Fix crash when building with _GLIBCXX_USE_CXX11_ABI=0 #686
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I don't 100% understand why this fixes the issue, but the situation is esoteric enough that it doesn't seem worth spending any more days on this problem
TingDaoK
approved these changes
Nov 27, 2024
waahm7
approved these changes
Nov 27, 2024
waahm7
reviewed
Nov 27, 2024
sfod
reviewed
Nov 27, 2024
CMakeLists.txt
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| # see: https://github.com/awslabs/aws-crt-cpp/pull/675 | ||
| if(NOT (CMAKE_CXX_COMPILER_ID STREQUAL "GNU" AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS "5.0")) | ||
| # Except where it causes problems, and the situation is weird enough that it's not worth investigating further. | ||
| string(FIND "${CMAKE_CXX_FLAGS}" "-D_GLIBCXX_USE_CXX11_ABI=0" found_ancient_abi_flag) |
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It's possible to set CXX flags via CMAKE_CXX_FLAGS_<CONFIG>.
The following command will add -D_GLIBCXX_USE_CXX11_ABI=0 option to compile command, but CMAKE_CXX_FLAGS will be empty:
cmake -S . -B build -DCMAKE_CXX_FLAGS_DEBUG="-D_GLIBCXX_USE_CXX11_ABI=0" -DCMAKE_BUILD_TYPE=Debug
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I don't think developers actually set CXX flags this way, but additional comment might help to debug in the future if someone decides to do it.
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Nice callout. Checking every variant _<CONFIG> variant now
I tried to be clever and use CheckCXXSourceCompiles, but this didn't take the _<CONFIG> variants into account
BTW check_cxx_source_compiles() doesn't use the _<CONFIG> flags
sfod
approved these changes
Nov 28, 2024
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Issue:
A user had been building aws-crt-cpp with
CXXFLAGS=-D_GLIBCXX_USE_CXX11_ABI=0, and that worked fine until the recent change where we started hiding symbols by default (PR #666)With symbols hidden by default, and
_GLIBCXX_USE_CXX11_ABI=0, tests would crash in the destructor ofAws::Crt::String(which isstd::stringwith a custom allocator).Description of changes:
Don't hide symbols when building for the ancient glibcxx ABI.
I don't 100% understand why this fixes the issue, but the situation is esoteric enough that it doesn't seem worth spending more days on this problem.
Background
See: https://gcc.gnu.org/onlinedocs/libstdc++/manual/using_dual_abi.html
GCC had to introduce a new ABI for C++11 which removed the copy-on-write optimization for strings, which is forbidden in C++11 and later (new ABI uses a small-string optimization instead). But GCC let users manually set
_GLIBCXX_USE_CXX11_ABI=0so they could opt back into the old ABI and continue working with libraries compiled for C++03.I don't think GCC intended devs to continue using this 10 years later, but some people are, because the old copy-on-write optimization has less memory usage.
By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.