risc-v support

[dkhayes117]

I'm getting linking errors during cargo build --bin hello

error: linking with `rust-lld` failed: exit code: 1
  |
  = note: "rust-lld" "-flavor" "gnu" "-L" "/home/dkhayes117/.rustup/toolchains/beta-x86_64-unknown-linux-gnu/lib/rustlib/riscv32imac-unknown-none-elf/lib" "/home/dkhayes117/IdeaProjects/defmt_test/target/riscv32imac-unknown-none-elf/debug/deps/hello-a9b45fbc99b62350.hello.1n7pvg5w-cgu.0.rcgu.o" "-o" "/home/dkhayes117/IdeaProjects/defmt_test/target/riscv32imac-unknown-none-elf/debug/deps/hello-a9b45fbc99b62350" "--gc-sections" "-L" "/home/dkhayes117/IdeaProjects/defmt_test/target/riscv32imac-unknown-none-elf/debug/deps" "-L" "/home/dkhayes117/IdeaProjects/defmt_test/target/debug/deps" "-L" "/home/dkhayes117/IdeaProjects/defmt_test/target/riscv32imac-unknown-none-elf/debug/build/defmt-786b78cb5fb56c90/out" "-L" "/home/dkhayes117/IdeaProjects/defmt_test/target/riscv32imac-unknown-none-elf/debug/build/hifive1-12e6de30a7c42179/out" "-L" "/home/dkhayes117/IdeaProjects/defmt_test/target/riscv32imac-unknown-none-elf/debug/build/e310x-c9d6b8bcdebcec36/out" "-L" "/home/dkhayes117/IdeaProjects/defmt_test/target/riscv32imac-unknown-none-elf/debug/build/riscv-b96e58c41469ec83/out" "-L" "/home/dkhayes117/IdeaProjects/defmt_test/target/riscv32imac-unknown-none-elf/debug/build/riscv-rt-7fa43864cbb5bfaa/out" "-L" "/home/dkhayes117/IdeaProjects/defmt_test/target/riscv32imac-unknown-none-elf/debug/build/riscv-rt-7fa43864cbb5bfaa/out" "-L" "/home/dkhayes117/.rustup/toolchains/beta-x86_64-unknown-linux-gnu/lib/rustlib/riscv32imac-unknown-none-elf/lib" "--start-group" "-Bstatic" "/tmp/rustcQiAIxg/libriscv_rt-c7d2a202c972997c.rlib" "/tmp/rustcQiAIxg/libriscv-6fb334952367127a.rlib" "--end-group" "/home/dkhayes117/.rustup/toolchains/beta-x86_64-unknown-linux-gnu/lib/rustlib/riscv32imac-unknown-none-elf/lib/libcompiler_builtins-c1fdd1f60c58bc16.rlib" "-Bdynamic"
  = note: rust-lld: error: undefined symbol: _mp_hook
          >>> referenced by lib.rs:301 (/home/dkhayes117/.cargo/registry/src/github.com-1ecc6299db9ec823/riscv-rt-0.6.2/src/lib.rs:301)
          >>>               /home/dkhayes117/IdeaProjects/defmt_test/target/riscv32imac-unknown-none-elf/debug/deps/hello-a9b45fbc99b62350.hello.1n7pvg5w-cgu.0.rcgu.o:(_start_rust)
          
          rust-lld: error: undefined symbol: __pre_init
          >>> referenced by lib.rs:302 (/home/dkhayes117/.cargo/registry/src/github.com-1ecc6299db9ec823/riscv-rt-0.6.2/src/lib.rs:302)
          >>>               /home/dkhayes117/IdeaProjects/defmt_test/target/riscv32imac-unknown-none-elf/debug/deps/hello-a9b45fbc99b62350.hello.1n7pvg5w-cgu.0.rcgu.o:(_start_rust)
          
          rust-lld: error: undefined symbol: _sbss
          >>> referenced by lib.rs:302 (/home/dkhayes117/.cargo/registry/src/github.com-1ecc6299db9ec823/riscv-rt-0.6.2/src/lib.rs:302)
          >>>               /home/dkhayes117/IdeaProjects/defmt_test/target/riscv32imac-unknown-none-elf/debug/deps/hello-a9b45fbc99b62350.hello.1n7pvg5w-cgu.0.rcgu.o:(_start_rust)
          >>> referenced by lib.rs:302 (/home/dkhayes117/.cargo/registry/src/github.com-1ecc6299db9ec823/riscv-rt-0.6.2/src/lib.rs:302)
          >>>               /home/dkhayes117/IdeaProjects/defmt_test/target/riscv32imac-unknown-none-elf/debug/deps/hello-a9b45fbc99b62350.hello.1n7pvg5w-cgu.0.rcgu.o:(_start_rust)
          
          rust-lld: error: undefined symbol: _ebss
          >>> referenced by lib.rs:302 (/home/dkhayes117/.cargo/registry/src/github.com-1ecc6299db9ec823/riscv-rt-0.6.2/src/lib.rs:302)
          >>>               /home/dkhayes117/IdeaProjects/defmt_test/target/riscv32imac-unknown-none-elf/debug/deps/hello-a9b45fbc99b62350.hello.1n7pvg5w-cgu.0.rcgu.o:(_start_rust)
          >>> referenced by lib.rs:302 (/home/dkhayes117/.cargo/registry/src/github.com-1ecc6299db9ec823/riscv-rt-0.6.2/src/lib.rs:302)
          >>>               /home/dkhayes117/IdeaProjects/defmt_test/target/riscv32imac-unknown-none-elf/debug/deps/hello-a9b45fbc99b62350.hello.1n7pvg5w-cgu.0.rcgu.o:(_start_rust)
          
          rust-lld: error: undefined symbol: _sdata
          >>> referenced by lib.rs:0 (/home/dkhayes117/.cargo/registry/src/github.com-1ecc6299db9ec823/r0-0.2.2/src/lib.rs:0)
          >>>               /home/dkhayes117/IdeaProjects/defmt_test/target/riscv32imac-unknown-none-elf/debug/deps/hello-a9b45fbc99b62350.hello.1n7pvg5w-cgu.0.rcgu.o:(_start_rust)
          >>> referenced by lib.rs:0 (/home/dkhayes117/.cargo/registry/src/github.com-1ecc6299db9ec823/r0-0.2.2/src/lib.rs:0)
          >>>               /home/dkhayes117/IdeaProjects/defmt_test/target/riscv32imac-unknown-none-elf/debug/deps/hello-a9b45fbc99b62350.hello.1n7pvg5w-cgu.0.rcgu.o:(_start_rust)
          
          rust-lld: error: undefined symbol: _sidata
          >>> referenced by lib.rs:0 (/home/dkhayes117/.cargo/registry/src/github.com-1ecc6299db9ec823/r0-0.2.2/src/lib.rs:0)
          >>>               /home/dkhayes117/IdeaProjects/defmt_test/target/riscv32imac-unknown-none-elf/debug/deps/hello-a9b45fbc99b62350.hello.1n7pvg5w-cgu.0.rcgu.o:(_start_rust)
          >>> referenced by lib.rs:0 (/home/dkhayes117/.cargo/registry/src/github.com-1ecc6299db9ec823/r0-0.2.2/src/lib.rs:0)
          >>>               /home/dkhayes117/IdeaProjects/defmt_test/target/riscv32imac-unknown-none-elf/debug/deps/hello-a9b45fbc99b62350.hello.1n7pvg5w-cgu.0.rcgu.o:(_start_rust)
          
          rust-lld: error: undefined symbol: trap_handler
          >>> referenced by lib.rs:329 (/home/dkhayes117/.cargo/registry/src/github.com-1ecc6299db9ec823/riscv-rt-0.6.2/src/lib.rs:329)
          >>>               /home/dkhayes117/IdeaProjects/defmt_test/target/riscv32imac-unknown-none-elf/debug/deps/hello-a9b45fbc99b62350.hello.1n7pvg5w-cgu.0.rcgu.o:(_start_trap_rust)
          
          rust-lld: error: undefined symbol: _max_hart_id
          >>> referenced by riscv-rt.o:(.init+0x52) in archive /tmp/rustcQiAIxg/libriscv_rt-c7d2a202c972997c.rlib
          >>> referenced by riscv-rt.o:(.init+0x56) in archive /tmp/rustcQiAIxg/libriscv_rt-c7d2a202c972997c.rlib
          
          rust-lld: error: undefined symbol: _stack_start
          >>> referenced by riscv-rt.o:(.init+0x5E) in archive /tmp/rustcQiAIxg/libriscv_rt-c7d2a202c972997c.rlib
          
          rust-lld: error: undefined symbol: _hart_stack_size
          >>> referenced by riscv-rt.o:(.init+0x66) in archive /tmp/rustcQiAIxg/libriscv_rt-c7d2a202c972997c.rlib
          >>> referenced by riscv-rt.o:(.init+0x6A) in archive /tmp/rustcQiAIxg/libriscv_rt-c7d2a202c972997c.rlib
          

error: aborting due to previous error

error: could not compile `defmt_test`.

To learn more, run the command again with --verbose.

[Lotterleben]

The template currently does not provide risc-v support. keeping this issue open as a reminder if/when we want to change that. :)