Re: [PATCH 6/8] gdbserver/linux-aarch64: When inferior stops, update its target description

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

On 9/8/22 07:41, Thiago Jung Bauermann via Gdb-patches wrote:
> Introduce new arch_update_tdesc method to the linux_process_target class.
> 
> This allows aarch64-linux to probe the inferior's vq register and provide
> an updated target description reflecting the new vector length.
> ---
>   gdbserver/linux-aarch64-low.cc | 21 +++++++++++++++++++++
>   gdbserver/linux-low.cc         | 18 ++++++++++++++++++
>   gdbserver/linux-low.h          |  5 +++++
>   3 files changed, 44 insertions(+)
> 
> diff --git a/gdbserver/linux-aarch64-low.cc b/gdbserver/linux-aarch64-low.cc
> index 8c4306ab8794..cc90eae1e36b 100644
> --- a/gdbserver/linux-aarch64-low.cc
> +++ b/gdbserver/linux-aarch64-low.cc
> @@ -99,6 +99,9 @@ protected:
>   
>     void low_arch_setup () override;
>   
> +  gdb::optional<const struct target_desc *>
> +    arch_update_tdesc (const thread_info *thread) override;
> +
>     bool low_cannot_fetch_register (int regno) override;
>   
>     bool low_cannot_store_register (int regno) override;
> @@ -902,6 +905,24 @@ aarch64_target::low_arch_setup ()
>     aarch64_linux_get_debug_reg_capacity (lwpid_of (current_thread));
>   }
>   
> +/* Implementation of linux target ops method "arch_update_tdesc".  */
> +
> +gdb::optional<const struct target_desc *>
> +aarch64_target::arch_update_tdesc (const thread_info *thread)
> +{
> +  gdb::optional<struct aarch64_features> features
> +      = aarch64_get_arch_features (thread);
> +
> +  if (!features.has_value())
> +    return {};
> +
> +  /* Adjust the register sets we should use for this particular set of
> +     features.  */
> +  aarch64_adjust_register_sets(*features);
> +
> +  return aarch64_linux_read_description (*features);
> +}
> +
>   /* Implementation of linux target ops method "get_regs_info".  */
>   
>   const regs_info *
> diff --git a/gdbserver/linux-low.cc b/gdbserver/linux-low.cc
> index d37eb120e114..2a7c6f166a65 100644
> --- a/gdbserver/linux-low.cc
> +++ b/gdbserver/linux-low.cc
> @@ -483,6 +483,12 @@ linux_process_target::arch_setup_thread (thread_info *thread)
>     low_arch_setup ();
>   }
>   
> +gdb::optional<const struct target_desc *>
> +linux_process_target::arch_update_tdesc (const thread_info *thread)
> +{
> +  return {};
> +}
> +
>   int
>   linux_process_target::handle_extended_wait (lwp_info **orig_event_lwp,
>   					    int wstat)
> @@ -2354,6 +2360,18 @@ linux_process_target::filter_event (int lwpid, int wstat)
>   	      return;
>   	    }
>   	}
> +      else
> +	{
> +	  /* Give the arch code an opportunity to update the target
> +	     description.  */
> +	  gdb::optional<const struct target_desc *> new_tdesc
> +	      = arch_update_tdesc (thread);
> +	  if (new_tdesc.has_value () && *new_tdesc != thread->tdesc)
> +	    {
> +	      regcache_release ();
> +	      thread->tdesc = *new_tdesc;
> +	    }
> +	}
>       }
>   
>     if (WIFSTOPPED (wstat) && child->must_set_ptrace_flags)
> diff --git a/gdbserver/linux-low.h b/gdbserver/linux-low.h
> index bd1ec31dc5a4..fba462744953 100644
> --- a/gdbserver/linux-low.h
> +++ b/gdbserver/linux-low.h
> @@ -602,6 +602,11 @@ class linux_process_target : public process_stratum_target
>     /* Architecture-specific setup for the current thread.  */
>     virtual void low_arch_setup () = 0;
>   
> +  /* Allows arch-specific code to update the target description when the
> +     inferior stops.  */
> +  virtual gdb::optional<const struct target_desc *>
> +    arch_update_tdesc (const thread_info *thread);
> +
>     /* Return false if we can fetch/store the register, true if we cannot
>        fetch/store the register.  */
>     virtual bool low_cannot_fetch_register (int regno) = 0;

LGTM for the aarch64 parts. Someone else must approve the generic changes.