Doc: Add the RISC-V stabilized target features

src/attributes/codegen.md

@@ -204,6 +204,66 @@ Feature        | Implicitly Enables | Feature Name
 `tme`          |                | FEAT_TME - Transactional Memory Extension
 `vh`           |                | FEAT_VHE - Virtualization Host Extensions
 
+#### `riscv32` or `riscv64`
+
+This platform requires that `#[target_feature]` is only applied to [`unsafe`
+functions][unsafe function].
+
+Further documentation on these features can be found in their respective
+specification. Many specifications are described in the [RISC-V ISA Manual] or
+in another manual hosted on the [RISC-V GitHub Account].
+
+[RISC-V ISA Manual]: https://github.com/riscv/riscv-isa-manual
+[RISC-V GitHub Account]: https://github.com/riscv
+
+Feature     | Implicitly Enables  | Description
+------------|---------------------|-------------------
+`a`         |                     | [A][rv-a] — Atomic instructions
+`c`         |                     | [C][rv-c] — Compressed instructions
+`m`         |                     | [M][rv-m] — Integer Multiplication and Division instructions
+`zb`        | `zba`, `zbc`, `zbs` | [Zb][rv-zb] — Bit Manipulation instructions
+`zba`       |                     | [Zba][rv-zb-zba] — Address Generation instructions
+`zbb`       |                     | [Zbb][rv-zb-zbb] — Basic bit-manipulation
+`zbc`       |                     | [Zbc][rv-zb-zbc] — Carry-less multiplication
+`zbkb`      |                     | [Zbkb][rv-zb-zbkb] — Bit Manipulation Instructions for Cryptography
+`zbkc`      |                     | [Zbkc][rv-zb-zbc] — Carry-less multiplication for Cryptography
+`zbkx`      |                     | [Zbkx][rv-zb-zbkx] — Crossbar permutations
+`zbs`       |                     | [Zbs][rv-zb-zbs] — Single-bit instructions
+`zk`        | `zkn`, `zkr`, `zks`, `zkt`, `zbkb`, `zbkc`, `zkbx` | [Zk][rv-zk] — Scalar Cryptography
+`zkn`       | `zknd`, `zkne`, `zknh`, `zbkb`, `zbkc`, `zkbx`     | [Zkn][rv-zkn] — NIST Algorithm suite extension
+`zknd`      |                                                    | [Zknd][rv-zknd] — NIST Suite: AES Decryption
+`zkne`      |                                                    | [Zkne][rv-zkne] — NIST Suite: AES Encryption
+`zknh`      |                                                    | [Zknh][rv-zknh] — NIST Suite: Hash Function Instructions
+`zkr`       |                                                    | [Zkr][rv-zkr] — Entropy Source Extension
+`zks`       | `zksed`, `zksh`, `zbkb`, `zbkc`, `zkbx`            | [Zks][rv-zks] — ShangMi Algorithm Suite
+`zksed`     |                                                    | [Zksed][rv-zksed] — ShangMi Suite: SM4 Block Cipher Instructions
+`zksh`      |                                                    | [Zksh][rv-zksh] — ShangMi Suite: SM3 Hash Function Instructions
+`zkt`       |                                                    | [Zkt][rv-zkt] — Data Independent Execution Latency Subset
+
+<!-- Keep links near each table to make it easier to move and update. -->
+
+[rv-a]: https://github.com/riscv/riscv-isa-manual/blob/de46343a245c6ee1f7b1a40c92fe1a86bd4f4978/src/a-st-ext.adoc
+[rv-c]: https://github.com/riscv/riscv-isa-manual/blob/de46343a245c6ee1f7b1a40c92fe1a86bd4f4978/src/c-st-ext.adoc
+[rv-m]: https://github.com/riscv/riscv-isa-manual/blob/de46343a245c6ee1f7b1a40c92fe1a86bd4f4978/src/m-st-ext.adoc
+[rv-zb]: https://github.com/riscv/riscv-bitmanip
+[rv-zb-zba]: https://github.com/riscv/riscv-bitmanip/blob/main/bitmanip/zba.adoc
+[rv-zb-zbb]: https://github.com/riscv/riscv-bitmanip/blob/main/bitmanip/zbb.adoc
+[rv-zb-zbc]: https://github.com/riscv/riscv-bitmanip/blob/main/bitmanip/zbc.adoc
+[rv-zb-zbkb]: https://github.com/riscv/riscv-bitmanip/blob/main/bitmanip/zbkb.adoc
+[rv-zb-zbkc]: https://github.com/riscv/riscv-bitmanip/blob/main/bitmanip/zbkc.adoc
+[rv-zb-zbkx]: https://github.com/riscv/riscv-bitmanip/blob/main/bitmanip/zbkx.adoc
+[rv-zb-zbs]: https://github.com/riscv/riscv-bitmanip/blob/main/bitmanip/zbs.adoc
+[rv-zk]: https://github.com/riscv/riscv-crypto/blob/e2dd7d98b7f34d477e38cb5fd7a3af4379525189/doc/scalar/riscv-crypto-scalar-zk.adoc
+[rv-zkn]: https://github.com/riscv/riscv-crypto/blob/e2dd7d98b7f34d477e38cb5fd7a3af4379525189/doc/scalar/riscv-crypto-scalar-zkn.adoc
+[rv-zkne]: https://github.com/riscv/riscv-crypto/blob/e2dd7d98b7f34d477e38cb5fd7a3af4379525189/doc/scalar/riscv-crypto-scalar-zkne.adoc
+[rv-zknd]: https://github.com/riscv/riscv-crypto/blob/e2dd7d98b7f34d477e38cb5fd7a3af4379525189/doc/scalar/riscv-crypto-scalar-zknd.adoc
+[rv-zknh]: https://github.com/riscv/riscv-crypto/blob/e2dd7d98b7f34d477e38cb5fd7a3af4379525189/doc/scalar/riscv-crypto-scalar-zknh.adoc
+[rv-zkr]: https://github.com/riscv/riscv-crypto/blob/e2dd7d98b7f34d477e38cb5fd7a3af4379525189/doc/scalar/riscv-crypto-scalar-zkr.adoc
+[rv-zks]: https://github.com/riscv/riscv-crypto/blob/e2dd7d98b7f34d477e38cb5fd7a3af4379525189/doc/scalar/riscv-crypto-scalar-zks.adoc
+[rv-zksed]: https://github.com/riscv/riscv-crypto/blob/e2dd7d98b7f34d477e38cb5fd7a3af4379525189/doc/scalar/riscv-crypto-scalar-zksed.adoc
+[rv-zksh]: https://github.com/riscv/riscv-crypto/blob/e2dd7d98b7f34d477e38cb5fd7a3af4379525189/doc/scalar/riscv-crypto-scalar-zksh.adoc
+[rv-zkt]: https://github.com/riscv/riscv-crypto/blob/e2dd7d98b7f34d477e38cb5fd7a3af4379525189/doc/scalar/riscv-crypto-scalar-zkr.adoc
+
 #### `wasm32` or `wasm64`
 
 `#[target_feature]` may be used with both safe and