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The Linux kernel doesn't use the official bkpt insn for breakpoints; instead it uses three instructions in the guaranteed-to-UNDEF space, and generates SIGTRAP for these rather than the SIGILL that most UNDEF insns generate: https://elixir.bootlin.com/linux/v5.9.8/source/arch/arm/kernel/ptrace.c#L197 Make QEMU treat these insns specially too. The main benefit of this is that if you're running a debugger on a guest program that runs into a GCC __builtin_trap() or LLVM "trap because execution should never reach here" then you'll get the expected signal rather than a SIGILL. Signed-off-by: Peter Maydell <peter.maydell@linaro.org> Reviewed-by: Richard Henderson <richard.henderson@linaro.org> Message-id: 20201117155634.6924-1-peter.maydell@linaro.org