Add target page for riscv64a23-unknown-linux-gnu

Author: ZhongyaoChen

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

@@ -388,6 +388,7 @@ target | std | host | notes
 [`riscv64gc-unknown-nuttx-elf`](platform-support/nuttx.md) | ✓ |  | RISC-V 64bit with NuttX
 [`riscv64gc-unknown-openbsd`](platform-support/openbsd.md) | ✓ | ✓ | OpenBSD/riscv64
 [`riscv64imac-unknown-nuttx-elf`](platform-support/nuttx.md) | ✓ |  | RISC-V 64bit with NuttX
+[`riscv64a23-unknown-linux-gnu`](platform-support/riscv64a23-unknown-linux-gnu.md) | ✓ | ✓ | RISC-V Linux (kernel 4.20+, glibc 2.29)
 [`s390x-unknown-linux-musl`](platform-support/s390x-unknown-linux-musl.md) | ✓ |  | S390x Linux (kernel 3.2, musl 1.2.3)
 `sparc-unknown-linux-gnu` | ✓ |  | 32-bit SPARC Linux
 [`sparc-unknown-none-elf`](./platform-support/sparc-unknown-none-elf.md) | * |  | Bare 32-bit SPARC V7+

src/doc/rustc/src/platform-support/riscv64a23-unknown-linux-gnu.md

@@ -0,0 +1,66 @@
+# `riscv64a23-unknown-linux-gnu`
+
+**Tier: 3**
+
+RISC-V targets using the ratified [RVA23 Profile](https://github.com/riscv/riscv-profiles/blob/main/rva23-profile.adoc).
+This target will enable all mandary features of rva23u64 and rva23s64 by default.
+
+
+## Target maintainers
+
+[@ZhongyaoChen](https://github.com/ZhongyaoChen)
+[@CaiWeiran](https://github.com/CaiWeiran)
+
+## Requirements
+
+This target requires:
+
+* Linux Kernel version 4.20 or later
+* glibc 2.17 or later
+
+
+## Building the target
+
+The target is distributed through `rustup`, and otherwise require no
+special configuration.
+
+If you need to build your own Rust for some reason though, the target can be build with:
+
+```bash
+./x build --target riscv64a23-unknown-linux-gnu
+```
+
+## Building Rust programs
+
+Add the target:
+
+```bash
+rustup target add riscv64a23-unknown-linux-gnu
+```
+
+Then cross compile crates with:
+
+```bash
+cargo build --target riscv64a23-unknown-linux-gnu
+```
+
+## Cross-compilation toolchains and Testing
+
+On Ubuntu 24.04, we can install compilation dependencies with:
+
+```bash
+apt install -y git python3 g++ g++-riscv64-linux-gnu
+```
+
+Then build target with:
+
+```bash
+./x build --target=riscv64a23-unknown-linux-gnu
+```
+
+There are no special requirements for testing and running the targets.
+For testing cross-builds on the host, you can use the docker image. It will automatically set up a RISC-V QEMU emulator and run all the test suite.
+
+```bash
+DEPLOY=1 ./src/ci/docker/run.sh riscv64a23-gnu
+```