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

[Sriraman Tallam <tmsriram at google dot com>]

Hi Ian,

   I made all the changes you mentioned. I removed the
inspect_unclaimed_object hooks and allowed the functionality to happen
in claim_file hook, so one handle. Please look at readsyms.cc in
particular as that has the biggest change to allow this to happen.

Thanks,
-Sri.


  	* archive.cc (Archive::get_elf_object_for_member): Add extra parameter
	to claim_file call.
	* 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 (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::load): Add the new interfaces to the transfer vector.
	(Plugin_manager::load_plugins): New parameter.
	(Plugin_manager::all_symbols_read): New parameter.
	(Plugin_manager::claim_file): New parameter. Save the elf object for
	unclaimed objects.
	(Plugin_manager::get_elf_object): New function.
	* plugin.h (input_objects): New function
	(Plugin__manager::load_plugins): New parameter.
	(Plugin_manager::claim_file): New parameter.
	(Plugin_manager::get_elf_object): New function.
	(Plugin_manager::in_claim_file_handler): New function.
	(Plugin_manager::in_claim_file_handler_): New member.
	(layout): New function.
	* readsyms.cc (Read_symbols::do_read_symbols): Call the claim_file
	handler with an extra parameter. Make the elf object before calling
	claim_file handler.
	* testsuite/plugin_test.c (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.
	(onload): Check if the new interfaces exist.

	* plugin-api.h
	(ld_plugin_section): New struct.
	(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_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.

On Tue, Jul 5, 2011 at 2:29 PM, Ian Lance Taylor <iant@google.com> wrote:
> 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
>

Attachment: latest_plugin_patch.txt
Description: Text document