Re: [PATCH 4/8] gdbserver/linux-aarch64: Factor out function to get aarch64_features

[Luis Machado <luis.machado@arm.com>]

On 9/8/22 07:41, Thiago Jung Bauermann via Gdb-patches wrote:
> It will be used in a subsequent commit.  There's no functional change.
> ---
>   gdbserver/linux-aarch64-low.cc | 45 ++++++++++++++++++++++------------
>   1 file changed, 29 insertions(+), 16 deletions(-)
> 
> diff --git a/gdbserver/linux-aarch64-low.cc b/gdbserver/linux-aarch64-low.cc
> index 576925838f49..9b57be73818e 100644
> --- a/gdbserver/linux-aarch64-low.cc
> +++ b/gdbserver/linux-aarch64-low.cc
> @@ -652,6 +652,28 @@ aarch64_target::low_delete_process (arch_process_info *info)
>     xfree (info);
>   }
>   
> +/* Matches HWCAP_PACA in kernel header arch/arm64/include/uapi/asm/hwcap.h.  */
> +#define AARCH64_HWCAP_PACA (1 << 30)
> +
> +static gdb::optional<struct aarch64_features>
> +aarch64_get_arch_features (const thread_info *thread)
> +{
> +  struct aarch64_features features;
> +  int vq = aarch64_sve_get_vq (thread->id.lwp ());
> +
> +  if (vq < 0)
> +    return {};

If we can't identify SVE properly, should we carry on and disable SVE support but enable all the other
features we can find?

> +
> +  features.vq = vq;
> +  /* A-profile PAC is 64-bit only.  */
> +  features.pauth = linux_get_hwcap (thread, 8) & AARCH64_HWCAP_PACA;
> +  /* A-profile MTE is 64-bit only.  */
> +  features.mte = linux_get_hwcap2 (thread, 8) & HWCAP2_MTE;
> +  features.tls = true;
> +
> +  return features;
> +}
> +
>   void
>   aarch64_target::low_new_thread (lwp_info *lwp)
>   {
> @@ -804,9 +826,6 @@ aarch64_adjust_register_sets (const struct aarch64_features &features)
>       }
>   }
>   
> -/* Matches HWCAP_PACA in kernel header arch/arm64/include/uapi/asm/hwcap.h.  */
> -#define AARCH64_HWCAP_PACA (1 << 30)
> -
>   /* Implementation of linux target ops method "low_arch_setup".  */
>   
>   void
> @@ -822,24 +841,18 @@ aarch64_target::low_arch_setup ()
>   
>     if (is_elf64)
>       {
> -      struct aarch64_features features;
> -      int vq = aarch64_sve_get_vq (tid);
> +      gdb::optional<struct aarch64_features> features
> +	  = aarch64_get_arch_features (current_thread);
>   
> -      /* If ptrace fails we can't determine vq, but the low_arch_setup method
> -	  always succeeds so all we can do here is assert that vq is valid.  */
> -      gdb_assert (vq >= 0);
> -      features.vq = vq;
> -      /* A-profile PAC is 64-bit only.  */
> -      features.pauth = linux_get_hwcap (current_thread, 8) & AARCH64_HWCAP_PACA;
> -      /* A-profile MTE is 64-bit only.  */
> -      features.mte = linux_get_hwcap2 (current_thread, 8) & HWCAP2_MTE;
> -      features.tls = true;
> +      /* If ptrace fails we can't determine vq, but low_arch_setup always
> +	 succeeds so all we can do here is assert that features is valid.  */
> +      gdb_assert (features.has_value ());
>   
> -      current_process ()->tdesc = aarch64_linux_read_description (features);
> +      current_process ()->tdesc = aarch64_linux_read_description (*features);
>   
>         /* Adjust the register sets we should use for this particular set of
>   	 features.  */
> -      aarch64_adjust_register_sets (features);
> +      aarch64_adjust_register_sets (*features);
>       }
>     else
>       current_process ()->tdesc = aarch32_linux_read_description ();