Add support for Arm64EC to the Standard Library

Author: dpaoliello

library/core/src/hint.rs

@@ -237,7 +237,7 @@ pub fn spin_loop() {
         crate::arch::riscv64::pause();
     }
 
-    #[cfg(target_arch = "aarch64")]
+    #[cfg(any(target_arch = "aarch64", target_arch = "arm64ec"))]
     {
         // SAFETY: the `cfg` attr ensures that we only execute this on aarch64 targets.
         unsafe { crate::arch::aarch64::__isb(crate::arch::aarch64::SY) };

library/panic_abort/src/lib.rs

@@ -81,6 +81,7 @@ pub unsafe fn __rust_start_panic(_payload: &mut dyn PanicPayload) -> u32 {
                     } else if #[cfg(target_arch = "aarch64")] {
                         core::arch::asm!("brk 0xF003", in("x0") FAST_FAIL_FATAL_APP_EXIT, options(noreturn, nostack));
                     } else {
+                        // This is currently used for ARM64EC since we don't support inline assembly.
                         core::intrinsics::abort();
                     }
                 }

library/std/src/sys/pal/common/alloc.rs

@@ -23,6 +23,7 @@ pub const MIN_ALIGN: usize = 8;
 #[cfg(any(
     target_arch = "x86_64",
     target_arch = "aarch64",
+    target_arch = "arm64ec",
     target_arch = "loongarch64",
     target_arch = "mips64",
     target_arch = "mips64r6",

library/std/src/sys/pal/windows/c/windows_sys.rs

@@ -1018,7 +1018,7 @@ impl Clone for CONTEXT_0_0 {
     }
 }
 #[repr(C)]
-#[cfg(target_arch = "x86_64")]
+#[cfg(any(target_arch = "x86_64", target_arch = "arm64ec"))]
 pub struct CONTEXT {
     pub P1Home: u64,
     pub P2Home: u64,
@@ -1067,30 +1067,30 @@ pub struct CONTEXT {
     pub LastExceptionToRip: u64,
     pub LastExceptionFromRip: u64,
 }
-#[cfg(target_arch = "x86_64")]
+#[cfg(any(target_arch = "x86_64", target_arch = "arm64ec"))]
 impl Copy for CONTEXT {}
-#[cfg(target_arch = "x86_64")]
+#[cfg(any(target_arch = "x86_64", target_arch = "arm64ec"))]
 impl Clone for CONTEXT {
     fn clone(&self) -> Self {
         *self
     }
 }
 #[repr(C)]
-#[cfg(target_arch = "x86_64")]
+#[cfg(any(target_arch = "x86_64", target_arch = "arm64ec"))]
 pub union CONTEXT_0 {
     pub FltSave: XSAVE_FORMAT,
     pub Anonymous: CONTEXT_0_0,
 }
-#[cfg(target_arch = "x86_64")]
+#[cfg(any(target_arch = "x86_64", target_arch = "arm64ec"))]
 impl Copy for CONTEXT_0 {}
-#[cfg(target_arch = "x86_64")]
+#[cfg(any(target_arch = "x86_64", target_arch = "arm64ec"))]
 impl Clone for CONTEXT_0 {
     fn clone(&self) -> Self {
         *self
     }
 }
 #[repr(C)]
-#[cfg(target_arch = "x86_64")]
+#[cfg(any(target_arch = "x86_64", target_arch = "arm64ec"))]
 pub struct CONTEXT_0_0 {
     pub Header: [M128A; 2],
     pub Legacy: [M128A; 8],
@@ -1111,9 +1111,9 @@ pub struct CONTEXT_0_0 {
     pub Xmm14: M128A,
     pub Xmm15: M128A,
 }
-#[cfg(target_arch = "x86_64")]
+#[cfg(any(target_arch = "x86_64", target_arch = "arm64ec"))]
 impl Copy for CONTEXT_0_0 {}
-#[cfg(target_arch = "x86_64")]
+#[cfg(any(target_arch = "x86_64", target_arch = "arm64ec"))]
 impl Clone for CONTEXT_0_0 {
     fn clone(&self) -> Self {
         *self
@@ -3339,7 +3339,7 @@ pub const FILE_WRITE_EA: FILE_ACCESS_RIGHTS = 16u32;
 pub const FILE_WRITE_THROUGH: NTCREATEFILE_CREATE_OPTIONS = 2u32;
 pub const FIONBIO: i32 = -2147195266i32;
 #[repr(C)]
-#[cfg(any(target_arch = "aarch64", target_arch = "x86_64"))]
+#[cfg(any(target_arch = "aarch64", target_arch = "arm64ec", target_arch = "x86_64"))]
 pub struct FLOATING_SAVE_AREA {
     pub ControlWord: u32,
     pub StatusWord: u32,
@@ -3351,9 +3351,9 @@ pub struct FLOATING_SAVE_AREA {
     pub RegisterArea: [u8; 80],
     pub Cr0NpxState: u32,
 }
-#[cfg(any(target_arch = "aarch64", target_arch = "x86_64"))]
+#[cfg(any(target_arch = "aarch64", target_arch = "arm64ec", target_arch = "x86_64"))]
 impl Copy for FLOATING_SAVE_AREA {}
-#[cfg(any(target_arch = "aarch64", target_arch = "x86_64"))]
+#[cfg(any(target_arch = "aarch64", target_arch = "arm64ec", target_arch = "x86_64"))]
 impl Clone for FLOATING_SAVE_AREA {
     fn clone(&self) -> Self {
         *self
@@ -4106,7 +4106,7 @@ impl Clone for WSABUF {
     }
 }
 #[repr(C)]
-#[cfg(any(target_arch = "aarch64", target_arch = "x86_64"))]
+#[cfg(any(target_arch = "aarch64", target_arch = "arm64ec", target_arch = "x86_64"))]
 pub struct WSADATA {
     pub wVersion: u16,
     pub wHighVersion: u16,
@@ -4116,9 +4116,9 @@ pub struct WSADATA {
     pub szDescription: [i8; 257],
     pub szSystemStatus: [i8; 129],
 }
-#[cfg(any(target_arch = "aarch64", target_arch = "x86_64"))]
+#[cfg(any(target_arch = "aarch64", target_arch = "arm64ec", target_arch = "x86_64"))]
 impl Copy for WSADATA {}
-#[cfg(any(target_arch = "aarch64", target_arch = "x86_64"))]
+#[cfg(any(target_arch = "aarch64", target_arch = "arm64ec", target_arch = "x86_64"))]
 impl Clone for WSADATA {
     fn clone(&self) -> Self {
         *self
@@ -4286,7 +4286,7 @@ pub const WSA_SECURE_HOST_NOT_FOUND: WSA_ERROR = 11032i32;
 pub const WSA_WAIT_EVENT_0: WSA_ERROR = 0i32;
 pub const WSA_WAIT_IO_COMPLETION: WSA_ERROR = 192i32;
 #[repr(C)]
-#[cfg(any(target_arch = "aarch64", target_arch = "x86_64"))]
+#[cfg(any(target_arch = "aarch64", target_arch = "arm64ec", target_arch = "x86_64"))]
 pub struct XSAVE_FORMAT {
     pub ControlWord: u16,
     pub StatusWord: u16,
@@ -4305,9 +4305,9 @@ pub struct XSAVE_FORMAT {
     pub XmmRegisters: [M128A; 16],
     pub Reserved4: [u8; 96],
 }
-#[cfg(any(target_arch = "aarch64", target_arch = "x86_64"))]
+#[cfg(any(target_arch = "aarch64", target_arch = "arm64ec", target_arch = "x86_64"))]
 impl Copy for XSAVE_FORMAT {}
-#[cfg(any(target_arch = "aarch64", target_arch = "x86_64"))]
+#[cfg(any(target_arch = "aarch64", target_arch = "arm64ec", target_arch = "x86_64"))]
 impl Clone for XSAVE_FORMAT {
     fn clone(&self) -> Self {
         *self

library/std/src/sys/pal/windows/mod.rs

@@ -325,6 +325,7 @@ pub fn dur2timeout(dur: Duration) -> c::DWORD {
 /// that function for more information on `__fastfail`
 #[cfg(not(miri))] // inline assembly does not work in Miri
 pub fn abort_internal() -> ! {
+    #[allow(unused_unsafe)]
     unsafe {
         cfg_if::cfg_if! {
             if #[cfg(any(target_arch = "x86", target_arch = "x86_64"))] {
@@ -334,6 +335,7 @@ pub fn abort_internal() -> ! {
             } else if #[cfg(target_arch = "aarch64")] {
                 core::arch::asm!("brk 0xF003", in("x0") c::FAST_FAIL_FATAL_APP_EXIT, options(noreturn, nostack));
             } else {
+                // This is currently used for ARM64EC since we don't support inline assembly.
                 core::intrinsics::abort();
             }
         }

src/doc/rustc/src/platform-support/arm64ec-pc-windows-msvc.md

@@ -11,48 +11,66 @@ applications on AArch64 Windows 11. See <https://learn.microsoft.com/en-us/windo
 
 ## Requirements
 
-Target only supports cross-compilation, `core` and `alloc` are supported but
-`std` is not.
-
 Builds Arm64EC static and dynamic libraries and executables which can be run on
 AArch64 Windows 11 devices. Arm64EC static libraries can also be linked into
 Arm64X dynamic libraries and executables.
 
-Uses `arm64ec` as its `target_arch` - code built for Arm64EC must be compatible
-with x86_64 code (e.g., same structure layouts, function signatures, etc.) but
-use AArch64 intrinsics.
-
-Only supported backend is LLVM 18 (or above).
+Only supported backend is LLVM 18.1.0 or above (18.1.2 or above is required for
+`raw-dylib` support).
+
+### Reusing code from other architectures - x86_64 or AArch64?
+
+Arm64EC uses `arm64ec` as its `target_arch`, but it is possible to reuse
+existing architecture-specific code in most cases. The best mental model for
+deciding which architecture to reuse is to is to think of Arm64EC as an x86_64
+process that happens to use the AArch64 instruction set (with some caveats) and
+has a completely custom ABI.
+
+To put this in practice:
+* Arm64EC interacts with the operating system, other processes and other DLLs as
+  x86_64.
+  - For example, [in `backtrace`](https://github.com/rust-lang/backtrace-rs/commit/ef39a7d7da58b4cae8c8f3fc67a8300fd8d2d0d9)
+    we use the x86_64 versions of `CONTEXT` and `RtlVirtualUnwind`.
+  - If you are configuring a search path to find DLLs (e.g., to load plugins or
+    addons into your application), you should use the same path as the x86_64
+    version of your application, not the AArch64 path (since Arm64EC (i.e.,
+    x86_64) processes cannot load native AArch64 DLLs).
+* Arm64EC uses AArch64 intrinsics.
+  - For example, <https://github.com/rust-lang/portable-simd/commit/ca4033f49b1f6019561b8b161b4097b4a07f2e1b>
+    and <https://github.com/rust-lang/stdarch/commit/166ef7ba22b6a1d908d4b29a36e68ceca324808a>.
+* Assembly for AArch64 might be reusable for Arm64EC, but there are many
+  caveats. For full details see [Microsoft's documentation on the Arm64EC ABI](https://learn.microsoft.com/en-us/windows/arm/arm64ec-abi)
+  but in brief:
+  - Arm64EC uses a restricted set of AArch64 registers.
+  - Arm64EC uses a different name mangling scheme than AArch64.
+  - Arm64EC requires entry and exit thunks be generated for some functions.
+  - Indirect calls must be done via a call checker.
+  - Control Flow Guard and stack checks use different functions than AArch64.
 
 ## Building the target
 
 You can build Rust with support for the targets by adding it to the `target`
-list in `config.toml` and disabling `std`:
+list in `config.toml`:
 
 ```toml
 [build]
 target = [ "arm64ec-pc-windows-msvc" ]
-
-[target.arm64ec-pc-windows-msvc]
-no-std = true
 ```
 
 ## Building Rust programs
 
 Rust does not yet ship pre-compiled artifacts for this target. To compile for
 this target, you will either need to build Rust with the target enabled (see
-"Building the target" above), or build your own copy of `core` by using
-`build-std` or similar.
+"Building the target" above), or build your own copy using `build-std` or
+similar.
 
 ## Testing
 
 Tests can be run on AArch64 Windows 11 devices.
 
-Since this is a `no_std` target, the Rust test suite is not supported.
-
 ## Cross-compilation toolchains and C code
 
-C code can be built using the Arm64-targetting MSVC toolchain.
+C code can be built using the Arm64-targetting MSVC or Clang toolchain.
 
 To compile: