Add AIX platform-support doc

Author: ecnelises

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

@@ -297,7 +297,7 @@ target | std | host | notes
 `powerpc64-wrs-vxworks` | ? |  |
 `powerpc64le-unknown-linux-musl` | ? |  |
 [`powerpc64-unknown-openbsd`](platform-support/openbsd.md) | ✓ | ✓ | OpenBSD/powerpc64
-`powerpc64-ibm-aix` | ? |  | 64-bit AIX (7.2 and newer)
+[`powerpc64-ibm-aix`](platform-support/aix.md) | ? |  | 64-bit AIX (7.2 and newer)
 `riscv32gc-unknown-linux-gnu` |   |   | RISC-V Linux (kernel 5.4, glibc 2.33)
 `riscv32gc-unknown-linux-musl` |   |   | RISC-V Linux (kernel 5.4, musl + RISCV32 support patches)
 `riscv32im-unknown-none-elf` | * |  | Bare RISC-V (RV32IM ISA)

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

@@ -0,0 +1,26 @@
+# `powerpc64-ibm-aix`
+
+**Tier: 3**
+
+Rust for AIX operating system, currently only 64-bit PowerPC is supported.
+
+## Target maintainers
+
+- QIU Chaofan `qiucofan@cn.ibm.com`, https://github.com/ecnelises
+- Kai LUO, `lkail@cn.ibm.com`, https://github.com/bzEq
+
+## Requirements
+
+This target supports host tools, std and alloc. This target cannot be cross-compiled as for now, mainly because of the unavailability of system linker on other platforms.
+
+Binary built for this target is expected to run on Power7 or newer CPU, and AIX 7.2 or newer version.
+
+Binary format of this platform is [XCOFF](https://www.ibm.com/docs/en/aix/7.2?topic=formats-xcoff-object-file-format). Archive file format is ['AIX big format'](https://www.ibm.com/docs/en/aix/7.2?topic=formats-ar-file-format-big).
+
+## Testing
+
+This target supports running test suites natively, but it's not available to cross-compile and execute in emulator.
+
+## Interoperability with C code
+
+This target supports C code. C code compiled by XL, Open XL and Clang are compatible with Rust. Typical triple of AIX on 64-bit PowerPC of these compilers are also `powerpc64-ibm-aix`.