Enable supported bitmanip extensions for Rust demos

Ibex supports a few more bitmanip extensions but they're not supported
in upstream LLVM / Rust.

sw/rust/.cargo/config.toml

@@ -5,6 +5,9 @@
 [build]
 target = "riscv32imc-unknown-none-elf"
 
+# Enable supported bitmanip extension features.
+rustflags = ["-Ctarget-feature=+zba,+zbb,+zbc,+zbs"]
+
 [target.riscv32imc-unknown-none-elf]
 runner = "../../util/load_demo_system.sh run"
 

sw/rust/demo/hello_world/README.md

@@ -9,7 +9,7 @@ How to run this demo:
 4. Run the gdb:
 
 ```console
-$ riscv32-unknown-elf-gdb ../../target/riscv32imc-unknown-none-elf/debug/led
+$ riscv32-unknown-elf-gdb ../../target/riscv32imcb-unknown-none-elf/debug/led
 
 (gdb) # Connect to OpenOCD
 (gdb) target remote :3333

sw/rust/riscv32imcb-unknown-none-elf.json

@@ -0,0 +1,23 @@
+{
+  "arch": "riscv32",
+  "atomic-cas": false,
+  "cpu": "generic-rv32",
+  "crt-objects-fallback": "false",
+  "data-layout": "e-m:e-p:32:32-i64:64-n32-S128",
+  "eh-frame-header": false,
+  "emit-debug-gdb-scripts": false,
+  "features": "+m,+c,+zba,+zbb,+zbc,+zbs,+forced-atomics",
+  "is-builtin": false,
+  "linker": "rust-lld",
+  "linker-flavor": "gnu-lld",
+  "llvm-target": "riscv32",
+  "max-atomic-width": 32,
+  "metadata": {
+    "description": "Bare RISC-V (RV32IMCBZbc ISA)",
+    "host_tools": false,
+    "std": false
+  },
+  "panic-strategy": "abort",
+  "relocation-model": "static",
+  "target-pointer-width": "32"
+}

sw/rust/rust-toolchain.toml

@@ -1,3 +1,3 @@
 [toolchain]
-targets = ["riscv32imc-unknown-none-elf"]
 channel = "nightly"
+components = ["rust-src"]