[libcxx-commits] [libcxx] [libc++] Remove ios_base::__xindex_ from the ABI (PR #198994)

[Vrukesh Panse via libcxx-commits]

vrukesh wrote:

@philnik777 

This patch potentially causes regression in bare-metal Arm-toolchain for Armv4T/Armv5TE/Armv6-M, by requiring unresolved __atomic_fetch_add_4.

Godbolt compiler explorer reproducer: https://godbolt.org/z/o1o677qKo

Github action: https://github.com/arm/arm-toolchain/actions/runs/27122992388

File path: test-results-build.sh-Ubuntu-22.04-x86_64/multilib-picolibc-builds/cxxlibs/armv5te_exn_rtti_size/build/libcxxabi/test/lit_results.junit.xml

Log snippet for your reference:
`
. - - -command stderr- - - - - -
| ld.lld: error: undefined symbol: __atomic_fetch_add_4
| >>> referenced by ios.cpp
| >>>               ios.cpp.obj:(std::__2::ios_base::xalloc()) in archive /home/runner/work/arm-toolchain/arm-toolchain/build/multilib-picolibc-builds/cxxlibs/armv5te_exn_rtti_size/build/libcxxabi/test-suite-install/lib/libc++.a
| clang++: error: linker command failed with exit code 1 (use -v to see invocation)

`


https://github.com/llvm/llvm-project/pull/198994