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

[H.J. Lu]

On Mon, Dec 6, 2010 at 4:05 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
>>
>> Without slim lto you never know if a duplicate symbol is a mistake
>> of the programmer or just the "fat lto" copy. Also ELF semantics
>> like weak are hard if you have multiple copies.
>>
>
> It isn't easy, but doable.
>

Here is my proposal.  Any comments?

Thanks.


-- 
H.J.
---
• 2 kinds of object files
	○ non-IR object file has
		§ non-IR sections
	○ IR object file has
		§ IR sections
		§ non-IR sections
• The output of "ld -r" with mixed IR/non-IR objects should work with:
	○ Compilers/linkers with IR support.
	○ Compilers/linkers without IR support.
• Add the mixed object file has
	○ IR sections
	○ non-IR sections:
		§ Object codes from IR sections.
		§ Object codes from non-IR object files.
	○ Object-only section:
		§ Section name won't be generated by any tools, something like
".objectonly\004".
		§ Contains non-IR object file.
		§ Input is discarded after link.
• Linker action:
	○ Classify each input object file:
		□ If there is a ".objectonly\004" section, it is a mixed object file.
		□ If there is a IR section, it is an IR object file.
		□ Otherwise, it is a non-IR object file.
	○ Relocatable link:
		§ Prepare for an object-only output.
		§ Prepare for a regular output.
		§ For each mixed object file,
			□ Add IR and non-IR sections to the regular output.
			□ For object-only section:
				® Extract object only file.
				® Add it to the object-only output.
				® Discard object-only section.
		§ For each IR object file,
			□ Add IR and non-IR sections to the regular output.
		§ For each non-IR object file,
			□ Add non-IR sections to the regular output.
			□ Add non-IR sections to the object-only output.
		§ Final output:
			□ If there are IR objects, non-IR objects and the object-only
output isn't empty:
				® Put the object-only output into the object-only section.
				® Add the object-only section to the regular output.
			□ Remove the object-only output.
	○ Normal link
		§ Prepare for output.
		§ For each mixed object file,
			□ Compile and add IR sections to the output.
			□ For object-only section:
				® Extract object only file.
				® Add it to the output.
				® Discard object-only section.
		§ For each IR object file,
			□ Compile and add IR sections to the output.
		§ For each non-IR object file,
			□ Add non-IR sections to the output.