It looks like we're at least attempting to set force-frame-pointers=yes:

[target.thumbv7em-none-eabihf]
rustflags = ["-C", "target-cpu=cortex-m7", "-Z", "macro-backtrace", "-C", "force-unwind-tables=yes", "-C", "force-frame-pointers=yes"]

I'll try to verify if that's actually the case. Are there any other situations that could cause the LR to get clobbered when calling noreturn functions?