Re: Update LTO plugin interface

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Fri, Dec 3, 2010 at 11:16 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Fri, Dec 3, 2010 at 11:10 AM, Cary Coutant <ccoutant@google.com> wrote:
>>>>> Another way to do this would be to put a marker in the command line
>>>>> that identifies where those libraries begin, and the linker could just
>>>>> go back and rescan those libraries if needed, before the final layout
>>>>> of the endcaps.
>>>>
>>>> I like that idea in general, but the difficulty is knowing where to put
>>>> the marker. ?E.g., the user is going to specify -lm, and we are going to
>>>> need to rescan it. ?If the user writes -lm -lmylib1 -lmylib2 we want to
>>>> rescan -lm but we don't really need to rescan mylib1 and mylib2.
>>>
>>> All those complexities make 2 stage linking more attractive. ?I
>>> think I can implement it in GNU linker with the current plugin API.
>>>
>>> Linker just needs to remember the command line options, including
>>>
>>> --start-group/--end-group
>>> -as-needed/--no-as-needed
>>> --copy-dt-needed-entries/--no-copy-dt-needed-entries
>>>
>>> in stage 1.
>>>
>>> In stage 2, it will place LTO trans files before the first IR file
>>> claimed by plugin and process the command line options.
>>>
>>> --whole-archive may need some special handling. ?Archives
>>> after --whole-archive will be ignored in stage 2.
>>
>> It seems to me that we just need to add a few more libraries as
>> pass-through libraries, being careful to add a pass-through option
>> only for libraries that are already on the command line. How does that
>> add up to "all those complexities"?
>>
>> With what you've written here, you've just added to the complexity of
>> your proposed solution, which makes it a much bigger change --
>> especially since what you're proposing will require changes in both
>> linkers. Adding pass-through options is a gcc driver change only.
>>
>
> I will implement 2 stage linking in GNU linker with the current plugin API.
> The change shouldn't be too big. ?pass-through isn't needed. ?If we
> keep it in GCC driver, my linker will simply ignore it.
>
> One benefit is everything will just work, with or without LTO.
>

I checked the first patch into hjl/lto branch at

http://git.kernel.org/?p=devel/binutils/hjl/x86.git;a=summary

Now I can collect stage 2 command line.

-- 
H.J.