Re: [PATCH v2 2/5] target/arm/kvm: Make uncalled stubs explicitly unreachable

[Auger Eric <eric.auger@redhat.com>]

Hi Drew,

On 8/5/20 11:16 AM, Andrew Jones wrote:
> When we compile without KVM support !defined(CONFIG_KVM) we generate
> stubs for functions that the linker will still encounter. Sometimes
> these stubs can be executed safely and are placed in paths where they
> get executed with or without KVM. Other functions should never be
> called without KVM. Those functions should be guarded by kvm_enabled(),
> but should also be robust to refactoring mistakes. Putting a
> g_assert_not_reached() in the function should help. Additionally,
> the g_assert_not_reached() calls may actually help the linker remove
> some code.
> 
> We remove the stubs for kvm_arm_get/put_virtual_time(), as they aren't
> necessary at all - the only caller is in kvm.c
> 
> Signed-off-by: Andrew Jones <drjones@redhat.com>
> ---
>  target/arm/kvm_arm.h | 44 +++++++++++++++++++++++++++-----------------
>  1 file changed, 27 insertions(+), 17 deletions(-)
> 
> diff --git a/target/arm/kvm_arm.h b/target/arm/kvm_arm.h
> index adb38514bf20..0da00eb6b20c 100644
> --- a/target/arm/kvm_arm.h
> +++ b/target/arm/kvm_arm.h
> @@ -344,16 +344,10 @@ int kvm_arm_set_irq(int cpu, int irqtype, int irq, int level);
>  
>  #else
>  
> -static inline void kvm_arm_set_cpu_features_from_host(ARMCPU *cpu)
> -{
> -    /*
> -     * This should never actually be called in the "not KVM" case,
> -     * but set up the fields to indicate an error anyway.
> -     */
> -    cpu->kvm_target = QEMU_KVM_ARM_TARGET_NONE;
> -    cpu->host_cpu_probe_failed = true;
> -}
> -
> +/*
> + * It's safe to call these functions without KVM support.
> + * They should either do nothing or return "not supported".
> + */
>  static inline void kvm_arm_add_vcpu_properties(Object *obj) {}
this one also is guarded by kvm_enabled() in target/arm/cpu.c
don't you want to add g_assert_not_reached()?
>  
>  static inline bool kvm_arm_aarch32_supported(void)
> @@ -371,23 +365,39 @@ static inline bool kvm_arm_sve_supported(void)
>      return false;
>  }
>  
> +/*
> + * These functions should never actually be called without KVM support.
> + */
> +static inline void kvm_arm_set_cpu_features_from_host(ARMCPU *cpu)
> +{
> +    g_assert_not_reached();
> +}
> +
>  static inline int kvm_arm_get_max_vm_ipa_size(MachineState *ms)
>  {
> -    return -ENOENT;
> +    g_assert_not_reached();
>  }
>  
>  static inline int kvm_arm_vgic_probe(void)
>  {
> -    return 0;
> +    g_assert_not_reached();
>  }
>  
> -static inline void kvm_arm_pmu_set_irq(CPUState *cs, int irq) {}
> -static inline void kvm_arm_pmu_init(CPUState *cs) {}
> +static inline void kvm_arm_pmu_set_irq(CPUState *cs, int irq)
> +{
> +    g_assert_not_reached();
> +}
>  
> -static inline void kvm_arm_sve_get_vls(CPUState *cs, unsigned long *map) {}
> +static inline void kvm_arm_pmu_init(CPUState *cs)
> +{
> +    g_assert_not_reached();
> +}
> +
> +static inline void kvm_arm_sve_get_vls(CPUState *cs, unsigned long *map)
> +{
> +    g_assert_not_reached();
> +}
>  
> -static inline void kvm_arm_get_virtual_time(CPUState *cs) {}
> -static inline void kvm_arm_put_virtual_time(CPUState *cs) {}
>  #endif
>  
>  static inline const char *gic_class_name(void)
> 

Besides,
Reviewed-by: Eric Auger <eric.auger@redhat.com>

Thanks

Eric