Update LTO plugin interface

[Ian Lance Taylor]

"H.J. Lu" <hjl.tools@gmail.com> writes:

> On Wed, Dec 1, 2010 at 12:55 PM, Ian Lance Taylor <iant@google.com> wrote:
>> "H.J. Lu" <hjl.tools@gmail.com> writes:
>>
>>> On Wed, Dec 1, 2010 at 12:37 PM, Ian Lance Taylor <iant@google.com> wrote:
>>>
>>>> Are you planning to have the plugin claim all files, even linker
>>>> scripts, and then pass only the command line files back to the linker?
>>>>
>>>
>>> Plugin will keep the same claim strategy.  For those aren't claimed by
>>> plugin, plugin will save and pass them back to linker only if they are
>>> specified at command line.
>>
>> Just to be clear, that does not make sense as written.  If the plugin
>> does not claim a file, it should not then pass it back to the linker.
>
> API has
>
> typedef
> enum ld_plugin_status
> (*ld_plugin_claim_file_handler) (
>   const struct ld_plugin_input_file *file, int *claimed);
>
> For linker script, archive, DSO and object file without IR,
> *claimed will return 0 and plugin will save and pass it back to
> linker later in  if it is specified at command line.

I don't understand what you wrote, so I am going to write what I think
happens.

The claim_file handler is an interface provided by the plugin itself.
The plugin will register it via LDPT_REGISTER_CLAIM_FILE_HOOK.  The
linker proper will call it for each input file.

In the case of the LTO plugin, this is the static function
claim_file_handler in lto-plugin.c.

If the plugin registers a claim_file handler, and, when the linker calls
it, it returns with *claimed == 0, then the linker will process the file
as it normally does.  Since the file will already have been processed,
it does not make sense for the plugin to then pass it back to the
linker.  The effect would be similar to listing the file twice on the
command line.


>> In fact, if the plugin claims all files, then as far as I can see your
>> new ld_plugin_input_file field is not required.  And if the plugin does
>> not claim all files, I don't see how this can work.
>
> Stage 2 linker should:
>
> 1. Discard all previous inputs.

How is this step done?


> My implementation is available on hjl/lto branch at

Thanks, but I don't see any changes to gold there, so I don't see what
you have done to change the plugin interface.

Ian