Rollup merge of #144551 - neuschaefer:a64be-musl, r=davidtwco

Add aarch64_be-unknown-linux-musl target

This PR adds a target definition for big-endian Aarch64 with musl-libc.

cc `@Gelbpunkt`

3 files changed, 51 insertions, 0 deletions

diff --git a/src/doc/rustc/src/SUMMARY.md b/src/doc/rustc/src/SUMMARY.md
index b53494ed98d..8ab10add8de 100644
--- a/src/doc/rustc/src/SUMMARY.md
+++ b/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)
diff --git a/src/doc/rustc/src/platform-support.md b/src/doc/rustc/src/platform-support.md
index 3bf87994297..6c044b84a5e 100644
--- a/src/doc/rustc/src/platform-support.md
+++ b/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
diff --git a/src/doc/rustc/src/platform-support/aarch64_be-unknown-linux-musl.md b/src/doc/rustc/src/platform-support/aarch64_be-unknown-linux-musl.md
new file mode 100644
index 00000000000..3e816dc8bfb
--- /dev/null
+++ b/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.