[PATCH] D104060: Machine IR Profile

[David Li via Phabricator via llvm-commits]

davidxl added a comment.

In D104060#2837248 <https://reviews.llvm.org/D104060#2837248>, @ellis wrote:

> In D104060#2836209 <https://reviews.llvm.org/D104060#2836209>, @davidxl wrote:
>
>> In D104060#2836015 <https://reviews.llvm.org/D104060#2836015>, @kyulee wrote:
>>
>>> Thanks for the patch D104556 <https://reviews.llvm.org/D104556> that uses PC relative relocations for reference! This avoids dynamic relocation, which is the prerequisite to make a section (region) be extractable.
>>> Unfortunately this is not sufficient because we need to find the references once they are extracted out because the address ranges (either in the original binary and the extracted binary) are not valid or can be altered.
>>> So, we need some notion of section (or region) relative addressing which is not all available in COFF/ELF/MachO. One trick in MIP is to introduce an anchor reference to express such addressing with two PC relative relocations.
>>> In fact, this anchor reference can be hoisted out into the header which we can share, which is not in this change yet.
>>
>> This is interesting.  Can you describe a little more with the fuzzy matching, perhaps with a small example to demonstrate how it works?
>
> If you're asking about our trick for the raw profile addresses, I have a comment above that describes it in detail (the comment title is "Section Layout"). If your asking about something else, could you please elaborate?

I was referring to this comment by kyulee@:  "because the address ranges (either in the original binary and the extracted binary) are not valid or can be altered." --  Is this about using stale profile  or something else? I might have misunderstood the part about 'address ranges can be altered' part.


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