Re: [Qemu-arm] [PATCH v1 2/2] target/arm: defer setting up of aarch64 gdb until arm_cpu_realize

[Peter Maydell]

On Thu, 13 Dec 2018 at 11:55, Alex Bennée <address@hidden> wrote:
>
> If we setup earlier we miss the parsing of the aarch64 state of the
> CPU. If the user has booted up with:
>
>   qemu-system-aarch64 -cpu host,aarch64=off -enable-kvm
>
> we end up presenting an aarch64 view of the world via the gdbstub and
> hilarity ensues.
>
> Reported-by: Ard Biesheuvel <address@hidden>
> Signed-off-by: Alex Bennée <address@hidden>
> Cc: Omair Javaid <address@hidden>
> ---
>  include/hw/arm/arm.h |  2 ++
>  target/arm/cpu.c     |  4 ++++
>  target/arm/cpu64.c   | 20 +++++++++++++++-----
>  3 files changed, 21 insertions(+), 5 deletions(-)
>
> diff --git a/include/hw/arm/arm.h b/include/hw/arm/arm.h
> index ffed39252d..f9a7a6e2fb 100644
> --- a/include/hw/arm/arm.h
> +++ b/include/hw/arm/arm.h
> @@ -171,4 +171,6 @@ void arm_write_secure_board_setup_dummy_smc(ARMCPU *cpu,
>     ticks.  */
>  extern int system_clock_scale;
>
> +void arm_cpu_enable_aarch64_gdbstub(CPUClass *cc);
> +
>  #endif /* HW_ARM_H */
> diff --git a/target/arm/cpu.c b/target/arm/cpu.c
> index 60411f6bfe..100a72ff81 100644
> --- a/target/arm/cpu.c
> +++ b/target/arm/cpu.c
> @@ -890,9 +890,13 @@ static void arm_cpu_realizefn(DeviceState *dev, Error 
> **errp)
>       * queries ID_ISAR0_EL1 on such a host, the value is UNKNOWN.
>       * Similarly, we cannot check ID_AA64PFR0 without AArch64 support.
>       */
> +#ifdef TARGET_AARCH64
>      if (arm_feature(&cpu->env, ARM_FEATURE_AARCH64)) {
> +        CPUClass *cc = CPU_GET_CLASS(cs);
>          no_aa32 = !cpu_isar_feature(aa64_aa32, cpu);
> +        arm_cpu_enable_aarch64_gdbstub(cc);
>      }
> +#endif

This seems weird, because the fields in cc are common
to all CPUs in the class, and so setting them on
realize of a specific instance based on properties of
the instance looks wrong... At least in theory there's
no reason we couldn't have one -cpu host CPU with
aarch64=off and one with aarch64=on, though I'm not
sure our UI allows the user to actually set the
properties per-cpu like that.

thanks
-- PMM