Add new tier 3 target: x86_64-unknown-none

compiler/rustc_target/src/spec/mod.rs

@@ -954,6 +954,8 @@ supported_targets! {
     ("armv6k-nintendo-3ds", armv6k_nintendo_3ds),
 
     ("armv7-unknown-linux-uclibceabihf", armv7_unknown_linux_uclibceabihf),
+
+    ("x86_64-unknown-none", x86_64_unknown_none),
 }
 
 /// Warnings encountered when parsing the target `json`.

compiler/rustc_target/src/spec/x86_64_unknown_none.rs

@@ -0,0 +1,41 @@
+// Generic x86-64 target for bare-metal code - Floating point disabled
+//
+// Can be used in conjunction with the `target-feature` and
+// `target-cpu` compiler flags to opt-in more hardware-specific
+// features.
+
+use super::{
+    CodeModel, LinkerFlavor, LldFlavor, PanicStrategy, RelocModel, RelroLevel, StackProbeType,
+    Target, TargetOptions,
+};
+
+pub fn target() -> Target {
+    let opts = TargetOptions {
+        cpu: "x86-64".to_string(),
+        max_atomic_width: Some(64),
+        // don't use probe-stack=inline-asm until rust#83139 and rust#84667 are resolved
+        stack_probes: StackProbeType::Call,
+        position_independent_executables: true,
+        static_position_independent_executables: true,
+        relro_level: RelroLevel::Full,
+        relocation_model: RelocModel::Pic,
+        linker_flavor: LinkerFlavor::Lld(LldFlavor::Ld),
+        linker: Some("rust-lld".to_owned()),
+        features:
+            "-mmx,-sse,-sse2,-sse3,-ssse3,-sse4.1,-sse4.2,-3dnow,-3dnowa,-avx,-avx2,+soft-float"
+                .to_string(),
+        executables: true,
+        disable_redzone: true,
+        panic_strategy: PanicStrategy::Abort,
+        code_model: Some(CodeModel::Kernel),
+        ..Default::default()
+    };
+    Target {
+        llvm_target: "x86_64-unknown-none-elf".to_string(),
+        pointer_width: 64,
+        data_layout: "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+            .to_string(),
+        arch: "x86_64".to_string(),
+        options: opts,
+    }
+}

src/doc/rustc/src/SUMMARY.md

@@ -15,6 +15,7 @@
 - [Platform Support](platform-support.md)
     - [aarch64-apple-ios-sim](platform-support/aarch64-apple-ios-sim.md)
     - [\*-kmc-solid_\*](platform-support/kmc-solid.md)
+    - [x86_64-unknown-none](platform-support/x86_64-unknown-none.md)
 - [Target Tier Policy](target-tier-policy.md)
 - [Targets](targets/index.md)
     - [Built-in Targets](targets/built-in.md)

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

@@ -285,6 +285,7 @@ target | std | host | notes
 `x86_64-unknown-haiku` | ✓ | ✓ | 64-bit Haiku
 `x86_64-unknown-hermit` | ? |  |
 `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-linuxkernel` | * |  | Linux kernel modules
 `x86_64-unknown-openbsd` | ✓ | ✓ | 64-bit OpenBSD

src/doc/rustc/src/platform-support/x86_64-unknown-none.md

@@ -0,0 +1,76 @@
+# `x86_64-unknown-none`
+
+**Tier: 3**
+
+Freestanding/bare-metal x86-64 binaries in ELF format: firmware, kernels, etc.
+
+## Target maintainers
+
+- Harald Hoyer `harald@profian.com`, https://github.com/haraldh
+- Mike Leany, https://github.com/mikeleany
+
+## Requirements
+
+This target is cross-compiled. There is no support for `std`. There is no
+default allocator, but it's possible to use `alloc` by supplying an allocator.
+
+By default, Rust code generated for this target does not use any vector or
+floating-point registers (e.g. SSE, AVX). This allows the generated code to run
+in environments, such as kernels, 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). You can change code generation to use additional CPU
+features via the `-C target-feature=` codegen options to rustc, or via the
+`#[target_feature]` mechanism within Rust code.
+
+By default, code generated with this target should run on any `x86_64`
+hardware; enabling additional target features may raise this baseline.
+
+Code generated with this target will use the `kernel` code model by default.
+You can change this using the `-C code-model=` option to rustc.
+
+On `x86_64-unknown-none`, `extern "C"` uses the [standard System V calling
+convention](https://gitlab.com/x86-psABIs/x86-64-ABI), without red zones.
+
+This target generated binaries in the ELF format. Any alternate formats or
+special considerations for binary layout will require linker options or linker
+scripts.
+
+## Building the target
+
+You can build Rust with support for the target by adding it to the `target`
+list in `config.toml`:
+
+```toml
+[build]
+build-stage = 1
+target = ["x86_64-unknown-none"]
+```
+
+## 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.
+
+## Testing
+
+As `x86_64-unknown-none` supports a variety of different environments and does
+not support `std`, this target does not support running the Rust testsuite.
+
+## Cross-compilation toolchains and C code
+
+If you want to compile C code along with Rust (such as for Rust crates with C
+dependencies), you will need an appropriate `x86_64` toolchain.
+
+Rust *may* be able to use an `x86_64-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
+`x86_64-unknown-none` (or `x86_64-elf-`) toolchain.
+
+On some `x86_64` 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-`x86_64` platform.