[PATCH] D147544: [BOLT] Move from RuntimeDyld to JITLink

Tue Apr 25 04:54:12 PDT 2023

jobnoorman added a comment.

In D147544#4293906 <https://reviews.llvm.org/D147544#4293906>, @maksfb wrote:

> Right. RuntimeDyld will not emit a section without relocations. E.g., for .debug_line, we have to make the section allocatable (https://github.com/llvm/llvm-project/blob/99cfaf0d5ed68d5d4e292fc87a10b1bb26201787/bolt/lib/Core/BinaryEmitter.cpp#L190-L199) and then force a dummy relocation against it (https://github.com/llvm/llvm-project/blob/5f2b0892d5b732a822728f96a57144f6542c155e/bolt/lib/Core/DebugData.cpp#L1631-L1637).
>
> Sounds like with JITLink at least the hack for the relocation is not needed. @lhames, could you please confirm that it's by design?

In `JITLink`, the pruning <https://github.com/llvm/llvm-project/blob/ca94b02e559242e6d1fcdd65320334438be69448/llvm/lib/ExecutionEngine/JITLink/JITLinkGeneric.cpp#L266-L337> of sections is based on symbol liveness. Only sections (blocks actually) that have live symbols pointing to them will be kept for linking. Which symbols are live, is controlled by BOLT. See `markSectionsLive` in `JITLinkLinker.cpp` in this patch.

The hack you are talking about has indeed been removed by this patch.

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D147544/new/

https://reviews.llvm.org/D147544