panic-probe should do bkpt not udf?

[jonathanpallant]

panic-probe currently executes a "udf" instruction to trigger a hard fault. probe-rs doesn't catch hard faults, and so if the hard fault handler is empty loop, probe-rs just hangs. You can set up a custom hard fault handler to do a bkpt instruction, but maybe panic-probe should just do that directly and save a trip via the hard fault mechanism.

[jonathanpallant]

Example when used with probe-rs and a custom hard-fault handler that does a semihosting exit:

ERROR panicked at src/bin/panic.rs:30:13:
index out of bounds: the len is 3 but the index is 3
└─ panic_probe::print_defmt::print @ /Users/jonathan/.cargo/registry/src/index.crates.io-6f17d22bba15001f/panic-probe-0.3.1/src/lib.rs:104
`dk::fail()` called; exiting ...
Frame 0: fail @ 0x00001308
       /Users/jonathan/.cargo/registry/src/index.crates.io-6f17d22bba15001f/cortex-m-semihosting-0.5.0/src/lib.rs:201:13
Frame 1: __cortex_m_rt_HardFault @ 0x000016a6 inline
       /Users/jonathan/Documents/ferrous-systems/rust-exercises/nrf52-code/radio-app/src/lib.rs:12:5
Frame 2: __cortex_m_rt_HardFault_trampoline @ 0x00000000000016a2
       /Users/jonathan/Documents/ferrous-systems/rust-exercises/nrf52-code/radio-app/src/lib.rs:10:1
Frame 3: "HardFault handler. Cause: Escalated UsageFault (Undefined instruction)." @ 0x000016a6
Frame 4: __udf @ 0x00001530 inline
       ./asm/lib.rs:48:1
Frame 5: __udf @ 0x0000000000001530
       ./asm/lib.rs:51:17
Frame 6: udf @ 0x0000151c
       /Users/jonathan/.cargo/registry/src/index.crates.io-6f17d22bba15001f/cortex-m-0.7.7/src/asm.rs:43:5
Frame 7: hard_fault @ 0x0000150e
       /Users/jonathan/.cargo/registry/src/index.crates.io-6f17d22bba15001f/panic-probe-0.3.1/src/lib.rs:86:5
Frame 8: panic @ 0x000014dc
       /Users/jonathan/.cargo/registry/src/index.crates.io-6f17d22bba15001f/panic-probe-0.3.1/src/lib.rs:54:9
Frame 9: panic_fmt @ 0x0000034a
       /rustc/82e1608dfa6e0b5569232559e3d385fea5a93112/library/core/src/panicking.rs:72:14
Frame 10: panic_bounds_check @ 0x000003fe
       /rustc/82e1608dfa6e0b5569232559e3d385fea5a93112/library/core/src/panicking.rs:190:5
Frame 11: bar @ 0x00000180
       /Users/jonathan/Documents/ferrous-systems/rust-exercises/nrf52-code/radio-app/src/bin/panic.rs:30:13
Frame 12: foo @ 0x00000176
       /Users/jonathan/Documents/ferrous-systems/rust-exercises/nrf52-code/radio-app/src/bin/panic.rs:24:2
Frame 13: __cortex_m_rt_main @ 0x000002de
       /Users/jonathan/Documents/ferrous-systems/rust-exercises/nrf52-code/radio-app/src/bin/panic.rs:13:5
Frame 14: __cortex_m_rt_main_trampoline @ 0x0000018a
       /Users/jonathan/Documents/ferrous-systems/rust-exercises/nrf52-code/radio-app/src/bin/panic.rs:9:1
Frame 15: memmove @ 0x0000013c
Frame 16: memmove @ 0x0000013c
Error: Semihosting indicates exit with failure code: 0x020023 (131107)