[PATCH] D125683: [runtimes] Replace LIBCXX_ENABLE_STATIC_ABI_LIBRARY & friends by a new LIBCXX_CXX_ABI choice

Fri Jun 17 14:46:44 PDT 2022

ldionne added inline comments.

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Comment at: clang/cmake/caches/Fuchsia-stage2.cmake:124
     set(RUNTIMES_${target}_LIBCXX_ENABLE_SHARED OFF CACHE BOOL "")
-    set(RUNTIMES_${target}_LIBCXX_ENABLE_STATIC_ABI_LIBRARY ON CACHE BOOL "")
     set(RUNTIMES_${target}_LIBCXX_ABI_VERSION 2 CACHE STRING "")
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phosek wrote:
> ldionne wrote:
> > phosek wrote:
> > > ldionne wrote:
> > > > ldionne wrote:
> > > > > phosek wrote:
> > > > > > ldionne wrote:
> > > > > > > phosek wrote:
> > > > > > > > ldionne wrote:
> > > > > > > > > Note that I am removing these options here because I don't think they are required -- since we specify `LIBCXXABI_ENABLE_SHARED=OFF`, there is no shared libc++abi to link against, so we should already be linking against `libc++abi.a` regardless of this change.
> > > > > > > > This option was set to merge `libc++abi.a` into `libc++.a` so to achieve the same effect, presumably we would need to set `-DLIBCXX_CXX_ABI=libcxxabi-objects`?
> > > > > > > I agree this is suspicious, but why is there no `LIBCXX_STATICALLY_LINK_ABI_IN_SHARED_LIBRARY` specified here then? I can add `-DLIBCXX_CXX_ABI=libcxxabi-objects`, I just want to make sure we both understand what's going on.
> > > > > > This is intentional. We are merging `libc++abi.a` into `libc++.a` but we ship `libc++abi.so` and `libc++.so` as separate (and use the generated linker script to pull in `libc++abi.so` when you pass `-lc++` to linker). I'd be fine merging `libc++abi.so` into `libc++.so` as well, but we'll need to figure out a transition plan since there are several places in our build right now that expect `libc++abi.so` to exist. We cannot land this change as is because that would break the `-static-libstdc++` use case, since Clang driver only passes `-lc++` to the linker and not `-lc++abi` and there's nothing that would pull `libc++abi.a` in.
> > > > > I see, so to summarize, basically you want to use `libcxxabi-objects` for the static `libc++.a`, but `libcxxabi` for the dynamic `libc++.so`. This change as currently laid out does not permit that to happen, since `libcxxabi-objects` implies that the objects are merged both in the static and in the shared library. I guess we could introduce a new `libcxxabi-objects-static` option, however that would be kind of strange. We can either do that, or wait for you to stop relying on `libc++abi.so` existing and switch to `libcxxabi-objects` wholesale for Fuchsia. WDYT?
> > > > Gentle ping. It would be nice to land this in one form or another. If you don't think Fuchsia can stop relying on `libc++abi.so` being there, I could add yet another `libcxxabi-objects-static` -- I still feel like that's better than the status quo.
> > > We discussed this on our team and we don't have any issues switching towards combined `libc++.so`, we just need to figure out a transition plan. Let me test this change locally to see if landing this as is will break anything.
> > Gentle ping -- did you get any time to investigate this?
> I did and we are currently hitting a failure related to our libunwind usage. I have created D127528 which should address it. 
Thanks! Since this has been landed, does it mean we can move forward with this patch?

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D125683/new/

https://reviews.llvm.org/D125683