add kernel target for RustyHermit

compiler/rustc_target/src/spec/aarch64_unknown_hermit.rs

@@ -3,6 +3,7 @@ use crate::spec::Target;
 pub fn target() -> Target {
     let mut base = super::hermit_base::opts();
     base.max_atomic_width = Some(128);
+    base.features = "+strict-align,+neon,+fp-armv8".to_string();
 
     Target {
         llvm_target: "aarch64-unknown-hermit".to_string(),

compiler/rustc_target/src/spec/aarch64_unknown_none_hermitkernel.rs

@@ -0,0 +1,16 @@
+use crate::spec::Target;
+
+pub fn target() -> Target {
+    let mut base = super::hermit_kernel_base::opts();
+    base.max_atomic_width = Some(128);
+    base.abi = "softfloat".to_string();
+    base.features = "+strict-align,-neon,-fp-armv8".to_string();
+
+    Target {
+        llvm_target: "aarch64-unknown-hermit".to_string(),
+        pointer_width: 64,
+        data_layout: "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128".to_string(),
+        arch: "aarch64".to_string(),
+        options: base,
+    }
+}

compiler/rustc_target/src/spec/mod.rs

@@ -964,6 +964,7 @@ supported_targets! {
     ("aarch64-unknown-hermit", aarch64_unknown_hermit),
     ("x86_64-unknown-hermit", x86_64_unknown_hermit),
 
+    ("aarch64-unknown-none-hermitkernel", aarch64_unknown_none_hermitkernel),
     ("x86_64-unknown-none-hermitkernel", x86_64_unknown_none_hermitkernel),
 
     ("riscv32i-unknown-none-elf", riscv32i_unknown_none_elf),

src/doc/rustc/src/SUMMARY.md

@@ -17,6 +17,7 @@
     - [aarch64-apple-ios-sim](platform-support/aarch64-apple-ios-sim.md)
     - [armv7-unknown-linux-uclibceabi](platform-support/armv7-unknown-linux-uclibceabi.md)
     - [armv7-unknown-linux-uclibceabihf](platform-support/armv7-unknown-linux-uclibceabihf.md)
+    - [aarch64-unknown-none-hermitkernel](platform-support/aarch64-unknown-none-hermitkernel.md)
     - [\*-kmc-solid_\*](platform-support/kmc-solid.md)
     - [*-unknown-openbsd](platform-support/openbsd.md)
     - [x86_64-unknown-none](platform-support/x86_64-unknown-none.md)

src/doc/rustc/src/platform-support.md

@@ -204,7 +204,8 @@ target | std | host | notes
 `aarch64-apple-tvos` | * |  | ARM64 tvOS
 [`aarch64-kmc-solid_asp3`](platform-support/kmc-solid.md) | ✓ |  | ARM64 SOLID with TOPPERS/ASP3
 `aarch64-unknown-freebsd` | ✓ | ✓ | ARM64 FreeBSD
-`aarch64-unknown-hermit` | ? |  |
+`aarch64-unknown-hermit` | ✓ |  | ARM64 HermitCore
+[`aarch64-unknown-none-hermitkernel`](platform-support/aarch64-unknown-none-hermitkernel.md) | * |  | ARM64 HermitCore kernel
 `aarch64-unknown-uefi` | * |  | ARM64 UEFI
 `aarch64-unknown-linux-gnu_ilp32` | ✓ | ✓ | ARM64 Linux (ILP32 ABI)
 `aarch64-unknown-netbsd` | ✓ | ✓ |
@@ -286,10 +287,10 @@ target | std | host | notes
 `x86_64-sun-solaris` | ? |  | Deprecated target for 64-bit Solaris 10/11, illumos
 `x86_64-unknown-dragonfly` | ✓ | ✓ | 64-bit DragonFlyBSD
 `x86_64-unknown-haiku` | ✓ | ✓ | 64-bit Haiku
-`x86_64-unknown-hermit` | ? |  |
+`x86_64-unknown-hermit` | ✓ |  | HermitCore
 `x86_64-unknown-l4re-uclibc` | ? |  |
 [`x86_64-unknown-none`](platform-support/x86_64-unknown-none.md) | * |  | Freestanding/bare-metal x86_64, softfloat
-`x86_64-unknown-none-hermitkernel` | ? |  | HermitCore kernel
+`x86_64-unknown-none-hermitkernel` | * |  | HermitCore kernel
 `x86_64-unknown-none-linuxkernel` | * |  | Linux kernel modules
 [`x86_64-unknown-openbsd`](platform-support/openbsd.md) | ✓ | ✓ | 64-bit OpenBSD
 `x86_64-unknown-uefi` | * |  | 64-bit UEFI

src/doc/rustc/src/platform-support/aarch64-unknown-none-hermitkernel.md

@@ -0,0 +1,77 @@
+# `aarch64-unknown-none-hermitkernel`
+
+**Tier: 3**
+
+Required to build the kernel for [HermitCore](https://github.com/hermitcore/hermit-playground)
+or [RustyHermit](https://github.com/hermitcore/rusty-hermit).
+The result is a bare-metal aarch64 binary in ELF format.
+
+## Target maintainers
+
+- Stefan Lankes, https://github.com/stlankes
+
+## Requirements
+
+This target is cross-compiled. There is no support for `std`, but the
+library operating system provides a simple allocator to use `alloc`.
+
+By default, Rust code generated for this target does not use any vector or
+floating-point registers. This allows the generated code to build the library
+operaring system, which may need to avoid the use of such
+registers or which may have special considerations about the use of such
+registers (e.g. saving and restoring them to avoid breaking userspace code
+using the same registers). In contrast to `aarch64-unknown-none-softfloat`,
+the target is completly relocatable, which is a required feature of RustyHermit.
+
+By default, code generated with this target should run on any `aarch64`
+hardware; enabling additional target features may raise this baseline.
+On `aarch64-unknown-none-hermitkernel`, `extern "C"` uses the [standard System V calling
+convention](https://github.com/ARM-software/abi-aa/releases/download/2021Q3/sysvabi64.pdf),
+without red zones.
+
+This target generated binaries in the ELF format.
+
+## Building the target
+
+Typical you should not use the target directly. The target `aarch64-unknown-hermit`
+builds the _user space_ of RustyHermit and supports red zones and floating-point
+operations.
+To build and link the kernel to the application, the crate
+[hermit-sys](https://github.com/hermitcore/rusty-hermit/tree/master/hermit-sys)
+should be used by adding the following lines to the `Cargo.toml` file of
+your application.
+
+```toml
+[target.'cfg(target_os = "hermit")'.dependencies]
+hermit-sys = "0.1.*"
+```
+
+The crate `hermit-sys` uses the target `aarch64-unknown-none-hermitkernel`
+to build the kernel.
+
+## Building Rust programs
+
+Rust does not yet ship pre-compiled artifacts for this target. To compile for
+this target, you need to build the crate `hermit-sys` (see
+"Building the target" above).
+
+## Testing
+
+As `aarch64-unknown-none-hermitkernel` does not support `std`
+and does not support running any Rust testsuite.
+
+## Cross-compilation toolchains and C code
+
+If you want to compile C code along with Rust you will need an
+appropriate `aarch64` toolchain.
+
+Rust *may* be able to use an `aarch64-linux-gnu-` toolchain with appropriate
+standalone flags to build for this toolchain (depending on the assumptions of
+that toolchain, see below), or you may wish to use a separate
+`aarch64-unknown-none` (or `aarch64-elf-`) toolchain.
+
+On some `aarch64` hosts that use ELF binaries, you *may* be able to use the host
+C toolchain, if it does not introduce assumptions about the host environment
+that don't match the expectations of a standalone environment. Otherwise, you
+may need a separate toolchain for standalone/freestanding development, just as
+when cross-compiling from a non-`aarch64` platform.