PATCH: Fix linker plugin support for gnu linker

[H.J. Lu]

On Sat, Jan 8, 2011 at 5:50 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Sat, Jan 8, 2011 at 7:44 AM, Richard Sandiford
> <rdsandiford@googlemail.com> wrote:
>> "H.J. Lu" <hjl.tools@gmail.com> writes:
>>> On Sat, Jan 8, 2011 at 6:46 AM, Richard Sandiford
>>> <rdsandiford@googlemail.com> wrote:
>>>> "H.J. Lu" <hjl.tools@gmail.com> writes:
>>>>> On Sat, Jan 8, 2011 at 4:10 AM, Richard Sandiford
>>>>> <rdsandiford@googlemail.com> wrote:
>>>>>> "H.J. Lu" <hongjiu.lu@intel.com> writes:
>>>>>>> This patch fixes linker plugin support for gnu linker with 2 stage
>>>>>>> linking and supports mixed LTO objects:
>>>>>>>
>>>>>>> http://www.kernel.org/pub/linux/devel/gcc/lto/mixed-IR/mixed-IR.pdf
>>>>>>>
>>>>>>> Any objections?
>>>>>>
>>>>>> One problem with the patch as written is that it doesn't cope with
>>>>>> the kind of embedded setup in which the startup file is specified
>>>>>> in a linker script.  E.g. on mipsisa64-elf, GCC doesn't know what
>>>>>> system you're targetting, and therefore doesn't what startup files or
>>>>>> board-specific libraries are needed.  You instead link with something
>>>>>> like -Tidt64.ld.  idt64.ld then contains:
>>>>>>
>>>>>> STARTUP(crt0.o)
>>>>>>
>>>>>> -T options are parsed immediately in-place, and don't show up in the
>>>>>> cmdline_options.  Things like STARTUP don't either.  This means that
>>>>>> crt0.o is dropped by the second stage link.
>>>>>>
>>>>>> The handling of -T also means that the system libraries:
>>>>>>
>>>>>> GROUP(-lc -lidt -lgcc)
>>>>>>
>>>>>> don't show up in the second link.  However, that brings up a broader
>>>>>> question (which might already have been answered, sorry).  The current
>>>>>> process -- that is, the process before the 2-stage patch -- seems to
>>>>>> rely on the GCC driver passing the equivalent of:
>>>>>>
>>>>>>  -pass-through=-lgcc -pass-through=-lc -pass-through=-lgcc
>>>>>>
>>>>>> to the plugin.  But on targets like mipsisa64-elf, GCC doesn't know
>>>>>
>>>>> hjl/lto-mixed branch ignores  -pass-through=XXX passed from gcc driver.
>>>>
>>>> Right, that's what I meant.  The fact that the 2-pass link doesn't
>>>> need those options means that it would solve the problem for free.
>>>> But at the moment it doesn't work because it ignores the linker script's
>>>> GROUP as well.
>>>
> ...
>>> I just need to handle STARTUP properly.
>>
>> And GROUP. :-)
>>
>>> If you can provide a native testcase on Linux/x86-64, I will fix it.
>>
>> Sorry, I don't have time to reproduce this on x86_64.  I'm just trying
>> to provide feeback to the patch submission.
>
> Please try commit bf235c35e8c2a386b13f034a8d3269b569b47acb
> and let me know if it works for you.
>

Please use commit 5f61c105470197418bfc258ad9487a423e101bff.

Thanks.

-- 
H.J.