Add x86_64-unknown-motor (Motor OS) tier 3 target

Add the initial no-std Motor OS compiler target.

Motor OS has been developed for several years in the open:
https://github.com/moturus/motor-os.

It has a more or less full implementation of Rust std library,
as well as tokio/mio ports.

Build instructions can be found here:
https://github.com/moturus/motor-os/blob/main/docs/build.md.

Signed-off-by: U. Lasiotus <lasiotus@motor-os.org>

Author: lasiotus

compiler/rustc_target/src/spec/base/mod.rs

@@ -21,6 +21,7 @@ pub(crate) mod linux_uclibc;
 pub(crate) mod linux_wasm;
 pub(crate) mod lynxos178;
 pub(crate) mod managarm_mlibc;
+pub(crate) mod motor;
 pub(crate) mod msvc;
 pub(crate) mod netbsd;
 pub(crate) mod nto_qnx;

compiler/rustc_target/src/spec/base/motor.rs

@@ -0,0 +1,37 @@
+use crate::spec::{
+    Cc, FramePointer, LinkerFlavor, Lld, PanicStrategy, StackProbeType, TargetOptions,
+};
+
+pub(crate) fn opts() -> TargetOptions {
+    let pre_link_args = TargetOptions::link_args(
+        LinkerFlavor::Gnu(Cc::No, Lld::No),
+        &[
+            "-e",
+            "motor_start",
+            "--no-undefined",
+            "--error-unresolved-symbols",
+            "--no-undefined-version",
+            "-u",
+            "__rust_abort",
+        ],
+    );
+    TargetOptions {
+        os: "motor".into(),
+        executables: true,
+        // TLS is false below because if true, the compiler assumes
+        // we handle TLS at the ELF loading level, which we don't.
+        // We use "OS level" TLS (see thread/local.rs in stdlib).
+        has_thread_local: false,
+        frame_pointer: FramePointer::NonLeaf,
+        linker_flavor: LinkerFlavor::Gnu(Cc::No, Lld::No),
+        main_needs_argc_argv: true,
+        panic_strategy: PanicStrategy::Abort,
+        pre_link_args,
+
+        // Note: disabling stack probles and stack protector below leads
+        // to weird bugs that can only be explained by compiler errors.
+        stack_probes: StackProbeType::Inline,
+        supports_stack_protector: true,
+        ..Default::default()
+    }
+}

compiler/rustc_target/src/spec/mod.rs

@@ -1642,6 +1642,7 @@ supported_targets! {
     ("aarch64-unknown-hermit", aarch64_unknown_hermit),
     ("riscv64gc-unknown-hermit", riscv64gc_unknown_hermit),
     ("x86_64-unknown-hermit", x86_64_unknown_hermit),
+    ("x86_64-unknown-motor", x86_64_unknown_motor),
 
     ("x86_64-unikraft-linux-musl", x86_64_unikraft_linux_musl),
 

compiler/rustc_target/src/spec/targets/x86_64_unknown_motor.rs

@@ -0,0 +1,38 @@
+use crate::spec::{
+    CodeModel, LinkSelfContainedDefault, LldFlavor, RelocModel, RelroLevel, Target, base,
+};
+
+pub(crate) fn target() -> Target {
+    let mut base = base::motor::opts();
+    base.cpu = "x86-64".into();
+    base.max_atomic_width = Some(64);
+    base.code_model = Some(CodeModel::Small);
+
+    // We want fully static relocatable binaries. It was surprisingly
+    // difficult to make it happen reliably, especially various
+    // linker-related options below. Mostly trial and error.
+    base.position_independent_executables = true;
+    base.relro_level = RelroLevel::Full;
+    base.static_position_independent_executables = true;
+    base.relocation_model = RelocModel::Pic;
+    base.lld_flavor_json = LldFlavor::Ld;
+    base.link_self_contained = LinkSelfContainedDefault::True;
+    base.dynamic_linking = false;
+    base.crt_static_default = true;
+    base.crt_static_respected = true;
+
+    Target {
+        llvm_target: "x86_64-unknown-none-elf".into(),
+        metadata: crate::spec::TargetMetadata {
+            description: Some("Motor OS".into()),
+            tier: Some(3),
+            host_tools: None,
+            std: None,
+        },
+        pointer_width: 64,
+        data_layout:
+            "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128".into(),
+        arch: "x86_64".into(),
+        options: base,
+    }
+}

src/bootstrap/src/core/sanity.rs

@@ -38,6 +38,7 @@ const STAGE0_MISSING_TARGETS: &[&str] = &[
     // just a dummy comment so the list doesn't get onelined
     "aarch64_be-unknown-hermit",
     "aarch64_be-unknown-none-softfloat",
+    "x86_64-unknown-motor",
 ];
 
 /// Minimum version threshold for libstdc++ required when using prebuilt LLVM
@@ -239,6 +240,10 @@ than building it.
             continue;
         }
 
+        if target.contains("motor") {
+            continue;
+        }
+
         // skip check for cross-targets
         if skip_target_sanity && target != &build.host_target {
             continue;

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

@@ -431,6 +431,7 @@ target | std | host | notes
 `x86_64-unknown-l4re-uclibc` | ? |  |
 [`x86_64-unknown-linux-none`](platform-support/x86_64-unknown-linux-none.md) | * |  | 64-bit Linux with no libc
 [`x86_64-unknown-managarm-mlibc`](platform-support/managarm.md) | ? |   | x86_64 Managarm
+[`x86_64-unknown-motor`[(platform-support/motor.md) | ? |  | x86_64 Motor OS
 [`x86_64-unknown-openbsd`](platform-support/openbsd.md) | ✓ | ✓ | 64-bit OpenBSD
 [`x86_64-unknown-trusty`](platform-support/trusty.md) | ✓ |  |
 `x86_64-uwp-windows-gnu` | ✓ |  |

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

@@ -0,0 +1,45 @@
+# `x86_64-unknown-motor`
+
+**Tier: 3**
+
+[Motor OS](https://motor-os.org/) is a new operating system for virtualized
+environments.
+
+## Target maintainers
+
+[@lasiotus](https://github.com/lasiotus)
+
+## Requirements
+
+This target is cross-compiled. There are no special requirements for the host.
+
+Motor OS uses the ELF file format.
+
+## Building the target
+
+The target can be built by enabling it for a `rustc` build, for example:
+
+```toml
+[build]
+build-stage = 2
+target = ["x86_64-unknown-motor"]
+```
+
+## Building Rust programs
+
+Rust standard library is fully supported/implemented, but is not yet part of
+the official Rust repo, so an out-of-tree building process should be
+followed, as described in the official
+[build doc](https://github.com/moturus/motor-os/blob/main/docs/build.md).
+
+## Testing
+
+Cross-compiled Rust binaries and test artifacts can be executed in Motor OS VMs,
+as described in e.g.
+[Hello Motor OS](https://github.com/moturus/motor-os/blob/main/docs/recipes/hello-motor-os.md)
+example.
+
+## Cross-compilation toolchains and C code
+
+C code can be compiled as part of Rust cargo projects. However, there is
+no libc support.

tests/assembly-llvm/targets/targets-elf.rs

@@ -658,6 +658,9 @@
 //@ revisions: x86_64_unknown_managarm_mlibc
 //@ [x86_64_unknown_managarm_mlibc] compile-flags: --target x86_64-unknown-managarm-mlibc
 //@ [x86_64_unknown_managarm_mlibc] needs-llvm-components: x86
+//@ revisions: x86_64_unknown_motor
+//@ [x86_64_unknown_motor] compile-flags: --target x86_64-unknown-motor
+//@ [x86_64_unknown_motor] needs-llvm-components: x86
 //@ revisions: x86_64_unknown_netbsd
 //@ [x86_64_unknown_netbsd] compile-flags: --target x86_64-unknown-netbsd
 //@ [x86_64_unknown_netbsd] needs-llvm-components: x86