Re: [PATCHv2 3/9] gdb: write target description into core file

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

On 1/20/21 5:23 PM, Andrew Burgess wrote:
> When a core file is created from within GDB add the target description
> into a note within the core file.
> 
> When loading a core file, if the target description note is present
> then load the target description from the core file.
> 
> The benefit of this is that we can be sure that, when analysing the
> core file within GDB, that we are using the exact same target
> description as was in use at the time the core file was created.
> 
> In future commits I intend to add support for bare metal core dumps
> for some targets.  These core dumps will include auxiliary registers,
> the availability of which can only be established by looking at the
> target description.
> 
> gdb/ChangeLog:
> 
> 	* corelow.c: Add 'xml-tdesc.h' include.
> 	(core_target::read_description): Load the target description from
> 	the core file when possible.
> 	* gcore.c: Add 'gdbsupport/tdesc.h' include.
> 	(write_gcore_file_1): Write out the target description.
> ---
>   gdb/ChangeLog |  9 +++++++++
>   gdb/corelow.c | 24 ++++++++++++++++++++++++
>   gdb/gcore.c   | 21 +++++++++++++++++++++
>   3 files changed, 54 insertions(+)
> 
> diff --git a/gdb/corelow.c b/gdb/corelow.c
> index a63eab4852b..fd8a5c71e22 100644
> --- a/gdb/corelow.c
> +++ b/gdb/corelow.c
> @@ -49,6 +49,7 @@
>   #include <unordered_map>
>   #include <unordered_set>
>   #include "gdbcmd.h"
> +#include "xml-tdesc.h"
>   
>   #ifndef O_LARGEFILE
>   #define O_LARGEFILE 0
> @@ -1000,6 +1001,29 @@ core_target::thread_alive (ptid_t ptid)
>   const struct target_desc *
>   core_target::read_description ()
>   {
> +  /* If the core file contains a target description note then we will use
> +     that in preference to anything else.  */
> +  bfd_size_type tdesc_note_size = 0;
> +  struct bfd_section *tdesc_note_section
> +    = bfd_get_section_by_name (core_bfd, ".gdb-tdesc");
> +  if (tdesc_note_section != nullptr)
> +    tdesc_note_size = bfd_section_size (tdesc_note_section);
> +  if (tdesc_note_size > 0)
> +    {
> +      gdb::char_vector contents (tdesc_note_size + 1);
> +      if (bfd_get_section_contents (core_bfd, tdesc_note_section,
> +				    contents.data (), (file_ptr) 0,
> +				    tdesc_note_size))
> +	{
> +	  /* Ensure we have a null terminator.  */
> +	  contents [tdesc_note_size] = '\0';
> +	  const struct target_desc *result
> +	    = string_read_description_xml (contents.data ());
> +	  if (result != NULL)
> +	    return result;

NULL -> nullptr

> +	}
> +    }
> +
>     if (m_core_gdbarch && gdbarch_core_read_description_p (m_core_gdbarch))
>       {
>         const struct target_desc *result;
> diff --git a/gdb/gcore.c b/gdb/gcore.c
> index d62aa3a7109..cecb9146994 100644
> --- a/gdb/gcore.c
> +++ b/gdb/gcore.c
> @@ -38,6 +38,7 @@
>   #include "gdbsupport/gdb_unlinker.h"
>   #include "gdbsupport/byte-vector.h"
>   #include "gdbsupport/scope-exit.h"
> +#include "gdbsupport/tdesc.h"
>   
>   /* The largest amount of memory to read from the target at once.  We
>      must throttle it to limit the amount of memory used by GDB during
> @@ -82,6 +83,26 @@ write_gcore_file_1 (bfd *obfd)
>       note_data = gdbarch_make_corefile_notes (target_gdbarch (), obfd,
>   					     &note_size);
>   
> +  /* Append the target description to the core file.  */
> +  const struct target_desc *tdesc = gdbarch_target_desc (target_gdbarch ());
> +  const char *tdesc_xml
> +    = tdesc == nullptr ? nullptr : tdesc_get_features_xml (tdesc);
> +  if (tdesc_xml != nullptr && *tdesc_xml != '\0')
> +    {
> +      /* Skip the leading '@'.  */
> +      if (*tdesc_xml == '@')
> +	++tdesc_xml;
> +
> +      /* Include the null terminator in the length.  */
> +      size_t tdesc_len = strlen (tdesc_xml) + 1;
> +
> +      /* Now add the target description into the core file.  */
> +      note_data.reset (elfcore_write_register_note (obfd,
> +						    note_data.release (),
> +						    &note_size, ".gdb-tdesc",
> +						    tdesc_xml, tdesc_len));
> +    }
> +
>     if (note_data == NULL || note_size == 0)
>       error (_("Target does not support core file generation."));
>   
> 

Otherwise this is OK.