doc: Add *-unknown-managarm-mlibc documentation

src/doc/rustc/src/SUMMARY.md

@@ -116,6 +116,7 @@
     - [\*-unikraft-linux-musl](platform-support/unikraft-linux-musl.md)
     - [\*-unknown-hermit](platform-support/hermit.md)
     - [\*-unknown-freebsd](platform-support/freebsd.md)
+    - [\*-unknown-managarm-mlibc](platform-support/managarm.md)
     - [\*-unknown-netbsd\*](platform-support/netbsd.md)
     - [\*-unknown-openbsd](platform-support/openbsd.md)
     - [\*-unknown-redox](platform-support/redox.md)

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

@@ -258,6 +258,7 @@ target | std | host | notes
 [`aarch64-unknown-hermit`](platform-support/hermit.md) | ✓ |  | ARM64 Hermit
 [`aarch64-unknown-illumos`](platform-support/illumos.md) | ✓ | ✓ | ARM64 illumos
 `aarch64-unknown-linux-gnu_ilp32` | ✓ | ✓ | ARM64 Linux (ILP32 ABI)
+[`aarch64-unknown-managarm-mlibc`](platform-support/managarm.md) | ? |   | ARM64 Managarm
 [`aarch64-unknown-netbsd`](platform-support/netbsd.md) | ✓ | ✓ | ARM64 NetBSD
 [`aarch64-unknown-nto-qnx700`](platform-support/nto-qnx.md) | ? |  | ARM64 QNX Neutrino 7.0 RTOS |
 [`aarch64-unknown-nto-qnx710`](platform-support/nto-qnx.md) | ✓ |  | ARM64 QNX Neutrino 7.1 RTOS with default network stack (io-pkt) |
@@ -388,6 +389,7 @@ target | std | host | notes
 `riscv64gc-unknown-freebsd` | ? |   | RISC-V FreeBSD
 `riscv64gc-unknown-fuchsia` | ? |   | RISC-V Fuchsia
 [`riscv64gc-unknown-hermit`](platform-support/hermit.md) | ✓ |   | RISC-V Hermit
+[`riscv64gc-unknown-managarm-mlibc`](platform-support/managarm.md) | ? |   | RISC-V Managarm
 [`riscv64gc-unknown-netbsd`](platform-support/netbsd.md) | ✓ | ✓ | RISC-V NetBSD
 [`riscv64gc-unknown-nuttx-elf`](platform-support/nuttx.md) | ✓ |  | RISC-V 64bit with NuttX
 [`riscv64gc-unknown-openbsd`](platform-support/openbsd.md) | ✓ | ✓ | OpenBSD/riscv64
@@ -428,6 +430,7 @@ target | std | host | notes
 [`x86_64-unknown-hurd-gnu`](platform-support/hurd.md) | ✓ | ✓ | 64-bit GNU/Hurd
 `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-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/managarm.md

@@ -0,0 +1,53 @@
+# `*-unknown-managarm-mlibc`
+
+**Tier: 3**
+
+## Target Maintainers
+
+- [@no92](https://github.com/no92)
+- [@64](https://github.com/64)
+- [@Dennisbonke](https://github.com/Dennisbonke)
+
+## Requirements
+
+This target is cross-compiled. There is currently no support for `std` yet. It generates binaries in the ELF format. Currently, we support the `x86_64`, `aarch64` and `riscv64gc` architectures. The examples below `$ARCH` should be substituted for one of the supported architectures.
+
+## Building the target
+
+Managarm has upstream support in LLVM since the release of 21.1.0.
+
+Set up your `bootstrap.toml` like this:
+
+```toml
+change-id = 142379
+
+[llvm]
+targets = "X86;AArch64;RISCV"
+download-ci-llvm = false
+
+[build]
+target = ["$ARCH-unknown-managarm-mlibc", "x86_64-unknown-linux-gnu"]
+
+[target.x86_64-unknown-linux-gnu]
+llvm-config = "/path/to/your/llvm/bin/llvm-config"
+
+[target.$ARCH-unknown-managarm-mlibc]
+llvm-config = "/path/to/your/llvm/bin/llvm-config"
+```
+
+## Building Rust programs
+
+Build a `$ARCH-managarm-gcc` using our [gcc fork](https://github.com/managarm/gcc).
+
+```toml
+[build]
+rustc = "/path/to/the/rust-prefix/bin/rustc"
+target = "$ARCH-unknown-managarm-mlibc"
+
+[target.$ARCH-unknown-managarm-mlibc]
+linker = "/path/to/the/managarm-gcc/bin/$ARCH-managarm-gcc"
+```
+
+## Testing
+
+This target does not support running the Rust testsuite yet.