Try a theory in CI: -fvisibility=hidden doesn't do anything #735
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What matters is -Wl,--exclude-libs=ALL for all of our shared objects, of which in the current commit there is only python and libpython, which already uses it.
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In general, if libX.so depends on libY.a, we don't want libY's symbols dynamically exported by libX. We want libX's use of libY to be private. We use two mechanisms for making this happen. -fvisibility=hidden, which works on the build of libY to mark the symbols themselves as hidden in the object file, and -Wl,--exclude-libs=ALL, which works on the build of libX to instruct the linker not to re-export symbols from static libraries. We set -fvisibility=hidden on some platforms but not all. We use -Wl,--exclude-libs=ALL on the build of Python itself on all platforms, which up to this point built our only dynamic objects (bin/python and libpython). Now that libtcl and libtk are dynamic, we need to do the same thing. I'm not sure if -fvisibility=hidden actually does anything useful for us, given the use of -Wl,--exclude-libs=ALL, and I think the fact that it's only set on some platforms is an oversight and demonstrates that it's not needed. See #735, which removes it; the builds pass vaildation.
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What matters is -Wl,--exclude-libs=ALL for all of our shared objects, of which in the current commit there is only python and libpython, which already uses it.