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Re: Plugin interfaces to do Pettis Hansen style code layout in the gold linker.


Sriraman Tallam <tmsriram@google.com> writes:

> * layout.cc (Layout::Layout): Initialize section_ordering_specified_,
> input_section_position_, and input_section_glob_.
> (read_layout_from_file): Call function section_ordering_specified.
> * layout.h (is_section_ordering_specified): New function.
> (section_ordering_specified): New function.
> (section_ordering_specified_): New boolean member.
> * main.cc(main): Call load_plugins after layout object is defined.
> * output.cc (Output_section::add_input_section): Use
> function section_ordering_specified to check if section ordering is
> needed.
> * output.cc (Output_section::add_relaxed_input_section): Use
> function section_ordering_specified to check if section ordering is
> needed.
> (Output_section::update_section_layout): New function.
> (Output_section::sort_attached_input_sections): Check if input section
> must be reordered.
> * output.h (Output_section::update_section_layout): New function.
> * plugin.cc (register_inspect_unclaimed_object): New function.
> (get_section_count): New function.
> (get_section_type): New function.
> (get_section_name): New function.
> (get_section_contents): New function.
> (update_section_order): New function.
> (allow_section_ordering): New function.
> (Plugin::inspect_unclaimed_object): New function.
> (Plugin_manager::inspect_unclaimed_object): New function.
> (Plugin_manager::get_unclaimed_object): New function.
> (Plugin::load): Add the new interfaces to the transfer vector.
> (Plugin_manager::load_plugins): New parameter.
> (Plugin_manager::all_symbols_read): New parameter.
> * plugin.h (input_objects): New function
> (Plugin::inspect_unclaimed_object): New function.
> (Plugin::set_inspect_unclaimed_object_handler): New function.
> (Plugin__manager::load_plugins): New parameter.
> (Plugin_manager::inspect_unclaimed_object): New function.
> (Plugin_manager::get_unclaimed_object): New function.
> (Plugin_manager::in_inspect_unclaimed_object_handler): New function.
> (Plugin_manager::set_inspect_unclaimed_object_handler): New function.
> (Plugin_manager::unclaimed_object): New function.
> (Plugin_manager::Unclaimed_object_list): New typedef.
> (Plugin_manager::unclaimed_objects_): New member.
> (Plugin_manager::in_inspect_unclaimed_object_handler_): New member.
> (layout): New function.
> * readsyms.cc (Read_symbols::do_read_symbols): Call the plugin handler.
> * testsuite/plugin_test.c (register_inspect_unclaimed_object_hook):
> New function pointer.
> (get_section_count): New function pointer.
> (get_section_type): New function pointer.
> (get_section_name): New function pointer.
> (get_section_contents): New function pointer.
> (update_section_order): New function pointer.
> (allow_section_ordering): New function pointer.
> (inspect_unclaimed_object_hook): New function.
> (onload): Check if the new interfaces exist.
> * plugin-api.h
> (unclaimed_obkect_handle): New typedef.
> (ld_plugin_section): New struct.
> (ld_plugin_inspect_unclaimed_object_handler): New typedef.
> (ld_plugin_register_inspect_unclaimed_object): New typedef.
> (ld_plugin_get_section_count): New typedef.
> (ld_plugin_get_section_type): New typedef.
> (ld_plugin_get_section_name): New typedef.
> (ld_plugin_get_section_contents): New typedef.
> (ld_plugin_update_section_order): New typedef.
> (ld_plugin_allow_section_ordering): New typedef.
> (LDPT_REGISTER_INSPECT_UNCLAIMED_OBJECT_HOOK): New enum value.
> (LDPT_GET_SECTION_COUNT): New enum value.
> (LDPT_GET_SECTION_TYPE): New enum value.
> (LDPT_GET_SECTION_NAME): New enum value.
> (LDPT_GET_SECTION_CONTENTS): New enum value.
> (LDPT_UPDATE_SECTION_ORDER): New enum value.
> (LDPT_ALLOW_SECTION_ORDERING): New enum value.
> (tv_get_section_count): New struct members.
> (tv_get_section_type): New struct members.
> (tv_get_section_name): New struct members.
> (tv_get_section_contents): New struct members.
> (tv_update_section_order): New struct members.
> (tv_allow_section_ordering): New struct members.


> +static enum ld_plugin_status
> +get_input_section_contents(const struct ld_plugin_section section,
> +                           const unsigned char** section_contents,
> +		           unsigned int* len);

Let's change the len parameter from "unsigned int*" to "size_t*".


> +// This updates the section order index of input sections according to the
> +// the order specified in the mapping from Section id to order index.
> +
> +void
> +Output_section::update_section_layout(
> +  const Section_layout_order& order_map)
> +{
> +  for (Input_section_list::iterator p = this->input_sections_.begin();
> +       p != this->input_sections_.end();
> +       ++p)
> +    {
> +      if ((*p).is_input_section()
> +	  || (*p).is_relaxed_input_section())
> +        {
> +	  Object* obj = ((*p).is_input_section()
> +			 ? (*p).relobj()
> +		         : (*p).relaxed_input_section()->relobj());
> +	  unsigned int shndx = (*p).shndx();
> +	  Section_layout_order::const_iterator it
> +	    = order_map.find(Section_id(obj, shndx));
> +	  if (it == order_map.end())
> +	    continue;
> +	  unsigned int section_order_index = it->second;
> +	  if (section_order_index != 0)
> +            {
> +              (*p).set_section_order_index(section_order_index);
> +              this->set_input_section_order_specified();
> +	    }
> +        }
> +    }
> +}

Please write "p->" instead of "(*p).".


> +// Specify the ordering of sections in the final layout. The sections are
> +// specified as (handle,shndx) pairs in the two arrays in the order in
> +// which they should appear in the final layout.
> +
> +static enum ld_plugin_status
> +update_section_order(const struct ld_plugin_section *section_list,
> +		     unsigned int num_sections)
> +{
> +  gold_assert(parameters->options().has_plugins());
> +
> +  if (num_sections == 0)
> +    return LDPS_OK;
> +
> +  if (section_list == NULL)
> +    return LDPS_ERR;
> +
> +  std::map<Section_id, unsigned int> order_map;
> +
> +  for (unsigned int i = 0; i < num_sections; ++i)
> +    {
> +      Object* obj = parameters->options().plugins()->get_unclaimed_object(
> +        section_list[i].handle);
> +      unsigned int shndx = section_list[i].shndx;
> +      Section_id secn_id(obj, shndx);
> +      order_map[secn_id] = i + 1;
> +    }
> +
> +  Layout* layout = parameters->options().plugins()->layout();
> +  gold_assert (layout != NULL);
> +
> +  for (Layout::Section_list::const_iterator p = layout->section_list().begin();
> +       p != layout->section_list().end();
> +       ++p)
> +    (*p)->update_section_layout(order_map);
> +
> +  return LDPS_OK;
> +}

You need to check the return value of get_unclaimed_object, and return
LDPS_ERR if it returns NULL.


> +      // Allow the plugins to inspect the unclaimed object now.
> +      if (parameters->options().has_plugins())
> +        parameters->options().plugins()->inspect_unclaimed_object(obj);

Can you remind me of why we need both inspect_unclaimed_object and
claim_file?  To me it seems that it might be logical to let claim_file
call get_section_count and so forth, and even update_section_order, and
then simply set *claimed to 0 if it doesn't want to claim the file.


> +/* The linker's interface for retrieving the name of specific section in
> +   an object. This interface should only be invoked in the
> +   inspect_unclaimed_object handler.  This function sets *SECTION_NAME_PTR
> +   to a null-terminated buffer allocated by malloc.  The plugin must free
> +   *SECTION_NAME_PTR.  */

s/of specific section/of a specific section/


> +/* The linker's interface for retrieving the contents of a specific section
> +   in an object.  This interface should only be invoked in the
> +   inspect_unclaimed_object handler.  This function sets *SECTION_CONTENTS to
> +   point to a buffer that is valid  until inspect_unclaimed_object handler
> +   returns.  It sets *LEN to the size of the buffer.  */

There seems to be an extra space after "valid".


The only important point in the above is whether we can eliminate
inspect_unclaimed_object.

Ian


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