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

[Jason Liu via Phabricator via cfe-commits]

jasonliu 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());
----------------
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.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D91455/new/

https://reviews.llvm.org/D91455