCap,
 };
 
-#[macro_export]
-macro_rules! offset__of {
-    ($type:path, $field:tt) => {{
-        // Check that the field actually exists. This will generate a compiler error if the field is
-        // accessed through a Deref impl.
-        #[allow(clippy::unneeded_field_pattern)]
-        let $type { $field: _, .. };
-
-        // Get a pointer to the uninitialized field.  This is taken from the docs for `addr_of_mut`.
-        let mut uninit = ::std::mem::MaybeUninit::<$type>::uninit();
-        let field_ptr = unsafe { ::std::ptr::addr_of_mut!((*uninit.as_mut_ptr()).$field) };
-
-        // Now get the offset.
-        (field_ptr as usize) - (uninit.as_mut_ptr() as usize)
-    }};
-}
-
 /// Gives the ID for a register to be used with `set_one_reg`.
 ///
 /// Pass the name of a field in `user_pt_regs` to get the corresponding register
@@ -41,18 +24,18 @@ macro_rules! offset__of {
 ///
 /// To get ID for registers `x0`-`x31`, refer to the `regs` field along with the
 /// register number, e.g. `arm64_core_reg!(regs, 5)` for `x5`. This is different
-/// to work around `offset__of!(kvm_sys::user_pt_regs, regs[$x])` not working.
+/// to work around `offset_of!(kvm_sys::user_pt_regs, regs[$x])` not working.
 #[macro_export]
 macro_rules! arm64_core_reg {
     ($reg: tt) => {{
-        let off = ($crate::offset__of!(::kvm_sys::user_pt_regs, $reg) / 4) as u64;
+        let off = (memoffset::offset_of!(::kvm_sys::user_pt_regs, $reg) / 4) as u64;
         ::kvm_sys::KVM_REG_ARM64
             | ::kvm_sys::KVM_REG_SIZE_U64
             | ::kvm_sys::KVM_REG_ARM_CORE as u64
             | off
     }};
     (regs, $x: literal) => {{
-        let off = (($crate::offset__of!(::kvm_sys::user_pt_regs, regs)
+        let off = ((memoffset::offset_of!(::kvm_sys::user_pt_regs, regs)
             + ($x * ::std::mem::size_of::<u64>()))
             / 4) as u64;
         ::kvm_sys::KVM_REG_ARM64