Re: "ld -r" on mixed IR/non-IR objects (

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

On Wed, Dec 8, 2010 at 9:36 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Wed, Dec 8, 2010 at 5:54 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
>> On Wed, Dec 8, 2010 at 1:19 AM, Andi Kleen <andi@firstfloor.org> wrote:
>>>> On 12/07/2010 04:20 PM, Andi Kleen wrote:
>>>>>
>>>>> The only problem left is mixing of lto and non lto objects. this right
>>>>> now is not handled. IMHO still the best way to handle it is to use
>>>>> slim lto and then simply separate link the "left overs" after deleting
>>>>> the LTO objects. This can be actually done with objcopy (with some
>>>>> limitations), doesn't even need linker support.
>>>>>
>>>>
>>>> Quite possibly a better way to deal with that is to provide a mechanism
>>>> for encapsulating arbitrary binary code objects inside the LTO IR.
>>>
>>> Then you would need to teach your assembler and everything
>>
>> The magic section is generated by linker directly. No changes to
>> assembler is required.
>>
>>> else that may generate ELF objects to generate this magic object. But why
>>> not just ELF directly? that is what it is after all.
>>
>> My proposal isn't specific to ELF.
>>
>>>
>>> To be honest I don't really see the point of all this complexity you
>>> guys are proposing just to save fat LTO. Fat LTO is always a bad idea
>>> because it's slow and ?does lots of redundant work. If LTO is to become
>>> a more wide spread mode it has to go simply because of the poor
>>> performance.
>>>
>>> With slim LTO passthrough is ?very straight-forward: simple pass
>>> through every section that is not LTO and generate code for the LTO
>>> sections. No new magic sections needed at all.
>>>
>>
>> My proposal works on both fat and slim LTO objects. ?The idea is
>> you can use "ld -r" on any combination of inputs and its output
>> still works as before "ld -r".
>>
>
> Here is the revised proposal.
>

The initial implementation of my proposal is available on hjl/lto-mixed
branch at

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

Simple case works.  More cleanups are needed.  Feedbacks
are welcome.

Thanks.


-- 
H.J.