[PATCH] D91455: [XCOFF][AIX] Generate LSDA data and compact unwind section on AIX

[David Tenty via Phabricator via llvm-commits]

daltenty added inline comments.


================
Comment at: llvm/lib/MC/MCObjectFileInfo.cpp:889
+  CompactUnwindSection =
+      Ctx->getXCOFFSection(".eh_info_table", XCOFF::StorageMappingClass::XMC_RW,
+                           XCOFF::XTY_SD, SectionKind::getData());
----------------
jasonliu wrote:
> daltenty wrote:
> > I think this may have been discussed elsewhere, but why do we want to emit this as a RW section?
> Yes, this has been discussed before. And it's a good question.
> If we emit this as an RO section, then we could not put 
> ```
> .vbyte	4, GCC_except_table1
> .vbyte	4, __xlcxx_personality_v1[DS]
> ```
> into this csect directly. 
> If we do that, we would hit linker error during link time. It seems that for read only csects (RO, PR mapping classes), we could not have relocation types like `R_POS` or `R_NEG` because the result coming out of it is not link-time constant. And the relocation types in read only csects needs to be link time constant.
> 
> Extra work (both compiler and runtime) will be needed if we want to make this RO.
Thanks for clarifying. I guess we'd presumably need to add the TOC indirections to get to the LSDA and personality routine's function descriptor,  similar  to elsewhere. 

Since this structure is version'd, seems like we have the flexibility to defer that work, so I guess that's OK.


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  https://reviews.llvm.org/D91455/new/

https://reviews.llvm.org/D91455