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

[Thiago Jung Bauermann <thiago.bauermann@linaro.org>]

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;