Add documentation for target armv7-rtems-eabihf

Author: thesummer

Cargo.toml

@@ -105,7 +105,6 @@ debug = 0
 strip = true
 
 [patch.crates-io]
-libc = { git = "https://github.com/thesummer/libc", rev = "2ada946801aec517051bb00cb83e890f9af5ad37" }
 # See comments in `library/rustc-std-workspace-core/README.md` for what's going on
 # here
 rustc-std-workspace-core = { path = 'library/rustc-std-workspace-core' }

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

@@ -274,6 +274,7 @@ target | std | host | notes
 `armv6-unknown-freebsd` | ✓ | ✓ | Armv6 FreeBSD
 [`armv6-unknown-netbsd-eabihf`](platform-support/netbsd.md) | ✓ | ✓ | Armv6 NetBSD w/hard-float
 [`armv6k-nintendo-3ds`](platform-support/armv6k-nintendo-3ds.md) | ? |  | Armv6k Nintendo 3DS, Horizon (Requires devkitARM toolchain)
+[`armv7-rtems-eabihf`](platform-support/armv7-rtems-eabihf.md) | ✓ |  | RTEMS OS for ARM BSPs
 [`armv7-sony-vita-newlibeabihf`](platform-support/armv7-sony-vita-newlibeabihf.md) | ✓ |  | Armv7-A Cortex-A9 Sony PlayStation Vita (requires VITASDK toolchain)
 [`armv7-unknown-linux-uclibceabi`](platform-support/armv7-unknown-linux-uclibceabi.md) | ✓ | ✓ | Armv7-A Linux with uClibc, softfloat
 [`armv7-unknown-linux-uclibceabihf`](platform-support/armv7-unknown-linux-uclibceabihf.md) | ✓ | ? | Armv7-A Linux with uClibc, hardfloat

src/doc/rustc/src/platform-support/armv7-rtems-eabihf.md

@@ -0,0 +1,51 @@
+# `armv7-rtems-eabihf`
+
+**Tier: 3**
+
+ARM targets for the [RTEMS realtime operating system](https://www.rtems.org)  using the RTEMS gcc cross-compiler for linking against the libraries of a specified Board Support Package (BSP).
+
+## Target maintainers
+
+- [@thesummer](https://github.com/thesummer)
+
+## Requirements
+
+The target does not support host tools. Only cross-compilation is possible.
+The cross-compiler toolchain can be obtained by following the installation instructions
+of the [RTEMS Documentation](https://docs.rtems.org/branches/master/user/index.html). Additionally to the cross-compiler also a compiled BSP
+for a board fitting the architecture needs to be available on the host.
+Currently tested has been the BSP `xilinx_zynq_a9_qemu` of RTEMS 6.
+
+`std` support is available, but not yet fully tested. Do NOT use in flight software!
+
+The target follows the EABI calling convention for `extern "C"`.
+
+The resulting binaries are in ELF format.
+
+## Building the target
+
+The target can be build by the standard compiler of Rust.
+## 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.
+
+In order to build an RTEMS executable it is also necessary to have a basic RTEMS configuration (in C) compiled to link against as this configures the operating system.
+An example can be found at this [`rtems-sys`](https://github.com/thesummer/rtems-sys) crate which could be added as an dependency to your application.
+
+## Testing
+
+The resulting binaries run fine on an emulated target (possibly also on a real Zedboard or similar).
+For example, on qemu the following command can execute the binary:
+```
+$ qemu-system-arm -no-reboot -serial null -serial mon:stdio -net none -nographic -M xilinx-zynq-a9 -m 512M -kernel <binary file>
+```
+
+While basic execution of the unit test harness seems to work. However, running the Rust testsuite on the (emulated) hardware has not yet been tested.
+
+## Cross-compilation toolchains and C code
+
+Compatible C-code can be built with the RTEMS cross-compiler toolchain `arm-rtems6-gcc`.
+For more information how to build the toolchain, RTEMS itself and RTEMS applications please have a look at the [RTEMS Documentation](https://docs.rtems.org/branches/master/user/index.html).