RP2040 probe-rs no defmt/RTT, linker errors

[Erhannis]

Ubuntu 24.04.1 LTS
RP2040 (Pico W)

For several hours I've been trying to get RTIC running (with defmt, and preferably debugging) on an RP2040. The results are a little baffling. I'm using probe-rs to flash the code.

I can compile and run https://github.com/rtic-rs/rtic/tree/master/examples/rp2040_local_i2c_init (if I add runner = "probe-rs run --chip RP2040 --protocol swd" to config.toml), but I get the warning "WARN probe_rs::util::rtt: No RTT header info was present in the ELF file. Does your firmware run RTT?" I've tried adding defmt-rtt to Cargo.toml, added "-C", "link-arg=-Tdefmt.x", to config.toml, tried adding rtt features to various packages, but either nothing happens or I get linker errors. (I did just discover I can get debugging to work on it, so that's a plus.)

I'm able to compile https://github.com/rtic-rs/defmt-app-template , once I fill in the various TODOs, but I get "ERROR probe_rs::cmd::run: Failed to attach to RTT, continuing...", and it doesn't seem like the code is actually running. Also, somehow when I copy the main code from the i2c_init example over the main code of the template (and tweak the imports to work), I get a linker error about defmt??? I can copy the old file (containing defmt calls) right back over it, and the linking error goes away, which baffles me. (I added some stuff to Cargo.toml to make the copied code compile, but haven't touched it since, and swapping the main code makes the linking error come and go, despite that both reference defmt.) Linker error:

erhannis@mnode7:~/projects/test-app$ cargo run
   Compiling test-app v0.1.0 (/home/erhannis/projects/test-app)
error: linking with `flip-link` failed: exit status: 1
  |
  = note: LC_ALL="C" PATH="/home/erhannis/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/bin:/home/erhannis/.wasmer/bin:/home/erhannis/pgms/mambaforge3/condabin:/home/erhannis/.sdkman/candidates/gradle/current/bin:/home/erhannis/pgms/flutter/bin:/home/erhannis/bin/:/usr/lib/qt6/bin/:/home/erhannis/.opam/default/bin:/home/erhannis/.cargo/bin:/home/erhannis/.local/bin:/home/erhannis/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin:/snap/bin:/home/erhannis/.dotnet/tools:/home/erhannis/.local/share/coursier/bin" VSLANG="1033" "flip-link" "-flavor" "gnu" "/tmp/rustciNKspS/symbols.o" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/minimal-44dce56ff7d869f1.minimal.14834bf9c00790d0-cgu.0.rcgu.o" "--as-needed" "-Bstatic" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/libpanic_probe-51d41fe991f3a057.rlib" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/librp2040_hal-1696bc028cd0826e.rlib" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/libitertools-c855ee4f78a10994.rlib" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/libeither-9a14dcb7a157a339.rlib" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/libembedded_io-0e865585565e23a7.rlib" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/librand_core-e56e4353620c994b.rlib" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/libbitfield-f6f9386f2683317a.rlib" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/libusb_device-b6aee9dc5b468803.rlib" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/libheapless-38d6f977d7718e54.rlib" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/libhash32-b0b5e1436bbe58d5.rlib" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/libbyteorder-0f93a574e5b7bc56.rlib" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/libportable_atomic-59941480fd693a83.rlib" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/libembedded_hal_nb-faa68e42fb8ccd19.rlib" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/libpio-d0cb521148a2df6b.rlib" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/libnum_enum-b2c2db6233258bc4.rlib" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/libarrayvec-6c2d978685ed7040.rlib" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/libfrunk-041ae04f04ccc508.rlib" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/libfrunk_core-5e62c96d28c43a8f.rlib" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/libembedded_dma-91c9f079a84ad61c.rlib" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/libstable_deref_trait-bdb0c312334f72f2.rlib" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/librtic-1b286aaa9e02534e.rlib" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/libatomic_polyfill-69f97e468f6f5417.rlib" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/libbare_metal-ab854f731422c31e.rlib" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/librtic_core-2c825e754fea243a.rlib" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/librtic_monotonics-3c89667bc9965ac9.rlib" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/librp2040_pac-788714f8184c7338.rlib" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/libcortex_m_rt-f6b85b8d60310977.rlib" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/libcortex_m-cfcbf5cca1cc7863.rlib" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/libembedded_hal-2b1b18ac0ab0cb11.rlib" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/libvoid-85fe3fb7b05902af.rlib" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/libnb-a88e4d1c73f85dfc.rlib" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/libnb-19b9fdb772e1f2c0.rlib" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/libvolatile_register-73613043dc7c5cc2.rlib" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/libvcell-d880b71bacd066ff.rlib" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/libbare_metal-d5a68899e31b9ad1.rlib" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/librtic_time-9da2a1160a89332c.rlib" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/libembedded_hal_async-76fcdad864db69cd.rlib" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/libembedded_hal-3fe5b323ff6ae444.rlib" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/librtic_common-3a89dd5a8509d6fd.rlib" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/libfutures_util-af33c17acb8f1a68.rlib" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/libpin_project_lite-74e020c4d44eef42.rlib" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/libfutures_task-63cfb7bee31907c1.rlib" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/libpin_utils-5a650b8bb6434b34.rlib" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/libfutures_core-52b26d7e9d197894.rlib" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/libcritical_section-754af05aeed63908.rlib" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/libfugit-fab517c4f3263a90.rlib" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/libgcd-629a4b9727d7fea8.rlib" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/libdefmt-977c56ad642145cb.rlib" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/libbitflags-f6aad9da853e795e.rlib" "/home/erhannis/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/thumbv6m-none-eabi/lib/librustc_std_workspace_core-3eaed70af7b15b94.rlib" "/home/erhannis/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/thumbv6m-none-eabi/lib/libcore-df1ccfea71d21752.rlib" "/home/erhannis/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/thumbv6m-none-eabi/lib/libcompiler_builtins-fbf8dd0c4df01e24.rlib" "-Bdynamic" "--eh-frame-hdr" "-z" "noexecstack" "-L" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/build/cortex-m-ab638b831eeb39ec/out" "-L" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/build/defmt-82973cb74e3f7ed8/out" "-L" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/build/rp2040-pac-cabba1dd47117897/out" "-L" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/build/cortex-m-rt-fd518bff6e425e98/out" "-o" "/home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/minimal-44dce56ff7d869f1" "--gc-sections" "-Tlink.x" "-Tdefmt.x" "--nmagic"
  = note: rust-lld: error: undefined symbol: _defmt_acquire
          >>> referenced by mod.rs:55 (/home/erhannis/.cargo/registry/src/index.crates.io-6f17d22bba15001f/defmt-0.3.8/src/export/mod.rs:55)
          >>>               panic_probe-51d41fe991f3a057.panic_probe.6d6f93a14a8cd9d1-cgu.0.rcgu.o:(rust_begin_unwind) in archive /home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/libpanic_probe-51d41fe991f3a057.rlib
          
          rust-lld: error: undefined symbol: _defmt_release
          >>> referenced by mod.rs:71 (/home/erhannis/.cargo/registry/src/index.crates.io-6f17d22bba15001f/defmt-0.3.8/src/export/mod.rs:71)
          >>>               panic_probe-51d41fe991f3a057.panic_probe.6d6f93a14a8cd9d1-cgu.0.rcgu.o:(rust_begin_unwind) in archive /home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/libpanic_probe-51d41fe991f3a057.rlib
          
          rust-lld: error: undefined symbol: _defmt_write
          >>> referenced by mod.rs:85 (src/export/mod.rs:85)
          >>>               defmt-977c56ad642145cb.defmt.ae29f38bc26cc943-cgu.0.rcgu.o:(core::fmt::Write::write_char::h4032266952560612) in archive /home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/libdefmt-977c56ad642145cb.rlib
          >>> referenced by mod.rs:85 (src/export/mod.rs:85)
          >>>               defmt-977c56ad642145cb.defmt.ae29f38bc26cc943-cgu.0.rcgu.o:(defmt::export::istr::h72e73aeae8519c9e) in archive /home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/libdefmt-977c56ad642145cb.rlib
          >>> referenced by mod.rs:85 (src/export/mod.rs:85)
          >>>               defmt-977c56ad642145cb.defmt.ae29f38bc26cc943-cgu.0.rcgu.o:(defmt::export::display::hb33614919521c731) in archive /home/erhannis/projects/test-app/target/thumbv6m-none-eabi/debug/deps/libdefmt-977c56ad642145cb.rlib
          >>> referenced 2 more times
          
          flip-link: the native linker failed to link the program normally; please check your project configuration and linker scripts
          

error: could not compile `test-app` (bin "minimal") due to 1 previous error

Another weird thing I noticed earlier - I was at some point able to flash code to the device via e.g. cargo run which didn't appear to run, but after I replugged the device it'd start running (e.g. led would start flashing). It's not doing it now, though.