Add aarch64_be-unknown-linux-musl target

compiler/rustc_target/src/spec/mod.rs

@@ -1954,6 +1954,7 @@ supported_targets! {
     ("armv7-unknown-linux-musleabihf", armv7_unknown_linux_musleabihf),
     ("aarch64-unknown-linux-gnu", aarch64_unknown_linux_gnu),
     ("aarch64-unknown-linux-musl", aarch64_unknown_linux_musl),
+    ("aarch64_be-unknown-linux-musl", aarch64_be_unknown_linux_musl),
     ("x86_64-unknown-linux-musl", x86_64_unknown_linux_musl),
     ("i686-unknown-linux-musl", i686_unknown_linux_musl),
     ("i586-unknown-linux-musl", i586_unknown_linux_musl),

compiler/rustc_target/src/spec/targets/aarch64_be_unknown_linux_musl.rs

@@ -0,0 +1,40 @@
+use rustc_abi::Endian;
+
+use crate::spec::{
+    FramePointer, SanitizerSet, StackProbeType, Target, TargetMetadata, TargetOptions, base,
+};
+
+pub(crate) fn target() -> Target {
+    let mut base = base::linux_musl::opts();
+    base.max_atomic_width = Some(128);
+    base.supports_xray = true;
+    base.features = "+v8a,+outline-atomics".into();
+    base.stack_probes = StackProbeType::Inline;
+    base.supported_sanitizers = SanitizerSet::ADDRESS
+        | SanitizerSet::CFI
+        | SanitizerSet::LEAK
+        | SanitizerSet::MEMORY
+        | SanitizerSet::THREAD;
+
+    Target {
+        llvm_target: "aarch64_be-unknown-linux-musl".into(),
+        metadata: TargetMetadata {
+            description: Some("ARM64 Linux (big-endian) with musl-libc 1.2.5".into()),
+            tier: Some(3),
+            host_tools: Some(false),
+            std: Some(true),
+        },
+        pointer_width: 64,
+        data_layout: "E-m:e-p270:32:32-p271:32:32-p272:64:64-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128-Fn32".into(),
+        arch: "aarch64".into(),
+        options: TargetOptions {
+            // the AAPCS64 expects use of non-leaf frame pointers per
+            // https://github.com/ARM-software/abi-aa/blob/4492d1570eb70c8fd146623e0db65b2d241f12e7/aapcs64/aapcs64.rst#the-frame-pointer
+            // and we tend to encounter interesting bugs in AArch64 unwinding code if we do not
+            frame_pointer: FramePointer::NonLeaf,
+            mcount: "\u{1}_mcount".into(),
+            endian: Endian::Big,
+            ..base
+        },
+    }
+}

src/doc/rustc/src/SUMMARY.md

@@ -49,6 +49,7 @@
     - [aarch64-nintendo-switch-freestanding](platform-support/aarch64-nintendo-switch-freestanding.md)
     - [aarch64-unknown-linux-musl](platform-support/aarch64-unknown-linux-musl.md)
     - [aarch64_be-unknown-none-softfloat](platform-support/aarch64_be-unknown-none-softfloat.md)
+    - [aarch64_be-unknown-linux-musl](platform-support/aarch64_be-unknown-linux-musl.md)
     - [amdgcn-amd-amdhsa](platform-support/amdgcn-amd-amdhsa.md)
     - [armeb-unknown-linux-gnueabi](platform-support/armeb-unknown-linux-gnueabi.md)
     - [arm-none-eabi](platform-support/arm-none-eabi.md)

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

@@ -273,6 +273,7 @@ target | std | host | notes
 [`aarch64_be-unknown-hermit`](platform-support/hermit.md) | ✓ |  | ARM64 Hermit (big-endian)
 `aarch64_be-unknown-linux-gnu` | ✓ | ✓ | ARM64 Linux (big-endian)
 `aarch64_be-unknown-linux-gnu_ilp32` | ✓ | ✓ | ARM64 Linux (big-endian, ILP32 ABI)
+[`aarch64_be-unknown-linux-musl`](platform-support/aarch64_be-unknown-linux-musl.md) | ✓ | ✓ | ARM64 Linux (big-endian) with musl-libc 1.2.5
 [`aarch64_be-unknown-netbsd`](platform-support/netbsd.md) | ✓ | ✓ | ARM64 NetBSD (big-endian)
 [`aarch64_be-unknown-none-softfloat`](platform-support/aarch64_be-unknown-none-softfloat.md) | * |  | Bare big-endian ARM64, softfloat
 [`amdgcn-amd-amdhsa`](platform-support/amdgcn-amd-amdhsa.md) | * |  | `-Ctarget-cpu=gfx...` to specify [the AMD GPU] to compile for

src/doc/rustc/src/platform-support/aarch64_be-unknown-linux-musl.md

@@ -0,0 +1,49 @@
+# aarch64_be-unknown-linux-musl
+
+**Tier: 3**
+
+ARM64 Linux (big-endian) with musl-libc.
+
+## Target maintainers
+
+[@neuschaefer](https://github.com/neuschaefer)
+[@Gelbpunkt](https://github.com/Gelbpunkt)
+
+## Requirements
+
+The target requires a `aarch64_be-*-linux-musl` toolchain, which likely has to
+be built from source because this is a rare combination.  [Buildroot] provides
+a way of doing so:
+
+- select _Target options_ → _Target Architecture_ → _AArch64 (big endian)_
+- select _Toolchain_ → _C library_ → _musl_
+- select _Toolchain_ → _Enable C++ support_
+
+Host tools are supported.
+
+[Buildroot]: https://buildroot.org/
+
+
+## Building the target
+
+The target can be enabled in bootstrap.toml:
+
+```toml
+[build]
+target = ["aarch64_be-unknown-linux-musl"]
+
+[target.aarch64_be-unknown-linux-musl]
+cc          = "/path/to/buildroot/host/bin/aarch64_be-buildroot-linux-musl-cc"
+cxx         = "/path/to/buildroot/host/bin/aarch64_be-buildroot-linux-musl-c++"
+linker      = "/path/to/buildroot/host/bin/aarch64_be-buildroot-linux-musl-cc"
+ar          = "/path/to/buildroot/host/bin/aarch64_be-buildroot-linux-musl-ar"
+ranlib      = "/path/to/buildroot/host/bin/aarch64_be-buildroot-linux-musl-ranlib"
+musl-root   = "/path/to/buildroot/staging"
+runner      = "qemu-aarch64_be -L /path/to/buildroot/target"
+crt-static  = "/path/to/buildroot/target"
+```
+
+
+## Testing
+
+Binaries can be run under `qemu-aarch64_be` or under a big-endian Linux kernel.

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

@@ -10,6 +10,9 @@
 //@ revisions: aarch64_be_unknown_linux_gnu_ilp32
 //@ [aarch64_be_unknown_linux_gnu_ilp32] compile-flags: --target aarch64_be-unknown-linux-gnu_ilp32
 //@ [aarch64_be_unknown_linux_gnu_ilp32] needs-llvm-components: aarch64
+//@ revisions: aarch64_be_unknown_linux_musl
+//@ [aarch64_be_unknown_linux_musl] compile-flags: --target aarch64_be-unknown-linux-musl
+//@ [aarch64_be_unknown_linux_musl] needs-llvm-components: aarch64
 //@ revisions: aarch64_be_unknown_netbsd
 //@ [aarch64_be_unknown_netbsd] compile-flags: --target aarch64_be-unknown-netbsd
 //@ [aarch64_be_unknown_netbsd] needs-llvm-components: aarch64