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:
> 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.
> add the TOC indirections to get to the LSDA and personality routine's
> function descriptor
Yep, that's one potential way to solve it. The downside of it would be
1. We might have more TC entries than we desired.
2. A small performance penalty to pay for the extra indirection. (But since we
already on the EH path, and it's slow anyway, might not be that big of a deal).
But as you already mentioned, we don't have to solve this issue right now.
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D91455/new/
https://reviews.llvm.org/D91455
_______________________________________________
cfe-commits mailing list
cfe-commits@lists.llvm.org
https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
