[PING][PATCH] Update the core file architecture if a target description is present

[Luis Machado <luis.machado@linaro.org>]

On 5/18/21 5:20 PM, Luis Machado wrote:
> At the moment, the core target has its own gdbarch (m_core_gdbarch), and that
> gets set from the core_bfd on the core target's constructor.
> 
> That gdbarch doesn't contain a target description because it is constructed
> before we get a chance to fetch the target description.
> 
> As a result, some hooks that depend on the target description being set are
> not set, and that leads to problems. One of the examples is
> gdbarch_report_signal_info, which is used to show AArch64 tag violation
> information.
> 
> Fix this by updating the core file gdbarch after fetching the target
> description.
> 
> gdb/ChangeLog:
> 
> YYYY-MM-DD  Luis Machado  <luis.machado@linaro.org>
> 
> 	* corelow.c: Include "observable.h".
> 	(class core_target) <set_core_gdbarch>: New method.
> 	(core_on_new_gdbarch): New function.
> 	(_initialize_corelow): Register with observer "architecture_changed".
> ---
>   gdb/corelow.c | 35 +++++++++++++++++++++++++++++++++++
>   1 file changed, 35 insertions(+)
> 
> diff --git a/gdb/corelow.c b/gdb/corelow.c
> index a1943ab2ea6..452b4dd4f9a 100644
> --- a/gdb/corelow.c
> +++ b/gdb/corelow.c
> @@ -50,6 +50,7 @@
>   #include <unordered_set>
>   #include "gdbcmd.h"
>   #include "xml-tdesc.h"
> +#include "observable.h"
>   
>   #ifndef O_LARGEFILE
>   #define O_LARGEFILE 0
> @@ -107,6 +108,12 @@ class core_target final : public process_stratum_target
>       return m_core_gdbarch;
>     }
>   
> +  /* Setter, see variable definition.  */
> +  void set_core_gdbarch (gdbarch *arch)
> +  {
> +    m_core_gdbarch = arch;
> +  }
> +
>     /* See definition.  */
>     void get_core_register_section (struct regcache *regcache,
>   				  const struct regset *regset,
> @@ -1185,6 +1192,30 @@ maintenance_print_core_file_backed_mappings (const char *args, int from_tty)
>       targ->info_proc_mappings (targ->core_gdbarch ());
>   }
>   
> +static void
> +core_on_new_gdbarch (struct gdbarch *newarch)
> +{
> +  /* The target architecture has changed.  Attempt to update the core
> +     target's architecture with NEWARCH's target description.  */
> +  struct gdbarch_info info;
> +
> +  gdbarch_info_init (&info);
> +  info.abfd = core_bfd;
> +  info.target_desc = gdbarch_target_desc (newarch);
> +
> +  struct gdbarch *new_core_arch = gdbarch_find_by_info (info);
> +
> +  /* If we've found a valid architecture, update the core target.  */
> +  if (new_core_arch != nullptr)
> +    {
> +      /* Update the core file architecture.  */
> +      struct core_target *target = get_current_core_target ();
> +
> +      if (target != nullptr)
> +	target->set_core_gdbarch (new_core_arch);
> +    }
> +}
> +
>   void _initialize_corelow ();
>   void
>   _initialize_corelow ()
> @@ -1194,4 +1225,8 @@ _initialize_corelow ()
>   	   maintenance_print_core_file_backed_mappings,
>   	   _("Print core file's file-backed mappings."),
>   	   &maintenanceprintlist);
> +
> +  /* Register observer to listen to architecture changes.  */
> +  gdb::observers::architecture_changed.attach (core_on_new_gdbarch,
> +					       "py-unwind");
>   }
>