Compatibility issue with rust 1.82.

[kareled]

Hello,
not sure where to log it, but with update to 1.82 nightly my project link fails with missing __defmt_default_panic␍

The project builds for armv7emhf and it links fine code unchanged with various rustc toolchains up to including 1.81 nightly. Always using nightly due to RTIC usage. With nightly from 2024-08-03 (my first obtained nightly of 1.82 family) it starts to complain and fail while being linked with:

  = note: rust-lld: error: C:\Users\gardas\git\develop\target\thumbv7em-none-eabihf\debug\build\defmt-e20cffcd2d13aae7\out\defmt.x:7: symbol not found: __defmt_default_panic␍
          rust-lld: error: C:\Users\gardas\git\develop\target\thumbv7em-none-eabihf\debug\build\defmt-e20cffcd2d13aae7\out\defmt.x:7: symbol not found: __defmt_default_panic␍
          rust-lld: error: C:\Users\gardas\git\develop\target\thumbv7em-none-eabihf\debug\build\defmt-e20cffcd2d13aae7\out\defmt.x:7: symbol not found: __defmt_default_panic␍
          rust-lld: error: C:\Users\gardas\git\develop\target\thumbv7em-none-eabihf\debug\build\defmt-e20cffcd2d13aae7\out\defmt.x:7: symbol not found: __defmt_default_panic␍

          flip-link: the native linker failed to link the program normally; please check your project configuration and linker scripts

If this is not defmt issue, please recommend where to report it while closing. Thanks!

[skade]

This is due to upstream bug rust-lang/rust#131164

[Urhengulas]

@Dirbaio said:

A possible workaround defmt could do is adding EXTERN(_defmt_panic) to the linker script. The side effect is it'd prevent the panic handler from being optimized out when it's truly unused, I think.

I can confirm this works as a workaround on current beta. Let's hope it won't be necessary, but if the upstream fix does not make it into stable we can use it.

[Urhengulas]

It probably should be EXTERN(__defmt_default_panic) instead of EXTERN(_defmt_panic)