---
title: "Fatal errors and assertions"
canonical_url: https://developer.repebble.com/pebbleos/docs/kernel/fatal/
last_updated: 2026-10-21
sdk_version: 4.33.1
---
# Fatal errors and assertions

Source: https://developer.repebble.com/pebbleos/docs/kernel/fatal/

`pbl/kernel/fatal.h` and `pbl/kernel/assert.h` are how firmware code, the kernel included, stops the system on an unrecoverable error:

- `pbl_panic()` always stops; `pbl_panic(fmt, ...)` adds a message;

- `PBL_ASSERT(expr, fmt, ...)` stops with a message when `expr` is false;

- `PBL_ASSERTN(expr)` stops without one, the cheapest check.

Assertions are always enabled. Messages must be string literals: with `CONFIG_LOG_HASHED` they become log tokens like any `PBL_LOG`, so they cost no flash, and a call site without a message is reduced to its return address.

`kernel/fatal.c` logs the error and the address of the code that raised it, then calls `pbl_fatal_error_handler()`, the one hook the platform implements. The firmware’s, in `fw/kernel/fault_handling.c`, records an assertion reboot reason, saves a core dump and reboots, or only kills the app when the error was raised by unprivileged code. Unit tests replace the whole of `kernel/fatal.c` with `tests/stubs/default/fatal.c`, so `cl_assert_panic()` can catch a panic.

Generated from PebbleOS [3a7b71785](https://github.com/coredevices/pebbleos/commit/3a7b71785fd439666c4a8bc116f561140e8dec01). This page is maintained in the pebbleos repository: [docs/kernel/fatal.md](https://github.com/coredevices/pebbleos/blob/3a7b71785fd439666c4a8bc116f561140e8dec01/docs/kernel/fatal.md).